//改写自https://github.com/asvd/dragscroll
//使用: var myDragScroll = dragScroll.create({});myDragScroll.reset();
//选项:container--.dragscroll元素容器
const dragScroll = (function ($) {

    function seal(options) {

        var newScrollX, newScrollY;

        options = $.extend({
            dragscroll: '.dragscroll',
            dragscrollno: '.dragscroll-no',
            xscroll: true, yscroll: true, throttle: null
        }, options);

        !options.dragscroll && (options.dragscroll = '.dragscroll');

        function _dragScroll(el) {

            var lastClientX, lastClientY, pushed = 0;

            function __mousedown(e) {
                if (!$(e.target).parentsUntil(options.dragscroll, options.dragscrollno).length) {
                    pushed = 1;
                    lastClientX = e.clientX;
                    lastClientY = e.clientY;
                }
            }

            function __mouseup(e) {
                pushed = 0;
            }

            function __mousemove(e) {
                if (pushed) {
                    var scroller = el.scroller || el;
                    if (options.xscroll) {
                        scroller.scrollLeft -=
                            newScrollX = - lastClientX + (lastClientX = e.clientX);
                    }
                    if (options.yscroll) {
                        scroller.scrollTop -=
                            newScrollY = - lastClientY + (lastClientY = e.clientY);
                    }
                    if (el === document.body) {
                        scroller = document.documentElement;
                        options.xscroll && (scroller.scrollLeft -= newScrollX);
                        options.yscroll && (scroller.scrollTop -= newScrollY);
                    }
                }
            }

            const _throttleMove = options.throttle ? options.throttle(__mousemove, 100) : __mousemove;

            $(el).off('mousedown', __mousedown).off('mouseup', __mouseup).off('mousemove', _throttleMove)
                .on('mousedown', __mousedown).on('mouseup', __mouseup).on('mousemove', _throttleMove)
                .on('mouseleave', function () { pushed = 0; })
                .on('selectstart', function (e) {
                    return !pushed;
                });
        }

        this.options = options;

        this.reset = function (options) {
            options && Object.assign(this.options, options);
            $(this.options.dragscroll, this.options.container).each(function () {
                _dragScroll(this);
            });
        };

        this.getOptions = function () { return Object.assign({}, this.options); };
    }

    return {
        create(options) { return new seal(options); }
    };

}(jQuery));