Fix cc39fa9: New orders are non-stop by default (#8689)

[openttd-github.git] / src / aircraft_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 aircraft_cmd.cpp
 * This file deals with aircraft and airport movements functionalities
 */

#include "stdafx.h"
#include "aircraft.h"
#include "landscape.h"
#include "news_func.h"
#include "newgrf_engine.h"
#include "newgrf_sound.h"
#include "spritecache.h"
#include "strings_func.h"
#include "command_func.h"
#include "window_func.h"
#include "date_func.h"
#include "vehicle_func.h"
#include "sound_func.h"
#include "cheat_type.h"
#include "company_base.h"
#include "ai/ai.hpp"
#include "game/game.hpp"
#include "company_func.h"
#include "effectvehicle_func.h"
#include "station_base.h"
#include "engine_base.h"
#include "core/random_func.hpp"
#include "core/backup_type.hpp"
#include "zoom_func.h"
#include "disaster_vehicle.h"
#include "newgrf_airporttiles.h"
#include "framerate_type.h"

#include "table/strings.h"

#include "safeguards.h"

void Aircraft::UpdateDeltaXY()
{
        this->x_offs = -1;
        this->y_offs = -1;
        this->x_extent = 2;
        this->y_extent = 2;

        switch (this->subtype) {
                default: NOT_REACHED();

                case AIR_AIRCRAFT:
                case AIR_HELICOPTER:
                        switch (this->state) {
                                default: break;
                                case ENDTAKEOFF:
                                case LANDING:
                                case HELILANDING:
                                case FLYING:
                                        this->x_extent = 24;
                                        this->y_extent = 24;
                                        break;
                        }
                        this->z_extent = 5;
                        break;

                case AIR_SHADOW:
                        this->z_extent = 1;
                        this->x_offs = 0;
                        this->y_offs = 0;
                        break;

                case AIR_ROTOR:
                        this->z_extent = 1;
                        break;
        }
}

static bool AirportMove(Aircraft *v, const AirportFTAClass *apc);
static bool AirportSetBlocks(Aircraft *v, const AirportFTA *current_pos, const AirportFTAClass *apc);
static bool AirportHasBlock(Aircraft *v, const AirportFTA *current_pos, const AirportFTAClass *apc);
static bool AirportFindFreeTerminal(Aircraft *v, const AirportFTAClass *apc);
static bool AirportFindFreeHelipad(Aircraft *v, const AirportFTAClass *apc);
static void CrashAirplane(Aircraft *v);

static const SpriteID _aircraft_sprite[] = {
        0x0EB5, 0x0EBD, 0x0EC5, 0x0ECD,
        0x0ED5, 0x0EDD, 0x0E9D, 0x0EA5,
        0x0EAD, 0x0EE5, 0x0F05, 0x0F0D,
        0x0F15, 0x0F1D, 0x0F25, 0x0F2D,
        0x0EED, 0x0EF5, 0x0EFD, 0x0F35,
        0x0E9D, 0x0EA5, 0x0EAD, 0x0EB5,
        0x0EBD, 0x0EC5
};

template <>
bool IsValidImageIndex<VEH_AIRCRAFT>(uint8 image_index)
{
        return image_index < lengthof(_aircraft_sprite);
}

/** Helicopter rotor animation states */
enum HelicopterRotorStates {
        HRS_ROTOR_STOPPED,
        HRS_ROTOR_MOVING_1,
        HRS_ROTOR_MOVING_2,
        HRS_ROTOR_MOVING_3,
};

/**
 * Find the nearest hangar to v
 * INVALID_STATION is returned, if the company does not have any suitable
 * airports (like helipads only)
 * @param v vehicle looking for a hangar
 * @return the StationID if one is found, otherwise, INVALID_STATION
 */
static StationID FindNearestHangar(const Aircraft *v)
{
        uint best = 0;
        StationID index = INVALID_STATION;
        TileIndex vtile = TileVirtXY(v->x_pos, v->y_pos);
        const AircraftVehicleInfo *avi = AircraftVehInfo(v->engine_type);
        uint max_range = v->acache.cached_max_range_sqr;

        /* Determine destinations where it's coming from and where it's heading to */
        const Station *last_dest = nullptr;
        const Station *next_dest = nullptr;
        if (max_range != 0) {
                if (v->current_order.IsType(OT_GOTO_STATION) ||
                                (v->current_order.IsType(OT_GOTO_DEPOT) && v->current_order.GetDepotActionType() != ODATFB_NEAREST_DEPOT)) {
                        last_dest = Station::GetIfValid(v->last_station_visited);
                        next_dest = Station::GetIfValid(v->current_order.GetDestination());
                } else {
                        last_dest = GetTargetAirportIfValid(v);
                        next_dest = Station::GetIfValid(v->GetNextStoppingStation().value);
                }
        }

        for (const Station *st : Station::Iterate()) {
                if (st->owner != v->owner || !(st->facilities & FACIL_AIRPORT) || !st->airport.HasHangar()) continue;

                const AirportFTAClass *afc = st->airport.GetFTA();

                /* don't crash the plane if we know it can't land at the airport */
                if ((afc->flags & AirportFTAClass::SHORT_STRIP) && (avi->subtype & AIR_FAST) && !_cheats.no_jetcrash.value) continue;

                /* the plane won't land at any helicopter station */
                if (!(afc->flags & AirportFTAClass::AIRPLANES) && (avi->subtype & AIR_CTOL)) continue;

                /* Check if our last and next destinations can be reached from the depot airport. */
                if (max_range != 0) {
                        uint last_dist = (last_dest != nullptr && last_dest->airport.tile != INVALID_TILE) ? DistanceSquare(st->airport.tile, last_dest->airport.tile) : 0;
                        uint next_dist = (next_dest != nullptr && next_dest->airport.tile != INVALID_TILE) ? DistanceSquare(st->airport.tile, next_dest->airport.tile) : 0;
                        if (last_dist > max_range || next_dist > max_range) continue;
                }

                /* v->tile can't be used here, when aircraft is flying v->tile is set to 0 */
                uint distance = DistanceSquare(vtile, st->airport.tile);
                if (distance < best || index == INVALID_STATION) {
                        best = distance;
                        index = st->index;
                }
        }
        return index;
}

void Aircraft::GetImage(Direction direction, EngineImageType image_type, VehicleSpriteSeq *result) const
{
        uint8 spritenum = this->spritenum;

        if (is_custom_sprite(spritenum)) {
                GetCustomVehicleSprite(this, direction, image_type, result);
                if (result->IsValid()) return;

                spritenum = this->GetEngine()->original_image_index;
        }

        assert(IsValidImageIndex<VEH_AIRCRAFT>(spritenum));
        result->Set(direction + _aircraft_sprite[spritenum]);
}

void GetRotorImage(const Aircraft *v, EngineImageType image_type, VehicleSpriteSeq *result)
{
        assert(v->subtype == AIR_HELICOPTER);

        const Aircraft *w = v->Next()->Next();
        if (is_custom_sprite(v->spritenum)) {
                GetCustomRotorSprite(v, false, image_type, result);
                if (result->IsValid()) return;
        }

        /* Return standard rotor sprites if there are no custom sprites for this helicopter */
        result->Set(SPR_ROTOR_STOPPED + w->state);
}

static void GetAircraftIcon(EngineID engine, EngineImageType image_type, VehicleSpriteSeq *result)
{
        const Engine *e = Engine::Get(engine);
        uint8 spritenum = e->u.air.image_index;

        if (is_custom_sprite(spritenum)) {
                GetCustomVehicleIcon(engine, DIR_W, image_type, result);
                if (result->IsValid()) return;

                spritenum = e->original_image_index;
        }

        assert(IsValidImageIndex<VEH_AIRCRAFT>(spritenum));
        result->Set(DIR_W + _aircraft_sprite[spritenum]);
}

void DrawAircraftEngine(int left, int right, int preferred_x, int y, EngineID engine, PaletteID pal, EngineImageType image_type)
{
        VehicleSpriteSeq seq;
        GetAircraftIcon(engine, image_type, &seq);

        Rect rect;
        seq.GetBounds(&rect);
        preferred_x = Clamp(preferred_x,
                        left - UnScaleGUI(rect.left),
                        right - UnScaleGUI(rect.right));

        seq.Draw(preferred_x, y, pal, pal == PALETTE_CRASH);

        if (!(AircraftVehInfo(engine)->subtype & AIR_CTOL)) {
                VehicleSpriteSeq rotor_seq;
                GetCustomRotorIcon(engine, image_type, &rotor_seq);
                if (!rotor_seq.IsValid()) rotor_seq.Set(SPR_ROTOR_STOPPED);
                rotor_seq.Draw(preferred_x, y - ScaleGUITrad(5), PAL_NONE, false);
        }
}

/**
 * Get the size of the sprite of an aircraft sprite heading west (used for lists).
 * @param engine The engine to get the sprite from.
 * @param[out] width The width of the sprite.
 * @param[out] height The height of the sprite.
 * @param[out] xoffs Number of pixels to shift the sprite to the right.
 * @param[out] yoffs Number of pixels to shift the sprite downwards.
 * @param image_type Context the sprite is used in.
 */
void GetAircraftSpriteSize(EngineID engine, uint &width, uint &height, int &xoffs, int &yoffs, EngineImageType image_type)
{
        VehicleSpriteSeq seq;
        GetAircraftIcon(engine, image_type, &seq);

        Rect rect;
        seq.GetBounds(&rect);

        width  = UnScaleGUI(rect.right - rect.left + 1);
        height = UnScaleGUI(rect.bottom - rect.top + 1);
        xoffs  = UnScaleGUI(rect.left);
        yoffs  = UnScaleGUI(rect.top);
}

/**
 * Build an aircraft.
 * @param tile     tile of the depot where aircraft is built.
 * @param flags    type of operation.
 * @param e        the engine to build.
 * @param data     unused.
 * @param[out] ret the vehicle that has been built.
 * @return the cost of this operation or an error.
 */
CommandCost CmdBuildAircraft(TileIndex tile, DoCommandFlag flags, const Engine *e, uint16 data, Vehicle **ret)
{
        const AircraftVehicleInfo *avi = &e->u.air;
        const Station *st = Station::GetByTile(tile);

        /* Prevent building aircraft types at places which can't handle them */
        if (!CanVehicleUseStation(e->index, st)) return CMD_ERROR;

