database.rules.json

{
    "rules": {
        "profiles": {
            "$user_id": {
                ".read": "$user_id === auth.uid",
                ".write": "$user_id === auth.uid"
            }
        },
        "rooms": {
            ".read": "auth !== null",
            "$room_id": {
                ".read": "auth !== null",
                ".write": "!data.exists() || data.child('admins').child(auth.uid).val() == true",
                "lastMessage": {
                    ".write": "auth !== null"
                }
            }
        },
        "messages": {
            ".read": "auth !== null",
            ".write": "auth !== null",
            ".indexOn": "roomId",
            "$message_id": {
                ".read": "auth !== null",
                ".write": "auth !== null"
            }
        },
        "status": {
            "$user_id": {
                ".read": "auth !== null",
                ".write": "$user_id === auth.uid"
            }
        },
        ".read": false,
        ".write": false
    }
}