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": "$user_id === auth.uid"
      }
    },
    "fcm_tokens": {
      ".indexOn": ".value",
      "$token_id": {
        ".read": false,
        ".write": "newData.val() === auth.uid"
      }
    },
    ".read": false,
    ".write": false
  }
}