        /* Make sure all aircraft end up in the first tile of the hangar. */
        tile = st->airport.GetHangarTile(st->airport.GetHangarNum(tile));

        if (flags & DC_EXEC) {
                Aircraft *v = new Aircraft(); // aircraft
                Aircraft *u = new Aircraft(); // shadow
                *ret = v;

                v->direction = DIR_SE;

                v->owner = u->owner = _current_company;

                v->tile = tile;

                uint x = TileX(tile) * TILE_SIZE + 5;
                uint y = TileY(tile) * TILE_SIZE + 3;

                v->x_pos = u->x_pos = x;
                v->y_pos = u->y_pos = y;

                u->z_pos = GetSlopePixelZ(x, y);
                v->z_pos = u->z_pos + 1;

                v->vehstatus = VS_HIDDEN | VS_STOPPED | VS_DEFPAL;
                u->vehstatus = VS_HIDDEN | VS_UNCLICKABLE | VS_SHADOW;

                v->spritenum = avi->image_index;

                v->cargo_cap = avi->passenger_capacity;
                v->refit_cap = 0;
                u->cargo_cap = avi->mail_capacity;
                u->refit_cap = 0;

                v->cargo_type = e->GetDefaultCargoType();
                u->cargo_type = CT_MAIL;

                v->name.clear();
                v->last_station_visited = INVALID_STATION;
                v->last_loading_station = INVALID_STATION;

                v->acceleration = avi->acceleration;
                v->engine_type = e->index;
                u->engine_type = e->index;

                v->subtype = (avi->subtype & AIR_CTOL ? AIR_AIRCRAFT : AIR_HELICOPTER);
                v->UpdateDeltaXY();

                u->subtype = AIR_SHADOW;
                u->UpdateDeltaXY();

                v->reliability = e->reliability;
                v->reliability_spd_dec = e->reliability_spd_dec;
                v->max_age = e->GetLifeLengthInDays();

                _new_vehicle_id = v->index;

                v->pos = GetVehiclePosOnBuild(tile);

                v->state = HANGAR;
                v->previous_pos = v->pos;
                v->targetairport = GetStationIndex(tile);
                v->SetNext(u);

                v->SetServiceInterval(Company::Get(_current_company)->settings.vehicle.servint_aircraft);

                v->date_of_last_service = _date;
                v->build_year = u->build_year = _cur_year;

                v->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);
                u->sprite_cache.sprite_seq.Set(SPR_IMG_QUERY);

                v->random_bits = VehicleRandomBits();
                u->random_bits = VehicleRandomBits();

                v->vehicle_flags = 0;
                if (e->flags & ENGINE_EXCLUSIVE_PREVIEW) SetBit(v->vehicle_flags, VF_BUILT_AS_PROTOTYPE);
                v->SetServiceIntervalIsPercent(Company::Get(_current_company)->settings.vehicle.servint_ispercent);

                v->InvalidateNewGRFCacheOfChain();

                v->cargo_cap = e->DetermineCapacity(v, &u->cargo_cap);

                v->InvalidateNewGRFCacheOfChain();

                UpdateAircraftCache(v, true);

                v->UpdatePosition();
                u->UpdatePosition();

                /* Aircraft with 3 vehicles (chopper)? */
                if (v->subtype == AIR_HELICOPTER) {
                        Aircraft *w = new Aircraft();
                        w->engine_type = e->index;
                        w->direction = DIR_N;
                        w->owner = _current_company;
                        w->x_pos = v->x_pos;
                        w->y_pos = v->y_pos;
                        w->z_pos = v->z_pos + ROTOR_Z_OFFSET;
                        w->vehstatus = VS_HIDDEN | VS_UNCLICKABLE;
                        w->spritenum = 0xFF;
                        w->subtype = AIR_ROTOR;
                        w->sprite_cache.sprite_seq.Set(SPR_ROTOR_STOPPED);
                        w->random_bits = VehicleRandomBits();
                        /* Use rotor's air.state to store the rotor animation frame */
                        w->state = HRS_ROTOR_STOPPED;
                        w->UpdateDeltaXY();

                        u->SetNext(w);
                        w->UpdatePosition();
                }
        }

        return CommandCost();
}


bool Aircraft::FindClosestDepot(TileIndex *location, DestinationID *destination, bool *reverse)
{
        const Station *st = GetTargetAirportIfValid(this);
        /* If the station is not a valid airport or if it has no hangars */
        if (st == nullptr || !CanVehicleUseStation(this, st) || !st->airport.HasHangar()) {
                /* the aircraft has to search for a hangar on its own */
                StationID station = FindNearestHangar(this);

                if (station == INVALID_STATION) return false;

                st = Station::Get(station);
        }

        if (location    != nullptr) *location    = st->xy;
        if (destination != nullptr) *destination = st->index;

        return true;
}

static void CheckIfAircraftNeedsService(Aircraft *v)
{
        if (Company::Get(v->owner)->settings.vehicle.servint_aircraft == 0 || !v->NeedsAutomaticServicing()) return;
        if (v->IsChainInDepot()) {
                VehicleServiceInDepot(v);
                return;
        }

        /* When we're parsing conditional orders and the like
         * we don't want to consider going to a depot too. */
        if (!v->current_order.IsType(OT_GOTO_DEPOT) && !v->current_order.IsType(OT_GOTO_STATION)) return;

        const Station *st = Station::Get(v->current_order.GetDestination());

        assert(st != nullptr);

        /* only goto depot if the target airport has a depot */
        if (st->airport.HasHangar() && CanVehicleUseStation(v, st)) {
                v->current_order.MakeGoToDepot(st->index, ODTFB_SERVICE);
                SetWindowWidgetDirty(WC_VEHICLE_VIEW, v->index, WID_VV_START_STOP);
        } else if (v->current_order.IsType(OT_GOTO_DEPOT)) {
                v->current_order.MakeDummy();
                SetWindowWidgetDirty(WC_VEHICLE_VIEW, v->index, WID_VV_START_STOP);
        }
}

Money Aircraft::GetRunningCost() const
{
        const Engine *e = this->GetEngine();
        uint cost_factor = GetVehicleProperty(this, PROP_AIRCRAFT_RUNNING_COST_FACTOR, e->u.air.running_cost);
        return GetPrice(PR_RUNNING_AIRCRAFT, cost_factor, e->GetGRF());
}

void Aircraft::OnNewDay()
{
        if (!this->IsNormalAircraft()) return;

        if ((++this->day_counter & 7) == 0) DecreaseVehicleValue(this);

        CheckOrders(this);

        CheckVehicleBreakdown(this);
        AgeVehicle(this);
        CheckIfAircraftNeedsService(this);

        if (this->running_ticks == 0) return;

        CommandCost cost(EXPENSES_AIRCRAFT_RUN, this->GetRunningCost() * this->running_ticks / (DAYS_IN_YEAR * DAY_TICKS));

        this->profit_this_year -= cost.GetCost();
        this->running_ticks = 0;

        SubtractMoneyFromCompanyFract(this->owner, cost);

        SetWindowDirty(WC_VEHICLE_DETAILS, this->index);
        SetWindowClassesDirty(WC_AIRCRAFT_LIST);
}

static void HelicopterTickHandler(Aircraft *v)
{
        Aircraft *u = v->Next()->Next();

        if (u->vehstatus & VS_HIDDEN) return;

        /* if true, helicopter rotors do not rotate. This should only be the case if a helicopter is
         * loading/unloading at a terminal or stopped */
        if (v->current_order.IsType(OT_LOADING) || (v->vehstatus & VS_STOPPED)) {
                if (u->cur_speed != 0) {
                        u->cur_speed++;
                        if (u->cur_speed >= 0x80 && u->state == HRS_ROTOR_MOVING_3) {
                                u->cur_speed = 0;
                        }
                }
        } else {
                if (u->cur_speed == 0) {
                        u->cur_speed = 0x70;
                }
                if (u->cur_speed >= 0x50) {
                        u->cur_speed--;
                }
        }

        int tick = ++u->tick_counter;
        int spd = u->cur_speed >> 4;

        VehicleSpriteSeq seq;
        if (spd == 0) {
                u->state = HRS_ROTOR_STOPPED;
                GetRotorImage(v, EIT_ON_MAP, &seq);
                if (u->sprite_cache.sprite_seq == seq) return;
        } else if (tick >= spd) {
                u->tick_counter = 0;
                u->state++;
                if (u->state > HRS_ROTOR_MOVING_3) u->state = HRS_ROTOR_MOVING_1;
                GetRotorImage(v, EIT_ON_MAP, &seq);
        } else {
                return;
        }

        u->sprite_cache.sprite_seq = seq;

        u->UpdatePositionAndViewport();
}

/**
 * Set aircraft position.
 * @param v Aircraft to position.
 * @param x New X position.
 * @param y New y position.
 * @param z New z position.
 */
void SetAircraftPosition(Aircraft *v, int x, int y, int z)
{
        v->x_pos = x;
        v->y_pos = y;
        v->z_pos = z;

        v->UpdatePosition();
        v->UpdateViewport(true, false);
        if (v->subtype == AIR_HELICOPTER) {
                GetRotorImage(v, EIT_ON_MAP, &v->Next()->Next()->sprite_cache.sprite_seq);
        }

        Aircraft *u = v->Next();

        int safe_x = Clamp(x, 0, MapMaxX() * TILE_SIZE);
        int safe_y = Clamp(y - 1, 0, MapMaxY() * TILE_SIZE);
        u->x_pos = x;
        u->y_pos = y - ((v->z_pos - GetSlopePixelZ(safe_x, safe_y)) >> 3);

        safe_y = Clamp(u->y_pos, 0, MapMaxY() * TILE_SIZE);
        u->z_pos = GetSlopePixelZ(safe_x, safe_y);
        u->sprite_cache.sprite_seq.CopyWithoutPalette(v->sprite_cache.sprite_seq); // the shadow is never coloured

        u->UpdatePositionAndViewport();

        u = u->Next();
        if (u != nullptr) {
                u->x_pos = x;
                u->y_pos = y;
                u->z_pos = z + ROTOR_Z_OFFSET;

                u->UpdatePositionAndViewport();
        }
}

/**
 * Handle Aircraft specific tasks when an Aircraft enters a hangar
 * @param *v Vehicle that enters the hangar
 */
void HandleAircraftEnterHangar(Aircraft *v)
{
        v->subspeed = 0;
        v->progress = 0;

        Aircraft *u = v->Next();
        u->vehstatus |= VS_HIDDEN;
        u = u->Next();
        if (u != nullptr) {
                u->vehstatus |= VS_HIDDEN;
                u->cur_speed = 0;
        }

        SetAircraftPosition(v, v->x_pos, v->y_pos, v->z_pos);
}

static void PlayAircraftSound(const Vehicle *v)
{
        if (!PlayVehicleSound(v, VSE_START)) {
                SndPlayVehicleFx(AircraftVehInfo(v->engine_type)->sfx, v);
        }
}


