Background:
Currently, message_send (in messagelib.php) and send_message (in lib/classes/message/manager.php) support 1:1 messaging. See: 'userto' and 'userfrom' used there. The table structure was re-worked to support group conversations (more than 2 users in a conversation - nothing to do with course groups here), but I'm not sure if the APIs all support sending messages in conversations like this. Certainly the unit tests seem to only test 1:1 conversations.

I'm also not sure whether the conversation creation code supports groups of more than 2 members, or whether we can create a conversation without an initial message being sent (which we'll perhaps need so we can fetch conversation details for the initial UI load - depending how we end up doing that bit)

Scope:

• Investigate message_send and send_message and check whether it's possible to send messages to a conversation using existing APIs. 
• Check also any other conversation creation code
• If the above is missing/incomplete: we will either need to update, or create new API allowing us to send a message to all members of a conversation.
  • We may be better off creating a new API allowing us to do this by conversation as with groups of 3+ we're not sending a message to a single user any more - needs investigation anyway.
• We should provide APIs to create conversations (collections of members), WITHOUT the need to send an initial message.
• We should add unit tests to message/tests/api_test.php to cover conversations with more than just 2 users to make sure everything works as expected.
  • Create conversation (can we create a conversation without an initial message - this is important!)
  • Send messages to conversaton
  • Unread counts for all users in the conversation (message_unread table from memory)