/**
 * Build a ship depot.
 * @param tile tile where ship depot is built
 * @param flags type of operation
 * @param p1 bit 0 depot orientation (Axis)
 * @param p2 unused
 * @param text unused
 * @return the cost of this operation or an error
 */
CommandCost CmdBuildShipDepot(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
	Axis axis = Extract<Axis, 0, 1>(p1);

	TileIndex tile2 = tile + (axis == AXIS_X ? TileDiffXY(1, 0) : TileDiffXY(0, 1));

	if (IsBridgeAbove(tile) || IsBridgeAbove(tile2)) return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);

	if (!Depot::CanAllocateItem()) return CMD_ERROR;

	CommandCost cost = CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_DEPOT_SHIP]);

	WaterClass wc1 = IsWaterTile(tile) ? GetWaterClass(tile) : WATER_CLASS_CANAL;
	Owner oc1 = HasTileWaterGround(tile) && GetWaterClass(tile) == WATER_CLASS_CANAL ? GetCanalOwner(tile) : _current_company;
	bool add_cost1 = !IsWaterTile(tile);

	CommandCost ret;
	/* At this point we got a flat tile with no bridge over it. Check for ownership */
	if (IsWaterTile(tile) && IsCanal(tile)) {
		ret = EnsureNoVehicleOnGround(tile);
		if (ret.Failed()) return ret;
		if (oc1 != OWNER_NONE) {
			ret = CheckTileOwnership(tile);
			if (ret.Failed() && !_settings_game.construction.build_on_competitor_canal) return ret;
		}
	} else {
		ret = DoCommand(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
		if (ret.Failed()) return ret;
		if (add_cost1) {
			cost.AddCost(ret);
			if (wc1 == WATER_CLASS_CANAL) cost.AddCost(_price[PR_BUILD_CANAL]);
		}
	}

	WaterClass wc2 = IsWaterTile(tile2) ? GetWaterClass(tile2) : WATER_CLASS_CANAL;
	Owner oc2 = HasTileWaterGround(tile2) && GetWaterClass(tile2) == WATER_CLASS_CANAL ? GetCanalOwner(tile2) : _current_company;
	bool add_cost2 = !IsWaterTile(tile2);

	/* At this point we got a flat tile2 with no bridge over it. Check for ownership */
	if (IsWaterTile(tile2) && IsCanal(tile2)) {
		ret = EnsureNoVehicleOnGround(tile2);
		if (ret.Failed()) return ret;
		if (oc2 != OWNER_NONE) {
			ret = CheckTileOwnership(tile2);
			if (ret.Failed() && !_settings_game.construction.build_on_competitor_canal) return ret;
		}
	} else {
		ret = DoCommand(tile2, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
		if (ret.Failed()) return ret;
		if (add_cost2) {
			cost.AddCost(ret);
			if (wc2 == WATER_CLASS_CANAL) cost.AddCost(_price[PR_BUILD_CANAL]);
		}
	}

	if (!IsTileFlat(tile) || !IsTileFlat(tile2)) {
		int z_slope1;
		Slope slope1 = GetTileSlope(tile, &z_slope1);
		int z_middle_corner_n = TileHeight(tile2);
		int z_middle_corner_s = TileHeight(TileAddByDiagDir(tile2, AxisToDiagDir(OtherAxis(axis))));
		int z_slope2;
		Slope slope2 = GetTileSlope(tile2, &z_slope2);

		/* Forbid these combinations. */
		if (IsSteepSlope(slope1) || IsSteepSlope(slope2)) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
		if (slope1 == SLOPE_NS && slope2 == SLOPE_EW || slope1 == SLOPE_EW && slope2 == SLOPE_NS) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
		if (z_middle_corner_n != z_middle_corner_s && (IsSlopeWithThreeCornersRaised(slope1) && IsSlopeWithOneCornerRaised(slope2) || IsSlopeWithOneCornerRaised(slope1) && IsSlopeWithThreeCornersRaised(slope2))) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
		if ((slope1 == slope2 || slope1 == ComplementSlope(slope2)) && IsInclinedSlope(slope1)) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
		if (((IsSlopeWithOneCornerRaised(slope2) || IsSlopeWithThreeCornersRaised(slope2) || slope2 == SLOPE_EW || slope2 == SLOPE_NS) && IsInclinedSlope(slope1) && DiagDirToAxis(GetInclinedSlopeDirection(slope1)) == axis) || ((IsSlopeWithOneCornerRaised(slope1) || IsSlopeWithThreeCornersRaised(slope1) || slope1 == SLOPE_EW || slope1 == SLOPE_NS) && IsInclinedSlope(slope2) && DiagDirToAxis(GetInclinedSlopeDirection(slope2)) == axis)) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);

