Allow manual tagging of links

I wanted to use Google Analytics to report on click-thrus to offsite links. Since the links are offsite, they're not automatically captured. The solution that Google recommends is to add an onClick attribute to the anchor tag. However, I felt finding and adding the appropriate javascript was too onerous / unrealistic for our editorial staff; I wanted to make it easier for them to tag offsite links.

Inspired by the gotwo module, I added a filter that would translate a new anchor tag attribute, gatag, into the appropriate onClick='javascript:...' attribute. I also added some admin settings to add an identifying string and optionally add source and / or destination information to every manually tagged link.

For example, our editors could enter the link <a href="http://youtube.com" gatag="entertainment">. The filter might translate that link into <a href="http://youtube.com" onClick="javascript: pageTracker._trackPageview('/tagged/entertainment');">. Alternatively, if the administrator has specified that information about both the source and destination of the link be included in the tag, the same link might also be translated to <a href="http://youtube.com" onClick="javascript: pageTracker._trackPageview('/tagged/entertainment/SOURCE/node/999999/DESTINATION/youtube.com');">. [I'm brand new to google analytics, and don't know much about how to segment data on the reports. If there's a better way to format the tag so it's easier to report on sources and or destinations, please modify the code appropriately.]

Please note that to use the filter, the admin has to a) enable the filter for the Full HTML input format (Filtered HTML strips out javascript), and b) give it a lower weight (higher priority) than the HTML filter (the HTML filter would strip out the gatag attribute). Also, any text that uses the gatag attribute must be entered in Full HTML format, so its usage is likely limited to editorial and other internal staff that have the right to post Full HTML content. [However, the actual translation of the attribute is done in a function that can be passed any text that starts with an anchor tag, e.g. the output of l(). So you might find other contexts in which you can use this extension.]

FYI, we're currently running an old version of this module (googleanalytics.info:; $Id: googleanalytics.info,v 1.2.2.1 2007/01/18 01:16:02 budda Exp $). Although the attached patch is relative to the latest released version, 5.x-1.4, I haven't actually tested it with that version. However, the code is completely new code and doesn't depend on existing functionality in the module, so it should work properly. (It does honor the googleanalytics_legacy_version variable to generate the appropriate function call.)

I hope you find this feature useful enough to incorporate into the module.

[Credits: I did use some of the code I found in the gotwo module as a starting point for this code.]