/**
 * Update cached values of an aircraft.
 * Currently caches callback 36 max speed.
 * @param v Vehicle
 * @param update_range Update the aircraft range.
 */
void UpdateAircraftCache(Aircraft *v, bool update_range)
{
        uint max_speed = GetVehicleProperty(v, PROP_AIRCRAFT_SPEED, 0);
        if (max_speed != 0) {
                /* Convert from original units to km-ish/h */
                max_speed = (max_speed * 128) / 10;

                v->vcache.cached_max_speed = max_speed;
        } else {
                /* Use the default max speed of the vehicle. */
                v->vcache.cached_max_speed = AircraftVehInfo(v->engine_type)->max_speed;
        }

        /* Update cargo aging period. */
        v->vcache.cached_cargo_age_period = GetVehicleProperty(v, PROP_AIRCRAFT_CARGO_AGE_PERIOD, EngInfo(v->engine_type)->cargo_age_period);
        Aircraft *u = v->Next(); // Shadow for mail
        u->vcache.cached_cargo_age_period = GetVehicleProperty(u, PROP_AIRCRAFT_CARGO_AGE_PERIOD, EngInfo(u->engine_type)->cargo_age_period);

        /* Update aircraft range. */
        if (update_range) {
                v->acache.cached_max_range = GetVehicleProperty(v, PROP_AIRCRAFT_RANGE, AircraftVehInfo(v->engine_type)->max_range);
                /* Squared it now so we don't have to do it later all the time. */
                v->acache.cached_max_range_sqr = v->acache.cached_max_range * v->acache.cached_max_range;
        }
}


/**
 * Special velocities for aircraft
 */
enum AircraftSpeedLimits {
        SPEED_LIMIT_TAXI     =     50,  ///< Maximum speed of an aircraft while taxiing
        SPEED_LIMIT_APPROACH =    230,  ///< Maximum speed of an aircraft on finals
        SPEED_LIMIT_BROKEN   =    320,  ///< Maximum speed of an aircraft that is broken
        SPEED_LIMIT_HOLD     =    425,  ///< Maximum speed of an aircraft that flies the holding pattern
        SPEED_LIMIT_NONE     = 0xFFFF,  ///< No environmental speed limit. Speed limit is type dependent
};

/**
 * Sets the new speed for an aircraft
 * @param v The vehicle for which the speed should be obtained
 * @param speed_limit The maximum speed the vehicle may have.
 * @param hard_limit If true, the limit is directly enforced, otherwise the plane is slowed down gradually
 * @return The number of position updates needed within the tick
 */
static int UpdateAircraftSpeed(Aircraft *v, uint speed_limit = SPEED_LIMIT_NONE, bool hard_limit = true)
{
        /**
         * 'acceleration' has the unit 3/8 mph/tick. This function is called twice per tick.
         * So the speed amount we need to accelerate is:
         *     acceleration * 3 / 16 mph = acceleration * 3 / 16 * 16 / 10 km-ish/h
         *                               = acceleration * 3 / 10 * 256 * (km-ish/h / 256)
         *                               ~ acceleration * 77 (km-ish/h / 256)
         */
        uint spd = v->acceleration * 77;
        byte t;

        /* Adjust speed limits by plane speed factor to prevent taxiing
         * and take-off speeds being too low. */
        speed_limit *= _settings_game.vehicle.plane_speed;

        /* adjust speed for broken vehicles */
        if (v->vehstatus & VS_AIRCRAFT_BROKEN) {
                if (SPEED_LIMIT_BROKEN < speed_limit) hard_limit = false;
                speed_limit = std::min<uint>(speed_limit, SPEED_LIMIT_BROKEN);
        }

        if (v->vcache.cached_max_speed < speed_limit) {
                if (v->cur_speed < speed_limit) hard_limit = false;
                speed_limit = v->vcache.cached_max_speed;
        }

        v->subspeed = (t = v->subspeed) + (byte)spd;

        /* Aircraft's current speed is used twice so that very fast planes are
         * forced to slow down rapidly in the short distance needed. The magic
         * value 16384 was determined to give similar results to the old speed/48
         * method at slower speeds. This also results in less reduction at slow
         * speeds to that aircraft do not get to taxi speed straight after
         * touchdown. */
        if (!hard_limit && v->cur_speed > speed_limit) {
                speed_limit = v->cur_speed - std::max(1, ((v->cur_speed * v->cur_speed) / 16384) / _settings_game.vehicle.plane_speed);
        }

        spd = std::min(v->cur_speed + (spd >> 8) + (v->subspeed < t), speed_limit);

        /* updates statusbar only if speed have changed to save CPU time */
        if (spd != v->cur_speed) {
                v->cur_speed = spd;
                SetWindowWidgetDirty(WC_VEHICLE_VIEW, v->index, WID_VV_START_STOP);
        }

        /* Adjust distance moved by plane speed setting */
        if (_settings_game.vehicle.plane_speed > 1) spd /= _settings_game.vehicle.plane_speed;

        /* Convert direction-independent speed into direction-dependent speed. (old movement method) */
        spd = v->GetOldAdvanceSpeed(spd);

        spd += v->progress;
        v->progress = (byte)spd;
        return spd >> 8;
}

/**
 * Get the tile height below the aircraft.
 * This function is needed because aircraft can leave the mapborders.
 *
 * @param v The vehicle to get the height for.
 * @return The height in pixels from 'z_pos' 0.
 */
int GetTileHeightBelowAircraft(const Vehicle *v)
{
        int safe_x = Clamp(v->x_pos, 0, MapMaxX() * TILE_SIZE);
        int safe_y = Clamp(v->y_pos, 0, MapMaxY() * TILE_SIZE);
        return TileHeight(TileVirtXY(safe_x, safe_y)) * TILE_HEIGHT;
}

/**
 * Get the 'flight level' bounds, in pixels from 'z_pos' 0 for a particular
 * vehicle for normal flight situation.
 * When the maximum is reached the vehicle should consider descending.
 * When the minimum is reached the vehicle should consider ascending.
 *
 * @param v              The vehicle to get the flight levels for.
 * @param[out] min_level The minimum bounds for flight level.
 * @param[out] max_level The maximum bounds for flight level.
 */
void GetAircraftFlightLevelBounds(const Vehicle *v, int *min_level, int *max_level)
{
        int base_altitude = GetTileHeightBelowAircraft(v);
        if (v->type == VEH_AIRCRAFT && Aircraft::From(v)->subtype == AIR_HELICOPTER) {
                base_altitude += HELICOPTER_HOLD_MAX_FLYING_ALTITUDE - PLANE_HOLD_MAX_FLYING_ALTITUDE;
        }

        /* Make sure eastbound and westbound planes do not "crash" into each
         * other by providing them with vertical separation
         */
        switch (v->direction) {
                case DIR_N:
                case DIR_NE:
                case DIR_E:
                case DIR_SE:
                        base_altitude += 10;
                        break;

                default: break;
        }

        /* Make faster planes fly higher so that they can overtake slower ones */
        base_altitude += std::min(20 * (v->vcache.cached_max_speed / 200) - 90, 0);

        if (min_level != nullptr) *min_level = base_altitude + AIRCRAFT_MIN_FLYING_ALTITUDE;
        if (max_level != nullptr) *max_level = base_altitude + AIRCRAFT_MAX_FLYING_ALTITUDE;
}

/**
 * Gets the maximum 'flight level' for the holding pattern of the aircraft,
 * in pixels 'z_pos' 0, depending on terrain below.
 *
 * @param v The aircraft that may or may not need to decrease its altitude.
 * @return Maximal aircraft holding altitude, while in normal flight, in pixels.
 */
int GetAircraftHoldMaxAltitude(const Aircraft *v)
{
        int tile_height = GetTileHeightBelowAircraft(v);

        return tile_height + ((v->subtype == AIR_HELICOPTER) ? HELICOPTER_HOLD_MAX_FLYING_ALTITUDE : PLANE_HOLD_MAX_FLYING_ALTITUDE);
}

template <class T>
int GetAircraftFlightLevel(T *v, bool takeoff)
{
        /* Aircraft is in flight. We want to enforce it being somewhere
         * between the minimum and the maximum allowed altitude. */
        int aircraft_min_altitude;
        int aircraft_max_altitude;
        GetAircraftFlightLevelBounds(v, &aircraft_min_altitude, &aircraft_max_altitude);
        int aircraft_middle_altitude = (aircraft_min_altitude + aircraft_max_altitude) / 2;

        /* If those assumptions would be violated, aircraft would behave fairly strange. */
        assert(aircraft_min_altitude < aircraft_middle_altitude);
        assert(aircraft_middle_altitude < aircraft_max_altitude);

        int z = v->z_pos;
        if (z < aircraft_min_altitude ||
                        (HasBit(v->flags, VAF_IN_MIN_HEIGHT_CORRECTION) && z < aircraft_middle_altitude)) {
                /* Ascend. And don't fly into that mountain right ahead.
                 * And avoid our aircraft become a stairclimber, so if we start
                 * correcting altitude, then we stop correction not too early. */
                SetBit(v->flags, VAF_IN_MIN_HEIGHT_CORRECTION);
                z += takeoff ? 2 : 1;
        } else if (!takeoff && (z > aircraft_max_altitude ||
                        (HasBit(v->flags, VAF_IN_MAX_HEIGHT_CORRECTION) && z > aircraft_middle_altitude))) {
                /* Descend lower. You are an aircraft, not an space ship.
                 * And again, don't stop correcting altitude too early. */
                SetBit(v->flags, VAF_IN_MAX_HEIGHT_CORRECTION);
                z--;
        } else if (HasBit(v->flags, VAF_IN_MIN_HEIGHT_CORRECTION) && z >= aircraft_middle_altitude) {
                /* Now, we have corrected altitude enough. */
                ClrBit(v->flags, VAF_IN_MIN_HEIGHT_CORRECTION);
        } else if (HasBit(v->flags, VAF_IN_MAX_HEIGHT_CORRECTION) && z <= aircraft_middle_altitude) {
                /* Now, we have corrected altitude enough. */
                ClrBit(v->flags, VAF_IN_MAX_HEIGHT_CORRECTION);
        }

        return z;
}

template int GetAircraftFlightLevel(DisasterVehicle *v, bool takeoff);
template int GetAircraftFlightLevel(Aircraft *v, bool takeoff);

/**
 * Find the entry point to an airport depending on direction which
 * the airport is being approached from. Each airport can have up to
 * four entry points for its approach system so that approaching
 * aircraft do not fly through each other or are forced to do 180
 * degree turns during the approach. The arrivals are grouped into
 * four sectors dependent on the DiagDirection from which the airport
 * is approached.
 *
 * @param v   The vehicle that is approaching the airport
 * @param apc The Airport Class being approached.
 * @param rotation The rotation of the airport.
 * @return   The index of the entry point
 */
static byte AircraftGetEntryPoint(const Aircraft *v, const AirportFTAClass *apc, Direction rotation)
{
        assert(v != nullptr);
        assert(apc != nullptr);

