Update: Translations from eints

[openttd-github.git] / src / town_cmd.cpp

/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */

/** @file town_cmd.cpp Handling of town tiles. */

#include "stdafx.h"
#include "road.h"
#include "road_internal.h" /* Cleaning up road bits */
#include "road_cmd.h"
#include "landscape.h"
#include "viewport_func.h"
#include "viewport_kdtree.h"
#include "command_func.h"
#include "company_func.h"
#include "industry.h"
#include "station_base.h"
#include "waypoint_base.h"
#include "station_kdtree.h"
#include "company_base.h"
#include "news_func.h"
#include "error.h"
#include "object.h"
#include "genworld.h"
#include "newgrf_debug.h"
#include "newgrf_house.h"
#include "newgrf_text.h"
#include "autoslope.h"
#include "tunnelbridge_map.h"
#include "strings_func.h"
#include "window_func.h"
#include "string_func.h"
#include "newgrf_cargo.h"
#include "cheat_type.h"
#include "animated_tile_func.h"
#include "subsidy_func.h"
#include "core/pool_func.hpp"
#include "town.h"
#include "town_kdtree.h"
#include "townname_func.h"
#include "core/random_func.hpp"
#include "core/backup_type.hpp"
#include "depot_base.h"
#include "object_map.h"
#include "object_base.h"
#include "ai/ai.hpp"
#include "game/game.hpp"
#include "town_cmd.h"
#include "landscape_cmd.h"
#include "road_cmd.h"
#include "terraform_cmd.h"
#include "tunnelbridge_cmd.h"
#include "timer/timer.h"
#include "timer/timer_game_calendar.h"
#include "timer/timer_game_economy.h"
#include "timer/timer_game_tick.h"

#include "table/strings.h"
#include "table/town_land.h"

#include "safeguards.h"

/* Initialize the town-pool */
TownPool _town_pool("Town");
INSTANTIATE_POOL_METHODS(Town)


TownKdtree _town_kdtree(&Kdtree_TownXYFunc);

void RebuildTownKdtree()
{
        std::vector<TownID> townids;
        for (const Town *town : Town::Iterate()) {
                townids.push_back(town->index);
        }
        _town_kdtree.Build(townids.begin(), townids.end());
}

/** Set if a town is being generated. */
static bool _generating_town = false;

/**
 * Check if a town 'owns' a bridge.
 * Bridges do not directly have an owner, so we check the tiles adjacent to the bridge ends.
 * If either adjacent tile belongs to the town then it will be assumed that the town built
 * the bridge.
 * @param tile The bridge tile to test
 * @param t The town we are interested in
 * @return true If town 'owns' a bridge.
 */
static bool TestTownOwnsBridge(TileIndex tile, const Town *t)
{
        if (!IsTileOwner(tile, OWNER_TOWN)) return false;

        TileIndex adjacent = tile + TileOffsByDiagDir(ReverseDiagDir(GetTunnelBridgeDirection(tile)));
        bool town_owned = IsTileType(adjacent, MP_ROAD) && IsTileOwner(adjacent, OWNER_TOWN) && GetTownIndex(adjacent) == t->index;

        if (!town_owned) {
                /* Or other adjacent road */
                adjacent = tile + TileOffsByDiagDir(ReverseDiagDir(GetTunnelBridgeDirection(GetOtherTunnelBridgeEnd(tile))));
                town_owned = IsTileType(adjacent, MP_ROAD) && IsTileOwner(adjacent, OWNER_TOWN) && GetTownIndex(adjacent) == t->index;
        }

        return town_owned;
}

Town::~Town()
{
        if (CleaningPool()) return;

        /* Delete town authority window
         * and remove from list of sorted towns */
        CloseWindowById(WC_TOWN_VIEW, this->index);

#ifdef WITH_ASSERT
        /* Check no industry is related to us. */
        for (const Industry *i : Industry::Iterate()) {
                assert(i->town != this);
        }

        /* ... and no object is related to us. */
        for (const Object *o : Object::Iterate()) {
                assert(o->town != this);
        }
#endif /* WITH_ASSERT */

        /* Check no tile is related to us. */
        for (TileIndex tile = 0; tile < Map::Size(); ++tile) {
                switch (GetTileType(tile)) {
                        case MP_HOUSE:
                                assert(GetTownIndex(tile) != this->index);
                                break;

                        case MP_ROAD:
                                assert(!HasTownOwnedRoad(tile) || GetTownIndex(tile) != this->index);
                                break;

                        case MP_TUNNELBRIDGE:
                                assert(!TestTownOwnsBridge(tile, this));
                                break;

                        default:
                                break;
                }
        }

        /* Clear the persistent storage list. */
        for (auto &psa : this->psa_list) {
                delete psa;
        }
        this->psa_list.clear();

        DeleteSubsidyWith(SourceType::Town, this->index);
        DeleteNewGRFInspectWindow(GSF_FAKE_TOWNS, this->index);
        CargoPacket::InvalidateAllFrom(SourceType::Town, this->index);
        MarkWholeScreenDirty();
}


/**
 * Invalidating of the "nearest town cache" has to be done
 * after removing item from the pool.
 */
void Town::PostDestructor(size_t)
{
        InvalidateWindowData(WC_TOWN_DIRECTORY, 0, TDIWD_FORCE_REBUILD);
        UpdateNearestTownForRoadTiles(false);

        /* Give objects a new home! */
        for (Object *o : Object::Iterate()) {
                if (o->town == nullptr) o->town = CalcClosestTownFromTile(o->location.tile, UINT_MAX);
        }
}

/**
 * Assign the town layout.
 * @param layout The desired layout. If TL_RANDOM, we pick one based on TileHash.
 */
void Town::InitializeLayout(TownLayout layout)
{
        if (layout != TL_RANDOM) {
                this->layout = layout;
                return;
        }

        this->layout = static_cast<TownLayout>(TileHash(TileX(this->xy), TileY(this->xy)) % (NUM_TLS - 1));
}

/**
 * Return a random valid town.
 * @return A random town, or nullptr if there are no towns.
 */
/* static */ Town *Town::GetRandom()
{
        if (Town::GetNumItems() == 0) return nullptr;
        int num = RandomRange((uint16_t)Town::GetNumItems());
        size_t index = MAX_UVALUE(size_t);

        while (num >= 0) {
                num--;
                index++;

                /* Make sure we have a valid town */
                while (!Town::IsValidID(index)) {
                        index++;
                        assert(index < Town::GetPoolSize());
                }
        }

        return Town::Get(index);
}

void Town::FillCachedName() const
{
        this->cached_name = GetTownName(this);
}

/**
 * Get the cost for removing this house.
 * @return The cost adjusted for inflation, etc.
 */
Money HouseSpec::GetRemovalCost() const
{
        return (_price[PR_CLEAR_HOUSE] * this->removal_cost) >> 8;
}

/* Local */
static int _grow_town_result;

/* The possible states of town growth. */
enum TownGrowthResult {
        GROWTH_SUCCEED         = -1,
        GROWTH_SEARCH_STOPPED  =  0
//      GROWTH_SEARCH_RUNNING >=  1
};

static bool TryBuildTownHouse(Town *t, TileIndex tile);
static Town *CreateRandomTown(uint attempts, uint32_t townnameparts, TownSize size, bool city, TownLayout layout);

static void TownDrawHouseLift(const TileInfo *ti)
{
        AddChildSpriteScreen(SPR_LIFT, PAL_NONE, 14, 60 - GetLiftPosition(ti->tile));
}

typedef void TownDrawTileProc(const TileInfo *ti);
static TownDrawTileProc * const _town_draw_tile_procs[1] = {
        TownDrawHouseLift
};

/**
 * Return a random direction
 *
 * @return a random direction
 */
static inline DiagDirection RandomDiagDir()
{
        return (DiagDirection)(RandomRange(DIAGDIR_END));
}

/**
 * Draw a house and its tile. This is a tile callback routine.
 * @param ti TileInfo of the tile to draw
 */
static void DrawTile_Town(TileInfo *ti)
{
        HouseID house_id = GetHouseType(ti->tile);

        if (house_id >= NEW_HOUSE_OFFSET) {
                /* Houses don't necessarily need new graphics. If they don't have a
                 * spritegroup associated with them, then the sprite for the substitute
                 * house id is drawn instead. */
                if (HouseSpec::Get(house_id)->grf_prop.spritegroup[0] != nullptr) {
                        DrawNewHouseTile(ti, house_id);
                        return;
                } else {
                        house_id = HouseSpec::Get(house_id)->grf_prop.subst_id;
                }
        }

        /* Retrieve pointer to the draw town tile struct */
        const DrawBuildingsTileStruct *dcts = &_town_draw_tile_data[house_id << 4 | TileHash2Bit(ti->x, ti->y) << 2 | GetHouseBuildingStage(ti->tile)];

        if (ti->tileh != SLOPE_FLAT) DrawFoundation(ti, FOUNDATION_LEVELED);

        DrawGroundSprite(dcts->ground.sprite, dcts->ground.pal);

        /* If houses are invisible, do not draw the upper part */
        if (IsInvisibilitySet(TO_HOUSES)) return;

        /* Add a house on top of the ground? */
        SpriteID image = dcts->building.sprite;
        if (image != 0) {
                AddSortableSpriteToDraw(image, dcts->building.pal,
                        ti->x + dcts->subtile_x,
                        ti->y + dcts->subtile_y,
                        dcts->width,
                        dcts->height,
                        dcts->dz,
                        ti->z,
                        IsTransparencySet(TO_HOUSES)
                );

                if (IsTransparencySet(TO_HOUSES)) return;
        }

        {
                int proc = dcts->draw_proc - 1;

                if (proc >= 0) _town_draw_tile_procs[proc](ti);
        }
}

static int GetSlopePixelZ_Town(TileIndex tile, uint, uint, bool)
{
        return GetTileMaxPixelZ(tile);
}

/**
 * Get the foundation for a house. This is a tile callback routine.
 * @param tile The tile to find a foundation for.
 * @param tileh The slope of the tile.
 */
static Foundation GetFoundation_Town(TileIndex tile, Slope tileh)
{
        HouseID hid = GetHouseType(tile);

        /* For NewGRF house tiles we might not be drawing a foundation. We need to
         * account for this, as other structures should
         * draw the wall of the foundation in this case.
         */
        if (hid >= NEW_HOUSE_OFFSET) {
                const HouseSpec *hs = HouseSpec::Get(hid);
                if (hs->grf_prop.spritegroup[0] != nullptr && HasBit(hs->callback_mask, CBM_HOUSE_DRAW_FOUNDATIONS)) {
                        uint32_t callback_res = GetHouseCallback(CBID_HOUSE_DRAW_FOUNDATIONS, 0, 0, hid, Town::GetByTile(tile), tile);
                        if (callback_res != CALLBACK_FAILED && !ConvertBooleanCallback(hs->grf_prop.grffile, CBID_HOUSE_DRAW_FOUNDATIONS, callback_res)) return FOUNDATION_NONE;
                }
        }
        return FlatteningFoundation(tileh);
}

/**
 * Animate a tile for a town.
 * Only certain houses can be animated.
 * The newhouses animation supersedes regular ones.
 * @param tile TileIndex of the house to animate.
 */
static void AnimateTile_Town(TileIndex tile)
{
        if (GetHouseType(tile) >= NEW_HOUSE_OFFSET) {
                AnimateNewHouseTile(tile);
                return;
        }

        if (TimerGameTick::counter & 3) return;

        /* If the house is not one with a lift anymore, then stop this animating.
         * Not exactly sure when this happens, but probably when a house changes.
         * Before this was just a return...so it'd leak animated tiles..
         * That bug seems to have been here since day 1?? */
        if (!(HouseSpec::Get(GetHouseType(tile))->building_flags & BUILDING_IS_ANIMATED)) {
                DeleteAnimatedTile(tile);
                return;
        }

        if (!LiftHasDestination(tile)) {
                uint i;

                /* Building has 6 floors, number 0 .. 6, where 1 is illegal.
                 * This is due to the fact that the first floor is, in the graphics,
                 *  the height of 2 'normal' floors.
                 * Furthermore, there are 6 lift positions from floor N (incl) to floor N + 1 (excl) */
                do {
                        i = RandomRange(7);
                } while (i == 1 || i * 6 == GetLiftPosition(tile));

                SetLiftDestination(tile, i);
        }

        int pos = GetLiftPosition(tile);
        int dest = GetLiftDestination(tile) * 6;
        pos += (pos < dest) ? 1 : -1;
        SetLiftPosition(tile, pos);

        if (pos == dest) {
                HaltLift(tile);
                DeleteAnimatedTile(tile);
        }

        MarkTileDirtyByTile(tile);
}

/**
 * Determines if a town is close to a tile.
 * @param tile TileIndex of the tile to query.
 * @param dist The maximum distance to be accepted.
 * @returns true if the tile is within the specified distance.
 */
static bool IsCloseToTown(TileIndex tile, uint dist)
{
        if (_town_kdtree.Count() == 0) return false;
        Town *t = Town::Get(_town_kdtree.FindNearest(TileX(tile), TileY(tile)));
        return DistanceManhattan(tile, t->xy) < dist;
}

/** Resize the sign (label) of the town after it changes population. */
void Town::UpdateVirtCoord()
{
        Point pt = RemapCoords2(TileX(this->xy) * TILE_SIZE, TileY(this->xy) * TILE_SIZE);

        if (this->cache.sign.kdtree_valid) _viewport_sign_kdtree.Remove(ViewportSignKdtreeItem::MakeTown(this->index));

        SetDParam(0, this->index);
        SetDParam(1, this->cache.population);
        this->cache.sign.UpdatePosition(pt.x, pt.y - 24 * ZOOM_BASE,
                _settings_client.gui.population_in_label ? STR_VIEWPORT_TOWN_POP : STR_VIEWPORT_TOWN,
                STR_VIEWPORT_TOWN_TINY_WHITE);

        _viewport_sign_kdtree.Insert(ViewportSignKdtreeItem::MakeTown(this->index));

        SetWindowDirty(WC_TOWN_VIEW, this->index);
}

/** Update the virtual coords needed to draw the town sign for all towns. */
void UpdateAllTownVirtCoords()
{
        for (Town *t : Town::Iterate()) {
                t->UpdateVirtCoord();
        }
}

/** Clear the cached_name of all towns. */
void ClearAllTownCachedNames()
{
        for (Town *t : Town::Iterate()) {
                t->cached_name.clear();
        }
}

/**
 * Change the town's population as recorded in the town cache, town label, and town directory.
 * @param t The town which has changed.
 * @param mod The population change (can be positive or negative).
 */
static void ChangePopulation(Town *t, int mod)
{
        t->cache.population += mod;
        if (_generating_town) [[unlikely]] return;

        InvalidateWindowData(WC_TOWN_VIEW, t->index); // Cargo requirements may appear/vanish for small populations
        if (_settings_client.gui.population_in_label) t->UpdateVirtCoord();

        InvalidateWindowData(WC_TOWN_DIRECTORY, 0, TDIWD_POPULATION_CHANGE);
}

/**
 * Get the total population, the sum of all towns in the world.
 * @return The calculated population of the world
 */
uint32_t GetWorldPopulation()
{
        uint32_t pop = 0;
        for (const Town *t : Town::Iterate()) pop += t->cache.population;
        return pop;
}

/**
 * Remove stations from nearby station list if a town is no longer in the catchment area of each.
 * To improve performance only checks stations that cover the provided house area (doesn't need to contain an actual house).
 * @param t Town to work on.
 * @param tile Location of house area (north tile).
 * @param flags BuildingFlags containing the size of house area.
 */
static void RemoveNearbyStations(Town *t, TileIndex tile, BuildingFlags flags)
{
        for (StationList::iterator it = t->stations_near.begin(); it != t->stations_near.end(); /* incremented inside loop */) {
                const Station *st = *it;

                bool covers_area = st->TileIsInCatchment(tile);
                if (flags & BUILDING_2_TILES_Y)   covers_area |= st->TileIsInCatchment(tile + TileDiffXY(0, 1));
                if (flags & BUILDING_2_TILES_X)   covers_area |= st->TileIsInCatchment(tile + TileDiffXY(1, 0));
                if (flags & BUILDING_HAS_4_TILES) covers_area |= st->TileIsInCatchment(tile + TileDiffXY(1, 1));

                if (covers_area && !st->CatchmentCoversTown(t->index)) {
                        it = t->stations_near.erase(it);
                } else {
                        ++it;
                }
        }
}

/**
 * Helper function for house construction stage progression.
 * @param tile TileIndex of the house (or parts of it) to construct.
 */
static void AdvanceSingleHouseConstruction(TileIndex tile)
{
        assert(IsTileType(tile, MP_HOUSE));

        /* Progress in construction stages */
        IncHouseConstructionTick(tile);
        if (GetHouseConstructionTick(tile) != 0) return;

        AnimateNewHouseConstruction(tile);

        if (IsHouseCompleted(tile)) {
                /* Now that construction is complete, we can add the population of the
                 * building to the town. */
                ChangePopulation(Town::GetByTile(tile), HouseSpec::Get(GetHouseType(tile))->population);
                ResetHouseAge(tile);
        }
        MarkTileDirtyByTile(tile);
}

/**
 * Increase the construction stage of a house.
 * @param tile The tile of the house under construction.
 */
static void AdvanceHouseConstruction(TileIndex tile)
{
        uint flags = HouseSpec::Get(GetHouseType(tile))->building_flags;
        if (flags & BUILDING_HAS_1_TILE)  AdvanceSingleHouseConstruction(TileAddXY(tile, 0, 0));
        if (flags & BUILDING_2_TILES_Y)   AdvanceSingleHouseConstruction(TileAddXY(tile, 0, 1));
        if (flags & BUILDING_2_TILES_X)   AdvanceSingleHouseConstruction(TileAddXY(tile, 1, 0));
        if (flags & BUILDING_HAS_4_TILES) AdvanceSingleHouseConstruction(TileAddXY(tile, 1, 1));
}

/**
 * Generate cargo for a house, scaled by the current economy scale.
 * @param t The current town.
 * @param ct Type of cargo to generate, usually CT_PASSENGERS or CT_MAIL.
 * @param amount The number of cargo units.
 * @param stations Available stations for this house.
 * @param affected_by_recession Is this cargo halved during recessions?
 */
static void TownGenerateCargo(Town *t, CargoID ct, uint amount, StationFinder &stations, bool affected_by_recession)
{
        if (amount == 0) return;

        /* All production is halved during a recession (except for NewGRF-supplied town cargo). */
        if (affected_by_recession && EconomyIsInRecession()) {
                amount = (amount + 1) >> 1;
        }

        /* Scale by cargo scale setting. */
        amount = ScaleByCargoScale(amount, true);

        /* Actually generate cargo and update town statistics. */
        t->supplied[ct].new_max += amount;
        t->supplied[ct].new_act += MoveGoodsToStation(ct, amount, SourceType::Town, t->index, stations.GetStations());;
}

/**
 * Generate cargo for a house using the original algorithm.
 * @param t The current town.
 * @param tpe The town production effect.
 * @param rate The town's product rate for this production.
 * @param stations Available stations for this house.
 */
static void TownGenerateCargoOriginal(Town *t, TownProductionEffect tpe, uint8_t rate, StationFinder &stations)
{
        for (const CargoSpec *cs : CargoSpec::town_production_cargoes[tpe]) {
                uint32_t r = Random();
                if (GB(r, 0, 8) < rate) {
                        CargoID cid = cs->Index();
                        uint amt = (GB(r, 0, 8) * cs->town_production_multiplier / TOWN_PRODUCTION_DIVISOR) / 8 + 1;

                        TownGenerateCargo(t, cid, amt, stations, true);
                }
        }
}

/**
 * Generate cargo for a house using the binominal algorithm.
 * @param t The current town.
 * @param tpe The town production effect.
 * @param rate The town's product rate for this production.
 * @param stations Available stations for this house.
 */
static void TownGenerateCargoBinominal(Town *t, TownProductionEffect tpe, uint8_t rate, StationFinder &stations)
{
        for (const CargoSpec *cs : CargoSpec::town_production_cargoes[tpe]) {
                CargoID cid = cs->Index();
                uint32_t r = Random();

