PHP is a scripting language. As such it is quite easy to put pieces of code that are used in different places into a separate file and include/require it when needed. This was and still is common practice, especially when not taking an object oriented approach.

So, what is wrong with it?

Every now and then I need to trace request processing in zen-cart to figure out what actually happens. This can be a very frustrating process as zen-cart does exaclty what I described above. Furthermore, there is code to load and instantiate classes and utility code on demand. Don’t get me wrong - this is perfectly legal and ZenMagick has also some code to do stuff like that.

What happened yesterday was that I was trying to fix a bug in ZenMagick code. On the checkout success page there is the option to select products that you are interested in and for whose you want to get update notifications. This was broken, as only one product got picked up, rather than all selected.

Eventually, I found that ZenMagick’s zm_href(..) function does not handle multiple values for a single request paramter correctly (for example: notify[]=3&notify[]=19) . The square brackets are the PHP way of creating an array of values in the request parameter arrays $_GET and $_POST, respectively.

Anyway, before I could find that, though, I had to find my way through includes, redirects to the same URL just with a different action value in the URL, redirects and eventually came across main_cart_actions.php. They only reason that I looked into that file was that a global searchfound the string notify in it. Now, thanks to the zen-cart event handling, there is lots of notify around, but still. So, it turns out that updates to product notifications are handled by the shopping cart! WTF!

The basic idea in zen-cart’s architecture of having a dedicated folder containing code to handle a particular request is not bad. But every time I am looking for something special, it’s handled in a special file that sits on a higher level. Makes sense as the code is shared between different requests. on the other hand it’s usually hard to find even though more often than not I look there first!