Industry placed on a canal logic

industry_cmd.cpp

if (HasTileWaterGround(cur_tile) && GetWaterClass(cur_tile) == WATER_CLASS_CANAL) {
	Owner oc = GetCanalOwner(cur_tile);
	bool is_canal = IsWaterTile(cur_tile);

	 /* We are in one of these two situations:
	 * 1. When prospecting, _current_company is OWNER_TOWN (founder can be company_0-14 / OWNER_DEITY)
	 * 2. When not prospecting, _current_company can be company_0-14 / OWNER_NONE / OWNER_DEITY (founder is equal to _current_company)
	 *
	 * For situation 1:
	 * a) On a clear water canal:
	 * - Allow prospecting on clear water canals in which the founder is the canal owner, or when the canal has no owner, or
	 *   when 'build_on_competitor_canal' is enabled and the canal owner is different than that of the founder.
	 * b) On a clearable object built over the canal:
	 * - Never allow prospecting on objects even if these can be cleared.
	 *
	 * For situation 2:
	 * a) On a clear water canal:
	 * - Allow random and deity creation on clear water canals when 'build_on_competitor_canal' is enabled, or when canal
	 *   has no owner.
	 * - Allow company funded creation on clear water canals in which the funding company is the canal owner, or when the canal
	 *   has no owner, or when 'build_on_competitor_canal' is enabled and the canal owner is different than that of the funding
	 *   company.
	 * b) On a clearable object built over the canal:
	 * - Allow random and deity creation on clearable objects which have no owner, but never on objects which have an owner,
	 *   even if the canal under the object has no owner.
	 * - Allow company funded creation on clearable objects in which the funding company is the object owner. And then, when
	 *   the canal under the object is owned by the funding company, or when 'build_on_competitor_canal' and the canal owner is
	 *   different than that of the funding company.
	 */
	Backup<CompanyID> cur_company(_current_company, is_canal ? founder : _current_company, FILE_LINE);
	ret = Command<CMD_LANDSCAPE_CLEAR>::Do(DC_AUTO | DC_NO_TEST_TOWN_RATING | DC_NO_MODIFY_TOWN_RATING, cur_tile);
	CommandCost ownership = is_canal ? CheckTileOwnership(cur_tile) : CheckOwnership(oc, cur_tile);
	cur_company.Restore();

	if (is_canal) {
		/* This is a clear water canal */
		if (ownership.Failed() && oc != OWNER_NONE &&
			_game_mode != GM_EDITOR && !_settings_game.construction.build_on_competitor_canal) return ownership;
	} else {
		/* This is a station, object, or industry on a canal */
		if (ret.Failed()) return ret;
		if (ownership.Failed() && oc != OWNER_NONE && !_settings_game.construction.build_on_competitor_canal) return ownership;
	}
} else {
	/* Clear the tiles, but do not affect town ratings */
	ret = Command<CMD_LANDSCAPE_CLEAR>::Do(DC_AUTO | DC_NO_TEST_TOWN_RATING | DC_NO_MODIFY_TOWN_RATING, cur_tile);
	if (ret.Failed()) return ret;
}