/**
 * 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:blue; background-color:yellow;'>";
		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, container, 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(!container){
		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;
	}else{
		var bodyText = $(container).html();
		for (var i = 0; i < searchArray.length; i++) {
			bodyText = doHighlight(bodyText, searchArray[i], highlightStartTag, highlightEndTag);
		}
	
		$(container).html(bodyText);
	} // if

	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 highlightSearchPrompt(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, container, treatAsPhrase, true, highlightStartTag, highlightEndTag);
}

/**
 * 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 highlightSearch(searchText, container, treatAsPhrase, textColor, bgColor) {
	if (!searchText) {
		return null;
	}

	// 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:";
	}

	return highlightSearchTerms(searchText, container, 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, container) {
	// 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, container, 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);
}