                /* Make a bitmask with up to 32 bits set, one for each potential pax. */
                int genmax = (rate + 7) / 8;
                uint32_t genmask = (genmax >= 32) ? 0xFFFFFFFF : ((1 << genmax) - 1);

                /* Mask random value by potential pax and count number of actual pax. */
                uint amt = CountBits(r & genmask) * cs->town_production_multiplier / TOWN_PRODUCTION_DIVISOR;

                TownGenerateCargo(t, cid, amt, stations, true);
        }
}

/**
 * Tile callback function.
 *
 * Tile callback function. Periodic tick handler for the tiles of a town.
 * @param tile been asked to do its stuff
 */
static void TileLoop_Town(TileIndex tile)
{
        HouseID house_id = GetHouseType(tile);

        /* NewHouseTileLoop returns false if Callback 21 succeeded, i.e. the house
         * doesn't exist any more, so don't continue here. */
        if (house_id >= NEW_HOUSE_OFFSET && !NewHouseTileLoop(tile)) return;

        if (!IsHouseCompleted(tile)) {
                /* Construction is not completed, so we advance a construction stage. */
                AdvanceHouseConstruction(tile);
                return;
        }

        const HouseSpec *hs = HouseSpec::Get(house_id);

        /* If the lift has a destination, it is already an animated tile. */
        if ((hs->building_flags & BUILDING_IS_ANIMATED) &&
                        house_id < NEW_HOUSE_OFFSET &&
                        !LiftHasDestination(tile) &&
                        Chance16(1, 2)) {
                AddAnimatedTile(tile);
        }

        Town *t = Town::GetByTile(tile);
        uint32_t r = Random();

        StationFinder stations(TileArea(tile, 1, 1));

        if (HasBit(hs->callback_mask, CBM_HOUSE_PRODUCE_CARGO)) {
                for (uint i = 0; i < 256; i++) {
                        uint16_t callback = GetHouseCallback(CBID_HOUSE_PRODUCE_CARGO, i, r, house_id, t, tile);

                        if (callback == CALLBACK_FAILED || callback == CALLBACK_HOUSEPRODCARGO_END) break;

                        CargoID cargo = GetCargoTranslation(GB(callback, 8, 7), hs->grf_prop.grffile);
                        if (!IsValidCargoID(cargo)) continue;

                        uint amt = GB(callback, 0, 8);
                        if (amt == 0) continue;

                        /* NewGRF-supplied town cargos are not affected by recessions. */
                        TownGenerateCargo(t, cargo, amt, stations, false);
                }
        } else {
                switch (_settings_game.economy.town_cargogen_mode) {
                        case TCGM_ORIGINAL:
                                /* Original (quadratic) cargo generation algorithm */
                                TownGenerateCargoOriginal(t, TPE_PASSENGERS, hs->population, stations);
                                TownGenerateCargoOriginal(t, TPE_MAIL, hs->mail_generation, stations);
                                break;

                        case TCGM_BITCOUNT:
                                /* Binomial distribution per tick, by a series of coin flips */
                                /* Reduce generation rate to a 1/4, using tile bits to spread out distribution.
                                 * As tick counter is incremented by 256 between each call, we ignore the lower 8 bits. */
                                if (GB(TimerGameTick::counter, 8, 2) == GB(tile.base(), 0, 2)) {
                                        TownGenerateCargoBinominal(t, TPE_PASSENGERS, hs->population, stations);
                                        TownGenerateCargoBinominal(t, TPE_MAIL, hs->mail_generation, stations);
                                }
                                break;

                        default:
                                NOT_REACHED();
                }
        }

        Backup<CompanyID> cur_company(_current_company, OWNER_TOWN);

        if ((hs->building_flags & BUILDING_HAS_1_TILE) &&
                        HasBit(t->flags, TOWN_IS_GROWING) &&
                        CanDeleteHouse(tile) &&
                        GetHouseAge(tile) >= hs->minimum_life &&
                        --t->time_until_rebuild == 0) {
                t->time_until_rebuild = GB(r, 16, 8) + 192;

                ClearTownHouse(t, tile);

                /* Rebuild with another house? */
                if (GB(r, 24, 8) >= 12) {
                        /* If we are multi-tile houses, make sure to replace the house
                         * closest to city center. If we do not do this, houses tend to
                         * wander away from roads and other houses. */
                        if (hs->building_flags & BUILDING_HAS_2_TILES) {
                                /* House tiles are always the most north tile. Move the new
                                 * house to the south if we are north of the city center. */
                                TileIndexDiffC grid_pos = TileIndexToTileIndexDiffC(t->xy, tile);
                                int x = Clamp(grid_pos.x, 0, 1);
                                int y = Clamp(grid_pos.y, 0, 1);

                                if (hs->building_flags & TILE_SIZE_2x2) {
                                        tile = TileAddXY(tile, x, y);
                                } else if (hs->building_flags & TILE_SIZE_1x2) {
                                        tile = TileAddXY(tile, 0, y);
                                } else if (hs->building_flags & TILE_SIZE_2x1) {
                                        tile = TileAddXY(tile, x, 0);
                                }
                        }

                        TryBuildTownHouse(t, tile);
                }
        }

        cur_company.Restore();
}

/**
 * Callback function to clear a house tile.
 * @param tile The tile to clear.
 * @param flags Type of operation.
 * @return The cost of this operation or an error.
 */
static CommandCost ClearTile_Town(TileIndex tile, DoCommandFlag flags)
{
        if (flags & DC_AUTO) return_cmd_error(STR_ERROR_BUILDING_MUST_BE_DEMOLISHED);
        if (!CanDeleteHouse(tile)) return CMD_ERROR;

        const HouseSpec *hs = HouseSpec::Get(GetHouseType(tile));

        CommandCost cost(EXPENSES_CONSTRUCTION);
        cost.AddCost(hs->GetRemovalCost());

        int rating = hs->remove_rating_decrease;
        Town *t = Town::GetByTile(tile);

        if (Company::IsValidID(_current_company)) {
                if (rating > t->ratings[_current_company] && !(flags & DC_NO_TEST_TOWN_RATING) &&
                                !_cheats.magic_bulldozer.value && _settings_game.difficulty.town_council_tolerance != TOWN_COUNCIL_PERMISSIVE) {
                        SetDParam(0, t->index);
                        return_cmd_error(STR_ERROR_LOCAL_AUTHORITY_REFUSES_TO_ALLOW_THIS);
                }
        }

        ChangeTownRating(t, -rating, RATING_HOUSE_MINIMUM, flags);
        if (flags & DC_EXEC) {
                ClearTownHouse(t, tile);
        }

        return cost;
}

static void AddProducedCargo_Town(TileIndex tile, CargoArray &produced)
{
        HouseID house_id = GetHouseType(tile);
        const HouseSpec *hs = HouseSpec::Get(house_id);
        Town *t = Town::GetByTile(tile);

        if (HasBit(hs->callback_mask, CBM_HOUSE_PRODUCE_CARGO)) {
                for (uint i = 0; i < 256; i++) {
                        uint16_t callback = GetHouseCallback(CBID_HOUSE_PRODUCE_CARGO, i, 0, house_id, t, tile);

                        if (callback == CALLBACK_FAILED || callback == CALLBACK_HOUSEPRODCARGO_END) break;

                        CargoID cargo = GetCargoTranslation(GB(callback, 8, 7), hs->grf_prop.grffile);

                        if (!IsValidCargoID(cargo)) continue;
                        produced[cargo]++;
                }
        } else {
                if (hs->population > 0) {
                        for (const CargoSpec *cs : CargoSpec::town_production_cargoes[TPE_PASSENGERS]) {
                                produced[cs->Index()]++;
                        }
                }
                if (hs->mail_generation > 0) {
                        for (const CargoSpec *cs : CargoSpec::town_production_cargoes[TPE_MAIL]) {
                                produced[cs->Index()]++;
                        }
                }
        }
}

/**
 * Fill cargo acceptance array and always_accepted mask, if cargo ID is valid.
 * @param cargo Cargo type to add.
 * @param amount Amount of cargo to add.
 * @param[out] acceptance Output array containing amount of cargo accepted.
 * @param[out] always_accepted Output mask of accepted cargo types.
 */
static void AddAcceptedCargoSetMask(CargoID cargo, uint amount, CargoArray &acceptance, CargoTypes &always_accepted)
{
        if (!IsValidCargoID(cargo) || amount == 0) return;
        acceptance[cargo] += amount;
        SetBit(always_accepted, cargo);
}

static void AddAcceptedCargo_Town(TileIndex tile, CargoArray &acceptance, CargoTypes &always_accepted)
{
        const HouseSpec *hs = HouseSpec::Get(GetHouseType(tile));
        CargoID accepts[lengthof(hs->accepts_cargo)];

        /* Set the initial accepted cargo types */
        for (uint8_t i = 0; i < lengthof(accepts); i++) {
                accepts[i] = hs->accepts_cargo[i];
        }

        /* Check for custom accepted cargo types */
        if (HasBit(hs->callback_mask, CBM_HOUSE_ACCEPT_CARGO)) {
                uint16_t callback = GetHouseCallback(CBID_HOUSE_ACCEPT_CARGO, 0, 0, GetHouseType(tile), Town::GetByTile(tile), tile);
                if (callback != CALLBACK_FAILED) {
                        /* Replace accepted cargo types with translated values from callback */
                        accepts[0] = GetCargoTranslation(GB(callback,  0, 5), hs->grf_prop.grffile);
                        accepts[1] = GetCargoTranslation(GB(callback,  5, 5), hs->grf_prop.grffile);
                        accepts[2] = GetCargoTranslation(GB(callback, 10, 5), hs->grf_prop.grffile);
                }
        }

        /* Check for custom cargo acceptance */
        if (HasBit(hs->callback_mask, CBM_HOUSE_CARGO_ACCEPTANCE)) {
                uint16_t callback = GetHouseCallback(CBID_HOUSE_CARGO_ACCEPTANCE, 0, 0, GetHouseType(tile), Town::GetByTile(tile), tile);
                if (callback != CALLBACK_FAILED) {
                        AddAcceptedCargoSetMask(accepts[0], GB(callback, 0, 4), acceptance, always_accepted);
                        AddAcceptedCargoSetMask(accepts[1], GB(callback, 4, 4), acceptance, always_accepted);
                        if (_settings_game.game_creation.landscape != LT_TEMPERATE && HasBit(callback, 12)) {
                                /* The 'S' bit indicates food instead of goods */
                                AddAcceptedCargoSetMask(GetCargoIDByLabel(CT_FOOD), GB(callback, 8, 4), acceptance, always_accepted);
                        } else {
                                AddAcceptedCargoSetMask(accepts[2], GB(callback, 8, 4), acceptance, always_accepted);
                        }
                        return;
                }
        }

        /* No custom acceptance, so fill in with the default values */
        for (uint8_t i = 0; i < lengthof(accepts); i++) {
                AddAcceptedCargoSetMask(accepts[i], hs->cargo_acceptance[i], acceptance, always_accepted);
        }
}

static void GetTileDesc_Town(TileIndex tile, TileDesc *td)
{
        const HouseID house = GetHouseType(tile);
        const HouseSpec *hs = HouseSpec::Get(house);
        bool house_completed = IsHouseCompleted(tile);

        td->str = hs->building_name;

        uint16_t callback_res = GetHouseCallback(CBID_HOUSE_CUSTOM_NAME, house_completed ? 1 : 0, 0, house, Town::GetByTile(tile), tile);
        if (callback_res != CALLBACK_FAILED && callback_res != 0x400) {
                if (callback_res > 0x400) {
                        ErrorUnknownCallbackResult(hs->grf_prop.grffile->grfid, CBID_HOUSE_CUSTOM_NAME, callback_res);
                } else {
                        StringID new_name = GetGRFStringID(hs->grf_prop.grffile->grfid, 0xD000 + callback_res);
                        if (new_name != STR_NULL && new_name != STR_UNDEFINED) {
                                td->str = new_name;
                        }
                }
        }

        if (!house_completed) {
                td->dparam = td->str;
                td->str = STR_LAI_TOWN_INDUSTRY_DESCRIPTION_UNDER_CONSTRUCTION;
        }

        if (hs->grf_prop.grffile != nullptr) {
                const GRFConfig *gc = GetGRFConfig(hs->grf_prop.grffile->grfid);
                td->grf = gc->GetName();
        }

        td->owner[0] = OWNER_TOWN;
}

static TrackStatus GetTileTrackStatus_Town(TileIndex, TransportType, uint, DiagDirection)
{
        /* not used */
        return 0;
}

static void ChangeTileOwner_Town(TileIndex, Owner, Owner)
{
        /* not used */
}

static bool GrowTown(Town *t);

/**
 * Handle the town tick for a single town, by growing the town if desired.
 * @param t The town to try growing.
 */
static void TownTickHandler(Town *t)
{
        if (HasBit(t->flags, TOWN_IS_GROWING)) {
                int i = (int)t->grow_counter - 1;
                if (i < 0) {
                        if (GrowTown(t)) {
                                i = t->growth_rate;
                        } else {
                                /* If growth failed wait a bit before retrying */
                                i = std::min<uint16_t>(t->growth_rate, Ticks::TOWN_GROWTH_TICKS - 1);
                        }
                }
                t->grow_counter = i;
        }
}

/** Iterate through all towns and call their tick handler. */
void OnTick_Town()
{
        if (_game_mode == GM_EDITOR) return;

        for (Town *t : Town::Iterate()) {
                TownTickHandler(t);
        }
}

/**
 * Return the RoadBits of a tile, ignoring depot and bay road stops.
 * @param tile The tile to check.
 * @return The roadbits of the given tile.
 */
static RoadBits GetTownRoadBits(TileIndex tile)
{
        if (IsRoadDepotTile(tile) || IsBayRoadStopTile(tile)) return ROAD_NONE;

        return GetAnyRoadBits(tile, RTT_ROAD, true);
}

/**
 * Get the road type that towns should build at this current moment.
 * They may have built a different type in the past.
 */
RoadType GetTownRoadType()
{
        RoadType best_rt = ROADTYPE_ROAD;
        const RoadTypeInfo *best = nullptr;
        const uint16_t assume_max_speed = 50;

        for (RoadType rt = ROADTYPE_BEGIN; rt != ROADTYPE_END; rt++) {
                if (RoadTypeIsTram(rt)) continue;

                const RoadTypeInfo *rti = GetRoadTypeInfo(rt);

                /* Unused road type. */
                if (rti->label == 0) continue;

                /* Can town build this road. */
                if (!HasBit(rti->flags, ROTF_TOWN_BUILD)) continue;

                /* Not yet introduced at this date. */
                if (IsInsideMM(rti->introduction_date, 0, CalendarTime::MAX_DATE.base()) && rti->introduction_date > TimerGameCalendar::date) continue;

                if (best != nullptr) {
                        if ((rti->max_speed == 0 ? assume_max_speed : rti->max_speed) < (best->max_speed == 0 ? assume_max_speed : best->max_speed)) continue;
                }

                best_rt = rt;
                best = rti;
        }

        return best_rt;
}

/**
 * Get the calendar date of the earliest town-buildable road type.
 * @return introduction date of earliest road type, or INT32_MAX if none available.
 */
static TimerGameCalendar::Date GetTownRoadTypeFirstIntroductionDate()
{
        const RoadTypeInfo *best = nullptr;
        for (RoadType rt = ROADTYPE_BEGIN; rt != ROADTYPE_END; rt++) {
                if (RoadTypeIsTram(rt)) continue;
                const RoadTypeInfo *rti = GetRoadTypeInfo(rt);
                if (rti->label == 0) continue; // Unused road type.
                if (!HasBit(rti->flags, ROTF_TOWN_BUILD)) continue; // Town can't build this road type.

                if (best != nullptr && rti->introduction_date >= best->introduction_date) continue;
                best = rti;
        }

        if (best == nullptr) return INT32_MAX;
        return best->introduction_date;
}

/**
 * Check if towns are able to build road.
 * @return true iff the towns are currently able to build road.
 */
bool CheckTownRoadTypes()
{
        auto min_date = GetTownRoadTypeFirstIntroductionDate();
        if (min_date <= TimerGameCalendar::date) return true;

        if (min_date < INT32_MAX) {
                SetDParam(0, min_date);
                ShowErrorMessage(STR_ERROR_NO_TOWN_ROADTYPES_AVAILABLE_YET, STR_ERROR_NO_TOWN_ROADTYPES_AVAILABLE_YET_EXPLANATION, WL_CRITICAL);
        } else {
                ShowErrorMessage(STR_ERROR_NO_TOWN_ROADTYPES_AVAILABLE_AT_ALL, STR_ERROR_NO_TOWN_ROADTYPES_AVAILABLE_AT_ALL_EXPLANATION, WL_CRITICAL);
        }
        return false;
}

/**
 * Check for parallel road inside a given distance.
 *   Assuming a road from (tile - TileOffsByDiagDir(dir)) to tile,
 *   is there a parallel road left or right of it within distance dist_multi?
 *
 * @param tile The current tile.
 * @param dir The target direction.
 * @param dist_multi The distance multiplier.
 * @return true if there is a parallel road.
 */
static bool IsNeighborRoadTile(TileIndex tile, const DiagDirection dir, uint dist_multi)
{
        if (!IsValidTile(tile)) return false;

        /* Lookup table for the used diff values */
        const TileIndexDiff tid_lt[3] = {
                TileOffsByDiagDir(ChangeDiagDir(dir, DIAGDIRDIFF_90RIGHT)),
                TileOffsByDiagDir(ChangeDiagDir(dir, DIAGDIRDIFF_90LEFT)),
                TileOffsByDiagDir(ReverseDiagDir(dir)),
        };

        dist_multi = (dist_multi + 1) * 4;
        for (uint pos = 4; pos < dist_multi; pos++) {
                /* Go (pos / 4) tiles to the left or the right */
                TileIndexDiff cur = tid_lt[(pos & 1) ? 0 : 1] * (pos / 4);

                /* Use the current tile as origin, or go one tile backwards */
                if (pos & 2) cur += tid_lt[2];

                /* Test for roadbit parallel to dir and facing towards the middle axis */
                if (IsValidTile(tile + cur) &&
                                GetTownRoadBits(TileAdd(tile, cur)) & DiagDirToRoadBits((pos & 2) ? dir : ReverseDiagDir(dir))) return true;
        }
        return false;
}

/**
 * Check if a Road is allowed on a given tile.
 *
 * @param t The current town.
 * @param tile The target tile.
 * @param dir The direction in which we want to extend the town.
 * @return true if it is allowed.
 */
static bool IsRoadAllowedHere(Town *t, TileIndex tile, DiagDirection dir)
{
        if (DistanceFromEdge(tile) == 0) return false;

        /* Prevent towns from building roads under bridges along the bridge. Looks silly. */
        if (IsBridgeAbove(tile) && GetBridgeAxis(tile) == DiagDirToAxis(dir)) return false;

        /* Check if there already is a road at this point? */
        if (GetTownRoadBits(tile) == ROAD_NONE) {
                /* No, try if we are able to build a road piece there.
                 * If that fails clear the land, and if that fails exit.
                 * This is to make sure that we can build a road here later. */
                RoadType rt = GetTownRoadType();
                if (Command<CMD_BUILD_ROAD>::Do(DC_AUTO | DC_NO_WATER, tile, (dir == DIAGDIR_NW || dir == DIAGDIR_SE) ? ROAD_Y : ROAD_X, rt, DRD_NONE, 0).Failed() &&
                                Command<CMD_LANDSCAPE_CLEAR>::Do(DC_AUTO | DC_NO_WATER, tile).Failed()) {
                        return false;
                }
        }

        Slope cur_slope = _settings_game.construction.build_on_slopes ? std::get<0>(GetFoundationSlope(tile)) : GetTileSlope(tile);
        bool ret = !IsNeighborRoadTile(tile, dir, t->layout == TL_ORIGINAL ? 1 : 2);
        if (cur_slope == SLOPE_FLAT) return ret;

