/*
 * 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, highlightStartTag, highlightEndTag)
{
    // the highlightStartTag and highlightEndTag parameters are optional
    if ((!highlightStartTag) || (!highlightEndTag)) {
        highlightStartTag = "<font style='color: #316AC5; background-color: #FFFFFF;'>";
        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();

    if (searchTerm.length > 0)
    {
        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;
    }
    else
    {
        return bodyText
    }
}


/*
 * 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, highlightStartTag, highlightEndTag)
{
    // 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], highlightStartTag, highlightEndTag);
    }

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

/*
 * This displays a dialog box that allows a user to enter their own
 * search terms to highlight on the page, and then passes the search
 * text or phrase to the highlightSearchTerms function. All parameters
 * are optional.
 */
function searchPrompt(defaultText, treatAsPhrase, textColor, bgColor)
{
    // This function prompts the user for any words that should
    // be highlighted on this web page
    if (!defaultText) {
      defaultText = "";
    }

    // we can optionally use our own highlight tag values
    if ((!textColor) || (!bgColor))
    {
        highlightStartTag = "";
        highlightEndTag = "";
    }
    else
    {
        highlightStartTag = "<font style='color:" + textColor + "; background-color:" + bgColor + ";'>";
        highlightEndTag = "</font>";
    }

    if (treatAsPhrase)
    {
        promptText = "Please enter the phrase you'd like to search for:";
    }
    else
    {
        promptText = "Please enter the words you'd like to search for, separated by spaces:";
    }

    searchText = prompt(promptText, defaultText);

    if (!searchText)
    {
        alert("No search terms were entered. Exiting function.");
        return false;
    }

    return highlightSearchTerms(searchText, treatAsPhrase, true, highlightStartTag, highlightEndTag);
}

/*
 * This function takes a referer/referrer string and parses it
 * to determine if it contains any search terms. If it does, the
 * search terms are passed to the highlightSearchTerms function
 * so they can be highlighted on the current page.
 */
function highlightGoogleSearchTerms(referrer)
{
    // This function has only been very lightly tested against
    // typical Google search URLs. If you wanted the Google search
    // terms to be automatically highlighted on a page, you could
    // call the function in the onload event of your <body> tag,
    // like this:
    //   <body onload='highlightGoogleSearchTerms(document.referrer);'>

    //var referrer = document.referrer;
    if (!referrer)
    {
        return false;
    }

    var queryPrefix = "q=";
    var startPos = referrer.toLowerCase().indexOf(queryPrefix);
    if ((startPos < 0) || (startPos + queryPrefix.length == referrer.length))
    {
        return false;
    }

    var endPos = referrer.indexOf("&", startPos);
    if (endPos < 0)
    {
        endPos = referrer.length;
    }

    var queryString = referrer.substring(startPos + queryPrefix.length, endPos);

    // fix the space characters
    queryString = queryString.replace(/%20/gi, " ");
    queryString = queryString.replace(/\+/gi, " ");

    // remove the quotes (if you're really creative, you could search for the
    // terms within the quotes as phrases, and everything else as single terms)
    queryString = queryString.replace(/%22/gi, "");
    queryString = queryString.replace(/\"/gi, "");

    return highlightSearchTerms(queryString, false);
}


/*
 * This function is just an easy way to test the highlightGoogleSearchTerms
 * function.
 */
function testHighlightGoogleSearchTerms()
{
    var referrerString = "http://www.google.com/search?q=javascript%20highlight&start=0";
    referrerString = prompt("Test the following referrer string:", referrerString);
    return highlightGoogleSearchTerms(referrerString);
}