        /* In the case the station doesn't exit anymore, set target tile 0.
         * It doesn't hurt much, aircraft will go to next order, nearest hangar
         * or it will simply crash in next tick */
        TileIndex tile = 0;

        const Station *st = Station::GetIfValid(v->targetairport);
        if (st != nullptr) {
                /* Make sure we don't go to INVALID_TILE if the airport has been removed. */
                tile = (st->airport.tile != INVALID_TILE) ? st->airport.tile : st->xy;
        }

        int delta_x = v->x_pos - TileX(tile) * TILE_SIZE;
        int delta_y = v->y_pos - TileY(tile) * TILE_SIZE;

        DiagDirection dir;
        if (abs(delta_y) < abs(delta_x)) {
                /* We are northeast or southwest of the airport */
                dir = delta_x < 0 ? DIAGDIR_NE : DIAGDIR_SW;
        } else {
                /* We are northwest or southeast of the airport */
                dir = delta_y < 0 ? DIAGDIR_NW : DIAGDIR_SE;
        }
        dir = ChangeDiagDir(dir, DiagDirDifference(DIAGDIR_NE, DirToDiagDir(rotation)));
        return apc->entry_points[dir];
}


static void MaybeCrashAirplane(Aircraft *v);

/**
 * Controls the movement of an aircraft. This function actually moves the vehicle
 * on the map and takes care of minor things like sound playback.
 * @todo    De-mystify the cur_speed values for helicopter rotors.
 * @param v The vehicle that is moved. Must be the first vehicle of the chain
 * @return  Whether the position requested by the State Machine has been reached
 */
static bool AircraftController(Aircraft *v)
{
        /* nullptr if station is invalid */
        const Station *st = Station::GetIfValid(v->targetairport);
        /* INVALID_TILE if there is no station */
        TileIndex tile = INVALID_TILE;
        Direction rotation = DIR_N;
        uint size_x = 1, size_y = 1;
        if (st != nullptr) {
                if (st->airport.tile != INVALID_TILE) {
                        tile = st->airport.tile;
                        rotation = st->airport.rotation;
                        size_x = st->airport.w;
                        size_y = st->airport.h;
                } else {
                        tile = st->xy;
                }
        }
        /* DUMMY if there is no station or no airport */
        const AirportFTAClass *afc = tile == INVALID_TILE ? GetAirport(AT_DUMMY) : st->airport.GetFTA();

        /* prevent going to INVALID_TILE if airport is deleted. */
        if (st == nullptr || st->airport.tile == INVALID_TILE) {
                /* Jump into our "holding pattern" state machine if possible */
                if (v->pos >= afc->nofelements) {
                        v->pos = v->previous_pos = AircraftGetEntryPoint(v, afc, DIR_N);
                } else if (v->targetairport != v->current_order.GetDestination()) {
                        /* If not possible, just get out of here fast */
                        v->state = FLYING;
                        UpdateAircraftCache(v);
                        AircraftNextAirportPos_and_Order(v);
                        /* get aircraft back on running altitude */
                        SetAircraftPosition(v, v->x_pos, v->y_pos, GetAircraftFlightLevel(v));
                        return false;
                }
        }

        /*  get airport moving data */
        const AirportMovingData amd = RotateAirportMovingData(afc->MovingData(v->pos), rotation, size_x, size_y);

        int x = TileX(tile) * TILE_SIZE;
        int y = TileY(tile) * TILE_SIZE;

        /* Helicopter raise */
        if (amd.flag & AMED_HELI_RAISE) {
                Aircraft *u = v->Next()->Next();

                /* Make sure the rotors don't rotate too fast */
                if (u->cur_speed > 32) {
                        v->cur_speed = 0;
                        if (--u->cur_speed == 32) {
                                if (!PlayVehicleSound(v, VSE_START)) {
                                        SoundID sfx = AircraftVehInfo(v->engine_type)->sfx;
                                        /* For compatibility with old NewGRF we ignore the sfx property, unless a NewGRF-defined sound is used.
                                         * The baseset has only one helicopter sound, so this only limits using plane or cow sounds. */
                                        if (sfx < ORIGINAL_SAMPLE_COUNT) sfx = SND_18_HELICOPTER;
                                        SndPlayVehicleFx(sfx, v);
                                }
                        }
                } else {
                        u->cur_speed = 32;
                        int count = UpdateAircraftSpeed(v);
                        if (count > 0) {
                                v->tile = 0;

                                int z_dest;
                                GetAircraftFlightLevelBounds(v, &z_dest, nullptr);

                                /* Reached altitude? */
                                if (v->z_pos >= z_dest) {
                                        v->cur_speed = 0;
                                        return true;
                                }
                                SetAircraftPosition(v, v->x_pos, v->y_pos, std::min(v->z_pos + count, z_dest));
                        }
                }
                return false;
        }

        /* Helicopter landing. */
        if (amd.flag & AMED_HELI_LOWER) {
                SetBit(v->flags, VAF_HELI_DIRECT_DESCENT);

                if (st == nullptr) {
                        /* FIXME - AircraftController -> if station no longer exists, do not land
                         * helicopter will circle until sign disappears, then go to next order
                         * what to do when it is the only order left, right now it just stays in 1 place */
                        v->state = FLYING;
                        UpdateAircraftCache(v);
                        AircraftNextAirportPos_and_Order(v);
                        return false;
                }

                /* Vehicle is now at the airport.
                 * Helicopter has arrived at the target landing pad, so the current position is also where it should land.
                 * Except for Oilrigs which are special due to being a 1x1 station, and helicopters land outside it. */
                if (st->airport.type != AT_OILRIG) {
                        x = v->x_pos;
                        y = v->y_pos;
                        tile = TileVirtXY(x, y);
                }
                v->tile = tile;

                /* Find altitude of landing position. */
                int z = GetSlopePixelZ(x, y) + 1 + afc->delta_z;

                if (z == v->z_pos) {
                        Vehicle *u = v->Next()->Next();

                        /*  Increase speed of rotors. When speed is 80, we've landed. */
                        if (u->cur_speed >= 80) {
                                ClrBit(v->flags, VAF_HELI_DIRECT_DESCENT);
                                return true;
                        }
                        u->cur_speed += 4;
                } else {
                        int count = UpdateAircraftSpeed(v);
                        if (count > 0) {
                                if (v->z_pos > z) {
                                        SetAircraftPosition(v, v->x_pos, v->y_pos, std::max(v->z_pos - count, z));
                                } else {
                                        SetAircraftPosition(v, v->x_pos, v->y_pos, std::min(v->z_pos + count, z));
                                }
                        }
                }
                return false;
        }

        /* Get distance from destination pos to current pos. */
        uint dist = abs(x + amd.x - v->x_pos) +  abs(y + amd.y - v->y_pos);

        /* Need exact position? */
        if (!(amd.flag & AMED_EXACTPOS) && dist <= (amd.flag & AMED_SLOWTURN ? 8U : 4U)) return true;

        /* At final pos? */
        if (dist == 0) {
                /* Change direction smoothly to final direction. */
                DirDiff dirdiff = DirDifference(amd.direction, v->direction);
                /* if distance is 0, and plane points in right direction, no point in calling
                 * UpdateAircraftSpeed(). So do it only afterwards */
                if (dirdiff == DIRDIFF_SAME) {
                        v->cur_speed = 0;
                        return true;
                }

                if (!UpdateAircraftSpeed(v, SPEED_LIMIT_TAXI)) return false;

                v->direction = ChangeDir(v->direction, dirdiff > DIRDIFF_REVERSE ? DIRDIFF_45LEFT : DIRDIFF_45RIGHT);
                v->cur_speed >>= 1;

                SetAircraftPosition(v, v->x_pos, v->y_pos, v->z_pos);
                return false;
        }

        if (amd.flag & AMED_BRAKE && v->cur_speed > SPEED_LIMIT_TAXI * _settings_game.vehicle.plane_speed) {
                MaybeCrashAirplane(v);
                if ((v->vehstatus & VS_CRASHED) != 0) return false;
        }

        uint speed_limit = SPEED_LIMIT_TAXI;
        bool hard_limit = true;

        if (amd.flag & AMED_NOSPDCLAMP)   speed_limit = SPEED_LIMIT_NONE;
        if (amd.flag & AMED_HOLD)       { speed_limit = SPEED_LIMIT_HOLD;     hard_limit = false; }
        if (amd.flag & AMED_LAND)       { speed_limit = SPEED_LIMIT_APPROACH; hard_limit = false; }
        if (amd.flag & AMED_BRAKE)      { speed_limit = SPEED_LIMIT_TAXI;     hard_limit = false; }

        int count = UpdateAircraftSpeed(v, speed_limit, hard_limit);
        if (count == 0) return false;

        /* If the plane will be a few subpixels away from the destination after
         * this movement loop, start nudging him towards the exact position for
         * the whole loop. Otherwise, heavily depending on the speed of the plane,
         * it is possible we totally overshoot the target, causing the plane to
         * make a loop, and trying again, and again, and again .. */
        bool nudge_towards_target = static_cast<uint>(count) + 3 > dist;

        if (v->turn_counter != 0) v->turn_counter--;

        do {

                GetNewVehiclePosResult gp;

                if (nudge_towards_target || (amd.flag & AMED_LAND)) {
                        /* move vehicle one pixel towards target */
                        gp.x = (v->x_pos != (x + amd.x)) ?
                                        v->x_pos + ((x + amd.x > v->x_pos) ? 1 : -1) :
                                        v->x_pos;
                        gp.y = (v->y_pos != (y + amd.y)) ?
                                        v->y_pos + ((y + amd.y > v->y_pos) ? 1 : -1) :
                                        v->y_pos;

                        /* Oilrigs must keep v->tile as st->airport.tile, since the landing pad is in a non-airport tile */
                        gp.new_tile = (st->airport.type == AT_OILRIG) ? st->airport.tile : TileVirtXY(gp.x, gp.y);

                } else {

                        /* Turn. Do it slowly if in the air. */
                        Direction newdir = GetDirectionTowards(v, x + amd.x, y + amd.y);
                        if (newdir != v->direction) {
                                if (amd.flag & AMED_SLOWTURN && v->number_consecutive_turns < 8 && v->subtype == AIR_AIRCRAFT) {
                                        if (v->turn_counter == 0 || newdir == v->last_direction) {
                                                if (newdir == v->last_direction) {
                                                        v->number_consecutive_turns = 0;
                                                } else {
                                                        v->number_consecutive_turns++;
                                                }
                                                v->turn_counter = 2 * _settings_game.vehicle.plane_speed;
                                                v->last_direction = v->direction;
                                                v->direction = newdir;
                                        }

                                        /* Move vehicle. */
                                        gp = GetNewVehiclePos(v);
                                } else {
                                        v->cur_speed >>= 1;
                                        v->direction = newdir;

