Mini Shell

/**
 * Only implements needed gestures for mobile.
 */
define(function(require) {

    'use strict';

    var eventUtil = require('./event');

    var GestureMgr = function () {

        /**
         * @private
         * @type {Array.<Object>}
         */
        this._track = [];
    };

    GestureMgr.prototype = {

        constructor: GestureMgr,

        recognize: function (event, target, root) {
            this._doTrack(event, target, root);
            return this._recognize(event);
        },

        clear: function () {
            this._track.length = 0;
            return this;
        },

        _doTrack: function (event, target, root) {
            var touches = event.touches;

            if (!touches) {
                return;
            }

            var trackItem = {
                points: [],
                touches: [],
                target: target,
                event: event
            };

            for (var i = 0, len = touches.length; i < len; i++) {
                var touch = touches[i];
                var pos = eventUtil.clientToLocal(root, touch);
                trackItem.points.push([pos.zrX, pos.zrY]);
                trackItem.touches.push(touch);
            }

            this._track.push(trackItem);
        },

        _recognize: function (event) {
            for (var eventName in recognizers) {
                if (recognizers.hasOwnProperty(eventName)) {
                    var gestureInfo = recognizers[eventName](this._track, event);
                    if (gestureInfo) {
                        return gestureInfo;
                    }
                }
            }
        }
    };

    function dist(pointPair) {
        var dx = pointPair[1][0] - pointPair[0][0];
        var dy = pointPair[1][1] - pointPair[0][1];

        return Math.sqrt(dx * dx + dy * dy);
    }

    function center(pointPair) {
        return [
            (pointPair[0][0] + pointPair[1][0]) / 2,
            (pointPair[0][1] + pointPair[1][1]) / 2
        ];
    }

    var recognizers = {

        pinch: function (track, event) {
            var trackLen = track.length;

            if (!trackLen) {
                return;
            }

            var pinchEnd = (track[trackLen - 1] || {}).points;
            var pinchPre = (track[trackLen - 2] || {}).points || pinchEnd;

            if (pinchPre
                && pinchPre.length > 1
                && pinchEnd
                && pinchEnd.length > 1
            ) {
                var pinchScale = dist(pinchEnd) / dist(pinchPre);
                !isFinite(pinchScale) && (pinchScale = 1);

                event.pinchScale = pinchScale;

                var pinchCenter = center(pinchEnd);
                event.pinchX = pinchCenter[0];
                event.pinchY = pinchCenter[1];

                return {
                    type: 'pinch',
                    target: track[0].target,
                    event: event
                };
            }
        }

        // Only pinch currently.
    };

    return GestureMgr;
});