Update: Translations from eints

[openttd-github.git] / src / autoreplace_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 autoreplace_cmd.cpp Deals with autoreplace execution but not the setup */

#include "stdafx.h"
#include "company_func.h"
#include "train.h"
#include "command_func.h"
#include "engine_func.h"
#include "vehicle_func.h"
#include "autoreplace_func.h"
#include "autoreplace_gui.h"
#include "articulated_vehicles.h"
#include "core/bitmath_func.hpp"
#include "core/random_func.hpp"
#include "vehiclelist.h"
#include "road.h"
#include "ai/ai.hpp"
#include "news_func.h"
#include "strings_func.h"
#include "autoreplace_cmd.h"
#include "group_cmd.h"
#include "order_cmd.h"
#include "train_cmd.h"
#include "vehicle_cmd.h"

#include "table/strings.h"

#include "safeguards.h"

extern void ChangeVehicleViewports(VehicleID from_index, VehicleID to_index);
extern void ChangeVehicleNews(VehicleID from_index, VehicleID to_index);
extern void ChangeVehicleViewWindow(VehicleID from_index, VehicleID to_index);

/**
 * Figure out if two engines got at least one type of cargo in common (refitting if needed)
 * @param engine_a one of the EngineIDs
 * @param engine_b the other EngineID
 * @return true if they can both carry the same type of cargo (or at least one of them got no capacity at all)
 */
static bool EnginesHaveCargoInCommon(EngineID engine_a, EngineID engine_b)
{
        CargoTypes available_cargoes_a = GetUnionOfArticulatedRefitMasks(engine_a, true);
        CargoTypes available_cargoes_b = GetUnionOfArticulatedRefitMasks(engine_b, true);
        return (available_cargoes_a == 0 || available_cargoes_b == 0 || (available_cargoes_a & available_cargoes_b) != 0);
}

/**
 * Checks some basic properties whether autoreplace is allowed
 * @param from Origin engine
 * @param to Destination engine
 * @param company Company to check for
 * @return true if autoreplace is allowed
 */
bool CheckAutoreplaceValidity(EngineID from, EngineID to, CompanyID company)
{
        assert(Engine::IsValidID(from) && Engine::IsValidID(to));

        const Engine *e_from = Engine::Get(from);
        const Engine *e_to = Engine::Get(to);
        VehicleType type = e_from->type;

        /* check that the new vehicle type is available to the company and its type is the same as the original one */
        if (!IsEngineBuildable(to, type, company)) return false;

        switch (type) {
                case VEH_TRAIN: {
                        /* make sure the railtypes are compatible */
                        if ((GetRailTypeInfo(e_from->u.rail.railtype)->compatible_railtypes & GetRailTypeInfo(e_to->u.rail.railtype)->compatible_railtypes) == 0) return false;

                        /* make sure we do not replace wagons with engines or vice versa */
                        if ((e_from->u.rail.railveh_type == RAILVEH_WAGON) != (e_to->u.rail.railveh_type == RAILVEH_WAGON)) return false;
                        break;
                }

                case VEH_ROAD:
                        /* make sure the roadtypes are compatible */
                        if ((GetRoadTypeInfo(e_from->u.road.roadtype)->powered_roadtypes & GetRoadTypeInfo(e_to->u.road.roadtype)->powered_roadtypes) == ROADTYPES_NONE) return false;

                        /* make sure that we do not replace a tram with a normal road vehicles or vice versa */
                        if (HasBit(e_from->info.misc_flags, EF_ROAD_TRAM) != HasBit(e_to->info.misc_flags, EF_ROAD_TRAM)) return false;
                        break;

                case VEH_AIRCRAFT:
                        /* make sure that we do not replace a plane with a helicopter or vice versa */
                        if ((e_from->u.air.subtype & AIR_CTOL) != (e_to->u.air.subtype & AIR_CTOL)) return false;
                        break;

                default: break;
        }

        /* the engines needs to be able to carry the same cargo */
        return EnginesHaveCargoInCommon(from, to);
}

/**
 * Check the capacity of all vehicles in a chain and spread cargo if needed.
 * @param v The vehicle to check.
 * @pre You can only do this if the consist is not loading or unloading. It
 *      must not carry reserved cargo, nor cargo to be unloaded or transferred.
 */
void CheckCargoCapacity(Vehicle *v)
{
        assert(v == nullptr || v->First() == v);

        for (Vehicle *src = v; src != nullptr; src = src->Next()) {
                assert(src->cargo.TotalCount() == src->cargo.ActionCount(VehicleCargoList::MTA_KEEP));

                /* Do we need to more cargo away? */
                if (src->cargo.TotalCount() <= src->cargo_cap) continue;

                /* We need to move a particular amount. Try that on the other vehicles. */
                uint to_spread = src->cargo.TotalCount() - src->cargo_cap;
                for (Vehicle *dest = v; dest != nullptr && to_spread != 0; dest = dest->Next()) {
                        assert(dest->cargo.TotalCount() == dest->cargo.ActionCount(VehicleCargoList::MTA_KEEP));
                        if (dest->cargo.TotalCount() >= dest->cargo_cap || dest->cargo_type != src->cargo_type) continue;