		/* Terraform these combinations. */
		if (slope1 == SLOPE_FLAT || slope2 == SLOPE_FLAT) {
			/* Mark the tile as already cleared for the terraform command.
			 * Do this for all tiles (like trees), not only objects. */
			ClearedObjectArea *coa = FindClearedObject(slope1 == SLOPE_FLAT ? tile2 : tile);
			if (coa == NULL) {
				coa = _cleared_object_areas.Append();
				coa->first_tile = slope1 == SLOPE_FLAT ? tile2 : tile;
				coa->area = TileArea(tile, axis == AXIS_X ? 2 : 1, axis == AXIS_Y ? 2 : 1);
			}
			/* Hide the tile from the terraforming command */
			TileIndex tile_flat_before = coa->first_tile;
			coa->first_tile = INVALID_TILE;
			ret = DoCommand(slope1 == SLOPE_FLAT ? tile2 : tile, slope1 == SLOPE_FLAT ? z_slope1 == z_slope2 ? slope2: ComplementSlope(slope2) : z_slope1 == z_slope2 ? slope1 : ComplementSlope(slope1), z_slope1 == z_slope2 ? 0 : 1, flags | DC_NO_WATER, CMD_TERRAFORM_LAND);
			coa->first_tile = tile_flat_before;
			if (ret.Failed()) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
			cost.AddCost(ret);
		} else {
			if ((IsSlopeWithThreeCornersRaised(slope1) || IsSlopeWithOneCornerRaised(slope1)) && (IsSlopeWithThreeCornersRaised(slope2) || IsSlopeWithOneCornerRaised(slope2))) {
				/* Mark the tile as already cleared for the terraform command.
				 * Do this for all tiles (like trees), not only objects. */
				ClearedObjectArea *coa = FindClearedObject(tile);
				if (coa == NULL) {
					coa = _cleared_object_areas.Append();
					coa->first_tile = tile;
					coa->area = TileArea(tile, axis == AXIS_X ? 2 : 1, axis == AXIS_Y ? 2 : 1);
				}
				/* Hide the tile from the terraforming command */
				TileIndex tile_3corner1_before = coa->first_tile;
				coa->first_tile = INVALID_TILE;
				ret = DoCommand(tile, IsSlopeWithThreeCornersRaised(slope1) ? ComplementSlope(slope1) : slope1, IsSlopeWithThreeCornersRaised(slope1) ? 1 : 0, flags | DC_NO_WATER, CMD_TERRAFORM_LAND);
				coa->first_tile = tile_3corner1_before;
				if (ret.Failed()) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
				cost.AddCost(ret);
				if (z_middle_corner_n == z_middle_corner_s) {
					/* Mark the tile as already cleared for the terraform command.
					 * Do this for all tiles (like trees), not only objects. */
					ClearedObjectArea *coa = FindClearedObject(tile2);
					if (coa == NULL) {
						coa = _cleared_object_areas.Append();
						coa->first_tile = tile2;
						coa->area = TileArea(tile, axis == AXIS_X ? 2 : 1, axis == AXIS_Y ? 2 : 1);
					}
					/* Hide the tile from the terraforming command */
					TileIndex tile_3corner2_before = coa->first_tile;
					coa->first_tile = INVALID_TILE;
					ret = DoCommand(tile2, IsSlopeWithThreeCornersRaised(slope2) ? ComplementSlope(slope2) : slope2, IsSlopeWithThreeCornersRaised(slope2) ? 1 : 0, flags | DC_NO_WATER, CMD_TERRAFORM_LAND);
					coa->first_tile = tile_3corner2_before;
					if (ret.Failed()) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
					cost.AddCost(ret);
				}
			} else {
				if ((IsInclinedSlope(slope1) && DiagDirToAxis(GetInclinedSlopeDirection(slope1)) == OtherAxis(axis) && (IsSlopeWithOneCornerRaised(slope2) || IsSlopeWithThreeCornersRaised(slope2))) || (IsInclinedSlope(slope2) && DiagDirToAxis(GetInclinedSlopeDirection(slope2)) == OtherAxis(axis) && (IsSlopeWithOneCornerRaised(slope1) || IsSlopeWithThreeCornersRaised(slope1)))) {
					/* Mark the tile as already cleared for the terraform command.
