/**
 * this jquery plugin displays pagination links inside the selected elements.
 *
 * @author gabriel birke (birke *at* d-scribe *dot* de)
 * @version 1.2
 * @param {int} maxentries number of entries to paginate
 * @param {object} opts several options (see readme for documentation)
 * @return {object} jquery object
 */
jquery.fn.pagination = function(maxentries, opts){
	opts = jquery.extend({
		items_per_page:10,
		num_display_entries:10,
		current_page:0,
		num_edge_entries:0,
		link_to:"#",
		prev_text:"prev",
		next_text:"next",
		ellipse_text:"...",
		prev_show_always:true,
		next_show_always:true,
		callback:function(){return false;}
	},opts||{});
	
	return this.each(function() {
		/**
		 * 计算最大分页显示数目
		 */
		function numpages() {
			return math.ceil(maxentries/opts.items_per_page);
		}	
		/**
		 * 极端分页的起始和结束点，这取决于current_page 和 num_display_entries.
		 * @返回 {数组(array)}
		 */
		function getinterval()  {
			var ne_half = math.ceil(opts.num_display_entries/2);
			var np = numpages();
			var upper_limit = np-opts.num_display_entries;
			var start = current_page>ne_half?math.max(math.min(current_page-ne_half, upper_limit), 0):0;
			var end = current_page>ne_half?math.min(current_page+ne_half, np):math.min(opts.num_display_entries, np);
			return [start,end];
		}
		
		/**
		 * 分页链接事件处理函数
		 * @参数 {int} page_id 为新页码
		 */
		function pageselected(page_id, evt){
			current_page = page_id;
			drawlinks();
			var continuepropagation = opts.callback(page_id, panel);
			if (!continuepropagation) {
				if (evt.stoppropagation) {
					evt.stoppropagation();
				}
				else {
					evt.cancelbubble = true;
				}
			}
			return continuepropagation;
		}
		
		/**
		 * 此函数将分页链接插入到容器元素中
		 */
		function drawlinks() {
			panel.empty();
			var interval = getinterval();
			var np = numpages();
			// 这个辅助函数返回一个处理函数调用有着正确page_id的pageselected。
			var getclickhandler = function(page_id) {
				return function(evt){ return pageselected(page_id,evt); }
			}
			//辅助函数用来产生一个单链接(如果不是当前页则产生span标签)
			var appenditem = function(page_id, appendopts){
				page_id = page_id<0?0:(page_id<np?page_id:np-1); // 规范page id值
				appendopts = jquery.extend({text:page_id+1, classes:""}, appendopts||{});
				if(page_id == current_page){
					var lnk = jquery("<span class='current'>"+(appendopts.text)+"</span>");
				}else{
					var lnk = jquery("<a>"+(appendopts.text)+"</a>")
						.bind("click", getclickhandler(page_id))
						.attr('href', opts.link_to.replace(/__id__/,page_id));		
				}
				if(appendopts.classes){lnk.addclass(appendopts.classes);}
				panel.append(lnk);
			}
			// 产生"previous"-链接
			if(opts.prev_text && (current_page > 0 || opts.prev_show_always)){
				appenditem(current_page-1,{text:opts.prev_text, classes:"prev"});
			}
			// 产生起始点
			if (interval[0] > 0 && opts.num_edge_entries > 0)
			{
				var end = math.min(opts.num_edge_entries, interval[0]);
				for(var i=0; i<end; i++) {
					appenditem(i);
				}
				if(opts.num_edge_entries < interval[0] && opts.ellipse_text)
				{
					jquery("<span>"+opts.ellipse_text+"</span>").appendto(panel);
				}
			}
			// 产生内部的些链接
			for(var i=interval[0]; i<interval[1]; i++) {
				appenditem(i);
			}
			// 产生结束点
			if (interval[1] < np && opts.num_edge_entries > 0)
			{
				if(np-opts.num_edge_entries > interval[1]&& opts.ellipse_text)
				{
					jquery("<span>"+opts.ellipse_text+"</span>").appendto(panel);
				}
				var begin = math.max(np-opts.num_edge_entries, interval[1]);
				for(var i=begin; i<np; i++) {
					appenditem(i);
				}
				
			}
			// 产生 "next"-链接
			if(opts.next_text && (current_page < np-1 || opts.next_show_always)){
				appenditem(current_page+1,{text:opts.next_text, classes:"next"});
			}
		}
		
		//从选项中提取current_page
		var current_page = opts.current_page;
		//创建一个显示条数和每页显示条数值
		maxentries = (!maxentries || maxentries < 0)?1:maxentries;
		opts.items_per_page = (!opts.items_per_page || opts.items_per_page < 0)?1:opts.items_per_page;
		//存储dom元素，以方便从所有的内部结构中获取
		var panel = jquery(this);
		// 获得附加功能的元素
		this.selectpage = function(page_id){ pageselected(page_id);}
		this.prevpage = function(){ 
			if (current_page > 0) {
				pageselected(current_page - 1);
				return true;
			}
			else {
				return false;
			}
		}
		this.nextpage = function(){ 
			if(current_page < numpages()-1) {
				pageselected(current_page+1);
				return true;
			}
			else {
				return false;
			}
		}
		// 所有初始化完成，绘制链接
		drawlinks();
        // 回调函数
        opts.callback(current_page, this);
	});
}