                        uint amount = std::min(to_spread, dest->cargo_cap - dest->cargo.TotalCount());
                        src->cargo.Shift(amount, &dest->cargo);
                        to_spread -= amount;
                }

                /* Any left-overs will be thrown away, but not their feeder share. */
                if (src->cargo_cap < src->cargo.TotalCount()) src->cargo.Truncate(src->cargo.TotalCount() - src->cargo_cap);
        }
}

/**
 * Transfer cargo from a single (articulated )old vehicle to the new vehicle chain
 * @param old_veh Old vehicle that will be sold
 * @param new_head Head of the completely constructed new vehicle chain
 * @param part_of_chain The vehicle is part of a train
 * @pre You can only do this if both consists are not loading or unloading.
 *      They must not carry reserved cargo, nor cargo to be unloaded or
 *      transferred.
 */
static void TransferCargo(Vehicle *old_veh, Vehicle *new_head, bool part_of_chain)
{
        assert(!part_of_chain || new_head->IsPrimaryVehicle());
        /* Loop through source parts */
        for (Vehicle *src = old_veh; src != nullptr; src = src->Next()) {
                assert(src->cargo.TotalCount() == src->cargo.ActionCount(VehicleCargoList::MTA_KEEP));
                if (!part_of_chain && src->type == VEH_TRAIN && src != old_veh && src != Train::From(old_veh)->other_multiheaded_part && !src->IsArticulatedPart()) {
                        /* Skip vehicles, which do not belong to old_veh */
                        src = src->GetLastEnginePart();
                        continue;
                }
                if (src->cargo_type >= NUM_CARGO || src->cargo.TotalCount() == 0) continue;

                /* Find free space in the new chain */
                for (Vehicle *dest = new_head; dest != nullptr && src->cargo.TotalCount() > 0; dest = dest->Next()) {
                        assert(dest->cargo.TotalCount() == dest->cargo.ActionCount(VehicleCargoList::MTA_KEEP));
                        if (!part_of_chain && dest->type == VEH_TRAIN && dest != new_head && dest != Train::From(new_head)->other_multiheaded_part && !dest->IsArticulatedPart()) {
                                /* Skip vehicles, which do not belong to new_head */
                                dest = dest->GetLastEnginePart();
                                continue;
                        }
                        if (dest->cargo_type != src->cargo_type) continue;

                        uint amount = std::min(src->cargo.TotalCount(), dest->cargo_cap - dest->cargo.TotalCount());
                        if (amount <= 0) continue;

                        src->cargo.Shift(amount, &dest->cargo);
                }
        }

        /* Update train weight etc., the old vehicle will be sold anyway */
        if (part_of_chain && new_head->type == VEH_TRAIN) Train::From(new_head)->ConsistChanged(CCF_LOADUNLOAD);
}

/**
 * Tests whether refit orders that applied to v will also apply to the new vehicle type
 * @param v The vehicle to be replaced
 * @param engine_type The type we want to replace with
 * @return true iff all refit orders stay valid
 */
static bool VerifyAutoreplaceRefitForOrders(const Vehicle *v, EngineID engine_type)
{
        CargoTypes union_refit_mask_a = GetUnionOfArticulatedRefitMasks(v->engine_type, false);
        CargoTypes union_refit_mask_b = GetUnionOfArticulatedRefitMasks(engine_type, false);

        const Vehicle *u = (v->type == VEH_TRAIN) ? v->First() : v;
        for (const Order *o : u->Orders()) {
                if (!o->IsRefit() || o->IsAutoRefit()) continue;
                CargoID cargo_type = o->GetRefitCargo();

                if (!HasBit(union_refit_mask_a, cargo_type)) continue;
                if (!HasBit(union_refit_mask_b, cargo_type)) return false;
        }

        return true;
}

/**
 * Gets the index of the first refit order that is incompatible with the requested engine type
 * @param v The vehicle to be replaced
 * @param engine_type The type we want to replace with
 * @return index of the incompatible order or -1 if none were found
 */
static int GetIncompatibleRefitOrderIdForAutoreplace(const Vehicle *v, EngineID engine_type)
{
        CargoTypes union_refit_mask = GetUnionOfArticulatedRefitMasks(engine_type, false);

        const Order *o;
        const Vehicle *u = (v->type == VEH_TRAIN) ? v->First() : v;

        const OrderList *orders = u->orders;
        if (orders == nullptr) return -1;
        for (VehicleOrderID i = 0; i < orders->GetNumOrders(); i++) {
                o = orders->GetOrderAt(i);
                if (!o->IsRefit()) continue;
                if (!HasBit(union_refit_mask, o->GetRefitCargo())) return i;
        }

        return -1;
}

/**
 * Function to find what type of cargo to refit to when autoreplacing
 * @param *v Original vehicle that is being replaced.
 * @param engine_type The EngineID of the vehicle that is being replaced to
 * @param part_of_chain The vehicle is part of a train
 * @return The cargo type to replace to
 *    CARGO_NO_REFIT is returned if no refit is needed
 *    INVALID_CARGO is returned when both old and new vehicle got cargo capacity and refitting the new one to the old one's cargo type isn't possible
 */
static CargoID GetNewCargoTypeForReplace(Vehicle *v, EngineID engine_type, bool part_of_chain)
{
        CargoTypes available_cargo_types, union_mask;
        GetArticulatedRefitMasks(engine_type, true, &union_mask, &available_cargo_types);

        if (union_mask == 0) return CARGO_NO_REFIT; // Don't try to refit an engine with no cargo capacity

