  var HANDLERS = {};
  /* The state of the current 'pointer'
   * The pointer represents the state of the current touch.
   * It contains normalized x and y coordinates from DOM events,
   * as well as other information abstracted from the DOM.
   */
  var pointer, lastPointer, forceSkipClickHijack = false;

  /**
   * The position of the most recent click if that click was on a label element.
   * @type {{x: number, y: number}?}
   */
  var lastLabelClickPos = null;

  // Used to attach event listeners once when multiple ng-apps are running.
  var isInitialized = false;
  
  angular
    .module('material.core.gestures', [ ])
    .provider('$mdGesture', MdGestureProvider)
    .factory('$$MdGestureHandler', MdGestureHandler)
    .run( attachToDocument );

  /**
     * @ngdoc service
     * @name $mdGestureProvider
     * @module material.core.gestures
     *
     * @description
     * In some scenarios on Mobile devices (without jQuery), the click events should NOT be hijacked.
     * `$mdGestureProvider` is used to configure the Gesture module to ignore or skip click hijacking on mobile
     * devices.
     *
     * <hljs lang="js">
     *   app.config(function($mdGestureProvider) {
     *
     *     // For mobile devices without jQuery loaded, do not
     *     // intercept click events during the capture phase.
     *     $mdGestureProvider.skipClickHijack();
     *
     *   });
     * </hljs>
     *
     */
  function MdGestureProvider() { }

  MdGestureProvider.prototype = {

    // Publish access to setter to configure a variable  BEFORE the
    // $mdGesture service is instantiated...
    skipClickHijack: function() {
      return forceSkipClickHijack = true;
    },

    /**
     * $get is used to build an instance of $mdGesture
     * @ngInject
     */
    $get : function($$MdGestureHandler, $$rAF, $timeout) {
         return new MdGesture($$MdGestureHandler, $$rAF, $timeout);
    }
  };



  /**
   * MdGesture factory construction function
   * @ngInject
   */
  function MdGesture($$MdGestureHandler, $$rAF, $timeout) {
    var userAgent = navigator.userAgent || navigator.vendor || window.opera;
    var isIos = userAgent.match(/ipad|iphone|ipod/i);
    var isAndroid = userAgent.match(/android/i);
    var hasJQuery =  (typeof window.jQuery !== 'undefined') && (angular.element === window.jQuery);

    var self = {
      handler: addHandler,
      register: register,
      // On mobile w/out jQuery, we normally intercept clicks. Should we skip that?
      isHijackingClicks: (isIos || isAndroid) && !hasJQuery && !forceSkipClickHijack
    };

    if (self.isHijackingClicks) {
      self.handler('click', {
        options: {
          maxDistance: 6
        },
        onEnd: function (ev, pointer) {
          if (pointer.distance < this.state.options.maxDistance) {
            this.dispatchEvent(ev, 'click');
          }
        }
      });
    }

    /*
     * Register an element to listen for a handler.
     * This allows an element to override the default options for a handler.
     * Additionally, some handlers like drag and hold only dispatch events if
     * the domEvent happens inside an element that's registered to listen for these events.
     *
     * @see GestureHandler for how overriding of default options works.
     * @example $mdGesture.register(myElement, 'drag', { minDistance: 20, horziontal: false })
     */
    function register(element, handlerName, options) {
      var handler = HANDLERS[handlerName.replace(/^\$md./, '')];
      if (!handler) {
        throw new Error('Failed to register element with handler ' + handlerName + '. ' +
        'Available handlers: ' + Object.keys(HANDLERS).join(', '));
      }
      return handler.registerElement(element, options);
    }

    /*
     * add a handler to $mdGesture. see below.
     */
    function addHandler(name, definition) {
      var handler = new $$MdGestureHandler(name);
      angular.extend(handler, definition);
      HANDLERS[name] = handler;

      return self;
    }

    /*
     * Register handlers. These listen to touch/start/move events, interpret them,
     * and dispatch gesture events depending on options & conditions. These are all
     * instances of GestureHandler.
     * @see GestureHandler 
     */
    return self
      /*
       * The press handler dispatches an event on touchdown/touchend.
       * It's a simple abstraction of touch/mouse/pointer start and end.
       */
      .handler('press', {
        onStart: function (ev, pointer) {
          this.dispatchEvent(ev, '$md.pressdown');
        },
        onEnd: function (ev, pointer) {
          this.dispatchEvent(ev, '$md.pressup');
        }
      })

