/**
 * Module dependencies
 */

var debug = require('debug')('jsonp');

/**
 * Module exports.
 */

module.exports = jsonp;

/**
 * Callback index.
 */

var count = 0;

/**
 * Noop function.
 */

function noop(){};

/**
 * JSONP handler
 *
 * Options:
 *  - param {String} qs parameter (`callback`)
 *  - timeout {Number} how long after a timeout error is emitted (`60000`)
 *
 * @param {String} url
 * @param {Object|Function} optional options / callback
 * @param {Function} optional callback
 */

function jsonp(url, opts, fn){
  if ('function' == typeof opts) {
    fn = opts;
    opts = {};
  }

  var opts = opts || {};
  var param = opts.param || 'callback';
  var timeout = null != opts.timeout ? opts.timeout : 60000;
  var enc = encodeURIComponent;
  var target = document.getElementsByTagName('script')[0];
  var script;
  var timer;

  // generate a unique id for this request
  var id = count++;

  if (timeout) {
    timer = setTimeout(function(){
      cleanup();
      fn && fn(new Error('Timeout'));
    }, timeout);
  }

  function cleanup(){
    target.parentNode.removeChild(script);
    window['__jp' + id] = noop;
  }

  window['__jp' + id] = function(data){
    debug('jsonp got', data);
    if (timer) clearTimeout(timer);
    cleanup();
    fn && fn(null, data);
  };

  // add qs component
  url += (~url.indexOf('?') ? '&' : '?') + param + '=' + enc('__jp' + id + '');
  url = url.replace('?&', '?');

  debug('jsonp req "%s"', url);

  // create script
  script = document.createElement('script');
  script.src = url;
  target.parentNode.insertBefore(script, target);
};