import { BehaviorStore, IStateUpdater } from './BehaviorStore';

/**
 * Prostore which uses BehaviorSubject to hold its state.
 * It mimics the React class component state management.
 * You can use setState to change part of the state of the store.
 *
 * It performs batched asynchronous state updates which means that
 * two consequent calls to setState will be batched and result
 * in dispatching only one store update in the next cycle of the event loop.
 */
export class AsyncBehaviorStore<
  State extends object
> extends BehaviorStore<State> {
  _queuedUpdates: IStateUpdater<State>[] = [];
  _queuedTimeout: any = null;

  constructor(initialState: State) {
    super(initialState);
  }

  /**
   * Update part of the store state.
   *
   * @param stateUpdate - object containing partial state update or updater function.
   *  If the function is provided, it is called with the current state and should return the partial state update
   */
  setState(stateUpdate: IStateUpdater<State>) {
    this._queuedUpdates.push(stateUpdate);
    if (!this._queuedTimeout) {
      this._queuedTimeout = setTimeout(() => this._applyQueuedUpdates(), 0);
    }
  }

  _applyQueuedUpdates() {
    let newState = this.state;
    for (let update of this._queuedUpdates) {
      newState = this._applyStateUpdater(newState, update);
    }
    this._queuedTimeout = null;
    this._queuedUpdates = [];
    this.state$.next(newState);
  }
}