Create a bot to send/receive messages through Facebook messenger

I need a backend api (or program) that running on java or .net that can send messages via facebook messenger (do not use Facebook APIs) using Selenium or other automation frameworks you are familiar with (if you use other automation frameworks, you must notify me for confirmation).
Key features:
1. Log in with the provided the user/password.
2. Send messages to specific Facebook users with provided information.
3. Send Messages from more than 2 senders to specified receiver in a short time.
4. Receive messages from Facebook users in real time (can get username information, message content).
5. Facebook will not block messages for spam reasons (the limitation is defined by you).