How to create our own custom event or custom transaction?

Hell @Brivium

How to create our own custom event or custom transaction?
I want to make a custom php page, that works as a simple API for other application. For example:

i create custom.php and place it at mywebsite.com/custom.php

My application will call mywebsite.com/custom.php?user=soehoe&key=somekey&amount=10&CreditName=credit&action=someaction&comment=other_application
where user = user name at forum, key=somekey that i will determine, amount is the credit that will be added/decreased.

Then custom.php will proses input data, and then will add/decrease some credits to/from user. The transaction should be listed in transaction history like normal transaction:



So, my question is how to make it happen?
I have try to insert new transaction manually into database table but it was failed. Please help