import _debug from 'debug';
import { nanoid } from 'nanoid';

let count = 0;
const noop = () => {};
const debug = _debug('jsonp');

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

export default (url, opts, fn) => {
  if ('function' == typeof opts) {
    fn = opts;
    opts = {};
  }

  const _root: any = window;

  if (!opts) opts = {};

  var prefix = opts.prefix || '__jp';

  // use the callback name that was passed if one was provided.
  // otherwise generate a unique name by incrementing our counter.
  var id = opts.name || prefix + nanoid(3) + count++;

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

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

  function cleanup() {
    if (script.parentNode) script.parentNode.removeChild(script);
    _root[id] = noop;
    if (timer) clearTimeout(timer);
  }

  function cancel() {
    if (_root[id]) {
      cleanup();
    }
  }

  _root[id] = function (data) {
    debug('jsonp got', data);
    cleanup();
    if (fn) fn(null, data);
  };

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

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

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

  return cancel;
};