/**

 * param 原生js方式实现判断用户的滑动方向

 * 返回1 向上

 * 返回2 向下

 * 返回3 向左

 * 返回4 向右

 */

class juedgeSlide {

    constructor() {

        this.startx = '';

        this.starty = '';

    }

    //获得角度

    getAngle(angx, angy) {

        return Math.atan2(angy, angx) * 180 / Math.PI;

    };

    //根据起点终点返回方向 1向上 2向下 3向左 4向右 0未滑动

    getDirection(startx, starty, endx, endy) {

        var angx = endx - startx;

        var angy = endy - starty;

        var result = 0;

        //如果滑动距离太短

        if (Math.abs(angx) < 2 && Math.abs(angy) < 2) {

            return result;

        }

        var angle = this.getAngle(angx, angy);

        if (angle >= -135 && angle <= -45) {

            result = 1;

        } else if (angle > 45 && angle < 135) {

            result = 2;

        } else if ((angle >= 135 && angle <= 180) || (angle >= -180 && angle < -135)) {

            result = 3;

        } else if (angle >= -45 && angle <= 45) {

            result = 4;

        }

        return result;

    }

    // 初始化函数

    init(callback) {

        var that = this;

        //手指接触屏幕

        document.addEventListener("touchstart", function (e) {

            that.startx = e.touches[0].pageX;

            that.starty = e.touches[0].pageY;

        }, false);

        document.addEventListener("touchmove", function (e) {

            var endx, endy;

            endx = e.changedTouches[0].pageX;

            endy = e.changedTouches[0].pageY;

            var direction = that.getDirection(that.startx, that.starty, endx, endy);

            callback(direction, true);

        }, false);

        //手指离开屏幕

        document.addEventListener("touchend", function (e) {

            var endx, endy;

            endx = e.changedTouches[0].pageX;

            endy = e.changedTouches[0].pageY;

            var direction = that.getDirection(that.startx, that.starty, endx, endy);

            callback(direction, false);

        }, false);

    }


}