                                        /* When leaving a terminal an aircraft often goes to a position
                                         * directly in front of it. If it would move while turning it
                                         * would need an two extra turns to end up at the correct position.
                                         * To make it easier just disallow all moving while turning as
                                         * long as an aircraft is on the ground. */
                                        gp.x = v->x_pos;
                                        gp.y = v->y_pos;
                                        gp.new_tile = gp.old_tile = v->tile;
                                }
                        } else {
                                v->number_consecutive_turns = 0;
                                /* Move vehicle. */
                                gp = GetNewVehiclePos(v);
                        }
                }

                v->tile = gp.new_tile;
                /* If vehicle is in the air, use tile coordinate 0. */
                if (amd.flag & (AMED_TAKEOFF | AMED_SLOWTURN | AMED_LAND)) v->tile = 0;

                /* Adjust Z for land or takeoff? */
                int z = v->z_pos;

                if (amd.flag & AMED_TAKEOFF) {
                        z = GetAircraftFlightLevel(v, true);
                } else if (amd.flag & AMED_HOLD) {
                        /* Let the plane drop from normal flight altitude to holding pattern altitude */
                        if (z > GetAircraftHoldMaxAltitude(v)) z--;
                } else if ((amd.flag & AMED_SLOWTURN) && (amd.flag & AMED_NOSPDCLAMP)) {
                        z = GetAircraftFlightLevel(v);
                }

                /* NewGRF airports (like a rotated intercontinental from OpenGFX+Airports) can be non-rectangular
                 * and their primary (north-most) tile does not have to be part of the airport.
                 * As such, the height of the primary tile can be different from the rest of the airport.
                 * Given we are landing/breaking, and as such are not a helicopter, we know that there has to be a hangar.
                 * We also know that the airport itself has to be completely flat (otherwise it is not a valid airport).
                 * Therefore, use the height of this hangar to calculate our z-value. */
                int airport_z = v->z_pos;
                if ((amd.flag & (AMED_LAND | AMED_BRAKE)) && st != nullptr) {
                        assert(st->airport.HasHangar());
                        TileIndex hangar_tile = st->airport.GetHangarTile(0);
                        airport_z = GetTileMaxPixelZ(hangar_tile) + 1; // To avoid clashing with the shadow
                }

                if (amd.flag & AMED_LAND) {
                        if (st->airport.tile == INVALID_TILE) {
                                /* Airport has been removed, abort the landing procedure */
                                v->state = FLYING;
                                UpdateAircraftCache(v);
                                AircraftNextAirportPos_and_Order(v);
                                /* get aircraft back on running altitude */
                                SetAircraftPosition(v, gp.x, gp.y, GetAircraftFlightLevel(v));
                                continue;
                        }

                        /* We're not flying below our destination, right? */
                        assert(airport_z <= z);
                        int t = std::max(1U, dist - 4);
                        int delta = z - airport_z;

                        /* Only start lowering when we're sufficiently close for a 1:1 glide */
                        if (delta >= t) {
                                z -= CeilDiv(z - airport_z, t);
                        }
                        if (z < airport_z) z = airport_z;
                }

                /* We've landed. Decrease speed when we're reaching end of runway. */
                if (amd.flag & AMED_BRAKE) {

                        if (z > airport_z) {
                                z--;
                        } else if (z < airport_z) {
                                z++;
                        }

                }

                SetAircraftPosition(v, gp.x, gp.y, z);
        } while (--count != 0);
        return false;
}

/**
 * Handle crashed aircraft \a v.
 * @param v Crashed aircraft.
 */
static bool HandleCrashedAircraft(Aircraft *v)
{
        v->crashed_counter += 3;

        Station *st = GetTargetAirportIfValid(v);

        /* make aircraft crash down to the ground */
        if (v->crashed_counter < 500 && st == nullptr && ((v->crashed_counter % 3) == 0) ) {
                int z = GetSlopePixelZ(Clamp(v->x_pos, 0, MapMaxX() * TILE_SIZE), Clamp(v->y_pos, 0, MapMaxY() * TILE_SIZE));
                v->z_pos -= 1;
                if (v->z_pos == z) {
                        v->crashed_counter = 500;
                        v->z_pos++;
                }
        }

        if (v->crashed_counter < 650) {
                uint32 r;
                if (Chance16R(1, 32, r)) {
                        static const DirDiff delta[] = {
                                DIRDIFF_45LEFT, DIRDIFF_SAME, DIRDIFF_SAME, DIRDIFF_45RIGHT
                        };

                        v->direction = ChangeDir(v->direction, delta[GB(r, 16, 2)]);
                        SetAircraftPosition(v, v->x_pos, v->y_pos, v->z_pos);
                        r = Random();
                        CreateEffectVehicleRel(v,
                                GB(r, 0, 4) - 4,
                                GB(r, 4, 4) - 4,
                                GB(r, 8, 4),
                                EV_EXPLOSION_SMALL);
                }
        } else if (v->crashed_counter >= 10000) {
                /*  remove rubble of crashed airplane */

                /* clear runway-in on all airports, set by crashing plane
                 * small airports use AIRPORT_BUSY, city airports use RUNWAY_IN_OUT_block, etc.
                 * but they all share the same number */
                if (st != nullptr) {
                        CLRBITS(st->airport.flags, RUNWAY_IN_block);
                        CLRBITS(st->airport.flags, RUNWAY_IN_OUT_block); // commuter airport
                        CLRBITS(st->airport.flags, RUNWAY_IN2_block);    // intercontinental
                }

                delete v;

                return false;
        }

        return true;
}


/**
 * Handle smoke of broken aircraft.
 * @param v Aircraft
 * @param mode Is this the non-first call for this vehicle in this tick?
 */
static void HandleAircraftSmoke(Aircraft *v, bool mode)
{
        static const struct {
                int8 x;
                int8 y;
        } smoke_pos[] = {
                {  5,  5 },
                {  6,  0 },
                {  5, -5 },
                {  0, -6 },
                { -5, -5 },
                { -6,  0 },
                { -5,  5 },
                {  0,  6 }
        };

        if (!(v->vehstatus & VS_AIRCRAFT_BROKEN)) return;

        /* Stop smoking when landed */
        if (v->cur_speed < 10) {
                v->vehstatus &= ~VS_AIRCRAFT_BROKEN;
                v->breakdown_ctr = 0;
                return;
        }

        /* Spawn effect et most once per Tick, i.e. !mode */
        if (!mode && (v->tick_counter & 0x0F) == 0) {
                CreateEffectVehicleRel(v,
                        smoke_pos[v->direction].x,
                        smoke_pos[v->direction].y,
                        2,
                        EV_BREAKDOWN_SMOKE_AIRCRAFT
                );
        }
}

void HandleMissingAircraftOrders(Aircraft *v)
{
        /*
         * We do not have an order. This can be divided into two cases:
         * 1) we are heading to an invalid station. In this case we must
         *    find another airport to go to. If there is nowhere to go,
         *    we will destroy the aircraft as it otherwise will enter
         *    the holding pattern for the first airport, which can cause
         *    the plane to go into an undefined state when building an
         *    airport with the same StationID.
         * 2) we are (still) heading to a (still) valid airport, then we
         *    can continue going there. This can happen when you are
         *    changing the aircraft's orders while in-flight or in for
         *    example a depot. However, when we have a current order to
         *    go to a depot, we have to keep that order so the aircraft
         *    actually stops.
         */
        const Station *st = GetTargetAirportIfValid(v);
        if (st == nullptr) {
                Backup<CompanyID> cur_company(_current_company, v->owner, FILE_LINE);
                CommandCost ret = DoCommand(v->tile, v->index, 0, DC_EXEC, CMD_SEND_VEHICLE_TO_DEPOT);
                cur_company.Restore();

                if (ret.Failed()) CrashAirplane(v);
        } else if (!v->current_order.IsType(OT_GOTO_DEPOT)) {
                v->current_order.Free();
        }
}


TileIndex Aircraft::GetOrderStationLocation(StationID station)
{
        /* Orders are changed in flight, ensure going to the right station. */
        if (this->state == FLYING) {
                AircraftNextAirportPos_and_Order(this);
        }

        /* Aircraft do not use dest-tile */
        return 0;
}

void Aircraft::MarkDirty()
{
        this->colourmap = PAL_NONE;
        this->UpdateViewport(true, false);
        if (this->subtype == AIR_HELICOPTER) {
                GetRotorImage(this, EIT_ON_MAP, &this->Next()->Next()->sprite_cache.sprite_seq);
        }
}


uint Aircraft::Crash(bool flooded)
{
        uint pass = Vehicle::Crash(flooded) + 2; // pilots
        this->crashed_counter = flooded ? 9000 : 0; // max 10000, disappear pretty fast when flooded

        return pass;
}

/**
 * Bring the aircraft in a crashed state, create the explosion animation, and create a news item about the crash.
 * @param v Aircraft that crashed.
 */
static void CrashAirplane(Aircraft *v)
{
        CreateEffectVehicleRel(v, 4, 4, 8, EV_EXPLOSION_LARGE);

        uint pass = v->Crash();
        SetDParam(0, pass);

        v->cargo.Truncate();
        v->Next()->cargo.Truncate();
        const Station *st = GetTargetAirportIfValid(v);
        StringID newsitem;
        if (st == nullptr) {
                newsitem = STR_NEWS_PLANE_CRASH_OUT_OF_FUEL;
        } else {
                SetDParam(1, st->index);
                newsitem = STR_NEWS_AIRCRAFT_CRASH;
        }

        AI::NewEvent(v->owner, new ScriptEventVehicleCrashed(v->index, v->tile, st == nullptr ? ScriptEventVehicleCrashed::CRASH_AIRCRAFT_NO_AIRPORT : ScriptEventVehicleCrashed::CRASH_PLANE_LANDING));
        Game::NewEvent(new ScriptEventVehicleCrashed(v->index, v->tile, st == nullptr ? ScriptEventVehicleCrashed::CRASH_AIRCRAFT_NO_AIRPORT : ScriptEventVehicleCrashed::CRASH_PLANE_LANDING));

        AddTileNewsItem(newsitem, NT_ACCIDENT, v->tile, nullptr, st != nullptr ? st->index : INVALID_STATION);

        ModifyStationRatingAround(v->tile, v->owner, -160, 30);
        if (_settings_client.sound.disaster) SndPlayVehicleFx(SND_12_EXPLOSION, v);
}

/**
 * Decide whether aircraft \a v should crash.
 * @param v Aircraft to test.
 */
static void MaybeCrashAirplane(Aircraft *v)
{

