// 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'];

  function handleCookieProperty(property) {
    var length = buf.unpack('n', offset)[0];
    offset += 2;
    cookie[property] = buf.unpackString(length, offset);
    offset += length;
  }

  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.unpack('n')[0];
    if (!typeToName[cookie.type]) {
      console.warn('Unknown address type');
    }
    offset += 2;
    //JSHint becomes angry when handleCookieProperty is declared inside loop
    cookieProperties.forEach(handleCookieProperty);
    auth.push(cookie);
  }
  return auth;
}

module.exports = function(display, host, cb) {
  var XAuthorityFile = process.env.XAUTHORITY;
  if (!XAuthorityFile) {
    if (process.platform.match(/^win/)) {
      // http://www.straightrunning.com/XmingNotes/trouble.php
      //
      // The Xming magic cookie program, xauth (user-based), uses an
      // Xauthority file (not the traditional .Xauthority file) in
      // the %HOME% directory. To use xauth from Command Processor
      // e.g. on Windows machine 192.168.0.2 with user colin...
      XAuthorityFile = process.env.USERPROFILE + '\\Xauthority';
    } else {
      XAuthorityFile = process.env.HOME + '/.Xauthority';
    }
  }

  fs.readFile(XAuthorityFile, function(err, data) {

    if (err) {
      if (err.code == 'ENOENT') {
        cb('', '');
        return;
      }
      throw err;
    }

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