        /* If the tile is not a slope in the right direction, then
         * maybe terraform some. */
        Slope desired_slope = (dir == DIAGDIR_NW || dir == DIAGDIR_SE) ? SLOPE_NW : SLOPE_NE;
        if (desired_slope != cur_slope && ComplementSlope(desired_slope) != cur_slope) {
                if (Chance16(1, 8)) {
                        CommandCost res = CMD_ERROR;
                        if (!_generating_world && Chance16(1, 10)) {
                                /* Note: Do not replace "^ SLOPE_ELEVATED" with ComplementSlope(). The slope might be steep. */
                                res = std::get<0>(Command<CMD_TERRAFORM_LAND>::Do(DC_EXEC | DC_AUTO | DC_NO_WATER,
                                                tile, Chance16(1, 16) ? cur_slope : cur_slope ^ SLOPE_ELEVATED, false));
                        }
                        if (res.Failed() && Chance16(1, 3)) {
                                /* We can consider building on the slope, though. */
                                return ret;
                        }
                }
                return false;
        }
        return ret;
}

static bool TerraformTownTile(TileIndex tile, Slope edges, bool dir)
{
        assert(tile < Map::Size());

        CommandCost r = std::get<0>(Command<CMD_TERRAFORM_LAND>::Do(DC_AUTO | DC_NO_WATER, tile, edges, dir));
        if (r.Failed() || r.GetCost() >= (_price[PR_TERRAFORM] + 2) * 8) return false;
        Command<CMD_TERRAFORM_LAND>::Do(DC_AUTO | DC_NO_WATER | DC_EXEC, tile, edges, dir);
        return true;
}

static void LevelTownLand(TileIndex tile)
{
        assert(tile < Map::Size());

        /* Don't terraform if land is plain or if there's a house there. */
        if (IsTileType(tile, MP_HOUSE)) return;
        Slope tileh = GetTileSlope(tile);
        if (tileh == SLOPE_FLAT) return;

        /* First try up, then down */
        if (!TerraformTownTile(tile, ~tileh & SLOPE_ELEVATED, true)) {
                TerraformTownTile(tile, tileh & SLOPE_ELEVATED, false);
        }
}

/**
 * Generate the RoadBits of a grid tile.
 *
 * @param t The current town.
 * @param tile The tile in reference to the town.
 * @param dir The direction to which we are growing.
 * @return The RoadBit of the current tile regarding the selected town layout.
 */
static RoadBits GetTownRoadGridElement(Town *t, TileIndex tile, DiagDirection dir)
{
        /* align the grid to the downtown */
        TileIndexDiffC grid_pos = TileIndexToTileIndexDiffC(t->xy, tile); // Vector from downtown to the tile
        RoadBits rcmd = ROAD_NONE;

        switch (t->layout) {
                default: NOT_REACHED();

                case TL_2X2_GRID:
                        if ((grid_pos.x % 3) == 0) rcmd |= ROAD_Y;
                        if ((grid_pos.y % 3) == 0) rcmd |= ROAD_X;
                        break;

                case TL_3X3_GRID:
                        if ((grid_pos.x % 4) == 0) rcmd |= ROAD_Y;
                        if ((grid_pos.y % 4) == 0) rcmd |= ROAD_X;
                        break;
        }

        /* Optimise only X-junctions */
        if (rcmd != ROAD_ALL) return rcmd;

        RoadBits rb_template;

        switch (GetTileSlope(tile)) {
                default:       rb_template = ROAD_ALL; break;
                case SLOPE_W:  rb_template = ROAD_NW | ROAD_SW; break;
                case SLOPE_SW: rb_template = ROAD_Y  | ROAD_SW; break;
                case SLOPE_S:  rb_template = ROAD_SW | ROAD_SE; break;
                case SLOPE_SE: rb_template = ROAD_X  | ROAD_SE; break;
                case SLOPE_E:  rb_template = ROAD_SE | ROAD_NE; break;
                case SLOPE_NE: rb_template = ROAD_Y  | ROAD_NE; break;
                case SLOPE_N:  rb_template = ROAD_NE | ROAD_NW; break;
                case SLOPE_NW: rb_template = ROAD_X  | ROAD_NW; break;
                case SLOPE_STEEP_W:
                case SLOPE_STEEP_S:
                case SLOPE_STEEP_E:
                case SLOPE_STEEP_N:
                        rb_template = ROAD_NONE;
                        break;
        }

        /* Stop if the template is compatible to the growth dir */
        if (DiagDirToRoadBits(ReverseDiagDir(dir)) & rb_template) return rb_template;
        /* If not generate a straight road in the direction of the growth */
        return DiagDirToRoadBits(dir) | DiagDirToRoadBits(ReverseDiagDir(dir));
}

/**
 * Grows the town with an extra house.
 *  Check if there are enough neighbor house tiles
 *  next to the current tile. If there are enough
 *  add another house.
 *
 * @param t The current town.
 * @param tile The target tile for the extra house.
 * @return true if an extra house has been added.
 */
static bool GrowTownWithExtraHouse(Town *t, TileIndex tile)
{
        /* We can't look further than that. */
        if (DistanceFromEdge(tile) == 0) return false;

        uint counter = 0; // counts the house neighbor tiles

        /* Check the tiles E,N,W and S of the current tile for houses */
        for (DiagDirection dir = DIAGDIR_BEGIN; dir < DIAGDIR_END; dir++) {
                /* Count both void and house tiles for checking whether there
                 * are enough houses in the area. This to make it likely that
                 * houses get build up to the edge of the map. */
                switch (GetTileType(TileAddByDiagDir(tile, dir))) {
                        case MP_HOUSE:
                        case MP_VOID:
                                counter++;
                                break;

                        default:
                                break;
                }

                /* If there are enough neighbors stop here */
                if (counter >= 3) {
                        if (TryBuildTownHouse(t, tile)) {
                                _grow_town_result = GROWTH_SUCCEED;
                                return true;
                        }
                        return false;
                }
        }
        return false;
}

/**
 * Grows the town with a road piece.
 *
 * @param t The current town.
 * @param tile The current tile.
 * @param rcmd The RoadBits we want to build on the tile.
 * @return true if the RoadBits have been added.
 */
static bool GrowTownWithRoad(const Town *t, TileIndex tile, RoadBits rcmd)
{
        RoadType rt = GetTownRoadType();
        if (Command<CMD_BUILD_ROAD>::Do(DC_EXEC | DC_AUTO | DC_NO_WATER, tile, rcmd, rt, DRD_NONE, t->index).Succeeded()) {
                _grow_town_result = GROWTH_SUCCEED;
                return true;
        }
        return false;
}

/**
 * Checks if a town road can be continued into the next tile.
 *  Road vehicle stations, bridges, and tunnels are fine, as long as they are facing the right direction.
 *
 * @param t The current town
 * @param tile The tile where the road would be built
 * @param road_dir The direction of the road
 * @return true if the road can be continued, else false
 */
static bool CanRoadContinueIntoNextTile(const Town *t, const TileIndex tile, const DiagDirection road_dir)
{
        const int delta = TileOffsByDiagDir(road_dir); // +1 tile in the direction of the road
        TileIndex next_tile = tile + delta; // The tile beyond which must be connectable to the target tile
        RoadBits rcmd = DiagDirToRoadBits(ReverseDiagDir(road_dir));
        RoadType rt = GetTownRoadType();

        /* Before we try anything, make sure the tile is on the map and not the void. */
        if (!IsValidTile(next_tile)) return false;

        /* If the next tile is a bridge or tunnel, allow if it's continuing in the same direction. */
        if (IsTileType(next_tile, MP_TUNNELBRIDGE)) {
                return GetTunnelBridgeTransportType(next_tile) == TRANSPORT_ROAD && GetTunnelBridgeDirection(next_tile) == road_dir;
        }

        /* If the next tile is a station, allow if it's a road station facing the proper direction. Otherwise return false. */
        if (IsTileType(next_tile, MP_STATION)) {
                /* If the next tile is a road station, allow if it can be entered by the new tunnel/bridge, otherwise disallow. */
                return IsAnyRoadStop(next_tile) && (GetRoadStopDir(next_tile) == ReverseDiagDir(road_dir) || (IsDriveThroughStopTile(next_tile) && GetRoadStopDir(next_tile) == road_dir));
        }

        /* If the next tile is a road depot, allow if it's facing the right way. */
        if (IsTileType(next_tile, MP_ROAD)) {
                return IsRoadDepot(next_tile) && GetRoadDepotDirection(next_tile) == ReverseDiagDir(road_dir);
        }

        /* If the next tile is a railroad track, check if towns are allowed to build level crossings.
         * If level crossing are not allowed, reject the construction. Else allow DoCommand to determine if the rail track is buildable. */
        if (IsTileType(next_tile, MP_RAILWAY) && !_settings_game.economy.allow_town_level_crossings) return false;

        /* If a road tile can be built, the construction is allowed. */
        return Command<CMD_BUILD_ROAD>::Do(DC_AUTO | DC_NO_WATER, next_tile, rcmd, rt, DRD_NONE, t->index).Succeeded();
}

/**
 * CircularTileSearch proc which checks for a nearby parallel bridge to avoid building redundant bridges.
 * @param tile The tile to search.
 * @param user_data Reference to the valid direction of the proposed bridge.
 * @return true if another bridge exists, else false.
 */
static bool RedundantBridgeExistsNearby(TileIndex tile, void *user_data)
{
        /* Don't look into the void. */
        if (!IsValidTile(tile)) return false;

        /* Only consider bridge head tiles. */
        if (!IsBridgeTile(tile)) return false;

        /* Only consider road bridges. */
        if (GetTunnelBridgeTransportType(tile) != TRANSPORT_ROAD) return false;

        /* If the bridge is facing the same direction as the proposed bridge, we've found a redundant bridge. */
        return (GetTileSlope(tile) & InclinedSlope(ReverseDiagDir(*(DiagDirection *)user_data)));
}

/**
 * Grows the town with a bridge.
 *  At first we check if a bridge is reasonable.
 *  If so we check if we are able to build it.
 *
 * @param t The current town
 * @param tile The current tile
 * @param bridge_dir The valid direction in which to grow a bridge
 * @return true if a bridge has been build else false
 */
static bool GrowTownWithBridge(const Town *t, const TileIndex tile, const DiagDirection bridge_dir)
{
        assert(bridge_dir < DIAGDIR_END);

        const Slope slope = GetTileSlope(tile);

        /* Make sure the direction is compatible with the slope.
         * Well we check if the slope has an up bit set in the
         * reverse direction. */
        if (slope != SLOPE_FLAT && slope & InclinedSlope(bridge_dir)) return false;

        /* Assure that the bridge is connectable to the start side */
        if (!(GetTownRoadBits(TileAddByDiagDir(tile, ReverseDiagDir(bridge_dir))) & DiagDirToRoadBits(bridge_dir))) return false;

        /* We are in the right direction */
        uint bridge_length = 0;       // This value stores the length of the possible bridge
        TileIndex bridge_tile = tile; // Used to store the other waterside

        const int delta = TileOffsByDiagDir(bridge_dir);

        /* To prevent really small towns from building disproportionately
         * long bridges, make the max a function of its population. */
        const uint TOWN_BRIDGE_LENGTH_CAP = 11;
        uint base_bridge_length = 5;
        uint max_bridge_length = std::min(t->cache.population / 1000 + base_bridge_length, TOWN_BRIDGE_LENGTH_CAP);

        if (slope == SLOPE_FLAT) {
                /* Bridges starting on flat tiles are only allowed when crossing rivers, rails or one-way roads. */
                do {
                        if (bridge_length++ >= base_bridge_length) {
                                /* Allow to cross rivers, not big lakes, nor large amounts of rails or one-way roads. */
                                return false;
                        }
                        bridge_tile += delta;
                } while (IsValidTile(bridge_tile) && ((IsWaterTile(bridge_tile) && !IsSea(bridge_tile)) || IsPlainRailTile(bridge_tile) || (IsNormalRoadTile(bridge_tile) && GetDisallowedRoadDirections(bridge_tile) != DRD_NONE)));
        } else {
                do {
                        if (bridge_length++ >= max_bridge_length) {
                                /* Ensure the bridge is not longer than the max allowed length. */
                                return false;
                        }
                        bridge_tile += delta;
                } while (IsValidTile(bridge_tile) && (IsWaterTile(bridge_tile) || IsPlainRailTile(bridge_tile) || (IsNormalRoadTile(bridge_tile) && GetDisallowedRoadDirections(bridge_tile) != DRD_NONE)));
        }

        /* Don't allow a bridge where the start and end tiles are adjacent with no span between. */
        if (bridge_length == 1) return false;

        /* Make sure the road can be continued past the bridge. At this point, bridge_tile holds the end tile of the bridge. */
        if (!CanRoadContinueIntoNextTile(t, bridge_tile, bridge_dir)) return false;

        /* If another parallel bridge exists nearby, this one would be redundant and shouldn't be built. We don't care about flat bridges. */
        TileIndex search = tile;
        DiagDirection direction_to_match = bridge_dir;
        if (slope != SLOPE_FLAT && CircularTileSearch(&search, bridge_length, 0, 0, RedundantBridgeExistsNearby, &direction_to_match)) return false;

        for (uint8_t times = 0; times <= 22; times++) {
                uint8_t bridge_type = RandomRange(MAX_BRIDGES - 1);

                /* Can we actually build the bridge? */
                RoadType rt = GetTownRoadType();
                if (Command<CMD_BUILD_BRIDGE>::Do(CommandFlagsToDCFlags(GetCommandFlags<CMD_BUILD_BRIDGE>()), tile, bridge_tile, TRANSPORT_ROAD, bridge_type, rt).Succeeded()) {
                        Command<CMD_BUILD_BRIDGE>::Do(DC_EXEC | CommandFlagsToDCFlags(GetCommandFlags<CMD_BUILD_BRIDGE>()), tile, bridge_tile, TRANSPORT_ROAD, bridge_type, rt);
                        _grow_town_result = GROWTH_SUCCEED;
                        return true;
                }
        }
        /* Quit if it selecting an appropriate bridge type fails a large number of times. */
        return false;
}

/**
 * Grows the town with a tunnel.
 *  First we check if a tunnel is reasonable.
 *  If so we check if we are able to build it.
 *
 * @param t The current town
 * @param tile The current tile
 * @param tunnel_dir The valid direction in which to grow a tunnel
 * @return true if a tunnel has been built, else false
 */
static bool GrowTownWithTunnel(const Town *t, const TileIndex tile, const DiagDirection tunnel_dir)
{
        assert(tunnel_dir < DIAGDIR_END);

        Slope slope = GetTileSlope(tile);

        /* Only consider building a tunnel if the starting tile is sloped properly. */
        if (slope != InclinedSlope(tunnel_dir)) return false;

        /* Assure that the tunnel is connectable to the start side */
        if (!(GetTownRoadBits(TileAddByDiagDir(tile, ReverseDiagDir(tunnel_dir))) & DiagDirToRoadBits(tunnel_dir))) return false;

        const int delta = TileOffsByDiagDir(tunnel_dir);
        int max_tunnel_length = 0;

        /* There are two conditions for building tunnels: Under a mountain and under an obstruction. */
        if (CanRoadContinueIntoNextTile(t, tile, tunnel_dir)) {
                /* Only tunnel under a mountain if the slope is continuous for at least 4 tiles. We want tunneling to be a last resort for large hills. */
                TileIndex slope_tile = tile;
                for (uint8_t tiles = 0; tiles < 4; tiles++) {
                        if (!IsValidTile(slope_tile)) return false;
                        slope = GetTileSlope(slope_tile);
                        if (slope != InclinedSlope(tunnel_dir) && !IsSteepSlope(slope) && !IsSlopeWithOneCornerRaised(slope)) return false;
                        slope_tile += delta;
                }

                /* More population means longer tunnels, but make sure we can at least cover the smallest mountain which neccesitates tunneling. */
                max_tunnel_length = (t->cache.population / 1000) + 7;
        } else {
                /* When tunneling under an obstruction, the length limit is 5, enough to tunnel under a four-track railway. */
                max_tunnel_length = 5;
        }

        uint8_t tunnel_length = 0;
        TileIndex tunnel_tile = tile; // Iteratator to store the other end tile of the tunnel.

        /* Find the end tile of the tunnel for length and continuation checks. */
        do {
                if (tunnel_length++ >= max_tunnel_length) return false;
                tunnel_tile += delta;
                /* The tunnel ends when start and end tiles are the same height. */
        } while (IsValidTile(tunnel_tile) && GetTileZ(tile) != GetTileZ(tunnel_tile));

        /* Don't allow a tunnel where the start and end tiles are adjacent. */
        if (tunnel_length == 1) return false;

        /* Make sure the road can be continued past the tunnel. At this point, tunnel_tile holds the end tile of the tunnel. */
        if (!CanRoadContinueIntoNextTile(t, tunnel_tile, tunnel_dir)) return false;

        /* Attempt to build the tunnel. Return false if it fails to let the town build a road instead. */
        RoadType rt = GetTownRoadType();
        if (Command<CMD_BUILD_TUNNEL>::Do(CommandFlagsToDCFlags(GetCommandFlags<CMD_BUILD_TUNNEL>()), tile, TRANSPORT_ROAD, rt).Succeeded()) {
                Command<CMD_BUILD_TUNNEL>::Do(DC_EXEC | CommandFlagsToDCFlags(GetCommandFlags<CMD_BUILD_TUNNEL>()), tile, TRANSPORT_ROAD, rt);
                _grow_town_result = GROWTH_SUCCEED;
                return true;
        }

        return false;
}

/**
 * Checks whether at least one surrounding road allows to build a house here.
 *
 * @param t The tile where the house will be built.
 * @return true if at least one surrounding roadtype allows building houses here.
 */
static inline bool RoadTypesAllowHouseHere(TileIndex t)
{
        static const TileIndexDiffC tiles[] = { {-1, -1}, {-1, 0}, {-1, 1}, {0, -1}, {0, 1}, {1, -1}, {1, 0}, {1, 1} };
        bool allow = false;

        for (const auto &ptr : tiles) {
                TileIndex cur_tile = t + ToTileIndexDiff(ptr);
                if (!IsValidTile(cur_tile)) continue;

                if (!(IsTileType(cur_tile, MP_ROAD) || IsAnyRoadStopTile(cur_tile))) continue;
                allow = true;

                RoadType road_rt = GetRoadTypeRoad(cur_tile);
                RoadType tram_rt = GetRoadTypeTram(cur_tile);
                if (road_rt != INVALID_ROADTYPE && !HasBit(GetRoadTypeInfo(road_rt)->flags, ROTF_NO_HOUSES)) return true;
                if (tram_rt != INVALID_ROADTYPE && !HasBit(GetRoadTypeInfo(tram_rt)->flags, ROTF_NO_HOUSES)) return true;
        }

        /* If no road was found surrounding the tile we can allow building the house since there is
         * nothing which forbids it, if a road was found but the execution reached this point, then
         * all the found roads don't allow houses to be built */
        return !allow;
}

/** Test if town can grow road onto a specific tile.
 * @param tile Tile to build upon.
 * @return true iff the tile's road type don't prevent extending the road.
 */
static bool TownCanGrowRoad(TileIndex tile)
{
        if (!IsTileType(tile, MP_ROAD)) return true;

        /* Allow extending on roadtypes which can be built by town, or if the road type matches the type the town will build. */
        RoadType rt = GetRoadTypeRoad(tile);
        return HasBit(GetRoadTypeInfo(rt)->flags, ROTF_TOWN_BUILD) || GetTownRoadType() == rt;
}

/**
 * Check if the town is allowed to build roads.
 * @return true If the town is allowed to build roads.
 */
static inline bool TownAllowedToBuildRoads()
{
        return _settings_game.economy.allow_town_roads || _generating_world || _game_mode == GM_EDITOR;
}

