/**
 * 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 ä¸ºæ–°é¡µç 
         */
        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;
        }

        /**
         * æ­¤å‡½æ•°å°†åˆ†é¡µé“¾æŽ¥æ’å…¥åˆ°å®¹å™¨å…ƒç´ ä¸­
         */
        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spanæ ‡ç­¾)
            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DOMå…ƒç´ ï¼Œä»¥æ–¹ä¾¿ä»Žæ‰€æœ‰çš„å†…éƒ¨ç»“æž„ä¸­èŽ·å–
        var panel = jQuery(this);
        // èŽ·å¾—é™„åŠ åŠŸèƒ½çš„å…ƒç´ 
        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);
    });
}