Messaging services

Questions

How many messages should a user be allowed to send?
- 10/min?
- 1/min?
- 1/sec?
How many recipients can be sent to at once?
- 10?
- 50?
- Infinite?
How should we configure Amazon SES?
- Proposal:
  - Reroute bounce and complaints to SNS
  - Have a worker disable emails to hard-bounced recipients
  - Also flip flags in settings for complaints
  - Store the bounce/complaint in a blob
Should users be notified of bounces?
Should some messages be stored as templates?
- If we start sending out notifications about Entity changes and the like, most of the contents will be similar except for the ID and some small part of the message body. We could conceivably add a flag to the MessageToUser object that tells the client to fill in a messages according to some simple template. Then we could store the key-values of the template in a blob (perhaps following the same schema as StringAnnotations) along with the message.
What options belong in the settings object?
- Send email when...
  - Update to a favorite-ed entity
  - Team is messaged
  - Message from user
  - Admin sends mail to everyone
- Mark message as read if forwarded to email?
When someone is added to a conversation, should they be allowed to see all previous messages within the conversation? Or should it be the client's job to forward each individual message to the person?

Objects

Name	DBO	Migration	DTO
MessageContent (Immutable after creation)	Primary key: ID Foreign key: CreatedBy (UserGroup) Foreign key: MessageBody (S3 File Handle ID) Etag CreatedOn	Backup via ID Note: Etag is required because MessageStatus is mutable.	Interface ID CreatedBy (principal ID) S3 File Handle ID CreatedOn
MessageToUser (Immutable after creation)	Foreign key: ID (MessageContent) Subject (nullable) Self foreign key: InReplyTo (ID) (nullable) Foreign key: InReplyToRootId Recursive foreign key to primary key	Secondary to MessageContent	Implements MessageContent Subject (string, optional) Set of recipient IDs inReplyTo (optional) inReplyToRoot (optional)
MessageRecipient (Immutable after creation)	Foreign key: ID (MessageContent) Foreign key: Recipient ID (UserGroup)	Secondary to MessageContent
MessageStatus	Foreign key: ID (MessageContent) Foreign key: Recipient ID (UserGroup) States: UNREAD, READ, ARCHIVED	Secondary to MessageContent	ID Recipient State
Comment (Immutable after creation)	Foreign key: ID (MessageContent) Target type (Enum ObjectType) Target ID TBD: references to other Comments in the conversation*	Secondary to MessageContent	Implements MessageContent Target type Target ID
CommentVotes	Primary key: Message ID Up votes Down votes Is-comment-inappropriate votes	TBD	ID Up Down
MessagingSettings	Foreign key: User ID (UserGroup) Etag Blob of settings	TBD	ID Notification settings Blacklist of blocked users
MessageBundle			Bundles the MessageToUser and Message Status
MessageRecipientSet			Set of recipient IDs

'* per Marcel, Comments may have a more complex set of references/relationships than Messages to Users have. Rather than just 'inReplyTo', it might be that one Comment is an 'answer' to another comment which is a question. Further, the multiple answers to a question may have 'previous' references which order them.

Message sender (worker)

Extend ObjectType to include a "MESSAGE" type
Have DBOMessage extend ObservableEntity and TaggableEntity
Send a change message when a message is created
Subscribe worker to the repo-changes topic
Look for MESSAGE-CREATED changes to process
The worker should always check to see if a message has already been sent, so that messages do not get resent every time the stack changes.
- A message has been sent if there is a recipient. The worker is in charge of making sure all sent messages have at least one recipient. In the case where a user sends a message to multiple recipients, all of which are not visible to the user, then the worker should bounce the message back to the user, along with a bounce message. This ensures the message has a row in the MessageStatus table.

Services

Sorting & Pagination
- Sort by creation date
- Sort by subject
- Sort by recipient name

Method	URI	Body	Parameters	Return	Description	Permission
POST	/message	Message	inReplyTo=null (i.e. another Message)	Message	Sends a message. Note, message delivery permission is on a recipient-by-recipient basis, asynchronous to the message creation. Unauthorized delivery may result in silent failure or a bounce message (TBD).	Authenticated User Must be admin to send to AUTH_USERS Must have SEND_MESSAGE permission on team to send to team
GET	/message/inbox		Sorting + pagination	Paginated results<MessageBundle>	Gets all messages the authenticated user has received	Authenticated User
GET	/message/outbox		Sorting + pagination	Paginated results<Message>	Gets all messages the authenticated user has sent	Authenticated User
GET	/message/{id}			Message	Gets a specific message	Sender or Receiver
POST	/message/{id}/forward	MessageRecipientSet		Message	Forwards a message to other recipients. This is equivalent to getting a (visible) message and POST-ing it to /message	Sender or Receiver
GET	/message/{id}/conversation		Sorting + pagination	Paginated results<Message>	Gets messages belonging in the same thread as the message ID. The list is filtered according to the user's ID.	Sender or Receiver
PUT	/message/status	MessageStatus			Marks a message as: READ UNREAD ARCHIVED	Receiver
POST	/entity/{id}/comments	Message		Message	Convenience method for commenting on an entity. The service fills out fields like message ID, thread ID, and recipients, leaving just subject and body for the user.	Authenticated user with SEND_MESSAGE permission on entity
GET	/entity/{id}/comments		Sorting + pagination	Paginated results<Message>	Gets message belonging to the thread tied to the entity.	Authenticated user with READ permission on entity
GET	/message/settings			MessageSettings	Gets the notification settings of the user	Authenticated User
PUT	/message/settings	MessageSettings			Changes notification settings	Authenticated User