/**
 * Grows the given town.
 * There are at the moment 3 possible way's for
 * the town expansion:
 *  @li Generate a random tile and check if there is a road allowed
 *  @li TL_ORIGINAL
 *  @li TL_BETTER_ROADS
 *  @li Check if the town geometry allows a road and which one
 *  @li TL_2X2_GRID
 *  @li TL_3X3_GRID
 *  @li Forbid roads, only build houses
 *
 * @param tile_ptr The current tile
 * @param cur_rb The current tiles RoadBits
 * @param target_dir The target road dir
 * @param t1 The current town
 */
static void GrowTownInTile(TileIndex *tile_ptr, RoadBits cur_rb, DiagDirection target_dir, Town *t1)
{
        RoadBits rcmd = ROAD_NONE;  // RoadBits for the road construction command
        TileIndex tile = *tile_ptr; // The main tile on which we base our growth

        assert(tile < Map::Size());

        if (cur_rb == ROAD_NONE) {
                /* Tile has no road. First reset the status counter
                 * to say that this is the last iteration. */
                _grow_town_result = GROWTH_SEARCH_STOPPED;

                if (!TownAllowedToBuildRoads()) return;
                if (!_settings_game.economy.allow_town_level_crossings && IsTileType(tile, MP_RAILWAY)) return;

                /* Remove hills etc */
                if (!_settings_game.construction.build_on_slopes || Chance16(1, 6)) LevelTownLand(tile);

                /* Is a road allowed here? */
                switch (t1->layout) {
                        default: NOT_REACHED();

                        case TL_3X3_GRID:
                        case TL_2X2_GRID:
                                rcmd = GetTownRoadGridElement(t1, tile, target_dir);
                                if (rcmd == ROAD_NONE) return;
                                break;

                        case TL_BETTER_ROADS:
                        case TL_ORIGINAL:
                                if (!IsRoadAllowedHere(t1, tile, target_dir)) return;

                                DiagDirection source_dir = ReverseDiagDir(target_dir);

                                if (Chance16(1, 4)) {
                                        /* Randomize a new target dir */
                                        do target_dir = RandomDiagDir(); while (target_dir == source_dir);
                                }

                                if (!IsRoadAllowedHere(t1, TileAddByDiagDir(tile, target_dir), target_dir)) {
                                        /* A road is not allowed to continue the randomized road,
                                         *  return if the road we're trying to build is curved. */
                                        if (target_dir != ReverseDiagDir(source_dir)) return;

                                        /* Return if neither side of the new road is a house */
                                        if (!IsTileType(TileAddByDiagDir(tile, ChangeDiagDir(target_dir, DIAGDIRDIFF_90RIGHT)), MP_HOUSE) &&
                                                        !IsTileType(TileAddByDiagDir(tile, ChangeDiagDir(target_dir, DIAGDIRDIFF_90LEFT)), MP_HOUSE)) {
                                                return;
                                        }

                                        /* That means that the road is only allowed if there is a house
                                         *  at any side of the new road. */
                                }

                                rcmd = DiagDirToRoadBits(target_dir) | DiagDirToRoadBits(source_dir);
                                break;
                }

        } else if (target_dir < DIAGDIR_END && !(cur_rb & DiagDirToRoadBits(ReverseDiagDir(target_dir)))) {
                if (!TownCanGrowRoad(tile)) return;

                /* Continue building on a partial road.
                 * Should be always OK, so we only generate
                 * the fitting RoadBits */
                _grow_town_result = GROWTH_SEARCH_STOPPED;

                if (!TownAllowedToBuildRoads()) return;

                switch (t1->layout) {
                        default: NOT_REACHED();

                        case TL_3X3_GRID:
                        case TL_2X2_GRID:
                                rcmd = GetTownRoadGridElement(t1, tile, target_dir);
                                break;

                        case TL_BETTER_ROADS:
                        case TL_ORIGINAL:
                                rcmd = DiagDirToRoadBits(ReverseDiagDir(target_dir));
                                break;
                }
        } else {
                bool allow_house = true; // Value which decides if we want to construct a house

                /* Reached a tunnel/bridge? Then continue at the other side of it, unless
                 * it is the starting tile. Half the time, we stay on this side then.*/
                if (IsTileType(tile, MP_TUNNELBRIDGE)) {
                        if (GetTunnelBridgeTransportType(tile) == TRANSPORT_ROAD && (target_dir != DIAGDIR_END || Chance16(1, 2))) {
                                *tile_ptr = GetOtherTunnelBridgeEnd(tile);
                        }
                        return;
                }

                /* Possibly extend the road in a direction.
                 * Randomize a direction and if it has a road, bail out. */
                target_dir = RandomDiagDir();
                RoadBits target_rb = DiagDirToRoadBits(target_dir);
                TileIndex house_tile; // position of a possible house

                if (cur_rb & target_rb) {
                        /* If it's a road turn possibly build a house in a corner.
                         * Use intersection with straight road as an indicator
                         * that we randomed corner house position.
                         * A turn (and we check for that later) always has only
                         * one common bit with a straight road so it has the same
                         * chance to be chosen as the house on the side of a road.
                         */
                        if ((cur_rb & ROAD_X) != target_rb) return;

                        /* Check whether it is a turn and if so determine
                         * position of the corner tile */
                        switch (cur_rb) {
                                case ROAD_N:
                                        house_tile = TileAddByDir(tile, DIR_S);
                                        break;
                                case ROAD_S:
                                        house_tile = TileAddByDir(tile, DIR_N);
                                        break;
                                case ROAD_E:
                                        house_tile = TileAddByDir(tile, DIR_W);
                                        break;
                                case ROAD_W:
                                        house_tile = TileAddByDir(tile, DIR_E);
                                        break;
                                default:
                                        return;  // not a turn
                        }
                        target_dir = DIAGDIR_END;
                } else {
                        house_tile = TileAddByDiagDir(tile, target_dir);
                }

                /* Don't walk into water. */
                if (HasTileWaterGround(house_tile)) return;

                if (!IsValidTile(house_tile)) return;

                if (target_dir != DIAGDIR_END && TownAllowedToBuildRoads()) {
                        switch (t1->layout) {
                                default: NOT_REACHED();

                                case TL_3X3_GRID: // Use 2x2 grid afterwards!
                                        GrowTownWithExtraHouse(t1, TileAddByDiagDir(house_tile, target_dir));
                                        [[fallthrough]];

                                case TL_2X2_GRID:
                                        rcmd = GetTownRoadGridElement(t1, tile, target_dir);
                                        allow_house = (rcmd & target_rb) == ROAD_NONE;
                                        break;

                                case TL_BETTER_ROADS: // Use original afterwards!
                                        GrowTownWithExtraHouse(t1, TileAddByDiagDir(house_tile, target_dir));
                                        [[fallthrough]];

                                case TL_ORIGINAL:
                                        /* Allow a house at the edge. 60% chance or
                                         * always ok if no road allowed. */
                                        rcmd = target_rb;
                                        allow_house = (!IsRoadAllowedHere(t1, house_tile, target_dir) || Chance16(6, 10));
                                        break;
                        }
                }

                allow_house &= RoadTypesAllowHouseHere(house_tile);

                if (allow_house) {
                        /* Build a house, but not if there already is a house there. */
                        if (!IsTileType(house_tile, MP_HOUSE)) {
                                /* Level the land if possible */
                                if (Chance16(1, 6)) LevelTownLand(house_tile);

                                /* And build a house.
                                 * Set result to -1 if we managed to build it. */
                                if (TryBuildTownHouse(t1, house_tile)) {
                                        _grow_town_result = GROWTH_SUCCEED;
                                }
                        }
                        return;
                }

                if (!TownCanGrowRoad(tile)) return;

                _grow_town_result = GROWTH_SEARCH_STOPPED;
        }

        /* Return if a water tile */
        if (HasTileWaterGround(tile)) return;

        /* Make the roads look nicer */
        rcmd = CleanUpRoadBits(tile, rcmd);
        if (rcmd == ROAD_NONE) return;

        /* Only use the target direction for bridges and tunnels to ensure they're connected.
         * The target_dir is as computed previously according to town layout, so
         * it will match it perfectly. */
        if (GrowTownWithBridge(t1, tile, target_dir)) return;
        if (GrowTownWithTunnel(t1, tile, target_dir)) return;

        GrowTownWithRoad(t1, tile, rcmd);
}

/**
 * Checks whether a road can be followed or is a dead end, that can not be extended to the next tile.
 * This only checks trivial but often cases.
 * @param tile Start tile for road.
 * @param dir Direction for road to follow or build.
 * @return true If road is or can be connected in the specified direction.
 */
static bool CanFollowRoad(TileIndex tile, DiagDirection dir)
{
        TileIndex target_tile = tile + TileOffsByDiagDir(dir);
        if (!IsValidTile(target_tile)) return false;
        if (HasTileWaterGround(target_tile)) return false;

        RoadBits target_rb = GetTownRoadBits(target_tile);
        if (TownAllowedToBuildRoads()) {
                /* Check whether a road connection exists or can be build. */
                switch (GetTileType(target_tile)) {
                        case MP_ROAD:
                                return target_rb != ROAD_NONE;

                        case MP_STATION:
                                return IsDriveThroughStopTile(target_tile);

                        case MP_TUNNELBRIDGE:
                                return GetTunnelBridgeTransportType(target_tile) == TRANSPORT_ROAD;

                        case MP_HOUSE:
                        case MP_INDUSTRY:
                        case MP_OBJECT:
                                return false;

                        default:
                                /* Checked for void and water earlier */
                                return true;
                }
        } else {
                /* Check whether a road connection already exists,
                 * and it leads somewhere else. */
                RoadBits back_rb = DiagDirToRoadBits(ReverseDiagDir(dir));
                return (target_rb & back_rb) != 0 && (target_rb & ~back_rb) != 0;
        }
}

/**
 * Try to grow a town at a given road tile.
 * @param t The town to grow.
 * @param tile The road tile to try growing from.
 * @return true if we successfully expanded the town.
 */
static bool GrowTownAtRoad(Town *t, TileIndex tile)
{
        /* Special case.
         * @see GrowTownInTile Check the else if
         */
        DiagDirection target_dir = DIAGDIR_END; // The direction in which we want to extend the town

        assert(tile < Map::Size());

        /* Number of times to search.
         * Better roads, 2X2 and 3X3 grid grow quite fast so we give
         * them a little handicap. */
        switch (t->layout) {
                case TL_BETTER_ROADS:
                        _grow_town_result = 10 + t->cache.num_houses * 2 / 9;
                        break;

                case TL_3X3_GRID:
                case TL_2X2_GRID:
                        _grow_town_result = 10 + t->cache.num_houses * 1 / 9;
                        break;

                default:
                        _grow_town_result = 10 + t->cache.num_houses * 4 / 9;
                        break;
        }

        do {
                RoadBits cur_rb = GetTownRoadBits(tile); // The RoadBits of the current tile

                /* Try to grow the town from this point */
                GrowTownInTile(&tile, cur_rb, target_dir, t);
                if (_grow_town_result == GROWTH_SUCCEED) return true;

                /* Exclude the source position from the bitmask
                 * and return if no more road blocks available */
                if (IsValidDiagDirection(target_dir)) cur_rb &= ~DiagDirToRoadBits(ReverseDiagDir(target_dir));
                if (cur_rb == ROAD_NONE) return false;

                if (IsTileType(tile, MP_TUNNELBRIDGE)) {
                        /* Only build in the direction away from the tunnel or bridge. */
                        target_dir = ReverseDiagDir(GetTunnelBridgeDirection(tile));
                } else {
                        /* Select a random bit from the blockmask, walk a step
                         * and continue the search from there. */
                        do {
                                if (cur_rb == ROAD_NONE) return false;
                                RoadBits target_bits;
                                do {
                                        target_dir = RandomDiagDir();
                                        target_bits = DiagDirToRoadBits(target_dir);
                                } while (!(cur_rb & target_bits));
                                cur_rb &= ~target_bits;
                        } while (!CanFollowRoad(tile, target_dir));
                }
                tile = TileAddByDiagDir(tile, target_dir);

                if (IsTileType(tile, MP_ROAD) && !IsRoadDepot(tile) && HasTileRoadType(tile, RTT_ROAD)) {
                        /* Don't allow building over roads of other cities */
                        if (IsRoadOwner(tile, RTT_ROAD, OWNER_TOWN) && Town::GetByTile(tile) != t) {
                                return false;
                        } else if (IsRoadOwner(tile, RTT_ROAD, OWNER_NONE) && _game_mode == GM_EDITOR) {
                                /* If we are in the SE, and this road-piece has no town owner yet, it just found an
                                 * owner :) (happy happy happy road now) */
                                SetRoadOwner(tile, RTT_ROAD, OWNER_TOWN);
                                SetTownIndex(tile, t->index);
                        }
                }

                /* Max number of times is checked. */
        } while (--_grow_town_result >= 0);

        return false;
}

/**
 * Generate a random road block.
 * The probability of a straight road
 * is somewhat higher than a curved.
 *
 * @return A RoadBits value with 2 bits set
 */
static RoadBits GenRandomRoadBits()
{
        uint32_t r = Random();
        uint a = GB(r, 0, 2);
        uint b = GB(r, 8, 2);
        if (a == b) b ^= 2;
        return (RoadBits)((ROAD_NW << a) + (ROAD_NW << b));
}

/**
 * Grow the town.
 * @param t The town to grow
 * @return true if we successfully grew the town with a road or house.
 */
static bool GrowTown(Town *t)
{
        static const TileIndexDiffC _town_coord_mod[] = {
                {-1,  0},
                { 1,  1},
                { 1, -1},
                {-1, -1},
                {-1,  0},
                { 0,  2},
                { 2,  0},
                { 0, -2},
                {-1, -1},
                {-2,  2},
                { 2,  2},
                { 2, -2},
                { 0,  0}
        };

        /* Current "company" is a town */
        Backup<CompanyID> cur_company(_current_company, OWNER_TOWN);

        TileIndex tile = t->xy; // The tile we are working with ATM

        /* Find a road that we can base the construction on. */
        for (const auto &ptr : _town_coord_mod) {
                if (GetTownRoadBits(tile) != ROAD_NONE) {
                        bool success = GrowTownAtRoad(t, tile);
                        cur_company.Restore();
                        return success;
                }
                tile = TileAdd(tile, ToTileIndexDiff(ptr));
        }

        /* No road available, try to build a random road block by
         * clearing some land and then building a road there. */
        if (TownAllowedToBuildRoads()) {
                tile = t->xy;
                for (const auto &ptr : _town_coord_mod) {
                        /* Only work with plain land that not already has a house */
                        if (!IsTileType(tile, MP_HOUSE) && IsTileFlat(tile)) {
                                if (Command<CMD_LANDSCAPE_CLEAR>::Do(DC_AUTO | DC_NO_WATER, tile).Succeeded()) {
                                        RoadType rt = GetTownRoadType();
                                        Command<CMD_BUILD_ROAD>::Do(DC_EXEC | DC_AUTO, tile, GenRandomRoadBits(), rt, DRD_NONE, t->index);
                                        cur_company.Restore();
                                        return true;
                                }
                        }
                        tile = TileAdd(tile, ToTileIndexDiff(ptr));
                }
        }

        cur_company.Restore();
        return false;
}

/**
 * Update the cached town zone radii of a town, based on the number of houses.
 * @param t The town to update.
 */
void UpdateTownRadius(Town *t)
{
        static const std::array<std::array<uint32_t, HZB_END>, 23> _town_squared_town_zone_radius_data = {{
                {  4,  0,  0,  0,  0}, // 0
                { 16,  0,  0,  0,  0},
                { 25,  0,  0,  0,  0},
                { 36,  0,  0,  0,  0},
                { 49,  0,  4,  0,  0},
                { 64,  0,  4,  0,  0}, // 20
                { 64,  0,  9,  0,  1},
                { 64,  0,  9,  0,  4},
                { 64,  0, 16,  0,  4},
                { 81,  0, 16,  0,  4},
                { 81,  0, 16,  0,  4}, // 40
                { 81,  0, 25,  0,  9},
                { 81, 36, 25,  0,  9},
                { 81, 36, 25, 16,  9},
                { 81, 49,  0, 25,  9},
                { 81, 64,  0, 25,  9}, // 60
                { 81, 64,  0, 36,  9},
                { 81, 64,  0, 36, 16},
                {100, 81,  0, 49, 16},
                {100, 81,  0, 49, 25},
                {121, 81,  0, 49, 25}, // 80
                {121, 81,  0, 49, 25},
                {121, 81,  0, 49, 36}, // 88
        }};

        if (t->cache.num_houses < std::size(_town_squared_town_zone_radius_data) * 4) {
                t->cache.squared_town_zone_radius = _town_squared_town_zone_radius_data[t->cache.num_houses / 4];
        } else {
                int mass = t->cache.num_houses / 8;
                /* Actually we are proportional to sqrt() but that's right because we are covering an area.
                 * The offsets are to make sure the radii do not decrease in size when going from the table
                 * to the calculated value.*/
                t->cache.squared_town_zone_radius[HZB_TOWN_EDGE] = mass * 15 - 40;
                t->cache.squared_town_zone_radius[HZB_TOWN_OUTSKIRT] = mass * 9 - 15;
                t->cache.squared_town_zone_radius[HZB_TOWN_OUTER_SUBURB] = 0;
                t->cache.squared_town_zone_radius[HZB_TOWN_INNER_SUBURB] = mass * 5 - 5;
                t->cache.squared_town_zone_radius[HZB_TOWN_CENTRE] = mass * 3 + 5;
        }
}

/**
 * Update the maximum amount of montly passengers and mail for a town, based on its population.
 * @param t The town to update.
 */
void UpdateTownMaxPass(Town *t)
{
        for (const CargoSpec *cs : CargoSpec::town_production_cargoes[TPE_PASSENGERS]) {
                t->supplied[cs->Index()].old_max = ScaleByCargoScale(t->cache.population >> 3, true);
        }
        for (const CargoSpec *cs : CargoSpec::town_production_cargoes[TPE_MAIL]) {
                t->supplied[cs->Index()].old_max = ScaleByCargoScale(t->cache.population >> 4, true);
        }
}

static void UpdateTownGrowthRate(Town *t);
static void UpdateTownGrowth(Town *t);

/**
 * Actually create a town.
 *
 * @param t The town.
 * @param tile Where to put it.
 * @param townnameparts The town name.
 * @param size The preset size of the town.
 * @param city Should we create a city?
 * @param layout The road layout of the town.
 * @param manual Was the town placed manually?
 */
static void DoCreateTown(Town *t, TileIndex tile, uint32_t townnameparts, TownSize size, bool city, TownLayout layout, bool manual)
{
        AutoRestoreBackup backup(_generating_town, true);

        t->xy = tile;
        t->cache.num_houses = 0;
        t->time_until_rebuild = 10;
        UpdateTownRadius(t);
        t->flags = 0;
        t->cache.population = 0;
        InitializeBuildingCounts(t);
        /* Spread growth across ticks so even if there are many
         * similar towns they're unlikely to grow all in one tick */
        t->grow_counter = t->index % Ticks::TOWN_GROWTH_TICKS;
        t->growth_rate = TownTicksToGameTicks(250);
        t->show_zone = false;

        _town_kdtree.Insert(t->index);

        /* Set the default cargo requirement for town growth */
        switch (_settings_game.game_creation.landscape) {
                case LT_ARCTIC:
                        if (FindFirstCargoWithTownAcceptanceEffect(TAE_FOOD) != nullptr) t->goal[TAE_FOOD] = TOWN_GROWTH_WINTER;
                        break;

                case LT_TROPIC:
                        if (FindFirstCargoWithTownAcceptanceEffect(TAE_FOOD) != nullptr) t->goal[TAE_FOOD] = TOWN_GROWTH_DESERT;
                        if (FindFirstCargoWithTownAcceptanceEffect(TAE_WATER) != nullptr) t->goal[TAE_WATER] = TOWN_GROWTH_DESERT;
                        break;
        }

        t->fund_buildings_months = 0;

        for (uint i = 0; i != MAX_COMPANIES; i++) t->ratings[i] = RATING_INITIAL;

        t->have_ratings = 0;
        t->exclusivity = INVALID_COMPANY;
        t->exclusive_counter = 0;
        t->statues = 0;

