function doHighlight(bodyText, searchTerm, highlightStartTag, highlightEndTag) {
    // the highlightStartTag and highlightEndTag parameters are optional
    if ((!highlightStartTag) || (!highlightEndTag)) {
        highlightStartTag = "<font style='color:blue; background-color:yellow;'>";
        highlightEndTag = "</font>";
    }

    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;
}

function highlightSearchTerms(searchText, treatAsPhrase, warnOnFailure, highlightStartTag, highlightEndTag) {

    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;
}

function searchPrompt(defaultText, treatAsPhrase, textColor, bgColor) {

    if (!defaultText) {
        defaultText = "";
    }

    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);
}

function highlightGoogleSearchTerms(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);
}

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);
}