{ // group
    "id": 1 // id of the group
    "name": "Chat Group" // name of group; if there are more than 2 members
    "members": [ "member1", "member2", ...] // ids of the group chat members; only they have access to the JSON document
    "chatlog": [ "timestamp": ["member1", "message1"], "timestamp": ["member2", "message1"], ...] // who sent which message in chronological order
}

{ // user
    "id": 1 // id of the user
    "name": "Max" // name of the user
    "chat_groups": [ "1", "2", ...] // ids of the groups, the user is a member of
}