        {
                TownNameParams tnp(_settings_game.game_creation.town_name);
                t->townnamegrfid = tnp.grfid;
                t->townnametype = tnp.type;
        }
        t->townnameparts = townnameparts;

        t->InitializeLayout(layout);

        t->larger_town = city;

        int x = (int)size * 16 + 3;
        if (size == TSZ_RANDOM) x = (Random() & 0xF) + 8;
        /* Don't create huge cities when founding town in-game */
        if (city && (!manual || _game_mode == GM_EDITOR)) x *= _settings_game.economy.initial_city_size;

        t->cache.num_houses += x;
        UpdateTownRadius(t);

        int i = x * 4;
        do {
                GrowTown(t);
        } while (--i);

        t->UpdateVirtCoord();
        InvalidateWindowData(WC_TOWN_DIRECTORY, 0, TDIWD_FORCE_REBUILD);

        t->cache.num_houses -= x;
        UpdateTownRadius(t);
        UpdateTownGrowthRate(t);
        UpdateTownMaxPass(t);
        UpdateAirportsNoise();
}

/**
 * Check if it's possible to place a town on a given tile.
 * @param tile The tile to check.
 * @return A zero cost if allowed, otherwise an error.
 */
static CommandCost TownCanBePlacedHere(TileIndex tile)
{
        /* Check if too close to the edge of map */
        if (DistanceFromEdge(tile) < 12) {
                return_cmd_error(STR_ERROR_TOO_CLOSE_TO_EDGE_OF_MAP_SUB);
        }

        /* Check distance to all other towns. */
        if (IsCloseToTown(tile, 20)) {
                return_cmd_error(STR_ERROR_TOO_CLOSE_TO_ANOTHER_TOWN);
        }

        /* Can only build on clear flat areas, possibly with trees. */
        if ((!IsTileType(tile, MP_CLEAR) && !IsTileType(tile, MP_TREES)) || !IsTileFlat(tile)) {
                return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
        }

        return CommandCost(EXPENSES_OTHER);
}

/**
 * Verifies this custom name is unique. Only custom names are checked.
 * @param name The name to check.
 * @return true if the name is unique
 */
static bool IsUniqueTownName(const std::string &name)
{
        for (const Town *t : Town::Iterate()) {
                if (!t->name.empty() && t->name == name) return false;
        }

        return true;
}

/**
 * Create a new town.
 * @param flags The type of operation.
 * @param tile The coordinates where town is built.
 * @param size The size of the town (@see TownSize).
 * @param city Should we build a city?
 * @param layout The town road layout (@see TownLayout).
 * @param random_location Should we use a random location? (randomize \c tile )
 * @param townnameparts Town name parts.
 * @param text Custom name for the town. If empty, the town name parts will be used.
 * @return The cost of this operation or an error.
 */
std::tuple<CommandCost, Money, TownID> CmdFoundTown(DoCommandFlag flags, TileIndex tile, TownSize size, bool city, TownLayout layout, bool random_location, uint32_t townnameparts, const std::string &text)
{
        TownNameParams par(_settings_game.game_creation.town_name);

        if (size >= TSZ_END) return { CMD_ERROR, 0, INVALID_TOWN };
        if (layout >= NUM_TLS) return { CMD_ERROR, 0, INVALID_TOWN };

        /* Some things are allowed only in the scenario editor and for game scripts. */
        if (_game_mode != GM_EDITOR && _current_company != OWNER_DEITY) {
                if (_settings_game.economy.found_town == TF_FORBIDDEN) return { CMD_ERROR, 0, INVALID_TOWN };
                if (size == TSZ_LARGE) return { CMD_ERROR, 0, INVALID_TOWN };
                if (random_location) return { CMD_ERROR, 0, INVALID_TOWN };
                if (_settings_game.economy.found_town != TF_CUSTOM_LAYOUT && layout != _settings_game.economy.town_layout) {
                        return { CMD_ERROR, 0, INVALID_TOWN };
                }
        } else if (_current_company == OWNER_DEITY && random_location) {
                /* Random parameter is not allowed for Game Scripts. */
                return { CMD_ERROR, 0, INVALID_TOWN };
        }

        if (text.empty()) {
                /* If supplied name is empty, townnameparts has to generate unique automatic name */
                if (!VerifyTownName(townnameparts, &par)) return { CommandCost(STR_ERROR_NAME_MUST_BE_UNIQUE), 0, INVALID_TOWN };
        } else {
                /* If name is not empty, it has to be unique custom name */
                if (Utf8StringLength(text) >= MAX_LENGTH_TOWN_NAME_CHARS) return { CMD_ERROR, 0, INVALID_TOWN };
                if (!IsUniqueTownName(text)) return { CommandCost(STR_ERROR_NAME_MUST_BE_UNIQUE), 0, INVALID_TOWN };
        }

        /* Allocate town struct */
        if (!Town::CanAllocateItem()) return { CommandCost(STR_ERROR_TOO_MANY_TOWNS), 0, INVALID_TOWN };

        if (!random_location) {
                CommandCost ret = TownCanBePlacedHere(tile);
                if (ret.Failed()) return { ret, 0, INVALID_TOWN };
        }

        static const uint8_t price_mult[][TSZ_RANDOM + 1] = {{ 15, 25, 40, 25 }, { 20, 35, 55, 35 }};
        /* multidimensional arrays have to have defined length of non-first dimension */
        static_assert(lengthof(price_mult[0]) == 4);

        CommandCost cost(EXPENSES_OTHER, _price[PR_BUILD_TOWN]);
        uint8_t mult = price_mult[city][size];

        cost.MultiplyCost(mult);

        /* Create the town */
        TownID new_town = INVALID_TOWN;
        if (flags & DC_EXEC) {
                if (cost.GetCost() > GetAvailableMoneyForCommand()) {
                        return { CommandCost(EXPENSES_OTHER), cost.GetCost(), INVALID_TOWN };
                }

                Backup<bool> old_generating_world(_generating_world, true);
                UpdateNearestTownForRoadTiles(true);
                Town *t;
                if (random_location) {
                        t = CreateRandomTown(20, townnameparts, size, city, layout);
                        if (t == nullptr) return { CommandCost(STR_ERROR_NO_SPACE_FOR_TOWN), 0, INVALID_TOWN };
                } else {
                        t = new Town(tile);
                        DoCreateTown(t, tile, townnameparts, size, city, layout, true);
                }

                new_town = t->index;
                UpdateNearestTownForRoadTiles(false);
                old_generating_world.Restore();

                if (t != nullptr && !text.empty()) {
                        t->name = text;
                        t->UpdateVirtCoord();
                }

                if (_game_mode != GM_EDITOR) {
                        /* 't' can't be nullptr since 'random' is false outside scenedit */
                        assert(!random_location);

                        if (_current_company == OWNER_DEITY) {
                                SetDParam(0, t->index);
                                AddTileNewsItem(STR_NEWS_NEW_TOWN_UNSPONSORED, NT_INDUSTRY_OPEN, tile);
                        } else {
                                SetDParam(0, _current_company);
                                NewsStringData *company_name = new NewsStringData(GetString(STR_COMPANY_NAME));

                                SetDParamStr(0, company_name->string);
                                SetDParam(1, t->index);

                                AddTileNewsItem(STR_NEWS_NEW_TOWN, NT_INDUSTRY_OPEN, tile, company_name);
                        }
                        AI::BroadcastNewEvent(new ScriptEventTownFounded(t->index));
                        Game::NewEvent(new ScriptEventTownFounded(t->index));
                }
        }
        return { cost, 0, new_town };
}

/**
 * Towns must all be placed on the same grid or when they eventually
 * interpenetrate their road networks will not mesh nicely; this
 * function adjusts a tile so that it aligns properly.
 *
 * @param tile The tile to start at.
 * @param layout The town layout in effect.
 * @return The adjusted tile.
 */
static TileIndex AlignTileToGrid(TileIndex tile, TownLayout layout)
{
        switch (layout) {
                case TL_2X2_GRID: return TileXY(TileX(tile) - TileX(tile) % 3, TileY(tile) - TileY(tile) % 3);
                case TL_3X3_GRID: return TileXY(TileX(tile) & ~3, TileY(tile) & ~3);
                default:          return tile;
        }
}

/**
 * Towns must all be placed on the same grid or when they eventually
 * interpenetrate their road networks will not mesh nicely; this
 * function tells you if a tile is properly aligned.
 *
 * @param tile The tile to start at.
 * @param layout The town layout in effect.
 * @return true if the tile is in the correct location.
 */
static bool IsTileAlignedToGrid(TileIndex tile, TownLayout layout)
{
        switch (layout) {
                case TL_2X2_GRID: return TileX(tile) % 3 == 0 && TileY(tile) % 3 == 0;
                case TL_3X3_GRID: return TileX(tile) % 4 == 0 && TileY(tile) % 4 == 0;
                default:          return true;
        }
}

/**
 * Used as the user_data for FindFurthestFromWater
 */
struct SpotData {
        TileIndex tile; ///< holds the tile that was found
        uint max_dist;  ///< holds the distance that tile is from the water
        TownLayout layout; ///< tells us what kind of town we're building
};

/**
 * CircularTileSearch callback; finds the tile furthest from any
 * water. slightly bit tricky, since it has to do a search of its own
 * in order to find the distance to the water from each square in the
 * radius.
 *
 * Also, this never returns true, because it needs to take into
 * account all locations being searched before it knows which is the
 * furthest.
 *
 * @param tile Start looking from this tile
 * @param user_data Storage area for data that must last across calls;
 * must be a pointer to struct SpotData
 *
 * @return always false
 */
static bool FindFurthestFromWater(TileIndex tile, void *user_data)
{
        SpotData *sp = (SpotData*)user_data;
        uint dist = GetClosestWaterDistance(tile, true);

        if (IsTileType(tile, MP_CLEAR) &&
                        IsTileFlat(tile) &&
                        IsTileAlignedToGrid(tile, sp->layout) &&
                        dist > sp->max_dist) {
                sp->tile = tile;
                sp->max_dist = dist;
        }

        return false;
}

/**
 * CircularTileSearch callback to find the nearest land tile.
 * @param tile Start looking from this tile
 */
static bool FindNearestEmptyLand(TileIndex tile, void *)
{
        return IsTileType(tile, MP_CLEAR);
}

/**
 * Given a spot on the map (presumed to be a water tile), find a good
 * coastal spot to build a city. We don't want to build too close to
 * the edge if we can help it (since that inhibits city growth) hence
 * the search within a search within a search. O(n*m^2), where n is
 * how far to search for land, and m is how far inland to look for a
 * flat spot.
 *
 * @param tile Start looking from this spot.
 * @param layout the road layout to search for
 * @return tile that was found
 */
static TileIndex FindNearestGoodCoastalTownSpot(TileIndex tile, TownLayout layout)
{
        SpotData sp = { INVALID_TILE, 0, layout };

        TileIndex coast = tile;
        if (CircularTileSearch(&coast, 40, FindNearestEmptyLand, nullptr)) {
                CircularTileSearch(&coast, 10, FindFurthestFromWater, &sp);
                return sp.tile;
        }

        /* if we get here just give up */
        return INVALID_TILE;
}

/**
 * Create a random town somewhere in the world.
 * @param attempts How many times should we try?
 * @param townnameparts The name of the town.
 * @param size The size preset of the town.
 * @param city Should we build a city?
 * @param layout The road layout to build.
 * @return The town object, or nullptr if we failed to create a town anywhere.
 */
static Town *CreateRandomTown(uint attempts, uint32_t townnameparts, TownSize size, bool city, TownLayout layout)
{
        assert(_game_mode == GM_EDITOR || _generating_world); // These are the preconditions for CMD_DELETE_TOWN

        if (!Town::CanAllocateItem()) return nullptr;

        do {
                /* Generate a tile index not too close from the edge */
                TileIndex tile = AlignTileToGrid(RandomTile(), layout);

                /* if we tried to place the town on water, slide it over onto
                 * the nearest likely-looking spot */
                if (IsTileType(tile, MP_WATER)) {
                        tile = FindNearestGoodCoastalTownSpot(tile, layout);
                        if (tile == INVALID_TILE) continue;
                }

                /* Make sure town can be placed here */
                if (TownCanBePlacedHere(tile).Failed()) continue;

                /* Allocate a town struct */
                Town *t = new Town(tile);

                DoCreateTown(t, tile, townnameparts, size, city, layout, false);

                /* if the population is still 0 at the point, then the
                 * placement is so bad it couldn't grow at all */
                if (t->cache.population > 0) return t;

                Backup<CompanyID> cur_company(_current_company, OWNER_TOWN);
                [[maybe_unused]] CommandCost rc = Command<CMD_DELETE_TOWN>::Do(DC_EXEC, t->index);
                cur_company.Restore();
                assert(rc.Succeeded());

                /* We already know that we can allocate a single town when
                 * entering this function. However, we create and delete
                 * a town which "resets" the allocation checks. As such we
                 * need to check again when assertions are enabled. */
                assert(Town::CanAllocateItem());
        } while (--attempts != 0);

        return nullptr;
}

static const uint8_t _num_initial_towns[4] = {5, 11, 23, 46};  // very low, low, normal, high

/**
 * Generate a number of towns with a given layout.
 * This function is used by the Random Towns button in Scenario Editor as well as in world generation.
 * @param layout The road layout to build.
 * @return true if towns have been successfully created.
 */
bool GenerateTowns(TownLayout layout)
{
        uint current_number = 0;
        uint difficulty = (_game_mode != GM_EDITOR) ? _settings_game.difficulty.number_towns : 0;
        uint total = (difficulty == (uint)CUSTOM_TOWN_NUMBER_DIFFICULTY) ? _settings_game.game_creation.custom_town_number : Map::ScaleBySize(_num_initial_towns[difficulty] + (Random() & 7));
        total = std::min<uint>(TownPool::MAX_SIZE, total);
        uint32_t townnameparts;
        TownNames town_names;

        SetGeneratingWorldProgress(GWP_TOWN, total);

        /* Pre-populate the town names list with the names of any towns already on the map */
        for (const Town *town : Town::Iterate()) {
                town_names.insert(town->GetCachedName());
        }

        /* First attempt will be made at creating the suggested number of towns.
         * Note that this is really a suggested value, not a required one.
         * We would not like the system to lock up just because the user wanted 100 cities on a 64*64 map, would we? */
        do {
                bool city = (_settings_game.economy.larger_towns != 0 && Chance16(1, _settings_game.economy.larger_towns));
                IncreaseGeneratingWorldProgress(GWP_TOWN);
                /* Get a unique name for the town. */
                if (!GenerateTownName(_random, &townnameparts, &town_names)) continue;
                /* try 20 times to create a random-sized town for the first loop. */
                if (CreateRandomTown(20, townnameparts, TSZ_RANDOM, city, layout) != nullptr) current_number++; // If creation was successful, raise a flag.
        } while (--total);

        town_names.clear();

        /* Build the town k-d tree again to make sure it's well balanced */
        RebuildTownKdtree();

        if (current_number != 0) return true;

        /* If current_number is still zero at this point, it means that not a single town has been created.
         * So give it a last try, but now more aggressive */
        if (GenerateTownName(_random, &townnameparts) &&
                        CreateRandomTown(10000, townnameparts, TSZ_RANDOM, _settings_game.economy.larger_towns != 0, layout) != nullptr) {
                return true;
        }

        /* If there are no towns at all and we are generating new game, bail out */
        if (Town::GetNumItems() == 0 && _game_mode != GM_EDITOR) {
                ShowErrorMessage(STR_ERROR_COULD_NOT_CREATE_TOWN, INVALID_STRING_ID, WL_CRITICAL);
        }

        return false;  // we are still without a town? we failed, simply
}


/**
 * Returns the bit corresponding to the town zone of the specified tile.
 * @param t Town on which town zone is to be found.
 * @param tile TileIndex where town zone needs to be found.
 * @return the bit position of the given zone, as defined in HouseZones.
 */
HouseZonesBits GetTownRadiusGroup(const Town *t, TileIndex tile)
{
        uint dist = DistanceSquare(tile, t->xy);

        if (t->fund_buildings_months && dist <= 25) return HZB_TOWN_CENTRE;

        HouseZonesBits smallest = HZB_TOWN_EDGE;
        for (HouseZonesBits i = HZB_BEGIN; i < HZB_END; i++) {
                if (dist < t->cache.squared_town_zone_radius[i]) smallest = i;
        }

        return smallest;
}

/**
 * Clears tile and builds a house or house part.
 * @param tile The tile to build upon.
 * @param t The town which will own the house.
 * @param counter The construction stage counter for the house.
 * @param stage The current construction stage of the house.
 * @param type The type of house.
 * @param random_bits Random bits for newgrf houses to use.
 * @pre The house can be built here.
 */
static inline void ClearMakeHouseTile(TileIndex tile, Town *t, uint8_t counter, uint8_t stage, HouseID type, uint8_t random_bits)
{
        [[maybe_unused]] CommandCost cc = Command<CMD_LANDSCAPE_CLEAR>::Do(DC_EXEC | DC_AUTO | DC_NO_WATER, tile);
        assert(cc.Succeeded());

        IncreaseBuildingCount(t, type);
        MakeHouseTile(tile, t->index, counter, stage, type, random_bits);
        if (HouseSpec::Get(type)->building_flags & BUILDING_IS_ANIMATED) AddAnimatedTile(tile, false);

        MarkTileDirtyByTile(tile);
}


/**
 * Write house information into the map. For multi-tile houses, all tiles are marked.
 * @param town The town related to this house
 * @param t The tile to build on. If a multi-tile house, this is the northern-most tile.
 * @param counter The counter of the construction stage.
 * @param stage The current construction stage.
 * @param The type of house.
 * @param random_bits Random bits for newgrf houses to use.
 * @pre The house can be built here.
 */
static void MakeTownHouse(TileIndex tile, Town *t, uint8_t counter, uint8_t stage, HouseID type, uint8_t random_bits)
{
        BuildingFlags size = HouseSpec::Get(type)->building_flags;

        ClearMakeHouseTile(tile, t, counter, stage, type, random_bits);
        if (size & BUILDING_2_TILES_Y)   ClearMakeHouseTile(tile + TileDiffXY(0, 1), t, counter, stage, ++type, random_bits);
        if (size & BUILDING_2_TILES_X)   ClearMakeHouseTile(tile + TileDiffXY(1, 0), t, counter, stage, ++type, random_bits);
        if (size & BUILDING_HAS_4_TILES) ClearMakeHouseTile(tile + TileDiffXY(1, 1), t, counter, stage, ++type, random_bits);

        ForAllStationsAroundTiles(TileArea(tile, (size & BUILDING_2_TILES_X) ? 2 : 1, (size & BUILDING_2_TILES_Y) ? 2 : 1), [t](Station *st, TileIndex) {
                t->stations_near.insert(st);
                return true;
        });
}


/**
 * Check if a house can be built here, based on slope, whether there's a bridge above, and if we can clear the land.
 * @param tile The tile to check.
 * @param noslope Are foundations prohibited for this house?
 * @return true iff house can be built here.
 */
static inline bool CanBuildHouseHere(TileIndex tile, bool noslope)
{
        /* cannot build on these slopes... */
        Slope slope = GetTileSlope(tile);
        if ((noslope && slope != SLOPE_FLAT) || IsSteepSlope(slope)) return false;

        /* at least one RoadTypes allow building the house here? */
        if (!RoadTypesAllowHouseHere(tile)) return false;

        /* building under a bridge? */
        if (IsBridgeAbove(tile)) return false;

        /* can we clear the land? */
        return Command<CMD_LANDSCAPE_CLEAR>::Do(DC_AUTO | DC_NO_WATER, tile).Succeeded();
}


/**
 * Check if a tile where we want to build a multi-tile house has an appropriate max Z.
 * @param tile The tile to check.
 * @param z The max Z level to allow.
 * @param noslope Are foundations disallowed for this house?
 * @return true iff house can be built here.
 * @see CanBuildHouseHere()
 */
static inline bool CheckBuildHouseSameZ(TileIndex tile, int z, bool noslope)
{
        if (!CanBuildHouseHere(tile, noslope)) return false;

