@Injectable()
export class StudentService {

  results$ = new Subject<any>();
  studentsAdded$ = new BehaviorSubject<any>(null);
  private resultArray: any[] = [];

  constructor(private afs: AngularFirestore) { }

  getRecordsBySearch(searchText: any) {
    // console.log(`MD: StudentService -> getRecordsBySearch -> getRecordsBySearch`);
    this.resultArray = [];
    this.results$.next([]);
    if (searchText) {
      // console.log(`MD: StudentService -> getRecordsBySearch -> searchText`, searchText);
      const studentsRef = this.afs.collection('students').ref;
      const fnameQuery = studentsRef.where('fname', '==', searchText);
      const lnameQuery = studentsRef.where('lname', '==', searchText);
      const gradeQuery = studentsRef.where('grade', '==', searchText);
      const queries = [fnameQuery, lnameQuery, gradeQuery];
      this.processQueries(queries);
    }
  }

  getRecordsByEmail(email: string) {
    this.resultArray = [];
    this.results$.next([]);
    const studentsRef = this.afs.collection('students').ref;
    const fe = studentsRef.where('fatherEmail', '==', email);
    const me = studentsRef.where('motherEmail', '==', email);
    const queries = [fe, me];
    this.processQueries(queries);
  }

  public processQueries(queries: Array<any>) {
    queries.forEach(query => {
    query.onSnapshot(querySnapshot => {
      querySnapshot.docs.forEach(queryDocumentSnapshot => {
        const data = queryDocumentSnapshot.data();
        this.resultArray.push(data);
        this.results$.next(this.resultArray);
        });
        // Prevent duplicates in array.  Duplication occurs upon a saved edit (assuming there was an actual change).
      const u = this.resultArray.filter((e, i) => this.resultArray.findIndex(a => a.id === e.id) === i);
      this.results$.next(u);
       });
    });
  }
}