From ef7c8884b89bd9cdee139f8c386da391a5e9b6d2 Mon Sep 17 00:00:00 2001
From: J0anJosep <juanjo.ng.83@gmail.com>
Date: Thu, 1 Apr 2021 21:19:02 +0200
Subject: [PATCH] Codechange: Add additional rules for placing trains in depots
 according to railtypes.

---
 src/lang/english.txt |  1 +
 src/train_cmd.cpp    | 89 +++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 88 insertions(+), 2 deletions(-)

diff --git a/src/lang/english.txt b/src/lang/english.txt
index 2b251064e4..36f555620a 100644
--- a/src/lang/english.txt
+++ b/src/lang/english.txt
@@ -5138,6 +5138,7 @@ STR_ERROR_AIRCRAFT_MUST_BE_STOPPED_INSIDE_HANGAR                :{WHITE}... must
 
 STR_ERROR_TRAINS_CAN_ONLY_BE_ALTERED_INSIDE_A_DEPOT             :{WHITE}Trains can only be altered when stopped inside a depot
 STR_ERROR_TRAIN_TOO_LONG                                        :{WHITE}Train too long
+STR_ERROR_INCOMPATIBLE_RAILTYPES_WITH_DEPOT                     :{WHITE}Train chain is incompatible with any tile of this depot
 STR_ERROR_CAN_T_REVERSE_DIRECTION_RAIL_VEHICLE                  :{WHITE}Can't reverse direction of vehicle...
 STR_ERROR_CAN_T_REVERSE_DIRECTION_RAIL_VEHICLE_MULTIPLE_UNITS   :{WHITE}... consists of multiple units
 STR_ERROR_INCOMPATIBLE_RAIL_TYPES                               :Incompatible rail types
diff --git a/src/train_cmd.cpp b/src/train_cmd.cpp
index d6c65140ca..52afef664f 100644
--- a/src/train_cmd.cpp
+++ b/src/train_cmd.cpp
@@ -1051,6 +1051,82 @@ static CommandCost CheckNewTrain(Train *original_dst, Train *dst, Train *origina
 	return_cmd_error(STR_ERROR_TOO_MANY_VEHICLES_IN_GAME);
 }
 
+/**
+ * Check if a train can be placed in a depot tile.
+ * @param train The train.
+ * @param tile The tile to check whether it is possible to place the train.
+ * @return whether it found a depot tile in which to place the train.
+ */
+bool CheckPlacement(const Train *train, TileIndex tile)
+{
+	assert(train != nullptr);
+	assert(IsRailDepotTile(tile));
+
+	RailType rt = GetRailType(tile);
+	for (const Train *t = train; t != nullptr; t = t->Next()) {
+		RailType rail_type = Engine::Get(t->engine_type)->u.rail.railtype;
+		if (!IsCompatibleRail(rail_type, rt)) return false;
+	}
+
+	return true;
+}
+
+/**
+ * Find a valid tile before placing a train in the depot.
+ * @param t The train to place in a rail depot tile.
+ * @return a compatible tile, if any, preferabily the one the first vehicle is or INVALID_TILE if none found.
+ */
+TileIndex LookForTileInDepot(const Train *train)
+{
+	assert(train != nullptr);
+	assert(IsRailDepotTile(train->tile));
+	TileIndex best_tile = INVALID_TILE;
+
+	/* First candidate is the original position of the train. */
+	if (CheckPlacement(train, train->tile)) {
+		if (HasPowerOnRail(train->railtype, GetRailType(train->tile))) return train->tile;
+		best_tile = train->tile;
+	}
+
+	/* Check all depot tiles. */
+	Depot *depot = Depot::GetByTile(train->tile);
+	for (std::vector<TileIndex>::iterator it = depot->depot_tiles.begin(); it != depot->depot_tiles.end(); ++it) {
+		if (CheckPlacement(train, *it)) {
+			if (HasPowerOnRail(train->railtype, GetRailType(*it))) return *it;
+			if (best_tile == INVALID_TILE) best_tile = *it;
+		}
+	}
+
+	return best_tile;
+}
+
+/**
+ * Find an appropriate depot tile for a train and place
+ * all the vehicle chain in the same depot tile.
+ * @param train The train to place.
+ */
+void PlaceOnRailDepot(Train *train)
+{
+	assert(train->First() == train);
+
+	TileIndex depot_tile = LookForTileInDepot(train);
+	assert(depot_tile != INVALID_TILE);
+
+	DiagDirection diag_dir = GetRailDepotDirection(depot_tile);
+	int x = TileX(depot_tile) * TILE_SIZE + _vehicle_initial_x_fract[diag_dir];
+	int y = TileY(depot_tile) * TILE_SIZE + _vehicle_initial_y_fract[diag_dir];
+	for (Train *t = train; t != nullptr; t = t->Next()) {
+		t->tile = depot_tile;
+		t->direction = DiagDirToDir(diag_dir);
+		t->vehstatus |= VS_HIDDEN;
+		t->track = TRACK_BIT_DEPOT;
+		t->x_pos = x;
+		t->y_pos = y;
+		t->z_pos = GetSlopePixelZ(x, y);
+		t->UpdatePosition();
+	}
+}
+
 /**
  * Check whether the train parts can be attached.
  * @param t the train to check
@@ -1061,6 +1137,8 @@ static CommandCost CheckTrainAttachment(Train *t)
 	/* No multi-part train, no need to check. */
 	if (t == nullptr || t->Next() == nullptr) return CommandCost();
 
+	if (LookForTileInDepot(t) == INVALID_TILE) return_cmd_error(STR_ERROR_INCOMPATIBLE_RAILTYPES_WITH_DEPOT);
+
 	/* The maximum length for a train. For each part we decrease this by one
 	 * and if the result is negative the train is simply too long. */
 	int allowed_len = _settings_game.vehicle.max_train_length * TILE_SIZE - t->gcache.cached_veh_length;
@@ -1426,8 +1504,15 @@ CommandCost CmdMoveRailVehicle(DoCommandFlag flags, VehicleID src_veh, VehicleID
 			CheckCargoCapacity(dst_head);
 		}
 
-		if (src_head != nullptr) src_head->First()->MarkDirty();
-		if (dst_head != nullptr) dst_head->First()->MarkDirty();
+		if (src_head != nullptr) {
+			PlaceOnRailDepot(src_head->First());
+			src_head->First()->MarkDirty();
+		}
+
+		if (dst_head != nullptr) {
+			PlaceOnRailDepot(dst_head->First());
+			dst_head->First()->MarkDirty();
+		}
 
 		/* We are undoubtedly changing something in the depot and train list. */
 		InvalidateWindowData(WC_VEHICLE_DEPOT, GetDepotIndex(src->tile));