static CommandCost DoBuildLock(TileIndex tile, DiagDirection dir, DoCommandFlag flags)
{
	CommandCost cost(EXPENSES_CONSTRUCTION);

	int delta = TileOffsByDiagDir(dir);
	CommandCost ret = EnsureNoVehicleOnGround(tile);
	if (ret.Succeeded()) ret = EnsureNoVehicleOnGround(tile + delta);
	if (ret.Succeeded()) ret = EnsureNoVehicleOnGround(tile - delta);
	if (ret.Failed()) return ret;

	/* middle tile */
	WaterClass wc_middle = IsWaterTile(tile) ? GetWaterClass(tile) : WATER_CLASS_CANAL;
	ret = DoCommand(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
	if (ret.Failed()) return ret;
	cost.AddCost(ret);

	/* lower tile */
	WaterClass wc_lower = IsWaterTile(tile - delta) ? GetWaterClass(tile - delta) : WATER_CLASS_CANAL;

	if (!IsWaterTile(tile - delta)) {
		ret = DoCommand(tile - delta, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
		if (ret.Failed()) return ret;
		cost.AddCost(ret);
		cost.AddCost(_price[PR_BUILD_CANAL]);
	}
	if (!IsTileFlat(tile - delta)) {
		return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
	}

	/* upper tile */
	WaterClass wc_upper = IsWaterTile(tile + delta) ? GetWaterClass(tile + delta) : WATER_CLASS_CANAL;

	if (!IsWaterTile(tile + delta)) {
		ret = DoCommand(tile + delta, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
		if (ret.Failed()) return ret;
		cost.AddCost(ret);
		cost.AddCost(_price[PR_BUILD_CANAL]);
	}
	if (!IsTileFlat(tile + delta)) {
		return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
	}

	if (IsBridgeAbove(tile) || IsBridgeAbove(tile - delta) || IsBridgeAbove(tile + delta)) {
		return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
	}

	if (flags & DC_EXEC) {
		/* Update company infrastructure counts. */
		Company *c = Company::GetIfValid(_current_company);
		if (c != NULL) {
			/* Counts for the water. */
			if (!IsWaterTile(tile - delta)) c->infrastructure.water++;
			if (!IsWaterTile(tile + delta)) c->infrastructure.water++;
			/* Count for the lock itself. */
			c->infrastructure.water += 3 * LOCK_DEPOT_TILE_FACTOR; // Lock is three tiles.
			DirtyCompanyInfrastructureWindows(_current_company);
		}

		MakeLock(tile, _current_company, dir, wc_lower, wc_upper, wc_middle);
		MarkTileDirtyByTile(tile);
		MarkTileDirtyByTile(tile - delta);
		MarkTileDirtyByTile(tile + delta);
		MarkCanalsAndRiversAroundDirty(tile - delta);
		MarkCanalsAndRiversAroundDirty(tile + delta);
	}
	cost.AddCost(_price[PR_BUILD_LOCK]);

	return cost;
}