/**
 * Middleware for monitoring the dispatch of async actions
 */
export class DispatchMonitor {
  /** Gets the Redux middleware */
  getMiddleware() {
    return store => {
      this.store = this.store || store;
      return next => action => {
        if (typeof action === 'function') {
          this.count++;
          return next(action)
            .then(value => {
              this.count--;
              if (this.count === 0) {
                this.callback();
              }
              return value;
            })
            .catch(err => this.callback(err));
        } else {
          return next(action);
        }
      };
    };
  }

  /** Returns a promise that resolves when all dispatched async actions have resolved. */
  wait() {
    return new Promise((resolve, reject) => {
      if (this.error) {
        reject(this.error);
      } else if (this.count === 0) {
        resolve(this.store.getState());
      } else {
        this.callback = error => {
          if (error) {
            reject(error);
          } else {
            resolve(this.store.getState());
          }
        };
      }
    });
  }

  private count: number = 0;
  private error: any;
  private store: any;
  private callback: (err?: any) => void = err => (this.error = err);
}