
Drupal.tableHeaderDoScroll = function() {
  if (typeof(Drupal.tableHeaderOnScroll)=='function') {
    Drupal.tableHeaderOnScroll();
  }
};

Drupal.behaviors.tableHeader = function (context) {
  // This breaks in anything less than IE 7. Prevent it from running.
  if (jQuery.browser.msie && parseInt(jQuery.browser.version, 10) < 7) {
    return;
  }

  // Keep track of all cloned table headers.
  var headers = [];

  $('table.sticky-enabled thead:not(.tableHeader-processed)', context).each(function () {
    // Clone thead so it inherits original jQuery properties.
    var headerClone = $(this).clone(true).insertBefore(this.parentNode).wrap('<table class="sticky-header"></table>').parent().css({
      position: 'fixed',
      top: '0px'
    });

    headerClone = $(headerClone)[0];
    headers.push(headerClone);

    // Store parent table.
    var table = $(this).parent('table')[0];
    headerClone.table = table;
    // Finish initialzing header positioning.
    tracker(headerClone);

    $(table).addClass('sticky-table');
    $(this).addClass('tableHeader-processed');
  });

  // Define the anchor holding var.
  var prevAnchor = '';

  // Track positioning and visibility.
  function tracker(e) {
    // Save positioning data.
    var viewHeight = document.documentElement.scrollHeight || document.body.scrollHeight;
    if (e.viewHeight != viewHeight) {
      e.viewHeight = viewHeight;
      e.vPosition = $(e.table).offset().top - 4;
      e.hPosition = $(e.table).offset().left;
      e.vLength = e.table.clientHeight - 100;
      // Resize header and its cell widths.
      var parentCell = $('th', e.table);
      $('th', e).each(function(index) {
        var cellWidth = parentCell.eq(index).css('width');
        // Exception for IE7.
        if (cellWidth == 'auto') {
          cellWidth = parentCell.get(index).clientWidth +'px';
        }
        $(this).css('width', cellWidth);
      });
      $(e).css('width', $(e.table).css('width'));
    }

    // Track horizontal positioning relative to the viewport and set visibility.
    var hScroll = document.documentElement.scrollLeft || document.body.scrollLeft;
    var vOffset = (document.documentElement.scrollTop || document.body.scrollTop) - e.vPosition;
    var visState = (vOffset > 0 && vOffset < e.vLength) ? 'visible' : 'hidden';
    $(e).css({left: -hScroll + e.hPosition +'px', visibility: visState});

    // Check the previous anchor to see if we need to scroll to make room for the header.
    // Get the height of the header table and scroll up that amount.
    if (prevAnchor != location.hash) {
      if (location.hash != '') {
        var offset = $(document).find('td' + location.hash).offset();
        if (offset) {
          var top = offset.top;
          var scrollLocation = top - $(e).height();
          $('body, html').scrollTop(scrollLocation);
        }
      }
      prevAnchor = location.hash;
    }
  }

  // Only attach to scrollbars once, even if Drupal.attachBehaviors is called
  //  multiple times.
  if (!$('body').hasClass('tableHeader-processed')) {
    $('body').addClass('tableHeader-processed');
    $(window).scroll(Drupal.tableHeaderDoScroll);
    $(document.documentElement).scroll(Drupal.tableHeaderDoScroll);
  }

  // Track scrolling.
  Drupal.tableHeaderOnScroll = function() {
    $(headers).each(function () {
      tracker(this);
    });
  };

  // Track resizing.
  var time = null;
  var resize = function () {
    // Ensure minimum time between adjustments.
    if (time) {
      return;
    }
    time = setTimeout(function () {
      $('table.sticky-header').each(function () {
        // Force cell width calculation.
        this.viewHeight = 0;
        tracker(this);
      });
      // Reset timer
      time = null;
    }, 250);
  };
  $(window).resize(resize);
};
