Geo3x3.dart

class Geo3x3 {
	static String encode(num lat, num lng, num level) {
		if (level < 1) {
			return "";
		}
		var res = "";
		var lng2 = lng;
		if (lng >= 0) {
			res = "E";
		} else {
			res = "W";
			lng2 += 180;
		}
		var lat2 = 90 - lat; // 0:the North Pole,  180:the South Pole
		var unit = 180.0;
		for (int i = 1; i < level; i++) {
			unit /= 3;
			final x = (lng2 / unit).toInt();
			final y = (lat2 / unit).toInt();
			res += (x + y * 3 + 1).toString();
			lng2 -= x * unit;
			lat2 -= y * unit;
		}
		return res;
	}
	static List decode(String code) {
		var unit = 180.0;
		var lat = 0.0;
		var lng = 0.0;
		var level = 1;

		var begin = 0;
		var flg = false;
		var c = code[0];
		if (c == '-' || c == 'W') {
			flg = true;
			begin = 1;
		} else if (c == '+' || c == 'E') {
			begin = 1;
		}
		final clen = code.length;
		for (int i = begin; i < clen; i++) {
			var n = "0123456789".indexOf(code[i]);
			if (n <= 0)
				break;
			unit /= 3;
			n--;
			lng += n % 3 * unit;
			lat += (n / 3).toInt() * unit;
			level++;
		}
		lat += unit / 2;
		lng += unit / 2;
		lat = 90 - lat;
		if (flg)
			lng -= 180.0;
		return [lat, lng, level.toDouble(), unit];
	}
}