+function ($) {
  'use strict';

  var now = Date.now || function () { return new Date().getTime(); };

  // Returns a function, that, as long as it continues to be invoked, will not
  // be triggered. The function will be called after it stops being called for
  // `wait` msec.
  //
  // This utility function was originally implemented at Underscore.js.
  var debounce = function (func, wait) {
    var timeout, args, context, timestamp, result;
    var later = function () {
      var last = now() - timestamp;
      if (last < wait) {
        timeout = setTimeout(later, wait - last);
      } else {
        timeout = null;
        result = func.apply(context, args);
        context = args = null;
      }
    };

    return function () {
      context = this;
      args = arguments;
      timestamp = now();
      if (!timeout) {
        timeout = setTimeout(later, wait);
      }
      return result;
    };
  };

  function Adapter () {}

  $.extend(Adapter.prototype, {
    // Public properties
    // -----------------

    id:        null, // Identity.
    completer: null, // Completer object which creates it.
    el:        null, // Textarea element.
    $el:       null, // jQuery object of the textarea.
    option:    null,

    // Public methods
    // --------------

    initialize: function (element, completer, option) {
      this.el        = element;
      this.$el       = $(element);
      this.id        = completer.id + this.constructor.name;
      this.completer = completer;
      this.option    = option;

      if (this.option.debounce) {
        this._onKeyup = debounce(this._onKeyup, this.option.debounce);
      }

      this._bindEvents();
    },

    destroy: function () {
      this.$el.off('.' + this.id); // Remove all event handlers.
      this.$el = this.el = this.completer = null;
    },

    // Update the element with the given value and strategy.
    //
    // value    - The selected object. It is one of the item of the array
    //            which was callbacked from the search function.
    // strategy - The Strategy associated with the selected value.
    select: function (/* value, strategy */) {
      throw new Error('Not implemented');
    },

    // Returns the caret's relative coordinates from body's left top corner.
    getCaretPosition: function () {
      var position = this._getCaretRelativePosition();
      var offset = this.$el.offset();

      // Calculate the left top corner of `this.option.appendTo` element.
      var $parent = this.option.appendTo;
      if ($parent) {
         if (!($parent instanceof $)) { $parent = $($parent); }
         var parentOffset = $parent.offsetParent().offset();
         offset.top -= parentOffset.top;
         offset.left -= parentOffset.left;
      }

      position.top += offset.top;
      position.left += offset.left;
      return position;
    },

    // Focus on the element.
    focus: function () {
      this.$el.focus();
    },

    // Private methods
    // ---------------

    _bindEvents: function () {
      this.$el.on('keyup.' + this.id, $.proxy(this._onKeyup, this));
    },

    _onKeyup: function (e) {
      if (this._skipSearch(e)) { return; }
      this.completer.trigger(this.getTextFromHeadToCaret(), true);
    },

    // Suppress searching if it returns true.
    _skipSearch: function (clickEvent) {
      switch (clickEvent.keyCode) {
        case 9:  // TAB
        case 13: // ENTER
        case 40: // DOWN
        case 38: // UP
          return true;
      }
      if (clickEvent.ctrlKey) switch (clickEvent.keyCode) {
        case 78: // Ctrl-N
        case 80: // Ctrl-P
          return true;
      }
    }
  });

  $.fn.textcomplete.Adapter = Adapter;
}(jQuery);