database-structure.json

{

    "users": {
        "iron-man-uid": {
            "name": "Iron Man",
            "email": "iron@starkindustries.com",
            "username": "ironman",
            "photo": "storage-photo-url"
        },
        "war-machine-uid": {
            "name": "War Machine",
            "email": "warmachine@starkindustries.com",
            "username": "warmachine",
            "photo": "storage-photo-url"
        },
        "other-user-uid": {
            "name": "Other User",
            "email": "other@email.com",
            "username": "otheruser",
            "photo": "storage-photo-url"
        }
    },

    "chats": { // /chats/iron-man-uid/war-machine-uid
        "iron-man-uid": {
            "war-machine-uid": {
                "lastMessage": "Hey War Machine!",
                "timestamp": 1491491503208,
                "title": "War Machine",
                "photo": "photo-url"
            },
            "other-user-uid": {
                "lastMessage": "Hello!",
                "timestamp": 1491491504565,
                "title": "Other User",
                "photo": "photo-url"
            }
        },
        "war-machine-uid": {
            "iron-man-uid": {
                "lastMessage": "Hey War Machine!",
                "timestamp": 1491491503208,
                "title": "Iron Man",
                "photo": "photo-url"
            }
        },
        "other-user-uid": {
            "iron-man-uid": {
                "lastMessage": "Hello!",
                "timestamp": 1491491504565,
                "title": "Iron Man",
                "photo": "photo-url"
            }
        }
    },

    "messages": {
        "iron-man-uid + war-machine-uid": {
            "message-uid-01": {
                "userId": "war-machine-uid",
                "text": "Hey Iron Man!",
                "timestamp": 1491499435726
            },
            "message-uid-02": {
                "sender": "Iron Man",
                "userId": "iron-man-uid",
                "text": "Hey War Machine!",
                "timestamp": 1491499434895
            }
        },
        "other-user-uid + iron-man-uid": {
            "message-uid-01": {
                "sender": "Other User",
                "userId": "other-user-uid",
                "text": "Hello!",
                "timestamp": 1491499435726
            }
        }
    }

}