      /*
       * The hold handler dispatches an event if the user keeps their finger within
       * the same <maxDistance> area for <delay> ms.
       * The hold handler will only run if a parent of the touch target is registered
       * to listen for hold events through $mdGesture.register()
       */
      .handler('hold', {
        options: {
          maxDistance: 6,
          delay: 500
        },
        onCancel: function () {
          $timeout.cancel(this.state.timeout);
        },
        onStart: function (ev, pointer) {
          // For hold, require a parent to be registered with $mdGesture.register()
          // Because we prevent scroll events, this is necessary.
          if (!this.state.registeredParent) return this.cancel();

          this.state.pos = {x: pointer.x, y: pointer.y};
          this.state.timeout = $timeout(angular.bind(this, function holdDelayFn() {
            this.dispatchEvent(ev, '$md.hold');
            this.cancel(); //we're done!
          }), this.state.options.delay, false);
        },
        onMove: function (ev, pointer) {
          // Don't scroll while waiting for hold.
          // If we don't preventDefault touchmove events here, Android will assume we don't
          // want to listen to anymore touch events. It will start scrolling and stop sending
          // touchmove events.
          ev.preventDefault();

          // If the user moves greater than <maxDistance> pixels, stop the hold timer
          // set in onStart
          var dx = this.state.pos.x - pointer.x;
          var dy = this.state.pos.y - pointer.y;
          if (Math.sqrt(dx * dx + dy * dy) > this.options.maxDistance) {
            this.cancel();
          }
        },
        onEnd: function () {
          this.onCancel();
        }
      })

      /*
       * The drag handler dispatches a drag event if the user holds and moves his finger greater than
       * <minDistance> px in the x or y direction, depending on options.horizontal.
       * The drag will be cancelled if the user moves his finger greater than <minDistance>*<cancelMultiplier> in
       * the perpindicular direction. Eg if the drag is horizontal and the user moves his finger <minDistance>*<cancelMultiplier>
       * pixels vertically, this handler won't consider the move part of a drag.
       */
      .handler('drag', {
        options: {
          minDistance: 6,
          horizontal: true,
          cancelMultiplier: 1.5
        },
        onStart: function (ev) {
          // For drag, require a parent to be registered with $mdGesture.register()
          if (!this.state.registeredParent) this.cancel();
        },
        onMove: function (ev, pointer) {
          var shouldStartDrag, shouldCancel;
          // Don't scroll while deciding if this touchmove qualifies as a drag event.
          // If we don't preventDefault touchmove events here, Android will assume we don't
          // want to listen to anymore touch events. It will start scrolling and stop sending
          // touchmove events.
          ev.preventDefault();

          if (!this.state.dragPointer) {
            if (this.state.options.horizontal) {
              shouldStartDrag = Math.abs(pointer.distanceX) > this.state.options.minDistance;
              shouldCancel = Math.abs(pointer.distanceY) > this.state.options.minDistance * this.state.options.cancelMultiplier;
            } else {
              shouldStartDrag = Math.abs(pointer.distanceY) > this.state.options.minDistance;
              shouldCancel = Math.abs(pointer.distanceX) > this.state.options.minDistance * this.state.options.cancelMultiplier;
            }

            if (shouldStartDrag) {
              // Create a new pointer representing this drag, starting at this point where the drag started.
              this.state.dragPointer = makeStartPointer(ev);
              updatePointerState(ev, this.state.dragPointer);
              this.dispatchEvent(ev, '$md.dragstart', this.state.dragPointer);

            } else if (shouldCancel) {
              this.cancel();
            }
          } else {
            this.dispatchDragMove(ev);
          }
        },
        // Only dispatch dragmove events every frame; any more is unnecessray
        dispatchDragMove: $$rAF.throttle(function (ev) {
          // Make sure the drag didn't stop while waiting for the next frame
          if (this.state.isRunning) {
            updatePointerState(ev, this.state.dragPointer);
            this.dispatchEvent(ev, '$md.drag', this.state.dragPointer);
          }
        }),
        onEnd: function (ev, pointer) {
          if (this.state.dragPointer) {
            updatePointerState(ev, this.state.dragPointer);
            this.dispatchEvent(ev, '$md.dragend', this.state.dragPointer);
          }
        }
      })

