API for PhpList integration with other web app

Hi everyone.
I am new to PHPList and I need to integrate it with a PHP web app I’m developing for a client.

I need to handle from my web app the user insert/update/delete, the subscription to a list and the creation of a message.
The message creation and the possibility to send it programmatically are crucial to this project.

Can anyone give me some tips on how to integrate these two app? Is there some API for the remote control of PHPList or at least there is a detailed PHPList database schema with some explanation for the tables and columns?

Thank everyone in advance. Giacomo