// TODO: http://en.wikipedia.org/wiki/X_Window_authorization

var fs = require('fs');
var Buffer = require('buffer').Buffer;
// add 'unpack' method for buffer
require('./unpackbuffer').addUnpack(Buffer);

function parseXauth( buf )
{
    var offset = 0;
    var auth = [];
    var cookieProperties = ['address', 'display', 'authName', 'authData'];

    while (offset < buf.length)
    {
        var cookie = {};
        var typeToName = {
            256: 'Local',
          65535: 'Wild',
            254: 'Netname',
            253: 'Krb5Principal',
            252: 'LocalHost',
              0: 'Internet',
              1: 'DECnet',
              2: 'Chaos',
              5: 'ServerInterpreted',
              6: 'InternetV6'
        };
        cookie.type = buf.readUInt16LE(offset);
        console.log('Cookie type: ');
        if (!typeToName[cookie.type]) {
            console.warn('Unknown address type');
        }
        offset += 2;
        cookieProperties.forEach(function(property) {
          var length = buf.unpack('n', offset)[0];
          offset += 2;
          if (cookie.type === 0 && property == 'address') { // Internet
            // 4 bytes of ip addess, convert to w.x.y.z string
            cookie.address = [ buf[offset], buf[offset+1], buf[offset+2], buf[offset+3]]
              .map(function(octet) { return octet.toString(10) }).join('.');
          } else {
            cookie[property] = buf.unpackString(length, offset);
          }
          offset += length;
        });
        auth.push(cookie);
    }
    return auth;
}

var os   = require('os');
var path = require('path');

function readXauthority(cb) {
  var filename = process.env.XAUTHORITY || path.join(os.homedir(), '.Xauthority');
  fs.readFile(filename, function(err, data) {
    if (!err)
      return cb(null, data);
    if(err.code == 'ENOENT') {
      // Xming/windows uses %HOME%/Xauthority ( .Xauthority with no dot ) - try with this name
      filename = process.env.XAUTHORITY || path.join(os.homedir(), 'Xauthority');
      return fs.readFile(filename, cb);
    } else {
      cb(err);
    }
  });
}

module.exports = function( display, host, cb )
{
  readXauthority(function(err, data) {
    if(err) return cb(err);

    var auth = parseXauth(data);
    for (var cookieNum in auth)
    {
      var cookie = auth[cookieNum];
      if (cookie.display === display && cookie.address === host)
        return cb( null, cookie );
    }
    cb(new Error('No auth cookie matching display=' + display + ' and  host=' + host));
  });
};