					 * Do this for all tiles (like trees), not only objects. */
					ClearedObjectArea *coa = FindClearedObject(IsInclinedSlope(slope1) ? tile : tile2);
					if (coa == NULL) {
						coa = _cleared_object_areas.Append();
						coa->first_tile = IsInclinedSlope(slope1) ? tile : tile2;
						coa->area = TileArea(tile, axis == AXIS_X ? 2 : 1, axis == AXIS_Y ? 2 : 1);
					}
					/* Hide the tile from the terraforming command */
					TileIndex tile_inclined1_before = coa->first_tile;
					coa->first_tile = INVALID_TILE;
					ret = DoCommand(IsInclinedSlope(slope1) ? tile : tile2, IsInclinedSlope(slope1) ? IsSlopeWithThreeCornersRaised(slope2) ? ComplementSlope(slope1) : slope1 : IsSlopeWithThreeCornersRaised(slope1) ? ComplementSlope(slope2) : slope2, IsInclinedSlope(slope1) ? IsSlopeWithThreeCornersRaised(slope2) ? 1 : 0 : IsSlopeWithThreeCornersRaised(slope1) ? 1 : 0, flags | DC_NO_WATER, CMD_TERRAFORM_LAND);
					coa->first_tile = tile_inclined1_before;
					if (ret.Failed()) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
					cost.AddCost(ret);
				} else {
					if ((slope1 == SLOPE_EW || slope1 == SLOPE_NS) && (IsSlopeWithOneCornerRaised(slope2) || IsSlopeWithThreeCornersRaised(slope2)) || (slope2 == SLOPE_NS || slope2 == SLOPE_EW) && (IsSlopeWithOneCornerRaised(slope1) || IsSlopeWithThreeCornersRaised(slope1))) {
						/* Mark the tile as already cleared for the terraform command.
						 * Do this for all tiles (like trees), not only objects. */
						ClearedObjectArea *coa = FindClearedObject((slope1 == SLOPE_EW || slope1 == SLOPE_NS) ? tile : tile2);
						if (coa == NULL) {
							coa = _cleared_object_areas.Append();
							coa->first_tile = (slope1 == SLOPE_EW || slope1 == SLOPE_NS) ? tile : tile2;
							coa->area = TileArea(tile, axis == AXIS_X ? 2 : 1, axis == AXIS_Y ? 2 : 1);
						}
						/* Hide the tile from the terraforming command */
						TileIndex tile_oppositecorners_before = coa->first_tile;
						coa->first_tile = INVALID_TILE;
						ret = DoCommand((slope1 == SLOPE_EW || slope1 == SLOPE_NS) ? tile : tile2, (slope1 == SLOPE_EW || slope1 == SLOPE_NS) ? IsSlopeWithOneCornerRaised(slope2) ? slope1 : ComplementSlope(slope1) : IsSlopeWithOneCornerRaised(slope1) ? slope2 : ComplementSlope(slope2), (slope1 == SLOPE_EW || slope1 == SLOPE_NS) ? IsSlopeWithOneCornerRaised(slope2) ? 0 : 1 : IsSlopeWithOneCornerRaised(slope1) ? 0 : 1, flags | DC_NO_WATER, CMD_TERRAFORM_LAND);
						coa->first_tile = tile_oppositecorners_before;
						if (ret.Failed()) return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
						cost.AddCost(ret);
					} else {
						/* Shouldn't reach here. */
						assert(false);
					}
				}
			}
		}
	}

	if (flags & DC_EXEC) {
		Depot *depot = new Depot(tile);
		depot->build_date = _date;

		if (add_cost1 && wc1 == WATER_CLASS_CANAL) Company::Get(_current_company)->infrastructure.water++;
		if (add_cost2 && wc2 == WATER_CLASS_CANAL) Company::Get(_current_company)->infrastructure.water++;
		Company::Get(_current_company)->infrastructure.water += 2 * LOCK_DEPOT_TILE_FACTOR;
		DirtyCompanyInfrastructureWindows(_current_company);

		MakeShipDepot(tile, _current_company, oc1, depot->index, DEPOT_PART_NORTH, axis, wc1);
		MakeShipDepot(tile2, _current_company, oc2, depot->index, DEPOT_PART_SOUTH, axis, wc2);
		MarkTileDirtyByTile(tile);
		MarkTileDirtyByTile(tile2);
		MakeDefaultName(depot);
	}

	return cost;
}