      /*
       * The swipe handler will dispatch a swipe event if, on the end of a touch,
       * the velocity and distance were high enough.
       * TODO: add vertical swiping with a `horizontal` option similar to the drag handler.
       */
      .handler('swipe', {
        options: {
          minVelocity: 0.65,
          minDistance: 10
        },
        onEnd: function (ev, pointer) {
          if (Math.abs(pointer.velocityX) > this.state.options.minVelocity &&
            Math.abs(pointer.distanceX) > this.state.options.minDistance) {
            var eventType = pointer.directionX == 'left' ? '$md.swipeleft' : '$md.swiperight';
            this.dispatchEvent(ev, eventType);
          }
        }
      });

  }

  /**
   * MdGestureHandler
   * A GestureHandler is an object which is able to dispatch custom dom events
   * based on native dom {touch,pointer,mouse}{start,move,end} events.
   *
   * A gesture will manage its lifecycle through the start,move,end, and cancel
   * functions, which are called by native dom events.
   *
   * A gesture has the concept of 'options' (eg a swipe's required velocity), which can be
   * overridden by elements registering through $mdGesture.register()
   */
  function GestureHandler (name) {
    this.name = name;
    this.state = {};
  }

  function MdGestureHandler() {
    var hasJQuery =  (typeof window.jQuery !== 'undefined') && (angular.element === window.jQuery);

    GestureHandler.prototype = {
      options: {},
      // jQuery listeners don't work with custom DOMEvents, so we have to dispatch events
      // differently when jQuery is loaded
      dispatchEvent: hasJQuery ?  jQueryDispatchEvent : nativeDispatchEvent,

      // These are overridden by the registered handler
      onStart: angular.noop,
      onMove: angular.noop,
      onEnd: angular.noop,
      onCancel: angular.noop,

      // onStart sets up a new state for the handler, which includes options from the
      // nearest registered parent element of ev.target.
      start: function (ev, pointer) {
        if (this.state.isRunning) return;
        var parentTarget = this.getNearestParent(ev.target);
        // Get the options from the nearest registered parent
        var parentTargetOptions = parentTarget && parentTarget.$mdGesture[this.name] || {};

        this.state = {
          isRunning: true,
          // Override the default options with the nearest registered parent's options
          options: angular.extend({}, this.options, parentTargetOptions),
          // Pass in the registered parent node to the state so the onStart listener can use
          registeredParent: parentTarget
        };
        this.onStart(ev, pointer);
      },
      move: function (ev, pointer) {
        if (!this.state.isRunning) return;
        this.onMove(ev, pointer);
      },
      end: function (ev, pointer) {
        if (!this.state.isRunning) return;
        this.onEnd(ev, pointer);
        this.state.isRunning = false;
      },
      cancel: function (ev, pointer) {
        this.onCancel(ev, pointer);
        this.state = {};
      },

      // Find and return the nearest parent element that has been registered to
      // listen for this handler via $mdGesture.register(element, 'handlerName').
      getNearestParent: function (node) {
        var current = node;
        while (current) {
          if ((current.$mdGesture || {})[this.name]) {
            return current;
          }
          current = current.parentNode;
        }
        return null;
      },

      // Called from $mdGesture.register when an element reigsters itself with a handler.
      // Store the options the user gave on the DOMElement itself. These options will
      // be retrieved with getNearestParent when the handler starts.
      registerElement: function (element, options) {
        var self = this;
        element[0].$mdGesture = element[0].$mdGesture || {};
        element[0].$mdGesture[this.name] = options || {};
        element.on('$destroy', onDestroy);

        return onDestroy;

        function onDestroy() {
          delete element[0].$mdGesture[self.name];
          element.off('$destroy', onDestroy);
        }
      }
    };

    return GestureHandler;

    /*
     * Dispatch an event with jQuery
     * TODO: Make sure this sends bubbling events
     *
     * @param srcEvent the original DOM touch event that started this.
     * @param eventType the name of the custom event to send (eg 'click' or '$md.drag')
     * @param eventPointer the pointer object that matches this event.
     */
    function jQueryDispatchEvent(srcEvent, eventType, eventPointer) {
      eventPointer = eventPointer || pointer;
      var eventObj = new angular.element.Event(eventType);

      eventObj.$material = true;
      eventObj.pointer = eventPointer;
      eventObj.srcEvent = srcEvent;

      angular.extend(eventObj, {
        clientX: eventPointer.x,
        clientY: eventPointer.y,
        screenX: eventPointer.x,
        screenY: eventPointer.y,
        pageX: eventPointer.x,
        pageY: eventPointer.y,
        ctrlKey: srcEvent.ctrlKey,
        altKey: srcEvent.altKey,
        shiftKey: srcEvent.shiftKey,
        metaKey: srcEvent.metaKey
      });
      angular.element(eventPointer.target).trigger(eventObj);
    }

