/**
 * this jquery plugin displays pagination links inside the selected elements.
 *
 * @author gabriel birke (birke *at* d-scribe *dot* de)
 * @version 1.1
 * @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() {
        /**
        * calculate the maximum number of pages
        */
        function numpages() {
            return math.ceil(maxentries / opts.items_per_page);
        }

        /**
        * calculate start and end point of pagination links depending on 
        * current_page and num_display_entries.
        * @return {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];
        }

        /**
        * this is the event handling function for the pagination links. 
        * @param {int} page_id the new page number
        */
        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;
        }

        /**
        * this function inserts the pagination links into the container element
        */
        function drawlinks() {
            panel.empty();
            var interval = getinterval();
            var np = numpages();
            // this helper function returns a handler function that calls pageselected with the right page_id
            var getclickhandler = function(page_id) {
                return function(evt) { return pageselected(page_id, evt); }
            }
            // helper function for generating a single link (or a span tag if it's the current page)
            var appenditem = function(page_id, appendopts) {
                page_id = page_id < 0 ? 0 : (page_id < np ? page_id : np - 1); // normalize page id to sane value
                appendopts = jquery.extend({ text: page_id + 1, classes: "current" }, appendopts || {});
                if (page_id == current_page) {
                    var lnk = $("<span class='current'>" + (appendopts.text) + "</span>");
                }
                else {
                    var lnk = $("<a>" + (appendopts.text) + "</a>")
						.bind("click", getclickhandler(page_id))
						.attr('href', opts.link_to.replace(/__id__/, page_id));


                }
                if (appendopts.classes) { lnk.removeattr('class'); lnk.addclass(appendopts.classes); }
                panel.append(lnk);
            }
            // generate "previous"-link
            if (opts.prev_text && (current_page > 0 || opts.prev_show_always)) {
                appenditem(current_page - 1, { text: opts.prev_text, classes: "disabled" });
            }
            // generate starting points
            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);
                }
            }
            // generate interval links
            for (var i = interval[0]; i < interval[1]; i++) {
                appenditem(i);
            }
            // generate ending points
            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);
                }

            }
            // generate "next"-link
            if (opts.next_text && (current_page < np - 1 || opts.next_show_always)) {
                appenditem(current_page + 1, { text: opts.next_text, classes: "disabled" });
            }
        }

        // extract current_page from options
        var current_page = opts.current_page;
        // create a sane value for maxentries and items_per_page
        maxentries = (!maxentries || maxentries < 0) ? 1 : maxentries;
        opts.items_per_page = (!opts.items_per_page || opts.items_per_page < 0) ? 1 : opts.items_per_page;
        // store dom element for easy access from all inner functions
        var panel = jquery(this);
        // attach control functions to the dom element 
        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;
            }
        }
        // when all initialisation is done, draw the links
        drawlinks();
    });
}