Domain

• User

{
    "id": B,
    "fullName": "User B",
    "userName": "markhaur",
    "groups": [G1,G2],
    "contacts": [A,C]
}

• Group

{
    "id": G2,
    "name": ...,
    "participants": [B, C]
}

• MessageSent

{
    "id": "123"
    "toGroups": [G1, G2]
    "toUsers": [C, D]
    "content": ...,
    "createdAt": ...,
    "sentAt": ...,
    "received": [
        {"by": B, "at": "12:00:00", "in": "G1"},
        {"by": B, "at": "12:00:00", "in": "G2"},
        {"by": C, "at": "12:05:00", "in": "G2"},
        {"by": C, "at": "12:05:00"},
        {"by": D, "at": "12:00:00"}
    ] 
    "seen": [
        {"by": B, "at": "12:01:05", "in": "G1"},
        {"by": B, "at": "12:01:00", "in": "G2"},
        {"by": C, "at": "12:10:00", "in": "G2"},
        {"by": C, "at": "12:10:05"},
        {"by": D, "at": "12:20:00"}
    ] 
}

• MessageReceived

// By B:
{
    "id": "123",
    "in": [G1,G2],
    "messageFrom": A,
    "content": ..., 
    "createdAt": ...,
    "sentAt": ...,
    "receivedAt": ...
}

// By C:
{
    "id": "123",
    "in": [DM*,G2],
    "messageFrom": A,
    "content": ..., 
    "createdAt": ...,
    "sentAt": ...,
    "receivedAt": ...
}
// *DM stands for Direct Message

// By D:
{
    "id": "123",
    "in": [DM],
    "messageFrom": A,
    "content": ..., 
    "createdAt": ...,
    "sentAt": ...,
    "receivedAt": ...
}

Usecases

• User A can send a Message to User B
• User B can send a Message to User A
• User A can send a Message to User B and User C (like forwarding a link to 2 users)
• User A can send a Message to a Group (User B and User C)

MongoDB 3 instances if messageFrom == A should we save locally? or save remotely as well?

instancesByUser := map[string]int{ "A": 2, "B": 1, "C": 3, }

C->A save in (instancesByUser(A)) // 2 save in (instancesByUser(C)) // 3

A->B save in (instancesByUser(B)) // 1 save in (instancesByUser(A)) // 2

Duplication?

CS1 CS2 ^ ^ A -> B

CS1 -> CS2 event