        /* if building on slopes is allowed, there will be flattening foundation (to tile max z) */
        if (GetTileMaxZ(tile) != z) return false;

        return true;
}


/**
 * Checks if a house of size 2x2 can be built at this tile.
 * @param tile The tile of the house's northernmost tile.
 * @param z The maximum tile z, so all tiles are the same height.
 * @param noslope Are foundations disallowed for this house?
 * @return true iff house can be built here.
 * @see CheckBuildHouseSameZ()
 */
static bool CheckFree2x2Area(TileIndex tile, int z, bool noslope)
{
        /* we need to check this tile too because we can be at different tile now */
        if (!CheckBuildHouseSameZ(tile, z, noslope)) return false;

        for (DiagDirection d = DIAGDIR_SE; d < DIAGDIR_END; d++) {
                tile += TileOffsByDiagDir(d);
                if (!CheckBuildHouseSameZ(tile, z, noslope)) return false;
        }

        return true;
}


/**
 * Checks if the current town layout allows building here.
 * @param t The town.
 * @param tile The tile to check.
 * @return true iff town layout allows building here.
 * @note see layouts
 */
static inline bool TownLayoutAllowsHouseHere(Town *t, TileIndex tile)
{
        /* Allow towns everywhere when we don't build roads */
        if (!TownAllowedToBuildRoads()) return true;

        TileIndexDiffC grid_pos = TileIndexToTileIndexDiffC(t->xy, tile);

        switch (t->layout) {
                case TL_2X2_GRID:
                        if ((grid_pos.x % 3) == 0 || (grid_pos.y % 3) == 0) return false;
                        break;

                case TL_3X3_GRID:
                        if ((grid_pos.x % 4) == 0 || (grid_pos.y % 4) == 0) return false;
                        break;

                default:
                        break;
        }

        return true;
}


/**
 * Checks if the current town layout allows a 2x2 building here.
 * @param t The town.
 * @param tile The tile to check.
 * @return true iff town layout allows a 2x2 building here.
 * @note see layouts
 */
static inline bool TownLayoutAllows2x2HouseHere(Town *t, TileIndex tile)
{
        /* Allow towns everywhere when we don't build roads */
        if (!TownAllowedToBuildRoads()) return true;

        /* Compute relative position of tile. (Positive offsets are towards north) */
        TileIndexDiffC grid_pos = TileIndexToTileIndexDiffC(t->xy, tile);

        switch (t->layout) {
                case TL_2X2_GRID:
                        grid_pos.x %= 3;
                        grid_pos.y %= 3;
                        if ((grid_pos.x != 2 && grid_pos.x != -1) ||
                                (grid_pos.y != 2 && grid_pos.y != -1)) return false;
                        break;

                case TL_3X3_GRID:
                        if ((grid_pos.x & 3) < 2 || (grid_pos.y & 3) < 2) return false;
                        break;

                default:
                        break;
        }

        return true;
}


/**
 * Checks if a 1x2 or 2x1 building is allowed here, accounting for road layout and tile heights.
 * Also, tests both building positions that occupy this tile.
 * @param tile The tile where the building should be built.
 * @param t The town.
 * @param maxz The maximum Z level, since all tiles must have the same height.
 * @param noslope Are foundations disallowed for this house?
 * @param second The diagdir from the first tile to the second tile.
 */
static bool CheckTownBuild2House(TileIndex *tile, Town *t, int maxz, bool noslope, DiagDirection second)
{
        /* 'tile' is already checked in BuildTownHouse() - CanBuildHouseHere() and slope test */

        TileIndex tile2 = *tile + TileOffsByDiagDir(second);
        if (TownLayoutAllowsHouseHere(t, tile2) && CheckBuildHouseSameZ(tile2, maxz, noslope)) return true;

        tile2 = *tile + TileOffsByDiagDir(ReverseDiagDir(second));
        if (TownLayoutAllowsHouseHere(t, tile2) && CheckBuildHouseSameZ(tile2, maxz, noslope)) {
                *tile = tile2;
                return true;
        }

        return false;
}


/**
 * Checks if a 1x2 or 2x1 building is allowed here, accounting for road layout and tile heights.
 * Also, tests all four building positions that occupy this tile.
 * @param tile The tile where the building should be built.
 * @param t The town.
 * @param maxz The maximum Z level, since all tiles must have the same height.
 * @param noslope Are foundations disallowed for this house?
 */
static bool CheckTownBuild2x2House(TileIndex *tile, Town *t, int maxz, bool noslope)
{
        TileIndex tile2 = *tile;

        for (DiagDirection d = DIAGDIR_SE;; d++) { // 'd' goes through DIAGDIR_SE, DIAGDIR_SW, DIAGDIR_NW, DIAGDIR_END
                if (TownLayoutAllows2x2HouseHere(t, tile2) && CheckFree2x2Area(tile2, maxz, noslope)) {
                        *tile = tile2;
                        return true;
                }
                if (d == DIAGDIR_END) break;
                tile2 += TileOffsByDiagDir(ReverseDiagDir(d)); // go clockwise
        }

        return false;
}

/**
 * Build a house at this tile.
 * @param t The town the house will belong to.
 * @param tile The tile to try building on.
 * @param hs The @a HouseSpec of the house.
 * @param house The @a HouseID of the house.
 * @param random_bits The random data to be associated with the house.
 */
static void BuildTownHouse(Town *t, TileIndex tile, const HouseSpec *hs, HouseID house, uint8_t random_bits)
{
        /* build the house */
        t->cache.num_houses++;

        uint8_t construction_counter = 0;
        uint8_t construction_stage = 0;

        if (_generating_world || _game_mode == GM_EDITOR) {
                uint32_t construction_random = Random();

                construction_stage = TOWN_HOUSE_COMPLETED;
                if (_generating_world && Chance16(1, 7)) construction_stage = GB(construction_random, 0, 2);

                if (construction_stage == TOWN_HOUSE_COMPLETED) {
                        ChangePopulation(t, hs->population);
                } else {
                        construction_counter = GB(construction_random, 2, 2);
                }
        }

        MakeTownHouse(tile, t, construction_counter, construction_stage, house, random_bits);
        UpdateTownRadius(t);
        UpdateTownGrowthRate(t);
}

/**
 * Tries to build a house at this tile.
 * @param t The town the house will belong to.
 * @param tile The tile to try building on.
 * @return false iff no house can be built on this tile.
 */
static bool TryBuildTownHouse(Town *t, TileIndex tile)
{
        /* forbidden building here by town layout */
        if (!TownLayoutAllowsHouseHere(t, tile)) return false;

        /* no house allowed at all, bail out */
        if (!CanBuildHouseHere(tile, false)) return false;

        Slope slope = GetTileSlope(tile);
        int maxz = GetTileMaxZ(tile);

        /* Get the town zone type of the current tile, as well as the climate.
         * This will allow to easily compare with the specs of the new house to build */
        HouseZonesBits rad = GetTownRadiusGroup(t, tile);

        /* Above snow? */
        int land = _settings_game.game_creation.landscape;
        if (land == LT_ARCTIC && maxz > HighestSnowLine()) land = -1;

        uint bitmask = (1 << rad) + (1 << (land + 12));

        /* bits 0-4 are used
         * bits 11-15 are used
         * bits 5-10 are not used. */
        static std::vector<std::pair<HouseID, uint>> probs;
        probs.clear();

        uint probability_max = 0;

        /* Generate a list of all possible houses that can be built. */
        for (const auto &hs : HouseSpec::Specs()) {
                /* Verify that the candidate house spec matches the current tile status */
                if ((~hs.building_availability & bitmask) != 0 || !hs.enabled || hs.grf_prop.override != INVALID_HOUSE_ID) continue;

                /* Don't let these counters overflow. Global counters are 32bit, there will never be that many houses. */
                if (hs.class_id != HOUSE_NO_CLASS) {
                        /* id_count is always <= class_count, so it doesn't need to be checked */
                        if (t->cache.building_counts.class_count[hs.class_id] == UINT16_MAX) continue;
                } else {
                        /* If the house has no class, check id_count instead */
                        if (t->cache.building_counts.id_count[hs.Index()] == UINT16_MAX) continue;
                }

                uint cur_prob = hs.probability;
                probability_max += cur_prob;
                probs.emplace_back(hs.Index(), cur_prob);
        }

        TileIndex baseTile = tile;

        while (probability_max > 0) {
                /* Building a multitile building can change the location of tile.
                 * The building would still be built partially on that tile, but
                 * its northern tile would be elsewhere. However, if the callback
                 * fails we would be basing further work from the changed tile.
                 * So a next 1x1 tile building could be built on the wrong tile. */
                tile = baseTile;

                uint r = RandomRange(probability_max);
                uint i;
                for (i = 0; i < probs.size(); i++) {
                        if (probs[i].second > r) break;
                        r -= probs[i].second;
                }

                HouseID house = probs[i].first;
                probability_max -= probs[i].second;

                /* remove tested house from the set */
                probs[i] = probs.back();
                probs.pop_back();

                const HouseSpec *hs = HouseSpec::Get(house);

                if (!_generating_world && _game_mode != GM_EDITOR && (hs->extra_flags & BUILDING_IS_HISTORICAL) != 0) {
                        continue;
                }

                if (TimerGameCalendar::year < hs->min_year || TimerGameCalendar::year > hs->max_year) continue;

                /* Special houses that there can be only one of. */
                uint oneof = 0;

                if (hs->building_flags & BUILDING_IS_CHURCH) {
                        SetBit(oneof, TOWN_HAS_CHURCH);
                } else if (hs->building_flags & BUILDING_IS_STADIUM) {
                        SetBit(oneof, TOWN_HAS_STADIUM);
                }

                if (t->flags & oneof) continue;

                /* Make sure there is no slope? */
                bool noslope = (hs->building_flags & TILE_NOT_SLOPED) != 0;
                if (noslope && slope != SLOPE_FLAT) continue;

                if (hs->building_flags & TILE_SIZE_2x2) {
                        if (!CheckTownBuild2x2House(&tile, t, maxz, noslope)) continue;
                } else if (hs->building_flags & TILE_SIZE_2x1) {
                        if (!CheckTownBuild2House(&tile, t, maxz, noslope, DIAGDIR_SW)) continue;
                } else if (hs->building_flags & TILE_SIZE_1x2) {
                        if (!CheckTownBuild2House(&tile, t, maxz, noslope, DIAGDIR_SE)) continue;
                } else {
                        /* 1x1 house checks are already done */
                }

                uint8_t random_bits = Random();

                if (HasBit(hs->callback_mask, CBM_HOUSE_ALLOW_CONSTRUCTION)) {
                        uint16_t callback_res = GetHouseCallback(CBID_HOUSE_ALLOW_CONSTRUCTION, 0, 0, house, t, tile, true, random_bits);
                        if (callback_res != CALLBACK_FAILED && !Convert8bitBooleanCallback(hs->grf_prop.grffile, CBID_HOUSE_ALLOW_CONSTRUCTION, callback_res)) continue;
                }

                /* Special houses that there can be only one of. */
                t->flags |= oneof;

                BuildTownHouse(t, tile, hs, house, random_bits);

                return true;
        }

        return false;
}

CommandCost CmdPlaceHouse(DoCommandFlag flags, TileIndex tile, HouseID house)
{
        if (_game_mode != GM_EDITOR) return CMD_ERROR;
        if (Town::GetNumItems() == 0) return_cmd_error(STR_ERROR_MUST_FOUND_TOWN_FIRST);

        if (static_cast<size_t>(house) >= HouseSpec::Specs().size()) return CMD_ERROR;
        const HouseSpec *hs = HouseSpec::Get(house);
        if (!hs->enabled) return CMD_ERROR;

        Town *t = ClosestTownFromTile(tile, UINT_MAX);

        /* cannot build on these slopes... */
        Slope slope = GetTileSlope(tile);
        if (IsSteepSlope(slope)) return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);

        /* building under a bridge? */
        if (IsBridgeAbove(tile)) return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);

        /* can we clear the land? */
        CommandCost cost = Command<CMD_LANDSCAPE_CLEAR>::Do(DC_AUTO | DC_NO_WATER, tile);
        if (!cost.Succeeded()) return cost;

        int maxz = GetTileMaxZ(tile);

        /* Make sure there is no slope? */
        bool noslope = (hs->building_flags & TILE_NOT_SLOPED) != 0;
        if (noslope && slope != SLOPE_FLAT) return_cmd_error(STR_ERROR_FLAT_LAND_REQUIRED);

        TileArea ta = tile;
        if (hs->building_flags & TILE_SIZE_2x2) ta.Add(TileAddXY(tile, 1, 1));
        if (hs->building_flags & TILE_SIZE_2x1) ta.Add(TileAddByDiagDir(tile, DIAGDIR_SW));
        if (hs->building_flags & TILE_SIZE_1x2) ta.Add(TileAddByDiagDir(tile, DIAGDIR_SE));

        /* Check additonal tiles covered by this house. */
        for (const TileIndex &subtile : ta) {
                cost = Command<CMD_LANDSCAPE_CLEAR>::Do(DC_AUTO | DC_NO_WATER, subtile);
                if (!cost.Succeeded()) return cost;

                if (!CheckBuildHouseSameZ(subtile, maxz, noslope)) return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
        }

        if (flags & DC_EXEC) {
                BuildTownHouse(t, tile, hs, house, Random());
        }

        return CommandCost();
}

/**
 * Update data structures when a house is removed
 * @param tile  Tile of the house
 * @param t     Town owning the house
 * @param house House type
 */
static void DoClearTownHouseHelper(TileIndex tile, Town *t, HouseID house)
{
        assert(IsTileType(tile, MP_HOUSE));
        DecreaseBuildingCount(t, house);
        DoClearSquare(tile);
        DeleteAnimatedTile(tile);

        DeleteNewGRFInspectWindow(GSF_HOUSES, tile.base());
}

/**
 * Determines if a given HouseID is part of a multitile house.
 * The given ID is set to the ID of the north tile and the TileDiff to the north tile is returned.
 *
 * @param house Is changed to the HouseID of the north tile of the same house
 * @return TileDiff from the tile of the given HouseID to the north tile
 */
TileIndexDiff GetHouseNorthPart(HouseID &house)
{
        if (house >= 3) { // house id 0,1,2 MUST be single tile houses, or this code breaks.
                if (HouseSpec::Get(house - 1)->building_flags & TILE_SIZE_2x1) {
                        house--;
                        return TileDiffXY(-1, 0);
                } else if (HouseSpec::Get(house - 1)->building_flags & BUILDING_2_TILES_Y) {
                        house--;
                        return TileDiffXY(0, -1);
                } else if (HouseSpec::Get(house - 2)->building_flags & BUILDING_HAS_4_TILES) {
                        house -= 2;
                        return TileDiffXY(-1, 0);
                } else if (HouseSpec::Get(house - 3)->building_flags & BUILDING_HAS_4_TILES) {
                        house -= 3;
                        return TileDiffXY(-1, -1);
                }
        }
        return 0;
}

/**
 * Clear a town house.
 * @param t The town which owns the house.
 * @param tile The tile to clear.
 */
void ClearTownHouse(Town *t, TileIndex tile)
{
        assert(IsTileType(tile, MP_HOUSE));

        HouseID house = GetHouseType(tile);

        /* The northernmost tile of the house is the main house. */
        tile += GetHouseNorthPart(house);

        const HouseSpec *hs = HouseSpec::Get(house);

        /* Remove population from the town if the house is finished. */
        if (IsHouseCompleted(tile)) {
                ChangePopulation(t, -hs->population);
        }

        t->cache.num_houses--;

        /* Clear flags for houses that only may exist once/town. */
        if (hs->building_flags & BUILDING_IS_CHURCH) {
                ClrBit(t->flags, TOWN_HAS_CHURCH);
        } else if (hs->building_flags & BUILDING_IS_STADIUM) {
                ClrBit(t->flags, TOWN_HAS_STADIUM);
        }

        /* Do the actual clearing of tiles */
        DoClearTownHouseHelper(tile, t, house);
        if (hs->building_flags & BUILDING_2_TILES_Y)   DoClearTownHouseHelper(tile + TileDiffXY(0, 1), t, ++house);
        if (hs->building_flags & BUILDING_2_TILES_X)   DoClearTownHouseHelper(tile + TileDiffXY(1, 0), t, ++house);
        if (hs->building_flags & BUILDING_HAS_4_TILES) DoClearTownHouseHelper(tile + TileDiffXY(1, 1), t, ++house);

        RemoveNearbyStations(t, tile, hs->building_flags);

        UpdateTownRadius(t);
}

/**
 * Rename a town (server-only).
 * @param flags type of operation
 * @param town_id town ID to rename
 * @param text the new name or an empty string when resetting to the default
 * @return the cost of this operation or an error
 */
CommandCost CmdRenameTown(DoCommandFlag flags, TownID town_id, const std::string &text)
{
        Town *t = Town::GetIfValid(town_id);
        if (t == nullptr) return CMD_ERROR;

        bool reset = text.empty();

        if (!reset) {
                if (Utf8StringLength(text) >= MAX_LENGTH_TOWN_NAME_CHARS) return CMD_ERROR;
                if (!IsUniqueTownName(text)) return_cmd_error(STR_ERROR_NAME_MUST_BE_UNIQUE);
        }

        if (flags & DC_EXEC) {
                t->cached_name.clear();
                if (reset) {
                        t->name.clear();
                } else {
                        t->name = text;
                }

                t->UpdateVirtCoord();
                InvalidateWindowData(WC_TOWN_DIRECTORY, 0, TDIWD_FORCE_RESORT);
                ClearAllStationCachedNames();
                ClearAllIndustryCachedNames();
                UpdateAllStationVirtCoords();
        }
        return CommandCost();
}

/**
 * Determines the first cargo with a certain town effect
 * @param effect Town effect of interest
 * @return first active cargo slot with that effect
 */
const CargoSpec *FindFirstCargoWithTownAcceptanceEffect(TownAcceptanceEffect effect)
{
        for (const CargoSpec *cs : CargoSpec::Iterate()) {
                if (cs->town_acceptance_effect == effect) return cs;
        }
        return nullptr;
}

/**
 * Change the cargo goal of a town.
 * @param flags Type of operation.
 * @param town_id Town ID to cargo game of.
 * @param tae TownEffect to change the game of.
 * @param goal The new goal value.
 * @return Empty cost or an error.
 */
CommandCost CmdTownCargoGoal(DoCommandFlag flags, TownID town_id, TownAcceptanceEffect tae, uint32_t goal)
{
        if (_current_company != OWNER_DEITY) return CMD_ERROR;

        if (tae < TAE_BEGIN || tae >= TAE_END) return CMD_ERROR;

        Town *t = Town::GetIfValid(town_id);
        if (t == nullptr) return CMD_ERROR;

        /* Validate if there is a cargo which is the requested TownEffect */
        const CargoSpec *cargo = FindFirstCargoWithTownAcceptanceEffect(tae);
        if (cargo == nullptr) return CMD_ERROR;

        if (flags & DC_EXEC) {
                t->goal[tae] = goal;
                UpdateTownGrowth(t);
                InvalidateWindowData(WC_TOWN_VIEW, town_id);
        }

        return CommandCost();
}

/**
 * Set a custom text in the Town window.
 * @param flags Type of operation.
 * @param town_id Town ID to change the text of.
 * @param text The new text (empty to remove the text).
 * @return Empty cost or an error.
 */
CommandCost CmdTownSetText(DoCommandFlag flags, TownID town_id, const std::string &text)
{
        if (_current_company != OWNER_DEITY) return CMD_ERROR;
        Town *t = Town::GetIfValid(town_id);
        if (t == nullptr) return CMD_ERROR;

        if (flags & DC_EXEC) {
                t->text.clear();
                if (!text.empty()) t->text = text;
                InvalidateWindowData(WC_TOWN_VIEW, town_id);
        }

        return CommandCost();
}

/**
 * Change the growth rate of the town.
 * @param flags Type of operation.
 * @param town_id Town ID to cargo game of.
 * @param growth_rate Amount of days between growth, or TOWN_GROWTH_RATE_NONE, or 0 to reset custom growth rate.
 * @return Empty cost or an error.
 */
CommandCost CmdTownGrowthRate(DoCommandFlag flags, TownID town_id, uint16_t growth_rate)
{
        if (_current_company != OWNER_DEITY) return CMD_ERROR;