        Station *st = Station::Get(v->targetairport);

        uint32 prob;
        if ((st->airport.GetFTA()->flags & AirportFTAClass::SHORT_STRIP) &&
                        (AircraftVehInfo(v->engine_type)->subtype & AIR_FAST) &&
                        !_cheats.no_jetcrash.value) {
                prob = 3276;
        } else {
                if (_settings_game.vehicle.plane_crashes == 0) return;
                prob = (0x4000 << _settings_game.vehicle.plane_crashes) / 1500;
        }

        if (GB(Random(), 0, 22) > prob) return;

        /* Crash the airplane. Remove all goods stored at the station. */
        for (CargoID i = 0; i < NUM_CARGO; i++) {
                st->goods[i].rating = 1;
                st->goods[i].cargo.Truncate();
        }

        CrashAirplane(v);
}

/**
 * Aircraft arrives at a terminal. If it is the first aircraft, throw a party.
 * Start loading cargo.
 * @param v Aircraft that arrived.
 */
static void AircraftEntersTerminal(Aircraft *v)
{
        if (v->current_order.IsType(OT_GOTO_DEPOT)) return;

        Station *st = Station::Get(v->targetairport);
        v->last_station_visited = v->targetairport;

        /* Check if station was ever visited before */
        if (!(st->had_vehicle_of_type & HVOT_AIRCRAFT)) {
                st->had_vehicle_of_type |= HVOT_AIRCRAFT;
                SetDParam(0, st->index);
                /* show newsitem of celebrating citizens */
                AddVehicleNewsItem(
                        STR_NEWS_FIRST_AIRCRAFT_ARRIVAL,
                        (v->owner == _local_company) ? NT_ARRIVAL_COMPANY : NT_ARRIVAL_OTHER,
                        v->index,
                        st->index
                );
                AI::NewEvent(v->owner, new ScriptEventStationFirstVehicle(st->index, v->index));
                Game::NewEvent(new ScriptEventStationFirstVehicle(st->index, v->index));
        }

        v->BeginLoading();
}

/**
 * Aircraft touched down at the landing strip.
 * @param v Aircraft that landed.
 */
static void AircraftLandAirplane(Aircraft *v)
{
        Station *st = Station::Get(v->targetairport);

        TileIndex vt = TileVirtXY(v->x_pos, v->y_pos);

        v->UpdateDeltaXY();

        AirportTileAnimationTrigger(st, vt, AAT_STATION_AIRPLANE_LAND);

        if (!PlayVehicleSound(v, VSE_TOUCHDOWN)) {
                SndPlayVehicleFx(SND_17_SKID_PLANE, v);
        }
}


/** set the right pos when heading to other airports after takeoff */
void AircraftNextAirportPos_and_Order(Aircraft *v)
{
        if (v->current_order.IsType(OT_GOTO_STATION) || v->current_order.IsType(OT_GOTO_DEPOT)) {
                v->targetairport = v->current_order.GetDestination();
        }

        const Station *st = GetTargetAirportIfValid(v);
        const AirportFTAClass *apc = st == nullptr ? GetAirport(AT_DUMMY) : st->airport.GetFTA();
        Direction rotation = st == nullptr ? DIR_N : st->airport.rotation;
        v->pos = v->previous_pos = AircraftGetEntryPoint(v, apc, rotation);
}

/**
 * Aircraft is about to leave the hangar.
 * @param v Aircraft leaving.
 * @param exit_dir The direction the vehicle leaves the hangar.
 * @note This function is called in AfterLoadGame for old savegames, so don't rely
 *       on any data to be valid, especially don't rely on the fact that the vehicle
 *       is actually on the ground inside a depot.
 */
void AircraftLeaveHangar(Aircraft *v, Direction exit_dir)
{
        v->cur_speed = 0;
        v->subspeed = 0;
        v->progress = 0;
        v->direction = exit_dir;
        v->vehstatus &= ~VS_HIDDEN;
        {
                Vehicle *u = v->Next();
                u->vehstatus &= ~VS_HIDDEN;

                /* Rotor blades */
                u = u->Next();
                if (u != nullptr) {
                        u->vehstatus &= ~VS_HIDDEN;
                        u->cur_speed = 80;
                }
        }

        VehicleServiceInDepot(v);
        SetAircraftPosition(v, v->x_pos, v->y_pos, v->z_pos);
        InvalidateWindowData(WC_VEHICLE_DEPOT, v->tile);
        SetWindowClassesDirty(WC_AIRCRAFT_LIST);
}

////////////////////////////////////////////////////////////////////////////////
///////////////////   AIRCRAFT MOVEMENT SCHEME  ////////////////////////////////
////////////////////////////////////////////////////////////////////////////////
static void AircraftEventHandler_EnterTerminal(Aircraft *v, const AirportFTAClass *apc)
{
        AircraftEntersTerminal(v);
        v->state = apc->layout[v->pos].heading;
}

/**
 * Aircraft arrived in an airport hangar.
 * @param v Aircraft in the hangar.
 * @param apc Airport description containing the hangar.
 */
static void AircraftEventHandler_EnterHangar(Aircraft *v, const AirportFTAClass *apc)
{
        VehicleEnterDepot(v);
        v->state = apc->layout[v->pos].heading;
}

/**
 * Handle aircraft movement/decision making in an airport hangar.
 * @param v Aircraft in the hangar.
 * @param apc Airport description containing the hangar.
 */
static void AircraftEventHandler_InHangar(Aircraft *v, const AirportFTAClass *apc)
{
        /* if we just arrived, execute EnterHangar first */
        if (v->previous_pos != v->pos) {
                AircraftEventHandler_EnterHangar(v, apc);
                return;
        }

        /* if we were sent to the depot, stay there */
        if (v->current_order.IsType(OT_GOTO_DEPOT) && (v->vehstatus & VS_STOPPED)) {
                v->current_order.Free();
                return;
        }

        if (!v->current_order.IsType(OT_GOTO_STATION) &&
                        !v->current_order.IsType(OT_GOTO_DEPOT))
                return;

        /* We are leaving a hangar, but have to go to the exact same one; re-enter */
        if (v->current_order.IsType(OT_GOTO_DEPOT) && v->current_order.GetDestination() == v->targetairport) {
                VehicleEnterDepot(v);
                return;
        }

        /* if the block of the next position is busy, stay put */
        if (AirportHasBlock(v, &apc->layout[v->pos], apc)) return;

        /* We are already at the target airport, we need to find a terminal */
        if (v->current_order.GetDestination() == v->targetairport) {
                /* FindFreeTerminal:
                 * 1. Find a free terminal, 2. Occupy it, 3. Set the vehicle's state to that terminal */
                if (v->subtype == AIR_HELICOPTER) {
                        if (!AirportFindFreeHelipad(v, apc)) return; // helicopter
                } else {
                        if (!AirportFindFreeTerminal(v, apc)) return; // airplane
                }
        } else { // Else prepare for launch.
                /* airplane goto state takeoff, helicopter to helitakeoff */
                v->state = (v->subtype == AIR_HELICOPTER) ? HELITAKEOFF : TAKEOFF;
        }
        const Station *st = Station::GetByTile(v->tile);
        AircraftLeaveHangar(v, st->airport.GetHangarExitDirection(v->tile));
        AirportMove(v, apc);
}

/** At one of the Airport's Terminals */
static void AircraftEventHandler_AtTerminal(Aircraft *v, const AirportFTAClass *apc)
{
        /* if we just arrived, execute EnterTerminal first */
        if (v->previous_pos != v->pos) {
                AircraftEventHandler_EnterTerminal(v, apc);
                /* on an airport with helipads, a helicopter will always land there
                 * and get serviced at the same time - setting */
                if (_settings_game.order.serviceathelipad) {
                        if (v->subtype == AIR_HELICOPTER && apc->num_helipads > 0) {
                                /* an excerpt of ServiceAircraft, without the invisibility stuff */
                                v->date_of_last_service = _date;
                                v->breakdowns_since_last_service = 0;
                                v->reliability = v->GetEngine()->reliability;
                                SetWindowDirty(WC_VEHICLE_DETAILS, v->index);
                        }
                }
                return;
        }

        if (v->current_order.IsType(OT_NOTHING)) return;

        /* if the block of the next position is busy, stay put */
        if (AirportHasBlock(v, &apc->layout[v->pos], apc)) return;

        /* airport-road is free. We either have to go to another airport, or to the hangar
         * ---> start moving */

        bool go_to_hangar = false;
        switch (v->current_order.GetType()) {
                case OT_GOTO_STATION: // ready to fly to another airport
                        break;
                case OT_GOTO_DEPOT:   // visit hangar for servicing, sale, etc.
                        go_to_hangar = v->current_order.GetDestination() == v->targetairport;
                        break;
                case OT_CONDITIONAL:
                        /* In case of a conditional order we just have to wait a tick
                         * longer, so the conditional order can actually be processed;
                         * we should not clear the order as that makes us go nowhere. */
                        return;
                default:  // orders have been deleted (no orders), goto depot and don't bother us
                        v->current_order.Free();
                        go_to_hangar = Station::Get(v->targetairport)->airport.HasHangar();
        }

        if (go_to_hangar && Station::Get(v->targetairport)->airport.HasHangar()) {
                v->state = HANGAR;
        } else {
                /* airplane goto state takeoff, helicopter to helitakeoff */
                v->state = (v->subtype == AIR_HELICOPTER) ? HELITAKEOFF : TAKEOFF;
        }
        AirportMove(v, apc);
}

static void AircraftEventHandler_General(Aircraft *v, const AirportFTAClass *apc)
{
        error("OK, you shouldn't be here, check your Airport Scheme!");
}

static void AircraftEventHandler_TakeOff(Aircraft *v, const AirportFTAClass *apc)
{
        PlayAircraftSound(v); // play takeoffsound for airplanes
        v->state = STARTTAKEOFF;
}

static void AircraftEventHandler_StartTakeOff(Aircraft *v, const AirportFTAClass *apc)
{
        v->state = ENDTAKEOFF;
        v->UpdateDeltaXY();
}

static void AircraftEventHandler_EndTakeOff(Aircraft *v, const AirportFTAClass *apc)
{
        v->state = FLYING;
        /* get the next position to go to, differs per airport */
        AircraftNextAirportPos_and_Order(v);
}

static void AircraftEventHandler_HeliTakeOff(Aircraft *v, const AirportFTAClass *apc)
{
        v->state = FLYING;
        v->UpdateDeltaXY();

        /* get the next position to go to, differs per airport */
        AircraftNextAirportPos_and_Order(v);

        /* Send the helicopter to a hangar if needed for replacement */
        if (v->NeedsAutomaticServicing()) {
                Backup<CompanyID> cur_company(_current_company, v->owner, FILE_LINE);
                DoCommand(v->tile, v->index | DEPOT_SERVICE | DEPOT_LOCATE_HANGAR, 0, DC_EXEC, CMD_SEND_VEHICLE_TO_DEPOT);
                cur_company.Restore();
        }
}

static void AircraftEventHandler_Flying(Aircraft *v, const AirportFTAClass *apc)
{
        Station *st = Station::Get(v->targetairport);

