// Geosyl.js – Convert Latitude longitude Pairs to Readable Words.
// based on David Troy's  https://github.com/davetroy/hash-js
// also see: http://www.movable-type.co.uk/scripts/hash.html
// Distributed under the MIT License

geosyl = (function(){

  var bits = [32, 16, 8, 4, 2, 1],
    vocals = 'aeiou'.split(''),
    consonants = 'kgsztdnhfpmyr'.split(''),
    syllables = [];

  vocals.forEach(function(vocal){
    consonants.forEach(function(consonant) {
      syllables.push(consonant + vocal);
    });
  });

  function refine_interval(interval, cd, mask) {
    var mid = (interval[0] + interval[1]) / 2;
    interval[cd & mask ? 0 : 1] = mid;
  }

  return {

    decode: function (hash) {

      hash = hash
        .replace(/\W/g, '')
        .toLowerCase()
        .match(/\w{2}/g);

      var isEven = 1,
        lat = [-90, 90],
        lng = [-180, 180],
        mask,
        part,
        i;

      for (i = 0; i < hash.length; i++) {
        part = hash[i];
        index = syllables.indexOf(part);
        for (j = 0; j < bits.length; j++) {
          mask = bits[j];
          if (isEven) {
            refine_interval(lng, index, mask);
          } else {
            refine_interval(lat, index, mask);
          }
          isEven = !isEven;
        }
      }

      return [lat[0], lng[0], lat[1], lng[1]];
    },

    encode: function(latitude, longitude, precision) {
      var isEven = true,
        lat = [-90, 90],
        lng = [-180, 180],
        bit = 0,
        index = 0,
        hash = [],
        mid;

      precision = precision || 9;

      while (hash.length < precision) {
        if (isEven) {
          mid = (lng[0] + lng[1]) / 2;
          if (longitude > mid) {
            index |= bits[bit];
            lng[0] = mid;
          } else
            lng[1] = mid;
        } else {
          mid = (lat[0] + lat[1]) / 2;
          if (latitude > mid) {
            index |= bits[bit];
            lat[0] = mid;
          } else
            lat[1] = mid;
        }

        isEven = !isEven;

        if (bit < bits.length-1) {
          bit++;
        } else {
          hash.push(syllables[index]);
          bit = 0;
          index = 0;
        }
      }
      return hash.map(function(syllable, index) {
        return syllable + ((
          index % 3 == 2 &&
          index < hash.length - 1
        ) ? ' ' : '');
      }).join('');
    }
  }
})();

var lat = 51.5,
  lng = 10,
  hash = geosyl.encode(lat, lng),
  bounds = geosyl.decode(hash);

console.log(lat, lng);
console.log(hash);
console.log(bounds);

console.log(Math.abs(bounds[0] - lat))
console.log(Math.abs(bounds[1] - lng))