Looks for a shortened amazon affiliate link like https://amzn.to/33GJdHb and converts it to the smile version (https://smile.amazon.com/dp/B00X0AWA6E/ref=as_li_ss_tl?ie=UTF8&linkCode=ll1&tag=playwiththewe-20&linkId=d88644f0ca89b94b52f5710bf6750b0a&language=en_US) at runtime. This process can be slow so there is some caching.
How the WordPress AmazonSmile plugin works – Long Version from http://thomasloughlin.com/amazon-smile-amazons-affiliate-program/
Adds a filter so the content is passed to a function.
Content is searched for a shortened Amazon Affiliate Link.
The ‘key’ is extracted from the url and checked against cache.
If the end url is not found, the full url is grabbed, converted to smile and thrown into cache.
It’s pretty simple to run, just drop it in the plugin directory and activate that’s all it takes.