    /*
     * NOTE: nativeDispatchEvent is very performance sensitive.
     * @param srcEvent the original DOM touch event that started this.
     * @param eventType the name of the custom event to send (eg 'click' or '$md.drag')
     * @param eventPointer the pointer object that matches this event.
     */
    function nativeDispatchEvent(srcEvent, eventType, eventPointer) {
      eventPointer = eventPointer || pointer;
      var eventObj;

      if (eventType === 'click') {
        eventObj = document.createEvent('MouseEvents');
        eventObj.initMouseEvent(
          'click', true, true, window, srcEvent.detail,
          eventPointer.x, eventPointer.y, eventPointer.x, eventPointer.y,
          srcEvent.ctrlKey, srcEvent.altKey, srcEvent.shiftKey, srcEvent.metaKey,
          srcEvent.button, srcEvent.relatedTarget || null
        );

      } else {
        eventObj = document.createEvent('CustomEvent');
        eventObj.initCustomEvent(eventType, true, true, {});
      }
      eventObj.$material = true;
      eventObj.pointer = eventPointer;
      eventObj.srcEvent = srcEvent;
      eventPointer.target.dispatchEvent(eventObj);
    }

  }

  /**
   * Attach Gestures: hook document and check shouldHijack clicks
   * @ngInject
   */
  function attachToDocument( $mdGesture, $$MdGestureHandler ) {

    // Polyfill document.contains for IE11.
    // TODO: move to util
    document.contains || (document.contains = function (node) {
      return document.body.contains(node);
    });

    if (!isInitialized && $mdGesture.isHijackingClicks ) {
      /*
       * If hijack clicks is true, we preventDefault any click that wasn't
       * sent by ngMaterial. This is because on older Android & iOS, a false, or 'ghost',
       * click event will be sent ~400ms after a touchend event happens.
       * The only way to know if this click is real is to prevent any normal
       * click events, and add a flag to events sent by material so we know not to prevent those.
       * 
       * Two exceptions to click events that should be prevented are:
       *  - click events sent by the keyboard (eg form submit)
       *  - events that originate from an Ionic app
       */
      document.addEventListener('click', function clickHijacker(ev) {
        var isKeyClick = ev.clientX === 0 && ev.clientY === 0;
        if (!isKeyClick && !ev.$material && !ev.isIonicTap
            && !isInputEventFromLabelClick(ev)) {
          ev.preventDefault();
          ev.stopPropagation();
          lastLabelClickPos = null;
        } else {
          lastLabelClickPos = null;
          if (ev.target.tagName.toLowerCase() == 'label') {
            lastLabelClickPos = {x: ev.x, y: ev.y};
          }
        }
      }, true);
      
      isInitialized = true;
    }

    // Listen to all events to cover all platforms.
    var START_EVENTS = 'mousedown touchstart pointerdown';
    var MOVE_EVENTS = 'mousemove touchmove pointermove';
    var END_EVENTS = 'mouseup mouseleave touchend touchcancel pointerup pointercancel';

    angular.element(document)
      .on(START_EVENTS, gestureStart)
      .on(MOVE_EVENTS, gestureMove)
      .on(END_EVENTS, gestureEnd)
      // For testing
      .on('$$mdGestureReset', function gestureClearCache () {
        lastPointer = pointer = null;
      });

    /*
     * When a DOM event happens, run all registered gesture handlers' lifecycle
     * methods which match the DOM event.
     * Eg when a 'touchstart' event happens, runHandlers('start') will call and
     * run `handler.cancel()` and `handler.start()` on all registered handlers.
     */
    function runHandlers(handlerEvent, event) {
      var handler;
      for (var name in HANDLERS) {
        handler = HANDLERS[name];
        if( handler instanceof $$MdGestureHandler ) {

          if (handlerEvent === 'start') {
            // Run cancel to reset any handlers' state
            handler.cancel();
          }
          handler[handlerEvent](event, pointer);

