db

Table user as U{
  id ObjectId [pk]
  lastname String
  firstname String
  email String
  password String
  picture String
}

Table contact as C{
  id ObjectId [pk]
  userId ObjectId 
  contactId ObjectId 
  status Boolean
}

Table message as M{
  id ObjectId [pk]
  sender ObjectId
  receiver ObjectId
  text String 
  file ArrayBuffer
}

Table chatgroup as CG{
  id ObjectId [pk]
  name String
  userAmount Number
  messageAmount Number
  admins ArrayObjectId 
  members ArrayObjectId
}

Ref: C.userId > U.id
Ref: C.contactId > U.id
Ref: M.sender > U.id
Ref: M.receiver > U.id
Ref: CG.admins > U.id
Ref: CG.members > U.id