        CargoID cargo_type;
        CargoTypes cargo_mask = GetCargoTypesOfArticulatedVehicle(v, &cargo_type);
        if (!HasAtMostOneBit(cargo_mask)) {
                CargoTypes new_engine_default_cargoes = GetCargoTypesOfArticulatedParts(engine_type);
                if ((cargo_mask & new_engine_default_cargoes) == cargo_mask) {
                        return CARGO_NO_REFIT; // engine_type is already a mixed cargo type which matches the incoming vehicle by default, no refit required
                }

                return INVALID_CARGO; // We cannot refit to mixed cargoes in an automated way
        }

        if (!IsValidCargoID(cargo_type)) {
                if (v->type != VEH_TRAIN) return CARGO_NO_REFIT; // If the vehicle does not carry anything at all, every replacement is fine.

                if (!part_of_chain) return CARGO_NO_REFIT;

                /* the old engine didn't have cargo capacity, but the new one does
                 * now we will figure out what cargo the train is carrying and refit to fit this */

                for (v = v->First(); v != nullptr; v = v->Next()) {
                        if (!v->GetEngine()->CanCarryCargo()) continue;
                        /* Now we found a cargo type being carried on the train and we will see if it is possible to carry to this one */
                        if (HasBit(available_cargo_types, v->cargo_type)) return v->cargo_type;
                }

                return CARGO_NO_REFIT; // We failed to find a cargo type on the old vehicle and we will not refit the new one
        } else {
                if (!HasBit(available_cargo_types, cargo_type)) return INVALID_CARGO; // We can't refit the vehicle to carry the cargo we want

                if (part_of_chain && !VerifyAutoreplaceRefitForOrders(v, engine_type)) return INVALID_CARGO; // Some refit orders lose their effect

                return cargo_type;
        }
}

/**
 * Get the EngineID of the replacement for a vehicle
 * @param v The vehicle to find a replacement for
 * @param c The vehicle's owner (it's faster to forward the pointer than refinding it)
 * @param always_replace Always replace, even if not old.
 * @param[out] e the EngineID of the replacement. INVALID_ENGINE if no replacement is found
 * @return Error if the engine to build is not available
 */
static CommandCost GetNewEngineType(const Vehicle *v, const Company *c, bool always_replace, EngineID &e)
{
        assert(v->type != VEH_TRAIN || !v->IsArticulatedPart());

        e = INVALID_ENGINE;

        if (v->type == VEH_TRAIN && Train::From(v)->IsRearDualheaded()) {
                /* we build the rear ends of multiheaded trains with the front ones */
                return CommandCost();
        }

        bool replace_when_old;
        e = EngineReplacementForCompany(c, v->engine_type, v->group_id, &replace_when_old);
        if (!always_replace && replace_when_old && !v->NeedsAutorenewing(c, false)) e = INVALID_ENGINE;

        /* Autoreplace, if engine is available */
        if (e != INVALID_ENGINE && IsEngineBuildable(e, v->type, _current_company)) {
                return CommandCost();
        }

        /* Autorenew if needed */
        if (v->NeedsAutorenewing(c)) e = v->engine_type;

        /* Nothing to do or all is fine? */
        if (e == INVALID_ENGINE || IsEngineBuildable(e, v->type, _current_company)) return CommandCost();

        /* The engine we need is not available. Report error to user */
        return CommandCost(STR_ERROR_RAIL_VEHICLE_NOT_AVAILABLE + v->type);
}

/**
 * Builds and refits a replacement vehicle
 * Important: The old vehicle is still in the original vehicle chain (used for determining the cargo when the old vehicle did not carry anything, but the new one does)
 * @param old_veh A single (articulated/multiheaded) vehicle that shall be replaced.
 * @param new_vehicle Returns the newly build and refitted vehicle
 * @param part_of_chain The vehicle is part of a train
 * @param flags The calling command flags.
 * @return cost or error
 */
static CommandCost BuildReplacementVehicle(Vehicle *old_veh, Vehicle **new_vehicle, bool part_of_chain, DoCommandFlag flags)
{
        *new_vehicle = nullptr;

        /* Shall the vehicle be replaced? */
        const Company *c = Company::Get(_current_company);
        EngineID e;
        CommandCost cost = GetNewEngineType(old_veh, c, true, e);
        if (cost.Failed()) return cost;
        if (e == INVALID_ENGINE) return CommandCost(); // neither autoreplace is set, nor autorenew is triggered

