(function (window, document, exportName, undefined) {
    'use strict';

    var isMultiTouch = false;
    var multiTouchStartPos;
    var eventTarget;
    var touchElements = {};

    // polyfills
    if (!document.createTouch) {
        document.createTouch = function (view, target, identifier, pageX, pageY, screenX, screenY, clientX, clientY) {
            // auto set
            if (clientX == undefined || clientY == undefined) {
                clientX = pageX - window.pageXOffset;
                clientY = pageY - window.pageYOffset;
            }

            return new Touch(target, identifier, {
                pageX: pageX,
                pageY: pageY,
                screenX: screenX,
                screenY: screenY,
                clientX: clientX,
                clientY: clientY
            });
        };
    }

    if (!document.createTouchList) {
        document.createTouchList = function () {
            var touchList = new TouchList();
            for (var i = 0; i < arguments.length; i++) {
                touchList[i] = arguments[i];
            }
            touchList.length = arguments.length;
            return touchList;
        };
    }

    /**
     * create an touch point
     * @constructor
     * @param target
     * @param identifier
     * @param pos
     * @param deltaX
     * @param deltaY
     * @returns {Object} touchPoint
     */
    function Touch(target, identifier, pos, deltaX, deltaY) {
        deltaX = deltaX || 0;
        deltaY = deltaY || 0;

        this.identifier = identifier;
        this.target = target;
        this.clientX = pos.clientX + deltaX;
        this.clientY = pos.clientY + deltaY;
        this.screenX = pos.screenX + deltaX;
        this.screenY = pos.screenY + deltaY;
        this.pageX = pos.pageX + deltaX;
        this.pageY = pos.pageY + deltaY;
    }

    /**
     * create empty touchlist with the methods
     * @constructor
     * @returns touchList
     */
    function TouchList() {
        var touchList = [];

        touchList.item = function (index) {
            return this[index] || null;
        };

        // specified by Mozilla
        touchList.identifiedTouch = function (id) {
            return this[id + 1] || null;
        };

        return touchList;
    }

    /**
     * Simple trick to fake touch event support
     * this is enough for most libraries like Modernizr and Hammer
     */
    function fakeTouchSupport() {
        var objs = [window, document.documentElement];
        var props = ['ontouchstart', 'ontouchmove', 'ontouchcancel', 'ontouchend'];

        for (var o = 0; o < objs.length; o++) {
            for (var p = 0; p < props.length; p++) {
                if (objs[o] && objs[o][props[p]] == undefined) {
                    objs[o][props[p]] = null;
                }
            }
        }
    }

    /**
     * we don't have to emulate on a touch device
     * @returns {boolean}
     */
    function hasTouchSupport() {
        return (
            'ontouchstart' in window || // touch events
            (window.Modernizr && window.Modernizr.touch) || // modernizr
            (navigator.msMaxTouchPoints || navigator.maxTouchPoints) > 2
        ); // pointer events
    }

    /**
     * disable mouseevents on the page
     * @param ev
     */
    function preventMouseEvents(ev) {
        // 注释启用默认事件
        // ev.preventDefault();
        // ev.stopPropagation();
    }

    /**
     * only trigger touches when the left mousebutton has been pressed
     * @param touchType
     * @returns {Function}
     */
    function onMouse(touchType) {
        return function (ev) {
            // prevent mouse events
            preventMouseEvents(ev);

            if (ev.which !== 1) {
                return;
            }

            // The EventTarget on which the touch point started when it was first placed on the surface,
            // even if the touch point has since moved outside the interactive area of that element.
            // also, when the target doesnt exist anymore, we update it
            if (ev.type == 'mousedown' || !eventTarget || (eventTarget && !eventTarget.dispatchEvent)) {
                eventTarget = ev.target;
            }

            // shiftKey has been lost, so trigger a touchend
            if (isMultiTouch && !ev.shiftKey) {
                triggerTouch('touchend', ev);
                isMultiTouch = false;
            }

            triggerTouch(touchType, ev);

            // we're entering the multi-touch mode!
            if (!isMultiTouch && ev.shiftKey) {
                isMultiTouch = true;
                multiTouchStartPos = {
                    pageX: ev.pageX,
                    pageY: ev.pageY,
                    clientX: ev.clientX,
                    clientY: ev.clientY,
                    screenX: ev.screenX,
                    screenY: ev.screenY
                };
                triggerTouch('touchstart', ev);
            }

            // reset
            if (ev.type == 'mouseup') {
                multiTouchStartPos = null;
                isMultiTouch = false;
                eventTarget = null;
            }
        };
    }

