local noise = AIAirport.GetNoiseLevelIncrease(tile, type);
local allowed_noise = AITown.GetAllowedNoise(AIAirport.GetNearestTown(tile, type));
local old_result = (noise != -1 && allowed_noise != -1 && noise <= allowed_noise);
assert(old_result == AIAirport.IsNoiseLevelIncreaseAllowed(tile, type));


/* static */ int ScriptAirport::GetNoiseLevelIncrease(TileIndex tile, AirportType type)
{
	extern Town *AirportGetNearestTown(const AirportSpec *as, const TileIterator &it, uint &mindist);
	extern uint8 GetAirportNoiseLevelForDistance(const AirportSpec *as, uint distance);

	if (!::IsValidTile(tile)) return -1;
	if (!IsAirportInformationAvailable(type)) return -1;

	const AirportSpec *as = ::AirportSpec::Get(type);
	if (!as->IsWithinMapBounds(0, tile)) return -1;

	if (_settings_game.economy.station_noise_level) {
		AirportTileTableIterator it(as->table[0], tile);
		uint dist;
		AirportGetNearestTown(as, it, dist);
		return GetAirportNoiseLevelForDistance(as, dist);
	}

	return 1;
}

/* static */ TownID ScriptAirport::GetNearestTown(TileIndex tile, AirportType type)
{
	extern Town *AirportGetNearestTown(const AirportSpec *as, const TileIterator &it, uint &mindist);

	if (!::IsValidTile(tile)) return INVALID_TOWN;
	if (!IsAirportInformationAvailable(type)) return INVALID_TOWN;

	const AirportSpec *as = AirportSpec::Get(type);
	if (!as->IsWithinMapBounds(0, tile)) return INVALID_TOWN;

	uint dist;
	return AirportGetNearestTown(as, AirportTileTableIterator(as->table[0], tile), dist)->index;
}

/* static */ int ScriptTown::GetAllowedNoise(TownID town_id)
{
	if (!IsValidTown(town_id)) return -1;

	const Town *t = ::Town::Get(town_id);
	if (_settings_game.economy.station_noise_level) {
		return t->MaxTownNoise() - t->noise_reached;
	}

	int num = 0;
	const Station *st;
	FOR_ALL_STATIONS(st) {
		if (st->town == t && (st->facilities & FACIL_AIRPORT) && st->airport.type != AT_OILRIG) num++;
	}
	return max(0, 2 - num);
}



/* static */ bool ScriptAirport::IsNoiseLevelIncreaseAllowed(TileIndex tile, AirportType type)
{
	extern Town *AirportGetNearestTown(const AirportSpec *as, const TileIterator &it, uint &mindist);
	extern uint8 GetAirportNoiseLevelForDistance(const AirportSpec *as, uint distance);

	if (!::IsValidTile(tile)) return false;
	if (!IsAirportInformationAvailable(type)) return false;

	const AirportSpec *as = ::AirportSpec::Get(type);
	if (!as->IsWithinMapBounds(0, tile)) return false;

	AirportTileTableIterator it(as->table[0], tile);
	uint dist;
	Town *t = AirportGetNearestTown(as, it, dist);
	if (!::Town::IsValidID(t->index)) return false;

	if (_settings_game.economy.station_noise_level) {
		return GetAirportNoiseLevelForDistance(as, dist) <= t->MaxTownNoise() - t->noise_reached;
	}

	int num = 0;
	const Station *st;
	FOR_ALL_STATIONS(st) {
		if (st->town == t && (st->facilities & FACIL_AIRPORT) && st->airport.type != AT_OILRIG) num++;
	}
	return 1 <= max(0, 2 - num);
}