// see https://github.com/splendeo/jquery.observe_field

(function($) {
  'use strict';

  $.fn.live_observe_field = function(frequency, callback) {

    frequency = frequency * 100; // translate to milliseconds

    return this.each(function() {
      var $this = $(this);
      var prev = $this.val();
      var prevChecked = $this.prop('checked');

      var check = function() {
        if (removed()) {
          // if removed clear the interval and don't fire the callback
          if (ti)
            clearInterval(ti);
          return;
        }

        var val = $this.val();
        var checked = $this.prop('checked');
        if (prev != val || checked != prevChecked) {
          prev = val;
          prevChecked = checked;
          $this.map(callback); // invokes the callback on $this
        }
      };

      var removed = function() {
        return $this.closest('html').length == 0;
      };

      var reset = function() {
        if (ti) {
          clearInterval(ti);
          ti = setInterval(check, frequency);
        }
      };

      check();
      var ti = setInterval(check, frequency); // invoke check periodically

      // reset counter after user interaction
      $this.bind('keyup click mousemove', reset); // mousemove is for selects
    });

  };

})(jQuery);