        /* Runway busy, not allowed to use this airstation or closed, circle. */
        if (CanVehicleUseStation(v, st) && (st->owner == OWNER_NONE || st->owner == v->owner) && !(st->airport.flags & AIRPORT_CLOSED_block)) {
                /* {32,FLYING,NOTHING_block,37}, {32,LANDING,N,33}, {32,HELILANDING,N,41},
                 * if it is an airplane, look for LANDING, for helicopter HELILANDING
                 * it is possible to choose from multiple landing runways, so loop until a free one is found */
                byte landingtype = (v->subtype == AIR_HELICOPTER) ? HELILANDING : LANDING;
                const AirportFTA *current = apc->layout[v->pos].next;
                while (current != nullptr) {
                        if (current->heading == landingtype) {
                                /* save speed before, since if AirportHasBlock is false, it resets them to 0
                                 * we don't want that for plane in air
                                 * hack for speed thingie */
                                uint16 tcur_speed = v->cur_speed;
                                uint16 tsubspeed = v->subspeed;
                                if (!AirportHasBlock(v, current, apc)) {
                                        v->state = landingtype; // LANDING / HELILANDING
                                        if (v->state == HELILANDING) SetBit(v->flags, VAF_HELI_DIRECT_DESCENT);
                                        /* it's a bit dirty, but I need to set position to next position, otherwise
                                         * if there are multiple runways, plane won't know which one it took (because
                                         * they all have heading LANDING). And also occupy that block! */
                                        v->pos = current->next_position;
                                        SETBITS(st->airport.flags, apc->layout[v->pos].block);
                                        return;
                                }
                                v->cur_speed = tcur_speed;
                                v->subspeed = tsubspeed;
                        }
                        current = current->next;
                }
        }
        v->state = FLYING;
        v->pos = apc->layout[v->pos].next_position;
}

static void AircraftEventHandler_Landing(Aircraft *v, const AirportFTAClass *apc)
{
        v->state = ENDLANDING;
        AircraftLandAirplane(v);  // maybe crash airplane

        /* check if the aircraft needs to be replaced or renewed and send it to a hangar if needed */
        if (v->NeedsAutomaticServicing()) {
                Backup<CompanyID> cur_company(_current_company, v->owner, FILE_LINE);
                DoCommand(v->tile, v->index | DEPOT_SERVICE, 0, DC_EXEC, CMD_SEND_VEHICLE_TO_DEPOT);
                cur_company.Restore();
        }
}

static void AircraftEventHandler_HeliLanding(Aircraft *v, const AirportFTAClass *apc)
{
        v->state = HELIENDLANDING;
        v->UpdateDeltaXY();
}

static void AircraftEventHandler_EndLanding(Aircraft *v, const AirportFTAClass *apc)
{
        /* next block busy, don't do a thing, just wait */
        if (AirportHasBlock(v, &apc->layout[v->pos], apc)) return;

        /* if going to terminal (OT_GOTO_STATION) choose one
         * 1. in case all terminals are busy AirportFindFreeTerminal() returns false or
         * 2. not going for terminal (but depot, no order),
         * --> get out of the way to the hangar. */
        if (v->current_order.IsType(OT_GOTO_STATION)) {
                if (AirportFindFreeTerminal(v, apc)) return;
        }
        v->state = HANGAR;

}

static void AircraftEventHandler_HeliEndLanding(Aircraft *v, const AirportFTAClass *apc)
{
        /*  next block busy, don't do a thing, just wait */
        if (AirportHasBlock(v, &apc->layout[v->pos], apc)) return;

        /* if going to helipad (OT_GOTO_STATION) choose one. If airport doesn't have helipads, choose terminal
         * 1. in case all terminals/helipads are busy (AirportFindFreeHelipad() returns false) or
         * 2. not going for terminal (but depot, no order),
         * --> get out of the way to the hangar IF there are terminals on the airport.
         * --> else TAKEOFF
         * the reason behind this is that if an airport has a terminal, it also has a hangar. Airplanes
         * must go to a hangar. */
        if (v->current_order.IsType(OT_GOTO_STATION)) {
                if (AirportFindFreeHelipad(v, apc)) return;
        }
        v->state = Station::Get(v->targetairport)->airport.HasHangar() ? HANGAR : HELITAKEOFF;
}

/**
 * Signature of the aircraft handler function.
 * @param v Aircraft to handle.
 * @param apc Airport state machine.
 */
typedef void AircraftStateHandler(Aircraft *v, const AirportFTAClass *apc);
/** Array of handler functions for each target of the aircraft. */
static AircraftStateHandler * const _aircraft_state_handlers[] = {
        AircraftEventHandler_General,        // TO_ALL         =  0
        AircraftEventHandler_InHangar,       // HANGAR         =  1
        AircraftEventHandler_AtTerminal,     // TERM1          =  2
        AircraftEventHandler_AtTerminal,     // TERM2          =  3
        AircraftEventHandler_AtTerminal,     // TERM3          =  4
        AircraftEventHandler_AtTerminal,     // TERM4          =  5
        AircraftEventHandler_AtTerminal,     // TERM5          =  6
        AircraftEventHandler_AtTerminal,     // TERM6          =  7
        AircraftEventHandler_AtTerminal,     // HELIPAD1       =  8
        AircraftEventHandler_AtTerminal,     // HELIPAD2       =  9
        AircraftEventHandler_TakeOff,        // TAKEOFF        = 10
        AircraftEventHandler_StartTakeOff,   // STARTTAKEOFF   = 11
        AircraftEventHandler_EndTakeOff,     // ENDTAKEOFF     = 12
        AircraftEventHandler_HeliTakeOff,    // HELITAKEOFF    = 13
        AircraftEventHandler_Flying,         // FLYING         = 14
        AircraftEventHandler_Landing,        // LANDING        = 15
        AircraftEventHandler_EndLanding,     // ENDLANDING     = 16
        AircraftEventHandler_HeliLanding,    // HELILANDING    = 17
        AircraftEventHandler_HeliEndLanding, // HELIENDLANDING = 18
        AircraftEventHandler_AtTerminal,     // TERM7          = 19
        AircraftEventHandler_AtTerminal,     // TERM8          = 20
        AircraftEventHandler_AtTerminal,     // HELIPAD3       = 21
};

static void AirportClearBlock(const Aircraft *v, const AirportFTAClass *apc)
{
        /* we have left the previous block, and entered the new one. Free the previous block */
        if (apc->layout[v->previous_pos].block != apc->layout[v->pos].block) {
                Station *st = Station::Get(v->targetairport);

                CLRBITS(st->airport.flags, apc->layout[v->previous_pos].block);
        }
}

static void AirportGoToNextPosition(Aircraft *v)
{
        /* if aircraft is not in position, wait until it is */
        if (!AircraftController(v)) return;

        const AirportFTAClass *apc = Station::Get(v->targetairport)->airport.GetFTA();

        AirportClearBlock(v, apc);
        AirportMove(v, apc); // move aircraft to next position
}

/* gets pos from vehicle and next orders */
static bool AirportMove(Aircraft *v, const AirportFTAClass *apc)
{
        /* error handling */
        if (v->pos >= apc->nofelements) {
                DEBUG(misc, 0, "[Ap] position %d is not valid for current airport. Max position is %d", v->pos, apc->nofelements-1);
                assert(v->pos < apc->nofelements);
        }

        const AirportFTA *current = &apc->layout[v->pos];
        /* we have arrived in an important state (eg terminal, hangar, etc.) */
        if (current->heading == v->state) {
                byte prev_pos = v->pos; // location could be changed in state, so save it before-hand
                byte prev_state = v->state;
                _aircraft_state_handlers[v->state](v, apc);
                if (v->state != FLYING) v->previous_pos = prev_pos;
                if (v->state != prev_state || v->pos != prev_pos) UpdateAircraftCache(v);
                return true;
        }

        v->previous_pos = v->pos; // save previous location

        /* there is only one choice to move to */
        if (current->next == nullptr) {
                if (AirportSetBlocks(v, current, apc)) {
                        v->pos = current->next_position;
                        UpdateAircraftCache(v);
                } // move to next position
                return false;
        }

        /* there are more choices to choose from, choose the one that
         * matches our heading */
        do {
                if (v->state == current->heading || current->heading == TO_ALL) {
                        if (AirportSetBlocks(v, current, apc)) {
                                v->pos = current->next_position;
                                UpdateAircraftCache(v);
                        } // move to next position
                        return false;
                }
                current = current->next;
        } while (current != nullptr);

        DEBUG(misc, 0, "[Ap] cannot move further on Airport! (pos %d state %d) for vehicle %d", v->pos, v->state, v->index);
        NOT_REACHED();
}

/** returns true if the road ahead is busy, eg. you must wait before proceeding. */
static bool AirportHasBlock(Aircraft *v, const AirportFTA *current_pos, const AirportFTAClass *apc)
{
        const AirportFTA *reference = &apc->layout[v->pos];
        const AirportFTA *next = &apc->layout[current_pos->next_position];

        /* same block, then of course we can move */
        if (apc->layout[current_pos->position].block != next->block) {
                const Station *st = Station::Get(v->targetairport);
                uint64 airport_flags = next->block;

                /* check additional possible extra blocks */
                if (current_pos != reference && current_pos->block != NOTHING_block) {
                        airport_flags |= current_pos->block;
                }

                if (st->airport.flags & airport_flags) {
                        v->cur_speed = 0;
                        v->subspeed = 0;
                        return true;
                }
        }
        return false;
}

/**
 * "reserve" a block for the plane
 * @param v airplane that requires the operation
 * @param current_pos of the vehicle in the list of blocks
 * @param apc airport on which block is requested to be set
 * @returns true on success. Eg, next block was free and we have occupied it
 */
static bool AirportSetBlocks(Aircraft *v, const AirportFTA *current_pos, const AirportFTAClass *apc)
{
        const AirportFTA *next = &apc->layout[current_pos->next_position];
        const AirportFTA *reference = &apc->layout[v->pos];

        /* if the next position is in another block, check it and wait until it is free */
        if ((apc->layout[current_pos->position].block & next->block) != next->block) {
                uint64 airport_flags = next->block;
                /* search for all all elements in the list with the same state, and blocks != N
                 * this means more blocks should be checked/set */
                const AirportFTA *current = current_pos;
                if (current == reference) current = current->next;
                while (current != nullptr) {
                        if (current->heading == current_pos->heading && current->block != 0) {
                                airport_flags |= current->block;
                                break;
                        }
                        current = current->next;
                }

                /* if the block to be checked is in the next position, then exclude that from
                 * checking, because it has been set by the airplane before */
                if (current_pos->block == next->block) airport_flags ^= next->block;