        /* Does it need to be refitted */
        CargoID refit_cargo = GetNewCargoTypeForReplace(old_veh, e, part_of_chain);
        if (!IsValidCargoID(refit_cargo)) {
                if (!IsLocalCompany() || (flags & DC_EXEC) == 0) return CommandCost();

                VehicleID old_veh_id = (old_veh->type == VEH_TRAIN) ? Train::From(old_veh)->First()->index : old_veh->index;
                SetDParam(0, old_veh_id);

                int order_id = GetIncompatibleRefitOrderIdForAutoreplace(old_veh, e);
                if (order_id != -1) {
                        /* Orders contained a refit order that is incompatible with the new vehicle. */
                        SetDParam(1, STR_ERROR_AUTOREPLACE_INCOMPATIBLE_REFIT);
                        SetDParam(2, order_id + 1); // 1-based indexing for display
                } else {
                        /* Current cargo is incompatible with the new vehicle. */
                        SetDParam(1, STR_ERROR_AUTOREPLACE_INCOMPATIBLE_CARGO);
                        SetDParam(2, CargoSpec::Get(old_veh->cargo_type)->name);
                }

                AddVehicleAdviceNewsItem(STR_NEWS_VEHICLE_AUTORENEW_FAILED, old_veh_id);
                return CommandCost();
        }

        /* Build the new vehicle */
        VehicleID new_veh_id;
        std::tie(cost, new_veh_id, std::ignore, std::ignore, std::ignore) = Command<CMD_BUILD_VEHICLE>::Do(DC_EXEC | DC_AUTOREPLACE, old_veh->tile, e, true, INVALID_CARGO, INVALID_CLIENT_ID);
        if (cost.Failed()) return cost;

        Vehicle *new_veh = Vehicle::Get(new_veh_id);
        *new_vehicle = new_veh;

        /* Refit the vehicle if needed */
        if (refit_cargo != CARGO_NO_REFIT) {
                uint8_t subtype = GetBestFittingSubType(old_veh, new_veh, refit_cargo);

                cost.AddCost(std::get<0>(Command<CMD_REFIT_VEHICLE>::Do(DC_EXEC, new_veh->index, refit_cargo, subtype, false, false, 0)));
                assert(cost.Succeeded()); // This should be ensured by GetNewCargoTypeForReplace()
        }

        /* Try to reverse the vehicle, but do not care if it fails as the new type might not be reversible */
        if (new_veh->type == VEH_TRAIN && HasBit(Train::From(old_veh)->flags, VRF_REVERSE_DIRECTION)) {
                Command<CMD_REVERSE_TRAIN_DIRECTION>::Do(DC_EXEC, new_veh->index, true);
        }

        return cost;
}

/**
 * Issue a start/stop command
 * @param v a vehicle
 * @param evaluate_callback shall the start/stop callback be evaluated?
 * @return success or error
 */
static inline CommandCost DoCmdStartStopVehicle(const Vehicle *v, bool evaluate_callback)
{
        return Command<CMD_START_STOP_VEHICLE>::Do(DC_EXEC | DC_AUTOREPLACE, v->index, evaluate_callback);
}

/**
 * Issue a train vehicle move command
 * @param v The vehicle to move
 * @param after The vehicle to insert 'v' after, or nullptr to start new chain
 * @param flags the command flags to use
 * @param whole_chain move all vehicles following 'v' (true), or only 'v' (false)
 * @return success or error
 */
static inline CommandCost CmdMoveVehicle(const Vehicle *v, const Vehicle *after, DoCommandFlag flags, bool whole_chain)
{
        return Command<CMD_MOVE_RAIL_VEHICLE>::Do(flags | DC_NO_CARGO_CAP_CHECK, v->index, after != nullptr ? after->index : INVALID_VEHICLE, whole_chain);
}

/**
 * Copy head specific things to the new vehicle chain after it was successfully constructed
 * @param old_head The old front vehicle (no wagons attached anymore)
 * @param new_head The new head of the completely replaced vehicle chain
 * @param flags the command flags to use
 */
static CommandCost CopyHeadSpecificThings(Vehicle *old_head, Vehicle *new_head, DoCommandFlag flags)
{
        CommandCost cost = CommandCost();

        /* Share orders */
        if (cost.Succeeded() && old_head != new_head) cost.AddCost(Command<CMD_CLONE_ORDER>::Do(DC_EXEC, CO_SHARE, new_head->index, old_head->index));

        /* Copy group membership */
        if (cost.Succeeded() && old_head != new_head) cost.AddCost(std::get<0>(Command<CMD_ADD_VEHICLE_GROUP>::Do(DC_EXEC, old_head->group_id, new_head->index, false, VehicleListIdentifier{})));

        /* Perform start/stop check whether the new vehicle suits newgrf restrictions etc. */
        if (cost.Succeeded()) {
                /* Start the vehicle, might be denied by certain things */
                assert((new_head->vehstatus & VS_STOPPED) != 0);
                cost.AddCost(DoCmdStartStopVehicle(new_head, true));

                /* Stop the vehicle again, but do not care about evil newgrfs allowing starting but not stopping :p */
                if (cost.Succeeded()) cost.AddCost(DoCmdStartStopVehicle(new_head, false));
        }

