// geohash.js
// Geohash library for Javascript
// (c) 2008 David Troy
// Distributed under the MIT License

BITS = [16, 8, 4, 2, 1];

BASE32 =                         "0123456789bcdefghjkmnpqrstuvwxyz";

NEIGHBORS = { right  : { even :  "bc01fg45238967deuvhjyznpkmstqrwx" },
              left   : { even :  "238967debc01fg45kmstqrwxuvhjyznp" },
              top    : { even :  "p0r21436x8zb9dcf5h7kjnmqesgutwvy" },
              bottom : { even :  "14365h7k9dcfesgujnmqp0r2twvyx8zb" } };
BORDERS   = { right  : { even : "bcfguvyz" },
              left   : { even : "0145hjnp" },
              top    : { even : "prxz" },
              bottom : { even : "028b" } };

NEIGHBORS.bottom.odd = NEIGHBORS.left.even;
NEIGHBORS.top.odd = NEIGHBORS.right.even;
NEIGHBORS.left.odd = NEIGHBORS.bottom.even;
NEIGHBORS.right.odd = NEIGHBORS.top.even;

BORDERS.bottom.odd = BORDERS.left.even;
BORDERS.top.odd = BORDERS.right.even;
BORDERS.left.odd = BORDERS.bottom.even;
BORDERS.right.odd = BORDERS.top.even;

function refine_interval(interval, cd, mask) {
  if (cd&mask)
    interval[0] = (interval[0] + interval[1])/2;
  else
    interval[1] = (interval[0] + interval[1])/2;
}

function calculateAdjacent(srcHash, dir) {
  srcHash = srcHash.toLowerCase();
  var lastChr = srcHash.charAt(srcHash.length-1);
  var type = (srcHash.length % 2) ? 'odd' : 'even';
  var base = srcHash.substring(0,srcHash.length-1);
  if (BORDERS[dir][type].indexOf(lastChr)!=-1)
    base = calculateAdjacent(base, dir);
  return base + BASE32.substr(NEIGHBORS[dir][type].indexOf(lastChr), 1);
}

function decodeGeoHash(geohash) {
  var is_even = 1;
  var lat = []; var lon = [];
  lat[0] = -90.0;  lat[1] = 90.0;
  lon[0] = -180.0; lon[1] = 180.0;
  lat_err = 90.0;  lon_err = 180.0;

  for (i=0; i<geohash.length; i++) {
    c = geohash.substr(i,1);
    cd = BASE32.indexOf(c);
    for (j=0; j<5; j++) {
      mask = BITS[j];
      if (is_even) {
        lon_err /= 2;
        refine_interval(lon, cd, mask);
      } else {
        lat_err /= 2;
        refine_interval(lat, cd, mask);
      }
      is_even = !is_even;
    }
  }
  lat[2] = (lat[0] + lat[1])/2;
  lon[2] = (lon[0] + lon[1])/2;

  return { latitude: lat, longitude: lon};
}

function encodeGeoHash(latitude, longitude) {
  var is_even=1;
  var i=0;
  var lat = []; var lon = [];
  var bit=0;
  var ch=0;
  var precision = 12;
  geohash = "";

  lat[0] = -90.0;  lat[1] = 90.0;
  lon[0] = -180.0; lon[1] = 180.0;
  
  while (geohash.length < precision) {
    if (is_even) {
      mid = (lon[0] + lon[1]) / 2;
      if (longitude > mid) {
        ch |= BITS[bit];
        lon[0] = mid;
      } else
        lon[1] = mid;
    } else {
      mid = (lat[0] + lat[1]) / 2;
      if (latitude > mid) {
        ch |= BITS[bit];
        lat[0] = mid;
      } else
        lat[1] = mid;
    }

    is_even = !is_even;
    if (bit < 4)
      bit++;
    else {
      geohash += BASE32.substr(ch,1);
      bit = 0;
      ch = 0;
    }
  }
  return geohash;
}