/*
 * Table of Contents jQuery Plugin - jquery.toc
 *
 * Copyright 2013 Nikhil Dabas
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied.  See the License for the specific language governing permissions and limitations
 * under the License.
 */

(function ($) {
    "use strict";

    // Builds a list with the table of contents in the current selector.
    // options:
    //   content: where to look for headings
    //   headings: string with a comma-separated list of selectors to be used as headings, ordered
    //   by their relative hierarchy level
    var toc = function (options) {
        return this.each(function () {
            var root = $(this),
                data = root.data(),
                thisOptions,
                stack = [root], // The upside-down stack keeps track of list elements
                listTag = this.tagName,
                currentLevel = 0,
                headingSelectors;

            // Defaults: plugin parameters override data attributes, which override our defaults
            thisOptions = $.extend(
                {content: "body", headings: "h1,h2,h3"},
                {content: data.toc || undefined, headings: data.tocHeadings || undefined},
                options
            );
            headingSelectors = thisOptions.headings.split(",");

            // Set up some automatic IDs if we do not already have them
            $(thisOptions.content).find(thisOptions.headings).attr("id", function (index, attr) {
                // Generate a valid ID: must start with a letter, and contain only letters and
                // numbers. All other characters are replaced with underscores.
                return attr ||
                    $(this).text().replace(/^[^A-Za-z]*/, "").replace(/[^A-Za-z0-9]+/g, "_");
            }).each(function () {
                // What level is the current heading?
                var elem = $(this), level = $.map(headingSelectors, function (selector, index) {
                    return elem.is(selector) ? index : undefined;
                })[0];

                if (level > currentLevel) {
                    // If the heading is at a deeper level than where we are, start a new nested
                    // list, but only if we already have some list items in the parent. If we do
                    // not, that means that we're skipping levels, so we can just add new list items
                    // at the current level.
                    // In the upside-down stack, unshift = push, and stack[0] = the top.
                    var parentItem = stack[0].children("li:last")[0];
                    if (parentItem) {
                        stack.unshift($("<" + listTag + "/>").appendTo(parentItem));
                    }
                } else {
                    // Truncate the stack to the current level by chopping off the 'top' of the
                    // stack. We also need to preserve at least one element in the stack - that is
                    // the containing element.
                    stack.splice(0, Math.min(currentLevel - level, Math.max(stack.length - 1, 0)));
                }

                // Add the list item
                $("<li/>").appendTo(stack[0]).append(
                    $("<a/>").text(elem.text()).attr("href", "#" + elem.attr("id"))
                );

                currentLevel = level;
            });
        });
    }, old = $.fn.toc;

    $.fn.toc = toc;

    $.fn.toc.noConflict = function () {
        $.fn.toc = old;
        return this;
    };

    // Data API
    $(function () {
        toc.call($("[data-toc]"));
    });
}(window.jQuery));