        /* Last do those things which do never fail (resp. we do not care about), but which are not undo-able */
        if (cost.Succeeded() && old_head != new_head && (flags & DC_EXEC) != 0) {
                /* Copy other things which cannot be copied by a command and which shall not stay resetted from the build vehicle command */
                new_head->CopyVehicleConfigAndStatistics(old_head);
                GroupStatistics::AddProfitLastYear(new_head);

                /* Switch vehicle windows/news to the new vehicle, so they are not closed/deleted when the old vehicle is sold */
                ChangeVehicleViewports(old_head->index, new_head->index);
                ChangeVehicleViewWindow(old_head->index, new_head->index);
                ChangeVehicleNews(old_head->index, new_head->index);
        }

        return cost;
}

/**
 * Replace a single unit in a free wagon chain
 * @param single_unit vehicle to let autoreplace/renew operator on
 * @param flags command flags
 * @param nothing_to_do is set to 'false' when something was done (only valid when not failed)
 * @return cost or error
 */
static CommandCost ReplaceFreeUnit(Vehicle **single_unit, DoCommandFlag flags, bool *nothing_to_do)
{
        Train *old_v = Train::From(*single_unit);
        assert(!old_v->IsArticulatedPart() && !old_v->IsRearDualheaded());

        CommandCost cost = CommandCost(EXPENSES_NEW_VEHICLES, (Money)0);

        /* Build and refit replacement vehicle */
        Vehicle *new_v = nullptr;
        cost.AddCost(BuildReplacementVehicle(old_v, &new_v, false, flags));

        /* Was a new vehicle constructed? */
        if (cost.Succeeded() && new_v != nullptr) {
                *nothing_to_do = false;

                if ((flags & DC_EXEC) != 0) {
                        /* Move the new vehicle behind the old */
                        CmdMoveVehicle(new_v, old_v, DC_EXEC, false);

                        /* Take over cargo
                         * Note: We do only transfer cargo from the old to the new vehicle.
                         *       I.e. we do not transfer remaining cargo to other vehicles.
                         *       Else you would also need to consider moving cargo to other free chains,
                         *       or doing the same in ReplaceChain(), which would be quite troublesome.
                         */
                        TransferCargo(old_v, new_v, false);

                        *single_unit = new_v;

                        AI::NewEvent(old_v->owner, new ScriptEventVehicleAutoReplaced(old_v->index, new_v->index));
                }

                /* Sell the old vehicle */
                cost.AddCost(Command<CMD_SELL_VEHICLE>::Do(flags, old_v->index, false, false, INVALID_CLIENT_ID));

                /* If we are not in DC_EXEC undo everything */
                if ((flags & DC_EXEC) == 0) {
                        Command<CMD_SELL_VEHICLE>::Do(DC_EXEC, new_v->index, false, false, INVALID_CLIENT_ID);
                }
        }

        return cost;
}

/** Struct for recording vehicle chain replacement information. */
struct ReplaceChainItem {
        Vehicle *old_veh; ///< Old vehicle to replace.
        Vehicle *new_veh; ///< Replacement vehicle, or nullptr if no replacement.
        Money cost; /// Cost of buying and refitting replacement.

        ReplaceChainItem(Vehicle *old_veh, Vehicle *new_veh, Money cost) : old_veh(old_veh), new_veh(new_veh), cost(cost) { }

        /**
         * Get vehicle to use for this position.
         * @return Either the new vehicle, or the old vehicle if there is no replacement.
         */
        Vehicle *GetVehicle() const { return new_veh == nullptr ? old_veh : new_veh; }
};

/**
 * Replace a whole vehicle chain
 * @param chain vehicle chain to let autoreplace/renew operator on
 * @param flags command flags
 * @param wagon_removal remove wagons when the resulting chain occupies more tiles than the old did
 * @param nothing_to_do is set to 'false' when something was done (only valid when not failed)
 * @return cost or error
 */
static CommandCost ReplaceChain(Vehicle **chain, DoCommandFlag flags, bool wagon_removal, bool *nothing_to_do)
{
        Vehicle *old_head = *chain;
        assert(old_head->IsPrimaryVehicle());

        CommandCost cost = CommandCost(EXPENSES_NEW_VEHICLES, (Money)0);

        if (old_head->type == VEH_TRAIN) {
                /* Store the length of the old vehicle chain, rounded up to whole tiles */
                uint16_t old_total_length = CeilDiv(Train::From(old_head)->gcache.cached_total_length, TILE_SIZE) * TILE_SIZE;

                std::vector<ReplaceChainItem> replacements;

                /* Collect vehicles and build replacements
                 * Note: The replacement vehicles can only successfully build as long as the old vehicles are still in their chain */
                for (Train *w = Train::From(old_head); w != nullptr; w = w->GetNextUnit()) {
                        ReplaceChainItem &replacement = replacements.emplace_back(w, nullptr, 0);

                        CommandCost ret = BuildReplacementVehicle(replacement.old_veh, &replacement.new_veh, true, flags);
                        cost.AddCost(ret);
                        if (cost.Failed()) break;