        }
      }
    }

    /*
     * gestureStart vets if a start event is legitimate (and not part of a 'ghost click' from iOS/Android)
     * If it is legitimate, we initiate the pointer state and mark the current pointer's type
     * For example, for a touchstart event, mark the current pointer as a 'touch' pointer, so mouse events
     * won't effect it.
     */
    function gestureStart(ev) {
      // If we're already touched down, abort
      if (pointer) return;

      var now = +Date.now();

      // iOS & old android bug: after a touch event, a click event is sent 350 ms later.
      // If <400ms have passed, don't allow an event of a different type than the previous event
      if (lastPointer && !typesMatch(ev, lastPointer) && (now - lastPointer.endTime < 1500)) {
        return;
      }

      pointer = makeStartPointer(ev);

      runHandlers('start', ev);
    }
    /*
     * If a move event happens of the right type, update the pointer and run all the move handlers.
     * "of the right type": if a mousemove happens but our pointer started with a touch event, do nothing.
     */
    function gestureMove(ev) {
      if (!pointer || !typesMatch(ev, pointer)) return;

      updatePointerState(ev, pointer);
      runHandlers('move', ev);
    }
    /*
     * If an end event happens of the right type, update the pointer, run endHandlers, and save the pointer as 'lastPointer'
     */
    function gestureEnd(ev) {
      if (!pointer || !typesMatch(ev, pointer)) return;

      updatePointerState(ev, pointer);
      pointer.endTime = +Date.now();

      runHandlers('end', ev);

      lastPointer = pointer;
      pointer = null;
    }

  }

  // ********************
  // Module Functions
  // ********************

  /*
   * Initiate the pointer. x, y, and the pointer's type.
   */
  function makeStartPointer(ev) {
    var point = getEventPoint(ev);
    var startPointer = {
      startTime: +Date.now(),
      target: ev.target,
      // 'p' for pointer events, 'm' for mouse, 't' for touch
      type: ev.type.charAt(0)
    };
    startPointer.startX = startPointer.x = point.pageX;
    startPointer.startY = startPointer.y = point.pageY;
    return startPointer;
  }

  /*
   * return whether the pointer's type matches the event's type.
   * Eg if a touch event happens but the pointer has a mouse type, return false.
   */
  function typesMatch(ev, pointer) {
    return ev && pointer && ev.type.charAt(0) === pointer.type;
  }

  /**
   * Gets whether the given event is an input event that was caused by clicking on an
   * associated label element.
   *
   * This is necessary because the browser will, upon clicking on a label element, fire an
   * *extra* click event on its associated input (if any). mdGesture is able to flag the label
   * click as with `$material` correctly, but not the second input click.
   *
   * In order to determine whether an input event is from a label click, we compare the (x, y) for
   * the event to the (x, y) for the most recent label click (which is cleared whenever a non-label
   * click occurs). Unfortunately, there are no event properties that tie the input and the label
   * together (such as relatedTarget).
   *
   * @param {MouseEvent} event
   * @returns {boolean}
   */
  function isInputEventFromLabelClick(event) {
    return lastLabelClickPos
        && lastLabelClickPos.x == event.x
        && lastLabelClickPos.y == event.y;
  }

  /*
   * Update the given pointer based upon the given DOMEvent.
   * Distance, velocity, direction, duration, etc
   */
  function updatePointerState(ev, pointer) {
    var point = getEventPoint(ev);
    var x = pointer.x = point.pageX;
    var y = pointer.y = point.pageY;

    pointer.distanceX = x - pointer.startX;
    pointer.distanceY = y - pointer.startY;
    pointer.distance = Math.sqrt(
      pointer.distanceX * pointer.distanceX + pointer.distanceY * pointer.distanceY
    );

    pointer.directionX = pointer.distanceX > 0 ? 'right' : pointer.distanceX < 0 ? 'left' : '';
    pointer.directionY = pointer.distanceY > 0 ? 'up' : pointer.distanceY < 0 ? 'down' : '';

    pointer.duration = +Date.now() - pointer.startTime;
    pointer.velocityX = pointer.distanceX / pointer.duration;
    pointer.velocityY = pointer.distanceY / pointer.duration;
  }

  /*
   * Normalize the point where the DOM event happened whether it's touch or mouse.
   * @returns point event obj with pageX and pageY on it.
   */
  function getEventPoint(ev) {
    ev = ev.originalEvent || ev; // support jQuery events
    return (ev.touches && ev.touches[0]) ||
      (ev.changedTouches && ev.changedTouches[0]) ||
      ev;
  }
