Firestore rules for TEAL based task app

firestore.rules

service cloud.firestore {
  match /databases/{database}/documents {

    function isAdmin() {
      return exists(/databases/$(database)/documents/admins/$(request.auth.uid));
    }

    function isUserAssigneeOrCreator() {
      return request.auth.uid == resource.assignee.id
        || request.auth.uid == resource.creator.id;
    }

    match /tasks/{anyTask=**} {
        allow read: if request.auth != null;
      allow create: if request.auth != null;
      allow update: if request.auth != null
        && (isUserAssigneeOrCreator() || isAdmin()) ;
      allow delete: if request.auth != null
        && (isUserAssigneeOrCreator() || isAdmin()) ;

        // Auth users can assign themself to task if no one assigned
        match /assignee {
          allow write: if request.auth != null && request.resource == null;
        }
    }

    match /users/{userId} {
      allow read: if request.auth != null; // Auth users can read
      allow write: if userId == request.auth.uid;
    }

    match /admins/{anyAdmin} {
        allow read: if false;
    }
  }
}