        Town *t = Town::GetIfValid(town_id);
        if (t == nullptr) return CMD_ERROR;

        if (flags & DC_EXEC) {
                if (growth_rate == 0) {
                        /* Just clear the flag, UpdateTownGrowth will determine a proper growth rate */
                        ClrBit(t->flags, TOWN_CUSTOM_GROWTH);
                } else {
                        uint old_rate = t->growth_rate;
                        if (t->grow_counter >= old_rate) {
                                /* This also catches old_rate == 0 */
                                t->grow_counter = growth_rate;
                        } else {
                                /* Scale grow_counter, so half finished houses stay half finished */
                                t->grow_counter = t->grow_counter * growth_rate / old_rate;
                        }
                        t->growth_rate = growth_rate;
                        SetBit(t->flags, TOWN_CUSTOM_GROWTH);
                }
                UpdateTownGrowth(t);
                InvalidateWindowData(WC_TOWN_VIEW, town_id);
        }

        return CommandCost();
}

/**
 * Change the rating of a company in a town
 * @param flags Type of operation.
 * @param town_id Town ID to change, bit 16..23 =
 * @param company_id Company ID to change.
 * @param rating New rating of company (signed int16_t).
 * @return Empty cost or an error.
 */
CommandCost CmdTownRating(DoCommandFlag flags, TownID town_id, CompanyID company_id, int16_t rating)
{
        if (_current_company != OWNER_DEITY) return CMD_ERROR;

        Town *t = Town::GetIfValid(town_id);
        if (t == nullptr) return CMD_ERROR;

        if (!Company::IsValidID(company_id)) return CMD_ERROR;

        int16_t new_rating = Clamp(rating, RATING_MINIMUM, RATING_MAXIMUM);
        if (flags & DC_EXEC) {
                t->ratings[company_id] = new_rating;
                InvalidateWindowData(WC_TOWN_AUTHORITY, town_id);
        }

        return CommandCost();
}

/**
 * Expand a town (scenario editor only).
 * @param flags Type of operation.
 * @param TownID Town ID to expand.
 * @param grow_amount Amount to grow, or 0 to grow a random size up to the current amount of houses.
 * @return Empty cost or an error.
 */
CommandCost CmdExpandTown(DoCommandFlag flags, TownID town_id, uint32_t grow_amount)
{
        if (_game_mode != GM_EDITOR && _current_company != OWNER_DEITY) return CMD_ERROR;
        Town *t = Town::GetIfValid(town_id);
        if (t == nullptr) return CMD_ERROR;

        if (flags & DC_EXEC) {
                /* The more houses, the faster we grow */
                if (grow_amount == 0) {
                        uint amount = RandomRange(ClampTo<uint16_t>(t->cache.num_houses / 10)) + 3;
                        t->cache.num_houses += amount;
                        UpdateTownRadius(t);

                        uint n = amount * 10;
                        do GrowTown(t); while (--n);

                        t->cache.num_houses -= amount;
                } else {
                        for (; grow_amount > 0; grow_amount--) {
                                /* Try several times to grow, as we are really suppose to grow */
                                for (uint i = 0; i < 25; i++) if (GrowTown(t)) break;
                        }
                }
                UpdateTownRadius(t);

                UpdateTownMaxPass(t);
        }

        return CommandCost();
}

/**
 * Delete a town (scenario editor or worldgen only).
 * @param flags Type of operation.
 * @param town_id Town ID to delete.
 * @return Empty cost or an error.
 */
CommandCost CmdDeleteTown(DoCommandFlag flags, TownID town_id)
{
        if (_game_mode != GM_EDITOR && !_generating_world) return CMD_ERROR;
        Town *t = Town::GetIfValid(town_id);
        if (t == nullptr) return CMD_ERROR;

        /* Stations refer to towns. */
        for (const Station *st : Station::Iterate()) {
                if (st->town == t) {
                        /* Non-oil rig stations are always a problem. */
                        if (!(st->facilities & FACIL_AIRPORT) || st->airport.type != AT_OILRIG) return CMD_ERROR;
                        /* We can only automatically delete oil rigs *if* there's no vehicle on them. */
                        CommandCost ret = Command<CMD_LANDSCAPE_CLEAR>::Do(flags, st->airport.tile);
                        if (ret.Failed()) return ret;
                }
        }

        /* Waypoints refer to towns. */
        for (const Waypoint *wp : Waypoint::Iterate()) {
                if (wp->town == t) return CMD_ERROR;
        }

        /* Depots refer to towns. */
        for (const Depot *d : Depot::Iterate()) {
                if (d->town == t) return CMD_ERROR;
        }

        /* Check all tiles for town ownership. First check for bridge tiles, as
         * these do not directly have an owner so we need to check adjacent
         * tiles. This won't work correctly in the same loop if the adjacent
         * tile was already deleted earlier in the loop. */
        for (TileIndex current_tile = 0; current_tile < Map::Size(); ++current_tile) {
                if (IsTileType(current_tile, MP_TUNNELBRIDGE) && TestTownOwnsBridge(current_tile, t)) {
                        CommandCost ret = Command<CMD_LANDSCAPE_CLEAR>::Do(flags, current_tile);
                        if (ret.Failed()) return ret;
                }
        }

        /* Check all remaining tiles for town ownership. */
        for (TileIndex current_tile = 0; current_tile < Map::Size(); ++current_tile) {
                bool try_clear = false;
                switch (GetTileType(current_tile)) {
                        case MP_ROAD:
                                try_clear = HasTownOwnedRoad(current_tile) && GetTownIndex(current_tile) == t->index;
                                break;

                        case MP_HOUSE:
                                try_clear = GetTownIndex(current_tile) == t->index;
                                break;

                        case MP_INDUSTRY:
                                try_clear = Industry::GetByTile(current_tile)->town == t;
                                break;

                        case MP_OBJECT:
                                if (Town::GetNumItems() == 1) {
                                        /* No towns will be left, remove it! */
                                        try_clear = true;
                                } else {
                                        Object *o = Object::GetByTile(current_tile);
                                        if (o->town == t) {
                                                if (o->type == OBJECT_STATUE) {
                                                        /* Statue... always remove. */
                                                        try_clear = true;
                                                } else {
                                                        /* Tell to find a new town. */
                                                        if (flags & DC_EXEC) o->town = nullptr;
                                                }
                                        }
                                }
                                break;

                        default:
                                break;
                }
                if (try_clear) {
                        CommandCost ret = Command<CMD_LANDSCAPE_CLEAR>::Do(flags, current_tile);
                        if (ret.Failed()) return ret;
                }
        }

        /* The town destructor will delete the other things related to the town. */
        if (flags & DC_EXEC) {
                _town_kdtree.Remove(t->index);
                if (t->cache.sign.kdtree_valid) _viewport_sign_kdtree.Remove(ViewportSignKdtreeItem::MakeTown(t->index));
                delete t;
        }

        return CommandCost();
}

/**
 * Factor in the cost of each town action.
 * @see TownActions
 */
const uint8_t _town_action_costs[TACT_COUNT] = {
        2, 4, 9, 35, 48, 53, 117, 175
};

/**
 * Perform the "small advertising campaign" town action.
 * @param t The town to advertise in.
 * @param flags Type of operation.
 * @return An empty cost.
 */
static CommandCost TownActionAdvertiseSmall(Town *t, DoCommandFlag flags)
{
        if (flags & DC_EXEC) {
                ModifyStationRatingAround(t->xy, _current_company, 0x40, 10);
        }
        return CommandCost();
}

/**
 * Perform the "medium advertising campaign" town action.
 * @param t The town to advertise in.
 * @param flags Type of operation.
 * @return An empty cost.
 */
static CommandCost TownActionAdvertiseMedium(Town *t, DoCommandFlag flags)
{
        if (flags & DC_EXEC) {
                ModifyStationRatingAround(t->xy, _current_company, 0x70, 15);
        }
        return CommandCost();
}

/**
 * Perform the "large advertising campaign" town action.
 * @param t The town to advertise in.
 * @param flags Type of operation.
 * @return An empty cost.
 */
static CommandCost TownActionAdvertiseLarge(Town *t, DoCommandFlag flags)
{
        if (flags & DC_EXEC) {
                ModifyStationRatingAround(t->xy, _current_company, 0xA0, 20);
        }
        return CommandCost();
}

/**
 * Perform the "local road reconstruction" town action.
 * @param t The town to grief in.
 * @param flags Type of operation.
 * @return An empty cost.
 */
static CommandCost TownActionRoadRebuild(Town *t, DoCommandFlag flags)
{
        /* Check if the company is allowed to fund new roads. */
        if (!_settings_game.economy.fund_roads) return CMD_ERROR;

        if (flags & DC_EXEC) {
                t->road_build_months = 6;

                SetDParam(0, _current_company);
                NewsStringData *company_name = new NewsStringData(GetString(STR_COMPANY_NAME));

                SetDParam(0, t->index);
                SetDParamStr(1, company_name->string);

                AddNewsItem(
                        TimerGameEconomy::UsingWallclockUnits() ? STR_NEWS_ROAD_REBUILDING_MINUTES : STR_NEWS_ROAD_REBUILDING_MONTHS,
                        NT_GENERAL, NF_NORMAL, NR_TOWN, t->index, NR_NONE, UINT32_MAX, company_name);
                AI::BroadcastNewEvent(new ScriptEventRoadReconstruction((ScriptCompany::CompanyID)(Owner)_current_company, t->index));
                Game::NewEvent(new ScriptEventRoadReconstruction((ScriptCompany::CompanyID)(Owner)_current_company, t->index));
        }
        return CommandCost();
}

/**
 * Check whether the land can be cleared.
 * @param tile Tile to check.
 * @return true if the tile can be cleared.
 */
static bool CheckClearTile(TileIndex tile)
{
        Backup<CompanyID> cur_company(_current_company, OWNER_NONE);
        CommandCost r = Command<CMD_LANDSCAPE_CLEAR>::Do(DC_NONE, tile);
        cur_company.Restore();
        return r.Succeeded();
}

/** Structure for storing data while searching the best place to build a statue. */
struct StatueBuildSearchData {
        TileIndex best_position; ///< Best position found so far.
        int tile_count;          ///< Number of tiles tried.

        StatueBuildSearchData(TileIndex best_pos, int count) : best_position(best_pos), tile_count(count) { }
};

/**
 * Search callback function for #TownActionBuildStatue.
 * @param tile Tile on which to perform the search.
 * @param user_data Reference to the statue search data.
 * @return Result of the test.
 */
static bool SearchTileForStatue(TileIndex tile, void *user_data)
{
        static const int STATUE_NUMBER_INNER_TILES = 25; // Number of tiles int the center of the city, where we try to protect houses.

        StatueBuildSearchData *statue_data = (StatueBuildSearchData *)user_data;
        statue_data->tile_count++;

        /* Statues can be build on slopes, just like houses. Only the steep slopes is a no go. */
        if (IsSteepSlope(GetTileSlope(tile))) return false;
        /* Don't build statues under bridges. */
        if (IsBridgeAbove(tile)) return false;

        /* A clear-able open space is always preferred. */
        if ((IsTileType(tile, MP_CLEAR) || IsTileType(tile, MP_TREES)) && CheckClearTile(tile)) {
                statue_data->best_position = tile;
                return true;
        }

        bool house = IsTileType(tile, MP_HOUSE);

        /* Searching inside the inner circle. */
        if (statue_data->tile_count <= STATUE_NUMBER_INNER_TILES) {
                /* Save first house in inner circle. */
                if (house && statue_data->best_position == INVALID_TILE && CheckClearTile(tile)) {
                        statue_data->best_position = tile;
                }

                /* If we have reached the end of the inner circle, and have a saved house, terminate the search. */
                return statue_data->tile_count == STATUE_NUMBER_INNER_TILES && statue_data->best_position != INVALID_TILE;
        }

        /* Searching outside the circle, just pick the first possible spot. */
        statue_data->best_position = tile; // Is optimistic, the condition below must also hold.
        return house && CheckClearTile(tile);
}

/**
 * Perform a 9x9 tiles circular search from the center of the town
 * in order to find a free tile to place a statue
 * @param t town to search in
 * @param flags Used to check if the statue must be built or not.
 * @return Empty cost or an error.
 */
static CommandCost TownActionBuildStatue(Town *t, DoCommandFlag flags)
{
        if (!Object::CanAllocateItem()) return_cmd_error(STR_ERROR_TOO_MANY_OBJECTS);

        TileIndex tile = t->xy;
        StatueBuildSearchData statue_data(INVALID_TILE, 0);
        if (!CircularTileSearch(&tile, 9, SearchTileForStatue, &statue_data)) return_cmd_error(STR_ERROR_STATUE_NO_SUITABLE_PLACE);

        if (flags & DC_EXEC) {
                Backup<CompanyID> cur_company(_current_company, OWNER_NONE);
                Command<CMD_LANDSCAPE_CLEAR>::Do(DC_EXEC, statue_data.best_position);
                cur_company.Restore();
                BuildObject(OBJECT_STATUE, statue_data.best_position, _current_company, t);
                SetBit(t->statues, _current_company); // Once found and built, "inform" the Town.
                MarkTileDirtyByTile(statue_data.best_position);
        }
        return CommandCost();
}

/**
 * Perform the "fund new buildings" town action.
 * @param t The town to fund buildings in.
 * @param flags Type of operation.
 * @return An empty cost.
 */
static CommandCost TownActionFundBuildings(Town *t, DoCommandFlag flags)
{
        /* Check if it's allowed to buy the rights */
        if (!_settings_game.economy.fund_buildings) return CMD_ERROR;

        if (flags & DC_EXEC) {
                /* And grow for 3 months */
                t->fund_buildings_months = 3;

                /* Enable growth (also checking GameScript's opinion) */
                UpdateTownGrowth(t);

                /* Build a new house, but add a small delay to make sure
                 * that spamming funding doesn't let town grow any faster
                 * than 1 house per 2 * TOWN_GROWTH_TICKS ticks.
                 * Also emulate original behaviour when town was only growing in
                 * TOWN_GROWTH_TICKS intervals, to make sure that it's not too
                 * tick-perfect and gives player some time window where they can
                 * spam funding with the exact same efficiency.
                 */
                t->grow_counter = std::min<uint16_t>(t->grow_counter, 2 * Ticks::TOWN_GROWTH_TICKS - (t->growth_rate - t->grow_counter) % Ticks::TOWN_GROWTH_TICKS);

                SetWindowDirty(WC_TOWN_VIEW, t->index);
        }
        return CommandCost();
}

/**
 * Perform the "buy exclusive transport rights" town action.
 * @param t The town to buy exclusivity in.
 * @param flags Type of operation.
 * @return An empty cost.
 */
static CommandCost TownActionBuyRights(Town *t, DoCommandFlag flags)
{
        /* Check if it's allowed to buy the rights */
        if (!_settings_game.economy.exclusive_rights) return CMD_ERROR;
        if (t->exclusivity != INVALID_COMPANY) return CMD_ERROR;

        if (flags & DC_EXEC) {
                t->exclusive_counter = 12;
                t->exclusivity = _current_company;

                ModifyStationRatingAround(t->xy, _current_company, 130, 17);

                SetWindowClassesDirty(WC_STATION_VIEW);

                /* Spawn news message */
                CompanyNewsInformation *cni = new CompanyNewsInformation(Company::Get(_current_company));
                SetDParam(0, STR_NEWS_EXCLUSIVE_RIGHTS_TITLE);
                SetDParam(1, TimerGameEconomy::UsingWallclockUnits() ? STR_NEWS_EXCLUSIVE_RIGHTS_DESCRIPTION_MINUTES : STR_NEWS_EXCLUSIVE_RIGHTS_DESCRIPTION_MONTHS);
                SetDParam(2, t->index);
                SetDParamStr(3, cni->company_name);
                AddNewsItem(STR_MESSAGE_NEWS_FORMAT, NT_GENERAL, NF_COMPANY, NR_TOWN, t->index, NR_NONE, UINT32_MAX, cni);
                AI::BroadcastNewEvent(new ScriptEventExclusiveTransportRights((ScriptCompany::CompanyID)(Owner)_current_company, t->index));
                Game::NewEvent(new ScriptEventExclusiveTransportRights((ScriptCompany::CompanyID)(Owner)_current_company, t->index));
        }
        return CommandCost();
}

/**
 * Perform the "bribe" town action.
 * @param t The town to bribe.
 * @param flags Type of operation.
 * @return An empty cost.
 */
static CommandCost TownActionBribe(Town *t, DoCommandFlag flags)
{
        if (flags & DC_EXEC) {
                if (Chance16(1, 14)) {
                        /* set as unwanted for 6 months */
                        t->unwanted[_current_company] = 6;

                        /* set all close by station ratings to 0 */
                        for (Station *st : Station::Iterate()) {
                                if (st->town == t && st->owner == _current_company) {
                                        for (GoodsEntry &ge : st->goods) ge.rating = 0;
                                }
                        }

                        /* only show error message to the executing player. All errors are handled command.c
                         * but this is special, because it can only 'fail' on a DC_EXEC */
                        if (IsLocalCompany()) ShowErrorMessage(STR_ERROR_BRIBE_FAILED, INVALID_STRING_ID, WL_INFO);

                        /* decrease by a lot!
                         * ChangeTownRating is only for stuff in demolishing. Bribe failure should
                         * be independent of any cheat settings
                         */
                        if (t->ratings[_current_company] > RATING_BRIBE_DOWN_TO) {
                                t->ratings[_current_company] = RATING_BRIBE_DOWN_TO;
                                SetWindowDirty(WC_TOWN_AUTHORITY, t->index);
                        }
                } else {
                        ChangeTownRating(t, RATING_BRIBE_UP_STEP, RATING_BRIBE_MAXIMUM, DC_EXEC);
                        if (t->exclusivity != _current_company && t->exclusivity != INVALID_COMPANY) {
                                t->exclusivity = INVALID_COMPANY;
                                t->exclusive_counter = 0;
                        }
                }
        }
        return CommandCost();
}

typedef CommandCost TownActionProc(Town *t, DoCommandFlag flags);
static TownActionProc * const _town_action_proc[] = {
        TownActionAdvertiseSmall,
        TownActionAdvertiseMedium,
        TownActionAdvertiseLarge,
        TownActionRoadRebuild,
        TownActionBuildStatue,
        TownActionFundBuildings,
        TownActionBuyRights,
        TownActionBribe
};

/**
 * Get a list of available town authority actions.
 * @param cid The company that is querying the town.
 * @param t The town that is queried.
 * @return The bitmasked value of enabled actions.
 */
TownActions GetMaskOfTownActions(CompanyID cid, const Town *t)
{
        TownActions buttons = TACT_NONE;

        /* Spectators and unwanted have no options */
        if (cid != COMPANY_SPECTATOR && !(_settings_game.economy.bribe && t->unwanted[cid])) {

                /* Actions worth more than this are not able to be performed */
                Money avail = GetAvailableMoney(cid);

                /* Check the action bits for validity and
                 * if they are valid add them */
                for (uint i = 0; i != lengthof(_town_action_costs); i++) {
                        const TownActions cur = (TownActions)(1 << i);

                        /* Is the company prohibited from bribing ? */
                        if (cur == TACT_BRIBE) {
                                /* Company can't bribe if setting is disabled */
                                if (!_settings_game.economy.bribe) continue;
                                /* Company can bribe if another company has exclusive transport rights,
                                 * or its standing with the town is less than outstanding. */
                                if (t->ratings[cid] >= RATING_BRIBE_MAXIMUM) {
                                        if (t->exclusivity == _current_company) continue;
                                        if (t->exclusive_counter == 0) continue;
                                }
                        }