                        replacement.cost = ret.GetCost();
                        if (replacement.new_veh != nullptr) *nothing_to_do = false;
                }
                Vehicle *new_head = replacements.front().GetVehicle();

                /* Note: When autoreplace has already failed here, old_vehs[] is not completely initialized. But it is also not needed. */
                if (cost.Succeeded()) {
                        /* Separate the head, so we can start constructing the new chain */
                        Train *second = Train::From(old_head)->GetNextUnit();
                        if (second != nullptr) cost.AddCost(CmdMoveVehicle(second, nullptr, DC_EXEC | DC_AUTOREPLACE, true));

                        assert(Train::From(new_head)->GetNextUnit() == nullptr);

                        /* Append engines to the new chain
                         * We do this from back to front, so that the head of the temporary vehicle chain does not change all the time.
                         * That way we also have less trouble when exceeding the unitnumber limit.
                         * OTOH the vehicle attach callback is more expensive this way :s */
                        Vehicle *last_engine = nullptr; ///< Shall store the last engine unit after this step
                        if (cost.Succeeded()) {
                                for (auto it = std::rbegin(replacements); it != std::rend(replacements); ++it) {
                                        Vehicle *append = it->GetVehicle();

                                        if (RailVehInfo(append->engine_type)->railveh_type == RAILVEH_WAGON) continue;

                                        if (it->new_veh != nullptr) {
                                                /* Move the old engine to a separate row with DC_AUTOREPLACE. Else
                                                 * moving the wagon in front may fail later due to unitnumber limit.
                                                 * (We have to attach wagons without DC_AUTOREPLACE.) */
                                                CmdMoveVehicle(it->old_veh, nullptr, DC_EXEC | DC_AUTOREPLACE, false);
                                        }

                                        if (last_engine == nullptr) last_engine = append;
                                        cost.AddCost(CmdMoveVehicle(append, new_head, DC_EXEC, false));
                                        if (cost.Failed()) break;
                                }
                                if (last_engine == nullptr) last_engine = new_head;
                        }

                        /* When wagon removal is enabled and the new engines without any wagons are already longer than the old, we have to fail */
                        if (cost.Succeeded() && wagon_removal && Train::From(new_head)->gcache.cached_total_length > old_total_length) cost = CommandCost(STR_ERROR_TRAIN_TOO_LONG_AFTER_REPLACEMENT);

                        /* Append/insert wagons into the new vehicle chain
                         * We do this from back to front, so we can stop when wagon removal or maximum train length (i.e. from mammoth-train setting) is triggered.
                         */
                        if (cost.Succeeded()) {
                                for (auto it = std::rbegin(replacements); it != std::rend(replacements); ++it) {
                                        assert(last_engine != nullptr);
                                        Vehicle *append = it->GetVehicle();

                                        if (RailVehInfo(append->engine_type)->railveh_type == RAILVEH_WAGON) {
                                                /* Insert wagon after 'last_engine' */
                                                CommandCost res = CmdMoveVehicle(append, last_engine, DC_EXEC, false);

                                                /* When we allow removal of wagons, either the move failing due
                                                 * to the train becoming too long, or the train becoming longer
                                                 * would move the vehicle to the empty vehicle chain. */
                                                if (wagon_removal && (res.Failed() ? res.GetErrorMessage() == STR_ERROR_TRAIN_TOO_LONG : Train::From(new_head)->gcache.cached_total_length > old_total_length)) {
                                                        CmdMoveVehicle(append, nullptr, DC_EXEC | DC_AUTOREPLACE, false);
                                                        break;
                                                }

                                                cost.AddCost(res);
                                                if (cost.Failed()) break;
                                        } else {
                                                /* We have reached 'last_engine', continue with the next engine towards the front */
                                                assert(append == last_engine);
                                                last_engine = Train::From(last_engine)->GetPrevUnit();
                                        }
                                }
                        }

                        /* Sell superfluous new vehicles that could not be inserted. */
                        if (cost.Succeeded() && wagon_removal) {
                                assert(Train::From(new_head)->gcache.cached_total_length <= _settings_game.vehicle.max_train_length * TILE_SIZE);
                                for (auto it = std::next(std::begin(replacements)); it != std::end(replacements); ++it) {
                                        Vehicle *wagon = it->new_veh;
                                        if (wagon == nullptr) continue;
                                        if (wagon->First() == new_head) break;

                                        assert(RailVehInfo(wagon->engine_type)->railveh_type == RAILVEH_WAGON);

                                        /* Sell wagon */
                                        [[maybe_unused]] CommandCost ret = Command<CMD_SELL_VEHICLE>::Do(DC_EXEC, wagon->index, false, false, INVALID_CLIENT_ID);
                                        assert(ret.Succeeded());
                                        it->new_veh = nullptr;

                                        /* Revert the money subtraction when the vehicle was built.
                                         * This value is different from the sell value, esp. because of refitting */
                                        cost.AddCost(-it->cost);
                                }
                        }

                        /* The new vehicle chain is constructed, now take over orders and everything... */
                        if (cost.Succeeded()) cost.AddCost(CopyHeadSpecificThings(old_head, new_head, flags));

