const firestore = firebase.firestore()


const doc$ = (path: string) => {

    return Observable.create(observer => {
        firestore
        .doc(path)
        .onSnapshot({
          next(doc) {
            observer.next(doc);
          }
        });
    });
 }


// Custom Operators

// Maps snapshot to raw data
const data = (opts?: firebase.firestore.SnapshotOptions) => (
  source: Observable<firebase.firestore.DocumentSnapshot>
) =>
  new Observable<firebase.firestore.DocumentData>(observer => {
    return source.subscribe({
      next(snap) {
        observer.next(snap.data());
      }
    });
  });



// Plucks specific properties from the document data, like a client-side projection query
const pick = (props: string[]) => (
  source: Observable<firebase.firestore.DocumentSnapshot>
) =>
  new Observable<firebase.firestore.DocumentData>(observer => {
    return source.subscribe({
      next(snap) {
        const data = snap.data();
        observer.next(_.pick(data, props)); // Using lodash here
      }
    });
  });