(function (global) {
    var transform = getTransform()

    function Drag(selector) {
        this.elem = typeof selector === 'object' ? selector : document.querySelector(selector)
        this.mouse_x = 0
        this.mouse_y = 0
        this.elem_x = 0
        this.elem_y = 0
        this.init()
    }

    Drag.prototype = {
        version: '2.0',
        init: function () {
            this.setDrag()
        },
        getElemPosition() {
            var position = {x: 0, y: 0}
            var elem = this.elem
            if (transform) {
                this.isTransform(elem, position)
            } else {
                this.isPosition(elem, position)
            }
            return position

        },
        isTransform: function (elem, position) {
            var styleValue = getStyleValue(elem, transform)
            if (styleValue !== 'none') {
                let styleValueArr = styleValue.match(/-?\d+/g)
                position.x = parseInt(styleValueArr[4].trim())
                position.y = parseInt(styleValueArr[5].trim())
            }
        },
        isPosition: function (elem, position) {
            if (getStyleValue(elem, 'position') === 'static') {
                this.elem.style['position'] = 'relative'
            } else {
                position.x = parseInt(getStyleValue(elem, 'left') ? getStyleValue(elem, 'left') : 0)
                position.y = parseInt(getStyleValue(elem, 'right') ? getStyleValue(elem, 'right') : 0)
            }
        },
        /**
         * @description 设置位置 例如 {x:10,y:10}
         * @param position {Object}
         */
        setElemPosition(position) {
            if (transform) {
                this.elem.style[transform] = `translate(${position.x}px,${position.y}px)`
            } else {
                this.elem.style['left'] = `${position.x}px`
                this.elem.style['right'] = `${position.y}px`
            }
        },
        /**
         * @description 给当前元素添加鼠标拖动处理的事件
         */
        setDrag: function () {
            var self = this
            this.elem.addEventListener('mousedown', start, false)

            /**
             * @description 记录按下鼠标时的位置,同时绑定mousemove和mouseup事件
             * @param event
             */
            function start(event) {

                self.mouse_x = event.pageX
                self.mouse_y = event.pageY

                let position = self.getElemPosition();

                self.elem_y = position.y
                self.elem_x = position.x

                document.addEventListener("mousemove", move, false)
                document.addEventListener("mouseup", end, false)
            }

            function move(event) {
                var target_mouse_x = event.pageX,
                    target_mouse_y = event.pageY,
                    distance_x = target_mouse_x - self.mouse_x,
                    distance_y = target_mouse_y - self.mouse_y,
                    position = self.getElemPosition();

                position.x = self.elem_x + distance_x;
                position.y = self.elem_y + distance_y;

                self.setElemPosition(position)
            }

            function end(event) {
                document.removeEventListener("mousemove", move)
                document.removeEventListener("mouseup", end)
            }
        }
    }


    function getTransform() {
        var transform = '',
            transforms = ["transform", "webkitTransform", "MozTransform", "msTransform", "OTransform"],
            len = transforms.length,
            index = 0,
            bodyStyle = document.body.style;
        for (; index < len; index++) {
            if (transforms[index] in bodyStyle) {
                return transforms[index]
            } else {
                return transform
            }
        }
    }

    function getStyleValue(elem, property) {
        if (document.defaultView.getComputedStyle) {
            return document.defaultView.getComputedStyle(elem, false)[property]
        } else {
            return elem.currentStyle[property]
        }
    }

    global.Drag = Drag
})(window)