/**
 * JQuery插件，在特定的DOM元素（出现滚动条）上滑动（鼠标左键按下，移动）时，DOM里的内容跟随鼠标移动 
 * DOM 元素上加上： unselectable="on" onselectstart="return false;" style="-moz-user-select:none;"
 * 防止拖动鼠标时，选择元素中的文字
 * Created by 广平 on 2017/5/19.
 */
;
(function($, window, document, undefined) {

	$.fn.movescroll = function(options) {

		var _defaults = {
			// 在哪个方向跟随移动
			axis : "Y",
			// 跟随的速度，大于1将超过鼠标移动的速度
			speed : 1
		};

		var settings = $.extend({}, _defaults, options);
		var $elemets = this;

		return $elemets.each(function() {
			var isDrag = false;
			var onMove = false;
			var mouseStartX = 0, mouseStartY = 0;
			var scrollStartLeft = 0, scrollStartTop = 0;	
			var $scroller = $(this);
			
			$scroller.on("mousedown", function(e) {
				isDrag = true;
				mouseStartX = parseInt(e.pageX);
				mouseStartY = parseInt(e.pageY);
				scrollStartLeft = parseInt($(this).scrollLeft());
				scrollStartTop = parseInt($(this).scrollTop());
			});
			$(window).on("mouseup", function(e) {
				isDrag = false;
				isScroll = false;
				onMove = false;
			});
			$scroller.on("scroll", function(e) {
				if(!onMove) {
					scrollStartLeft = parseInt($(this).scrollLeft());
					scrollStartTop = parseInt($(this).scrollTop());
					isDrag = false;
				}
				onMove = false;
			});
			$scroller.on("mousemove", function(e) {
				onMove = true;
				if (isDrag) {
					var moveX = parseInt(e.pageX) - mouseStartX;
					var moveY = parseInt(e.pageY) - mouseStartY;
					if(settings.axis == 'X') {
						$(this).scrollLeft(-moveX * settings.speed + scrollStartLeft);
					} else if (settings.axis == 'Y') {
						$(this).scrollTop(-moveY * settings.speed + scrollStartTop);
					}
				} 
			});
		});
	};

}(jQuery, window, document));