/**
 * Ensure this tile is not a target for ships to get to a nearby dock.
 * @note Also takes into account Oil Rigs, even those under construction.
 * @param tile Tile to query
 * @param diagdir Optional diagonal direction to look for axis compatibility.
 * @return Succeeded if the tile is not a ship docking area of a nearby dock,
 *         or an error message if the tile is a ship docking area of a nearby
           dock.
 * @note If the axis of a provided diagdir is equal to the axis of a nearby
 *       docking area, it returns Succeeded. If diagdir is not provided, only
 *       the docking area location is ensured.
 */
static CommandCost EnsureNoDockingTile(TileIndex tile, DiagDirection diagdir = INVALID_DIAGDIR)
{
	Axis axis = diagdir == INVALID_DIAGDIR ? INVALID_AXIS : DiagDirToAxis(diagdir);

	for (DiagDirection rot = DIAGDIR_BEGIN; rot < DIAGDIR_END; rot++) {
		TileIndex tc = TileAddByDiagDir(tile, rot);
		if (IsTileType(tc, MP_STATION) && (IsDock(tc) || IsOilRig(tc))) {
			Station *dock = Station::GetByTile(tc);
			TileIndex docking_location = TILE_ADD(dock->dock_tile, ToTileIndexDiff(GetDockOffset(dock->dock_tile)));
			if (axis == INVALID_AXIS) {
				return_cmd_error(STR_ERROR_TOO_CLOSE_TO_ANOTHER_DOCK);
			} else {
				if (tile == docking_location) {
					Axis axis_tc = DiagDirToAxis(rot);
					if (axis != axis_tc) {
						return_cmd_error(STR_ERROR_TOO_CLOSE_TO_ANOTHER_DOCK);
					}
				}
			}
		}
		if (axis != AXIS_X && DiagDirToAxis(rot) == AXIS_X) {
			if (IsTileType(tc + TileDiffXY(-1, 0), MP_INDUSTRY) && GetIndustryGfx(tc + TileDiffXY(-1, 0)) == GFX_OILRIG_1) {
				return_cmd_error(STR_ERROR_SITE_UNSUITABLE);
			}
		}
	}

	return CommandCost();
}