                        if (cost.Succeeded()) {
                                /* Success ! */
                                if ((flags & DC_EXEC) != 0 && new_head != old_head) {
                                        *chain = new_head;
                                        AI::NewEvent(old_head->owner, new ScriptEventVehicleAutoReplaced(old_head->index, new_head->index));
                                }

                                /* Transfer cargo of old vehicles and sell them */
                                for (auto it = std::begin(replacements); it != std::end(replacements); ++it) {
                                        Vehicle *w = it->old_veh;
                                        /* Is the vehicle again part of the new chain?
                                         * Note: We cannot test 'new_vehs[i] != nullptr' as wagon removal might cause to remove both */
                                        if (w->First() == new_head) continue;

                                        if ((flags & DC_EXEC) != 0) TransferCargo(w, new_head, true);

                                        /* Sell the vehicle.
                                         * Note: This might temporarily construct new trains, so use DC_AUTOREPLACE to prevent
                                         *       it from failing due to engine limits. */
                                        cost.AddCost(Command<CMD_SELL_VEHICLE>::Do(flags | DC_AUTOREPLACE, w->index, false, false, INVALID_CLIENT_ID));
                                        if ((flags & DC_EXEC) != 0) {
                                                it->old_veh = nullptr;
                                                if (it == std::begin(replacements)) old_head = nullptr;
                                        }
                                }

                                if ((flags & DC_EXEC) != 0) CheckCargoCapacity(new_head);
                        }

                        /* If we are not in DC_EXEC undo everything, i.e. rearrange old vehicles.
                         * We do this from back to front, so that the head of the temporary vehicle chain does not change all the time.
                         * Note: The vehicle attach callback is disabled here :) */
                        if ((flags & DC_EXEC) == 0) {
                                /* Separate the head, so we can reattach the old vehicles */
                                Train *second = Train::From(old_head)->GetNextUnit();
                                if (second != nullptr) CmdMoveVehicle(second, nullptr, DC_EXEC | DC_AUTOREPLACE, true);

                                assert(Train::From(old_head)->GetNextUnit() == nullptr);

                                for (auto it = std::rbegin(replacements); it != std::rend(replacements); ++it) {
                                        [[maybe_unused]] CommandCost ret = CmdMoveVehicle(it->old_veh, old_head, DC_EXEC | DC_AUTOREPLACE, false);
                                        assert(ret.Succeeded());
                                }
                        }
                }

                /* Finally undo buying of new vehicles */
                if ((flags & DC_EXEC) == 0) {
                        for (auto it = std::rbegin(replacements); it != std::rend(replacements); ++it) {
                                if (it->new_veh != nullptr) {
                                        Command<CMD_SELL_VEHICLE>::Do(DC_EXEC, it->new_veh->index, false, false, INVALID_CLIENT_ID);
                                        it->new_veh = nullptr;
                                }
                        }
                }
        } else {
                /* Build and refit replacement vehicle */
                Vehicle *new_head = nullptr;
                cost.AddCost(BuildReplacementVehicle(old_head, &new_head, true, flags));

                /* Was a new vehicle constructed? */
                if (cost.Succeeded() && new_head != nullptr) {
                        *nothing_to_do = false;

                        /* The new vehicle is constructed, now take over orders and everything... */
                        cost.AddCost(CopyHeadSpecificThings(old_head, new_head, flags));

                        if (cost.Succeeded()) {
                                /* The new vehicle is constructed, now take over cargo */
                                if ((flags & DC_EXEC) != 0) {
                                        TransferCargo(old_head, new_head, true);
                                        *chain = new_head;

                                        AI::NewEvent(old_head->owner, new ScriptEventVehicleAutoReplaced(old_head->index, new_head->index));
                                }

                                /* Sell the old vehicle */
                                cost.AddCost(Command<CMD_SELL_VEHICLE>::Do(flags, old_head->index, false, false, INVALID_CLIENT_ID));
                        }

                        /* If we are not in DC_EXEC undo everything */
                        if ((flags & DC_EXEC) == 0) {
                                Command<CMD_SELL_VEHICLE>::Do(DC_EXEC, new_head->index, false, false, INVALID_CLIENT_ID);
                        }
                }
        }

        return cost;
}

/**
 * Autoreplaces a vehicle
 * Trains are replaced as a whole chain, free wagons in depot are replaced on their own
 * @param flags type of operation
 * @param veh_id Index of vehicle
 * @return the cost of this operation or an error
 */
CommandCost CmdAutoreplaceVehicle(DoCommandFlag flags, VehicleID veh_id)
{
        Vehicle *v = Vehicle::GetIfValid(veh_id);
        if (v == nullptr) return CMD_ERROR;