                Station *st = Station::Get(v->targetairport);
                if (st->airport.flags & airport_flags) {
                        v->cur_speed = 0;
                        v->subspeed = 0;
                        return false;
                }

                if (next->block != NOTHING_block) {
                        SETBITS(st->airport.flags, airport_flags); // occupy next block
                }
        }
        return true;
}

/**
 * Combination of aircraft state for going to a certain terminal and the
 * airport flag for that terminal block.
 */
struct MovementTerminalMapping {
        AirportMovementStates state; ///< Aircraft movement state when going to this terminal.
        uint64 airport_flag;         ///< Bitmask in the airport flags that need to be free for this terminal.
};

/** A list of all valid terminals and their associated blocks. */
static const MovementTerminalMapping _airport_terminal_mapping[] = {
        {TERM1, TERM1_block},
        {TERM2, TERM2_block},
        {TERM3, TERM3_block},
        {TERM4, TERM4_block},
        {TERM5, TERM5_block},
        {TERM6, TERM6_block},
        {TERM7, TERM7_block},
        {TERM8, TERM8_block},
        {HELIPAD1, HELIPAD1_block},
        {HELIPAD2, HELIPAD2_block},
        {HELIPAD3, HELIPAD3_block},
};

/**
 * Find a free terminal or helipad, and if available, assign it.
 * @param v Aircraft looking for a free terminal or helipad.
 * @param i First terminal to examine.
 * @param last_terminal Terminal number to stop examining.
 * @return A terminal or helipad has been found, and has been assigned to the aircraft.
 */
static bool FreeTerminal(Aircraft *v, byte i, byte last_terminal)
{
        assert(last_terminal <= lengthof(_airport_terminal_mapping));
        Station *st = Station::Get(v->targetairport);
        for (; i < last_terminal; i++) {
                if ((st->airport.flags & _airport_terminal_mapping[i].airport_flag) == 0) {
                        /* TERMINAL# HELIPAD# */
                        v->state = _airport_terminal_mapping[i].state; // start moving to that terminal/helipad
                        SETBITS(st->airport.flags, _airport_terminal_mapping[i].airport_flag); // occupy terminal/helipad
                        return true;
                }
        }
        return false;
}

/**
 * Get the number of terminals at the airport.
 * @param apc Airport description.
 * @return Number of terminals.
 */
static uint GetNumTerminals(const AirportFTAClass *apc)
{
        uint num = 0;

        for (uint i = apc->terminals[0]; i > 0; i--) num += apc->terminals[i];

        return num;
}

/**
 * Find a free terminal, and assign it if available.
 * @param v Aircraft to handle.
 * @param apc Airport state machine.
 * @return Found a free terminal and assigned it.
 */
static bool AirportFindFreeTerminal(Aircraft *v, const AirportFTAClass *apc)
{
        /* example of more terminalgroups
         * {0,HANGAR,NOTHING_block,1}, {0,TERMGROUP,TERM_GROUP1_block,0}, {0,TERMGROUP,TERM_GROUP2_ENTER_block,1}, {0,0,N,1},
         * Heading TERMGROUP denotes a group. We see 2 groups here:
         * 1. group 0 -- TERM_GROUP1_block (check block)
         * 2. group 1 -- TERM_GROUP2_ENTER_block (check block)
         * First in line is checked first, group 0. If the block (TERM_GROUP1_block) is free, it
         * looks at the corresponding terminals of that group. If no free ones are found, other
         * possible groups are checked (in this case group 1, since that is after group 0). If that
         * fails, then attempt fails and plane waits
         */
        if (apc->terminals[0] > 1) {
                const Station *st = Station::Get(v->targetairport);
                const AirportFTA *temp = apc->layout[v->pos].next;

                while (temp != nullptr) {
                        if (temp->heading == TERMGROUP) {
                                if (!(st->airport.flags & temp->block)) {
                                        /* read which group do we want to go to?
                                         * (the first free group) */
                                        uint target_group = temp->next_position + 1;

                                        /* at what terminal does the group start?
                                         * that means, sum up all terminals of
                                         * groups with lower number */
                                        uint group_start = 0;
                                        for (uint i = 1; i < target_group; i++) {
                                                group_start += apc->terminals[i];
                                        }

                                        uint group_end = group_start + apc->terminals[target_group];
                                        if (FreeTerminal(v, group_start, group_end)) return true;
                                }
                        } else {
                                /* once the heading isn't 255, we've exhausted the possible blocks.
                                 * So we cannot move */
                                return false;
                        }
                        temp = temp->next;
                }
        }

        /* if there is only 1 terminalgroup, all terminals are checked (starting from 0 to max) */
        return FreeTerminal(v, 0, GetNumTerminals(apc));
}

/**
 * Find a free helipad, and assign it if available.
 * @param v Aircraft to handle.
 * @param apc Airport state machine.
 * @return Found a free helipad and assigned it.
 */
static bool AirportFindFreeHelipad(Aircraft *v, const AirportFTAClass *apc)
{
        /* if an airport doesn't have helipads, use terminals */
        if (apc->num_helipads == 0) return AirportFindFreeTerminal(v, apc);

        /* only 1 helicoptergroup, check all helipads
         * The blocks for helipads start after the last terminal (MAX_TERMINALS) */
        return FreeTerminal(v, MAX_TERMINALS, apc->num_helipads + MAX_TERMINALS);
}

/**
 * Handle the 'dest too far' flag and the corresponding news message for aircraft.
 * @param v The aircraft.
 * @param too_far True if the current destination is too far away.
 */
static void AircraftHandleDestTooFar(Aircraft *v, bool too_far)
{
        if (too_far) {
                if (!HasBit(v->flags, VAF_DEST_TOO_FAR)) {
                        SetBit(v->flags, VAF_DEST_TOO_FAR);
                        SetWindowWidgetDirty(WC_VEHICLE_VIEW, v->index, WID_VV_START_STOP);
                        AI::NewEvent(v->owner, new ScriptEventAircraftDestTooFar(v->index));
                        if (v->owner == _local_company) {
                                /* Post a news message. */
                                SetDParam(0, v->index);
                                AddVehicleAdviceNewsItem(STR_NEWS_AIRCRAFT_DEST_TOO_FAR, v->index);
                        }
                }
                return;
        }

        if (HasBit(v->flags, VAF_DEST_TOO_FAR)) {
                /* Not too far anymore, clear flag and message. */
                ClrBit(v->flags, VAF_DEST_TOO_FAR);
                SetWindowWidgetDirty(WC_VEHICLE_VIEW, v->index, WID_VV_START_STOP);
                DeleteVehicleNews(v->index, STR_NEWS_AIRCRAFT_DEST_TOO_FAR);
        }
}

static bool AircraftEventHandler(Aircraft *v, int loop)
{
        if (v->vehstatus & VS_CRASHED) {
                return HandleCrashedAircraft(v);
        }

        if (v->vehstatus & VS_STOPPED) return true;

        v->HandleBreakdown();

        HandleAircraftSmoke(v, loop != 0);
        ProcessOrders(v);
        v->HandleLoading(loop != 0);

        if (v->current_order.IsType(OT_LOADING) || v->current_order.IsType(OT_LEAVESTATION)) return true;

        if (v->state >= ENDTAKEOFF && v->state <= HELIENDLANDING) {
                /* If we are flying, unconditionally clear the 'dest too far' state. */
                AircraftHandleDestTooFar(v, false);
        } else if (v->acache.cached_max_range_sqr != 0) {
                /* Check the distance to the next destination. This code works because the target
                 * airport is only updated after take off and not on the ground. */
                Station *cur_st = Station::GetIfValid(v->targetairport);
                Station *next_st = v->current_order.IsType(OT_GOTO_STATION) || v->current_order.IsType(OT_GOTO_DEPOT) ? Station::GetIfValid(v->current_order.GetDestination()) : nullptr;

                if (cur_st != nullptr && cur_st->airport.tile != INVALID_TILE && next_st != nullptr && next_st->airport.tile != INVALID_TILE) {
                        uint dist = DistanceSquare(cur_st->airport.tile, next_st->airport.tile);
                        AircraftHandleDestTooFar(v, dist > v->acache.cached_max_range_sqr);
                }
        }

        if (!HasBit(v->flags, VAF_DEST_TOO_FAR)) AirportGoToNextPosition(v);

        return true;
}

bool Aircraft::Tick()
{
        if (!this->IsNormalAircraft()) return true;

        PerformanceAccumulator framerate(PFE_GL_AIRCRAFT);

        this->tick_counter++;

        if (!(this->vehstatus & VS_STOPPED)) this->running_ticks++;

        if (this->subtype == AIR_HELICOPTER) HelicopterTickHandler(this);

        this->current_order_time++;

        for (uint i = 0; i != 2; i++) {
                /* stop if the aircraft was deleted */
                if (!AircraftEventHandler(this, i)) return false;
        }

        return true;
}


/**
 * Returns aircraft's target station if v->target_airport
 * is a valid station with airport.
 * @param v vehicle to get target airport for
 * @return pointer to target station, nullptr if invalid
 */
Station *GetTargetAirportIfValid(const Aircraft *v)
{
        assert(v->type == VEH_AIRCRAFT);

        Station *st = Station::GetIfValid(v->targetairport);
        if (st == nullptr) return nullptr;

        return st->airport.tile == INVALID_TILE ? nullptr : st;
}

/**
 * Updates the status of the Aircraft heading or in the station
 * @param st Station been updated
 */
void UpdateAirplanesOnNewStation(const Station *st)
{
        /* only 1 station is updated per function call, so it is enough to get entry_point once */
        const AirportFTAClass *ap = st->airport.GetFTA();
        Direction rotation = st->airport.tile == INVALID_TILE ? DIR_N : st->airport.rotation;

        for (Aircraft *v : Aircraft::Iterate()) {
                if (!v->IsNormalAircraft() || v->targetairport != st->index) continue;
                assert(v->state == FLYING);

                Order *o = &v->current_order;
                /* The aircraft is heading to a hangar, but the new station doesn't have one,
                 * or the aircraft can't land on the new station. Cancel current order. */
                if (o->IsType(OT_GOTO_DEPOT) && !(o->GetDepotOrderType() & ODTFB_PART_OF_ORDERS) && o->GetDestination() == st->index &&
                                (!st->airport.HasHangar() || !CanVehicleUseStation(v, st))) {
                        o->MakeDummy();
                        SetWindowWidgetDirty(WC_VEHICLE_VIEW, v->index, WID_VV_START_STOP);
                }
                v->pos = v->previous_pos = AircraftGetEntryPoint(v, ap, rotation);
                UpdateAircraftCache(v);
        }

        /* Heliports don't have a hangar. Invalidate all go to hangar orders from all aircraft. */
        if (!st->airport.HasHangar()) RemoveOrderFromAllVehicles(OT_GOTO_DEPOT, st->index, true);
}