private static _database: IDBDatabase;

  constructor() {
    this.getDatabase().subscribe(db => IndexedDbService._database = db);
  }

  private getDatabase(): Observable<IDBDatabase> {
    if (!!IndexedDbService._database) return of(IndexedDbService._database);

    return new Observable((observer: Observer<IDBDatabase>) => {
      const request: IDBOpenDBRequest = indexedDB.open(this.DATABASE_NAME, 1);

      request.onsuccess = (event: Event) => {
        observer.next((<IDBOpenDBRequest>event.target).result);
        observer.complete();
      };

      request.onerror = (event: Event) => observer.error((<IDBOpenDBRequest>event.target).error.name);

      request.onupgradeneeded = (event: Event) => {
        observer.next((<IDBOpenDBRequest>event.target).result);
        IndexedDbService._database.createObjectStore(StoreNames.RSI, {keyPath: 'id', autoIncrement: true});
      }
    });
  }