        CommandCost ret = CheckOwnership(v->owner);
        if (ret.Failed()) return ret;

        if (v->vehstatus & VS_CRASHED) return CMD_ERROR;

        bool free_wagon = false;
        if (v->type == VEH_TRAIN) {
                Train *t = Train::From(v);
                if (t->IsArticulatedPart() || t->IsRearDualheaded()) return CMD_ERROR;
                free_wagon = !t->IsFrontEngine();
                if (free_wagon && t->First()->IsFrontEngine()) return CMD_ERROR;
        } else {
                if (!v->IsPrimaryVehicle()) return CMD_ERROR;
        }
        if (!v->IsChainInDepot()) return CMD_ERROR;

        const Company *c = Company::Get(_current_company);
        bool wagon_removal = c->settings.renew_keep_length;

        const Group *g = Group::GetIfValid(v->group_id);
        if (g != nullptr) wagon_removal = HasBit(g->flags, GroupFlags::GF_REPLACE_WAGON_REMOVAL);

        /* Test whether any replacement is set, before issuing a whole lot of commands that would end in nothing changed */
        Vehicle *w = v;
        bool any_replacements = false;
        while (w != nullptr) {
                EngineID e;
                CommandCost cost = GetNewEngineType(w, c, false, e);
                if (cost.Failed()) return cost;
                any_replacements |= (e != INVALID_ENGINE);
                w = (!free_wagon && w->type == VEH_TRAIN ? Train::From(w)->GetNextUnit() : nullptr);
        }

        CommandCost cost = CommandCost(EXPENSES_NEW_VEHICLES, (Money)0);
        bool nothing_to_do = true;

        if (any_replacements) {
                bool was_stopped = free_wagon || ((v->vehstatus & VS_STOPPED) != 0);

                /* Stop the vehicle */
                if (!was_stopped) cost.AddCost(DoCmdStartStopVehicle(v, true));
                if (cost.Failed()) return cost;

                assert(free_wagon || v->IsStoppedInDepot());

                /* We have to construct the new vehicle chain to test whether it is valid.
                 * Vehicle construction needs random bits, so we have to save the random seeds
                 * to prevent desyncs and to replay newgrf callbacks during DC_EXEC */
                SavedRandomSeeds saved_seeds;
                SaveRandomSeeds(&saved_seeds);
                if (free_wagon) {
                        cost.AddCost(ReplaceFreeUnit(&v, flags & ~DC_EXEC, &nothing_to_do));
                } else {
                        cost.AddCost(ReplaceChain(&v, flags & ~DC_EXEC, wagon_removal, &nothing_to_do));
                }
                RestoreRandomSeeds(saved_seeds);

                if (cost.Succeeded() && (flags & DC_EXEC) != 0) {
                        if (free_wagon) {
                                ret = ReplaceFreeUnit(&v, flags, &nothing_to_do);
                        } else {
                                ret = ReplaceChain(&v, flags, wagon_removal, &nothing_to_do);
                        }
                        assert(ret.Succeeded() && ret.GetCost() == cost.GetCost());
                }

                /* Restart the vehicle */
                if (!was_stopped) cost.AddCost(DoCmdStartStopVehicle(v, false));
        }

        if (cost.Succeeded() && nothing_to_do) cost = CommandCost(STR_ERROR_AUTOREPLACE_NOTHING_TO_DO);
        return cost;
}

/**
 * Change engine renewal parameters
 * @param flags operation to perform
 * @param id_g engine group
 * @param old_engine_type old engine type
 * @param new_engine_type new engine type
 * @param when_old replace when engine gets old?
 * @return the cost of this operation or an error
 */
CommandCost CmdSetAutoReplace(DoCommandFlag flags, GroupID id_g, EngineID old_engine_type, EngineID new_engine_type, bool when_old)
{
        Company *c = Company::GetIfValid(_current_company);
        if (c == nullptr) return CMD_ERROR;

        CommandCost cost;

        if (Group::IsValidID(id_g) ? Group::Get(id_g)->owner != _current_company : !IsAllGroupID(id_g) && !IsDefaultGroupID(id_g)) return CMD_ERROR;
        if (!Engine::IsValidID(old_engine_type)) return CMD_ERROR;
        if (Group::IsValidID(id_g) && Group::Get(id_g)->vehicle_type != Engine::Get(old_engine_type)->type) return CMD_ERROR;

        if (new_engine_type != INVALID_ENGINE) {
                if (!Engine::IsValidID(new_engine_type)) return CMD_ERROR;
                if (!CheckAutoreplaceValidity(old_engine_type, new_engine_type, _current_company)) return CMD_ERROR;

                cost = AddEngineReplacementForCompany(c, old_engine_type, new_engine_type, id_g, when_old, flags);
        } else {
                cost = RemoveEngineReplacementForCompany(c, old_engine_type, id_g, flags);
        }

        if (flags & DC_EXEC) {
                GroupStatistics::UpdateAutoreplace(_current_company);
                if (IsLocalCompany()) SetWindowDirty(WC_REPLACE_VEHICLE, Engine::Get(old_engine_type)->type);

                const VehicleType vt = Engine::Get(old_engine_type)->type;
                SetWindowDirty(GetWindowClassForVehicleType(vt), VehicleListIdentifier(VL_GROUP_LIST, vt, _current_company).Pack());
        }
        if ((flags & DC_EXEC) && IsLocalCompany()) InvalidateAutoreplaceWindow(old_engine_type, id_g);

        return cost;
}