                        /* Is the company not able to buy exclusive rights ? */
                        if (cur == TACT_BUY_RIGHTS && (!_settings_game.economy.exclusive_rights || t->exclusive_counter != 0)) continue;

                        /* Is the company not able to fund buildings ? */
                        if (cur == TACT_FUND_BUILDINGS && !_settings_game.economy.fund_buildings) continue;

                        /* Is the company not able to fund local road reconstruction? */
                        if (cur == TACT_ROAD_REBUILD && !_settings_game.economy.fund_roads) continue;

                        /* Is the company not able to build a statue ? */
                        if (cur == TACT_BUILD_STATUE && HasBit(t->statues, cid)) continue;

                        if (avail >= _town_action_costs[i] * _price[PR_TOWN_ACTION] >> 8) {
                                buttons |= cur;
                        }
                }
        }

        return buttons;
}

/**
 * Do a town action.
 * This performs an action such as advertising, building a statue, funding buildings,
 * but also bribing the town-council
 * @param flags type of operation
 * @param town_id town to do the action at
 * @param action action to perform, @see _town_action_proc for the list of available actions
 * @return the cost of this operation or an error
 */
CommandCost CmdDoTownAction(DoCommandFlag flags, TownID town_id, uint8_t action)
{
        Town *t = Town::GetIfValid(town_id);
        if (t == nullptr || action >= lengthof(_town_action_proc)) return CMD_ERROR;

        if (!HasBit(GetMaskOfTownActions(_current_company, t), action)) return CMD_ERROR;

        CommandCost cost(EXPENSES_OTHER, _price[PR_TOWN_ACTION] * _town_action_costs[action] >> 8);

        CommandCost ret = _town_action_proc[action](t, flags);
        if (ret.Failed()) return ret;

        if (flags & DC_EXEC) {
                SetWindowDirty(WC_TOWN_AUTHORITY, town_id);
        }

        return cost;
}

template <typename Func>
static void ForAllStationsNearTown(Town *t, Func func)
{
        /* Ideally the search radius should be close to the actual town zone 0 radius.
         * The true radius is not stored or calculated anywhere, only the squared radius. */
        /* The efficiency of this search might be improved for large towns and many stations on the map,
         * by using an integer square root approximation giving a value not less than the true square root. */
        uint search_radius = t->cache.squared_town_zone_radius[HZB_TOWN_EDGE] / 2;
        ForAllStationsRadius(t->xy, search_radius, [&](const Station * st) {
                if (DistanceSquare(st->xy, t->xy) <= t->cache.squared_town_zone_radius[HZB_TOWN_EDGE]) {
                        func(st);
                }
        });
}

/**
 * Monthly callback to update town and station ratings.
 * @param t The town to update.
 */
static void UpdateTownRating(Town *t)
{
        /* Increase company ratings if they're low */
        for (const Company *c : Company::Iterate()) {
                if (t->ratings[c->index] < RATING_GROWTH_MAXIMUM) {
                        t->ratings[c->index] = std::min((int)RATING_GROWTH_MAXIMUM, t->ratings[c->index] + RATING_GROWTH_UP_STEP);
                }
        }

        ForAllStationsNearTown(t, [&](const Station *st) {
                if (st->time_since_load <= 20 || st->time_since_unload <= 20) {
                        if (Company::IsValidID(st->owner)) {
                                int new_rating = t->ratings[st->owner] + RATING_STATION_UP_STEP;
                                t->ratings[st->owner] = std::min<int>(new_rating, INT16_MAX); // do not let it overflow
                        }
                } else {
                        if (Company::IsValidID(st->owner)) {
                                int new_rating = t->ratings[st->owner] + RATING_STATION_DOWN_STEP;
                                t->ratings[st->owner] = std::max(new_rating, INT16_MIN);
                        }
                }
        });

        /* clamp all ratings to valid values */
        for (uint i = 0; i < MAX_COMPANIES; i++) {
                t->ratings[i] = Clamp(t->ratings[i], RATING_MINIMUM, RATING_MAXIMUM);
        }

        SetWindowDirty(WC_TOWN_AUTHORITY, t->index);
}


/**
 * Updates town grow counter after growth rate change.
 * Preserves relative house builting progress whenever it can.
 * @param t The town to calculate grow counter for
 * @param prev_growth_rate Town growth rate before it changed (one that was used with grow counter to be updated)
 */
static void UpdateTownGrowCounter(Town *t, uint16_t prev_growth_rate)
{
        if (t->growth_rate == TOWN_GROWTH_RATE_NONE) return;
        if (prev_growth_rate == TOWN_GROWTH_RATE_NONE) {
                t->grow_counter = std::min<uint16_t>(t->growth_rate, t->grow_counter);
                return;
        }
        t->grow_counter = RoundDivSU((uint32_t)t->grow_counter * (t->growth_rate + 1), prev_growth_rate + 1);
}

/**
 * Calculates amount of active stations in the range of town (HZB_TOWN_EDGE).
 * @param t The town to calculate stations for
 * @returns Amount of active stations
 */
static int CountActiveStations(Town *t)
{
        int n = 0;
        ForAllStationsNearTown(t, [&](const Station * st) {
                if (st->time_since_load <= 20 || st->time_since_unload <= 20) {
                        n++;
                }
        });
        return n;
}

/**
 * Calculates town growth rate in normal conditions (custom growth rate not set).
 * If town growth speed is set to None(0) returns the same rate as if it was Normal(2).
 * @param t The town to calculate growth rate for
 * @returns Calculated growth rate
 */
static uint GetNormalGrowthRate(Town *t)
{
        /**
         * Note:
         * Unserviced+unfunded towns get an additional malus in UpdateTownGrowth(),
         * so the "320" is actually not better than the "420".
         */
        static const uint16_t _grow_count_values[2][6] = {
                { 120, 120, 120, 100,  80,  60 }, // Fund new buildings has been activated
                { 320, 420, 300, 220, 160, 100 }  // Normal values
        };

        int n = CountActiveStations(t);
        uint16_t m = _grow_count_values[t->fund_buildings_months != 0 ? 0 : 1][std::min(n, 5)];

        uint growth_multiplier = _settings_game.economy.town_growth_rate != 0 ? _settings_game.economy.town_growth_rate - 1 : 1;

        m >>= growth_multiplier;
        if (t->larger_town) m /= 2;

        return TownTicksToGameTicks(m / (t->cache.num_houses / 50 + 1));
}

/**
 * Updates town growth rate.
 * @param t The town to update growth rate for
 */
static void UpdateTownGrowthRate(Town *t)
{
        if (HasBit(t->flags, TOWN_CUSTOM_GROWTH)) return;
        uint old_rate = t->growth_rate;
        t->growth_rate = GetNormalGrowthRate(t);
        UpdateTownGrowCounter(t, old_rate);
        SetWindowDirty(WC_TOWN_VIEW, t->index);
}

/**
 * Updates town growth state (whether it is growing or not).
 * @param t The town to update growth for
 */
static void UpdateTownGrowth(Town *t)
{
        UpdateTownGrowthRate(t);

        ClrBit(t->flags, TOWN_IS_GROWING);
        SetWindowDirty(WC_TOWN_VIEW, t->index);

        if (_settings_game.economy.town_growth_rate == 0 && t->fund_buildings_months == 0) return;

        if (t->fund_buildings_months == 0) {
                /* Check if all goals are reached for this town to grow (given we are not funding it) */
                for (int i = TAE_BEGIN; i < TAE_END; i++) {
                        switch (t->goal[i]) {
                                case TOWN_GROWTH_WINTER:
                                        if (TileHeight(t->xy) >= GetSnowLine() && t->received[i].old_act == 0 && t->cache.population > 90) return;
                                        break;
                                case TOWN_GROWTH_DESERT:
                                        if (GetTropicZone(t->xy) == TROPICZONE_DESERT && t->received[i].old_act == 0 && t->cache.population > 60) return;
                                        break;
                                default:
                                        if (t->goal[i] > t->received[i].old_act) return;
                                        break;
                        }
                }
        }

        if (HasBit(t->flags, TOWN_CUSTOM_GROWTH)) {
                if (t->growth_rate != TOWN_GROWTH_RATE_NONE) SetBit(t->flags, TOWN_IS_GROWING);
                SetWindowDirty(WC_TOWN_VIEW, t->index);
                return;
        }

        if (t->fund_buildings_months == 0 && CountActiveStations(t) == 0 && !Chance16(1, 12)) return;

        SetBit(t->flags, TOWN_IS_GROWING);
        SetWindowDirty(WC_TOWN_VIEW, t->index);
}

/**
 * Checks whether the local authority allows construction of a new station (rail, road, airport, dock) on the given tile
 * @param tile The tile where the station shall be constructed.
 * @param flags Command flags. DC_NO_TEST_TOWN_RATING is tested.
 * @return Succeeded or failed command.
 */
CommandCost CheckIfAuthorityAllowsNewStation(TileIndex tile, DoCommandFlag flags)
{
        /* The required rating is hardcoded to RATING_VERYPOOR (see below), not the authority attitude setting, so we can bail out like this. */
        if (_settings_game.difficulty.town_council_tolerance == TOWN_COUNCIL_PERMISSIVE) return CommandCost();

        if (!Company::IsValidID(_current_company) || (flags & DC_NO_TEST_TOWN_RATING)) return CommandCost();

        Town *t = ClosestTownFromTile(tile, _settings_game.economy.dist_local_authority);
        if (t == nullptr) return CommandCost();

        if (t->ratings[_current_company] > RATING_VERYPOOR) return CommandCost();

        SetDParam(0, t->index);
        return_cmd_error(STR_ERROR_LOCAL_AUTHORITY_REFUSES_TO_ALLOW_THIS);
}

/**
 * Return the town closest to the given tile within \a threshold.
 * @param tile      Starting point of the search.
 * @param threshold Biggest allowed distance to the town.
 * @return Closest town to \a tile within \a threshold, or \c nullptr if there is no such town.
 *
 * @note This function only uses distance, the #ClosestTownFromTile function also takes town ownership into account.
 */
Town *CalcClosestTownFromTile(TileIndex tile, uint threshold)
{
        if (Town::GetNumItems() == 0) return nullptr;

        TownID tid = _town_kdtree.FindNearest(TileX(tile), TileY(tile));
        Town *town = Town::Get(tid);
        if (DistanceManhattan(tile, town->xy) < threshold) return town;
        return nullptr;
}

/**
 * Return the town closest (in distance or ownership) to a given tile, within a given threshold.
 * @param tile      Starting point of the search.
 * @param threshold Biggest allowed distance to the town.
 * @return Closest town to \a tile within \a threshold, or \c nullptr if there is no such town.
 *
 * @note If you only care about distance, you can use the #CalcClosestTownFromTile function.
 */
Town *ClosestTownFromTile(TileIndex tile, uint threshold)
{
        switch (GetTileType(tile)) {
                case MP_ROAD:
                        if (IsRoadDepot(tile)) return CalcClosestTownFromTile(tile, threshold);

                        if (!HasTownOwnedRoad(tile)) {
                                TownID tid = GetTownIndex(tile);

                                if (tid == INVALID_TOWN) {
                                        /* in the case we are generating "many random towns", this value may be INVALID_TOWN */
                                        if (_generating_world) return CalcClosestTownFromTile(tile, threshold);
                                        assert(Town::GetNumItems() == 0);
                                        return nullptr;
                                }

                                assert(Town::IsValidID(tid));
                                Town *town = Town::Get(tid);

                                if (DistanceManhattan(tile, town->xy) >= threshold) town = nullptr;

                                return town;
                        }
                        [[fallthrough]];

                case MP_HOUSE:
                        return Town::GetByTile(tile);

                default:
                        return CalcClosestTownFromTile(tile, threshold);
        }
}

static bool _town_rating_test = false; ///< If \c true, town rating is in test-mode.
static std::map<const Town *, int> _town_test_ratings; ///< Map of towns to modified ratings, while in town rating test-mode.

/**
 * Switch the town rating to test-mode, to allow commands to be tested without affecting current ratings.
 * The function is safe to use in nested calls.
 * @param mode Test mode switch (\c true means go to test-mode, \c false means leave test-mode).
 */
void SetTownRatingTestMode(bool mode)
{
        static int ref_count = 0; // Number of times test-mode is switched on.
        if (mode) {
                if (ref_count == 0) {
                        _town_test_ratings.clear();
                }
                ref_count++;
        } else {
                assert(ref_count > 0);
                ref_count--;
        }
        _town_rating_test = !(ref_count == 0);
}

/**
 * Get the rating of a town for the #_current_company.
 * @param t Town to get the rating from.
 * @return Rating of the current company in the given town.
 */
static int GetRating(const Town *t)
{
        if (_town_rating_test) {
                auto it = _town_test_ratings.find(t);
                if (it != _town_test_ratings.end()) {
                        return it->second;
                }
        }
        return t->ratings[_current_company];
}

/**
 * Changes town rating of the current company
 * @param t Town to affect
 * @param add Value to add
 * @param max Minimum (add < 0) resp. maximum (add > 0) rating that should be achievable with this change.
 * @param flags Command flags, especially DC_NO_MODIFY_TOWN_RATING is tested
 */
void ChangeTownRating(Town *t, int add, int max, DoCommandFlag flags)
{
        /* if magic_bulldozer cheat is active, town doesn't penalize for removing stuff */
        if (t == nullptr || (flags & DC_NO_MODIFY_TOWN_RATING) ||
                        !Company::IsValidID(_current_company) ||
                        (_cheats.magic_bulldozer.value && add < 0)) {
                return;
        }

        int rating = GetRating(t);
        if (add < 0) {
                if (rating > max) {
                        rating += add;
                        if (rating < max) rating = max;
                }
        } else {
                if (rating < max) {
                        rating += add;
                        if (rating > max) rating = max;
                }
        }
        if (_town_rating_test) {
                _town_test_ratings[t] = rating;
        } else {
                SetBit(t->have_ratings, _current_company);
                t->ratings[_current_company] = rating;
                SetWindowDirty(WC_TOWN_AUTHORITY, t->index);
        }
}

/**
 * Does the town authority allow the (destructive) action of the current company?
 * @param flags Checking flags of the command.
 * @param t     Town that must allow the company action.
 * @param type  Type of action that is wanted.
 * @return A succeeded command if the action is allowed, a failed command if it is not allowed.
 */
CommandCost CheckforTownRating(DoCommandFlag flags, Town *t, TownRatingCheckType type)
{
        /* if magic_bulldozer cheat is active, town doesn't restrict your destructive actions */
        if (t == nullptr || !Company::IsValidID(_current_company) ||
                        _cheats.magic_bulldozer.value || (flags & DC_NO_TEST_TOWN_RATING)) {
                return CommandCost();
        }

        /* minimum rating needed to be allowed to remove stuff */
        static const int needed_rating[][TOWN_RATING_CHECK_TYPE_COUNT] = {
                /*                  ROAD_REMOVE,                    TUNNELBRIDGE_REMOVE */
                {    RATING_ROAD_NEEDED_LENIENT,    RATING_TUNNEL_BRIDGE_NEEDED_LENIENT}, // Lenient
                {    RATING_ROAD_NEEDED_NEUTRAL,    RATING_TUNNEL_BRIDGE_NEEDED_NEUTRAL}, // Neutral
                {    RATING_ROAD_NEEDED_HOSTILE,    RATING_TUNNEL_BRIDGE_NEEDED_HOSTILE}, // Hostile
                { RATING_ROAD_NEEDED_PERMISSIVE, RATING_TUNNEL_BRIDGE_NEEDED_PERMISSIVE}, // Permissive
        };

        /* check if you're allowed to remove the road/bridge/tunnel
         * owned by a town no removal if rating is lower than ... depends now on
         * difficulty setting. Minimum town rating selected by difficulty level
         */
        int needed = needed_rating[_settings_game.difficulty.town_council_tolerance][type];

        if (GetRating(t) < needed) {
                SetDParam(0, t->index);
                return_cmd_error(STR_ERROR_LOCAL_AUTHORITY_REFUSES_TO_ALLOW_THIS);
        }

        return CommandCost();
}

static IntervalTimer<TimerGameEconomy> _economy_towns_monthly({TimerGameEconomy::MONTH, TimerGameEconomy::Priority::TOWN}, [](auto)
{
        for (Town *t : Town::Iterate()) {
                /* Check for active town actions and decrement their counters. */
                if (t->road_build_months != 0) t->road_build_months--;
                if (t->fund_buildings_months != 0) t->fund_buildings_months--;

                if (t->exclusive_counter != 0) {
                        if (--t->exclusive_counter == 0) t->exclusivity = INVALID_COMPANY;
                }

                /* Check for active failed bribe cooloff periods and decrement them. */
                for (const Company *c : Company::Iterate()) {
                        if (t->unwanted[c->index] > 0) t->unwanted[c->index]--;
                }

                /* Update cargo statistics. */
                for (auto &supplied : t->supplied) supplied.NewMonth();
                for (auto &received : t->received) received.NewMonth();

                UpdateTownGrowth(t);
                UpdateTownRating(t);

                SetWindowDirty(WC_TOWN_VIEW, t->index);
        }
});

static IntervalTimer<TimerGameEconomy> _economy_towns_yearly({TimerGameEconomy::YEAR, TimerGameEconomy::Priority::TOWN}, [](auto)
{
        /* Increment house ages */
        for (TileIndex t = 0; t < Map::Size(); t++) {
                if (!IsTileType(t, MP_HOUSE)) continue;
                IncrementHouseAge(t);
        }
});

static CommandCost TerraformTile_Town(TileIndex tile, DoCommandFlag flags, int z_new, Slope tileh_new)
{
        if (AutoslopeEnabled()) {
                HouseID house = GetHouseType(tile);
                GetHouseNorthPart(house); // modifies house to the ID of the north tile
                const HouseSpec *hs = HouseSpec::Get(house);

                /* Here we differ from TTDP by checking TILE_NOT_SLOPED */
                if (((hs->building_flags & TILE_NOT_SLOPED) == 0) && !IsSteepSlope(tileh_new) &&
                                (GetTileMaxZ(tile) == z_new + GetSlopeMaxZ(tileh_new))) {
                        bool allow_terraform = true;

                        /* Call the autosloping callback per tile, not for the whole building at once. */
                        house = GetHouseType(tile);
                        hs = HouseSpec::Get(house);
                        if (HasBit(hs->callback_mask, CBM_HOUSE_AUTOSLOPE)) {
                                /* If the callback fails, allow autoslope. */
                                uint16_t res = GetHouseCallback(CBID_HOUSE_AUTOSLOPE, 0, 0, house, Town::GetByTile(tile), tile);
                                if (res != CALLBACK_FAILED && ConvertBooleanCallback(hs->grf_prop.grffile, CBID_HOUSE_AUTOSLOPE, res)) allow_terraform = false;
                        }

                        if (allow_terraform) return CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_FOUNDATION]);
                }
        }

        return Command<CMD_LANDSCAPE_CLEAR>::Do(flags, tile);
}

/** Tile callback functions for a town */
extern const TileTypeProcs _tile_type_town_procs = {
        DrawTile_Town,           // draw_tile_proc
        GetSlopePixelZ_Town,     // get_slope_z_proc
        ClearTile_Town,          // clear_tile_proc
        AddAcceptedCargo_Town,   // add_accepted_cargo_proc
        GetTileDesc_Town,        // get_tile_desc_proc
        GetTileTrackStatus_Town, // get_tile_track_status_proc
        nullptr,                    // click_tile_proc
        AnimateTile_Town,        // animate_tile_proc
        TileLoop_Town,           // tile_loop_proc
        ChangeTileOwner_Town,    // change_tile_owner_proc
        AddProducedCargo_Town,   // add_produced_cargo_proc
        nullptr,                    // vehicle_enter_tile_proc
        GetFoundation_Town,      // get_foundation_proc
        TerraformTile_Town,      // terraform_tile_proc
};

std::span<const DrawBuildingsTileStruct> GetTownDrawTileData()
{
        return _town_draw_tile_data;
}