//check if page is re-direct from search page, if yes -> highlight search keywords
function isSearchPage()
{
    var search_engines = ['(hkedcity\\.net/edb/teachingresources/search/)',
                          '(hkedcity\\.net/edb/teachingresources/search/\\?site_key=)'
                          ];

    var search_page = '';
    var search_match = null;
    var search_regex = new RegExp('');
    var search_referrer = document.referrer;

    for (var i = 0; i < search_engines.length; i++) {
            search_page = search_engines[i];
            search_regex = new RegExp('^http://www\\.?' + search_page, 'i');
            search_match = search_referrer.match(search_regex);
            if (search_match) {
                return true;
            }
    }
    return false;
}
/*
 * This is the function that actually highlights a text string by
 * adding HTML tags before and after all occurrences of the search
 * term. You can pass your own tags if you'd like, or if the
 * highlightStartTag or highlightEndTag parameters are omitted or
 * are empty strings then the default <font> tags will be used.
 */
function doHighlight(bodyText, searchTerm) 
{
 //   var highlightStartTag = "<font style='color: black; background-color:yellow; font-weight:bold;'>";
    var highlightStartTag = "<font style='background-color:yellow;'>";
    var highlightEndTag = "</font>";
  
  // find all occurences of the search term in the given text,
  // and add some "highlight" tags to them (we're not using a
  // regular expression search, because we want to filter out
  // matches that occur within HTML tags and script blocks, so
  // we have to do a little extra validation)
  var newText = "";
  var i = -1;
  var lcSearchTerm = searchTerm.toLowerCase();
  var lcBodyText = bodyText.toLowerCase();
    
  while (bodyText.length > 0) {
    i = lcBodyText.indexOf(lcSearchTerm, i+1);
    if (i < 0) {
      newText += bodyText;
      bodyText = "";
    } else {
      // skip anything inside an HTML tag
      if (bodyText.lastIndexOf(">", i) >= bodyText.lastIndexOf("<", i)) {
        // skip anything inside a <script> block
        if (lcBodyText.lastIndexOf("/script>", i) >= lcBodyText.lastIndexOf("<script", i)) {
          newText += bodyText.substring(0, i) + highlightStartTag + bodyText.substr(i, searchTerm.length) + highlightEndTag;
          bodyText = bodyText.substr(i + searchTerm.length);
          lcBodyText = bodyText.toLowerCase();
          i = -1;
        }
      }
    }
  }
  
  return newText;
}


/*
 * This is sort of a wrapper function to the doHighlight function.
 * It takes the searchText that you pass, optionally splits it into
 * separate words, and transforms the text on the current web page.
 * Only the "searchText" parameter is required; all other parameters
 * are optional and can be omitted.
 */
function highlightSearchTerms(searchText, treatAsPhrase, warnOnFailure)
{
  if (searchText.length > 0) {
      if (isSearchPage()) {
          // if the treatAsPhrase parameter is true, then we should search for
          // the entire phrase that was entered; otherwise, we will split the
          // search string so that each word is searched for and highlighted
          // individually
          if (treatAsPhrase) {
           searchArray = [searchText];
          } else {
            searchArray = searchText.split(" ");
          }

          if (!document.body || typeof(document.body.innerHTML) == "undefined") {
            if (warnOnFailure) {
              alert("Sorry, for some reason the text of this page is unavailable. Searching will not work.");
            }
            return false;
          }

          var bodyText = document.body.innerHTML;
          for (var i = 0; i < searchArray.length; i++) {
            bodyText = doHighlight(bodyText, searchArray[i]);
          }

          document.body.innerHTML = bodyText;
          return true;
      }
  }
  return true;
}