// https://github.com/ghiculescu/jekyll-table-of-contents
(function($){
  $.fn.toc = function(options) {
    var defaults = {
      noBackToTopLinks: false,
      title: '',
      minimumHeaders: 3,
      headers: 'h1, h2, h3, h4',
      listType: 'ol', // values: [ol|ul]
    },
    settings = $.extend(defaults, options);

    var headers = $(settings.headers).filter(function() {
      // get all headers with an ID
      var previousSiblingName = $(this).prev().attr( "name" );
      if (!this.id && previousSiblingName) {
        this.id = $(this).attr( "id", previousSiblingName.replace(/\./g, "-") );
      }
      return this.id;
    }), output = $(this);
    if (!headers.length || headers.length < settings.minimumHeaders || !output.length) {
      return;
    }

    var get_level = function(ele) { return parseInt(ele.nodeName.replace("H", ""), 10); }
    var highest_level = headers.map(function(_, ele) { return get_level(ele); }).get().sort()[0];

    // There is a javascript click listener (defined later in this file) for the below to scroll up.
    var return_to_top = '<div class="icon-arrow-up back-to-top" style="text-align:right;">Up↑</div>';

    var level = get_level(headers[0]),
      this_level,
      html = settings.title + " <"+settings.listType+" id=\"toc_ul\" class=\"nav\">";
    headers.on('click', function() {
      if (!settings.noBackToTopLinks) {
        window.location.hash = this.id;
      }
    })
    .addClass('clickable-header').after(return_to_top)
    .each(function(_, header) {
      this_level = get_level(header);
      if (!settings.noBackToTopLinks && this_level === highest_level) {
        $(header).addClass('top-level-header');
      }
      if (this_level === level) // same level as before; same indenting
        html += "<li><a href='#" + header.id + "'>" + header.innerText + "</a>";
      else if (this_level <= level){ // higher level than before; end parent ol
        for(i = this_level; i < level; i++) {
          html += "</li></"+settings.listType+">"
        }
        html += "<li><a href='#" + header.id + "'>" + header.innerText + "</a>";
      }
      else if (this_level > level) { // lower level than before; expand the previous to contain a ol
        for(i = this_level; i > level; i--) {
          html += "<"+settings.listType+"><li>"
        }
        html += "<a href='#" + header.id + "'>" + header.innerText + "</a>";
      }
      level = this_level; // update for the next one
    });
    html += "</"+settings.listType+">";

    // Listener for "Back to top" links under headings.
    if (!settings.noBackToTopLinks) {
      $(document).on('click', '.back-to-top', function() {
        $(window).scrollTop(0);
        window.location.hash = '';
      });
    }

      output.html(html);
  };
})(jQuery);