    /**
     * trigger a touch event
     * @param eventName
     * @param mouseEv
     */
    function triggerTouch(eventName, mouseEv) {
        var touchEvent = document.createEvent('Event');
        touchEvent.initEvent(eventName, true, true);

        touchEvent.altKey = mouseEv.altKey;
        touchEvent.ctrlKey = mouseEv.ctrlKey;
        touchEvent.metaKey = mouseEv.metaKey;
        touchEvent.shiftKey = mouseEv.shiftKey;

        touchEvent.touches = getActiveTouches(mouseEv, eventName);
        touchEvent.targetTouches = getActiveTouches(mouseEv, eventName);
        touchEvent.changedTouches = getChangedTouches(mouseEv, eventName);

        eventTarget.dispatchEvent(touchEvent);
    }

    /**
     * create a touchList based on the mouse event
     * @param mouseEv
     * @returns {TouchList}
     */
    function createTouchList(mouseEv) {
        var touchList = new TouchList();

        if (isMultiTouch) {
            var f = TouchEmulator.multiTouchOffset;
            var deltaX = multiTouchStartPos.pageX - mouseEv.pageX;
            var deltaY = multiTouchStartPos.pageY - mouseEv.pageY;

            touchList.push(new Touch(eventTarget, 1, multiTouchStartPos, deltaX * -1 - f, deltaY * -1 + f));
            touchList.push(new Touch(eventTarget, 2, multiTouchStartPos, deltaX + f, deltaY - f));
        } else {
            touchList.push(new Touch(eventTarget, 1, mouseEv, 0, 0));
        }

        return touchList;
    }

    /**
     * receive all active touches
     * @param mouseEv
     * @returns {TouchList}
     */
    function getActiveTouches(mouseEv, eventName) {
        // empty list
        if (mouseEv.type == 'mouseup') {
            return new TouchList();
        }

        var touchList = createTouchList(mouseEv);
        if (isMultiTouch && mouseEv.type != 'mouseup' && eventName == 'touchend') {
            touchList.splice(1, 1);
        }
        return touchList;
    }

    /**
     * receive a filtered set of touches with only the changed pointers
     * @param mouseEv
     * @param eventName
     * @returns {TouchList}
     */
    function getChangedTouches(mouseEv, eventName) {
        var touchList = createTouchList(mouseEv);

        // we only want to return the added/removed item on multitouch
        // which is the second pointer, so remove the first pointer from the touchList
        //
        // but when the mouseEv.type is mouseup, we want to send all touches because then
        // no new input will be possible
        if (isMultiTouch && mouseEv.type != 'mouseup' && (eventName == 'touchstart' || eventName == 'touchend')) {
            touchList.splice(0, 1);
        }

        return touchList;
    }

    /**
     * show the touchpoints on the screen
     */
    function showTouches(ev) {
        var touch, i, el, styles;

        // first all visible touches
        for (i = 0; i < ev.touches.length; i++) {
            touch = ev.touches[i];
            el = touchElements[touch.identifier];
            if (!el) {
                el = touchElements[touch.identifier] = document.createElement('div');
                document.body.appendChild(el);
            }

            styles = TouchEmulator.template(touch);
            for (var prop in styles) {
                el.style[prop] = styles[prop];
            }
        }

        // remove all ended touches
        if (ev.type == 'touchend' || ev.type == 'touchcancel') {
            for (i = 0; i < ev.changedTouches.length; i++) {
                touch = ev.changedTouches[i];
                el = touchElements[touch.identifier];
                if (el) {
                    el.parentNode.removeChild(el);
                    delete touchElements[touch.identifier];
                }
            }
        }
    }

    /**
     * TouchEmulator initializer
     */
    function TouchEmulator() {
        if (hasTouchSupport()) {
            return;
        }

        fakeTouchSupport();

        window.addEventListener('mousedown', onMouse('touchstart'), true);
        window.addEventListener('mousemove', onMouse('touchmove'), true);
        window.addEventListener('mouseup', onMouse('touchend'), true);

        window.addEventListener('mouseenter', preventMouseEvents, true);
        window.addEventListener('mouseleave', preventMouseEvents, true);
        window.addEventListener('mouseout', preventMouseEvents, true);
        window.addEventListener('mouseover', preventMouseEvents, true);

        // it uses itself!
        window.addEventListener('touchstart', showTouches, true);
        window.addEventListener('touchmove', showTouches, true);
        window.addEventListener('touchend', showTouches, true);
        window.addEventListener('touchcancel', showTouches, true);
    }

    // start distance when entering the multitouch mode
    TouchEmulator.multiTouchOffset = 75;

    /**
     * css template for the touch rendering
     * @param touch
     * @returns object
     */
    TouchEmulator.template = function (touch) {
        var size = 0;
        var transform = 'translate(' + (touch.clientX - size / 2) + 'px, ' + (touch.clientY - size / 2) + 'px)';
        return {
            position: 'fixed',
            left: 0,
            top: 0,
            background: '#fff',
            border: 'solid 1px #999',
            opacity: 0.6,
            borderRadius: '100%',
            height: size + 'px',
            width: size + 'px',
            padding: 0,
            margin: 0,
            display: 'block',
            overflow: 'hidden',
            pointerEvents: 'none',
            webkitUserSelect: 'none',
            mozUserSelect: 'none',
            userSelect: 'none',
            webkitTransform: transform,
            mozTransform: transform,
            transform: transform,
            zIndex: 100
        };
    };

    // export
    if (typeof define == 'function' && define.amd) {
        define(function () {
            return TouchEmulator;
        });
    } else if (typeof module != 'undefined' && module.exports) {
        module.exports = TouchEmulator;
    } else {
        window[exportName] = TouchEmulator;
    }
})(window, document, 'TouchEmulator');
