import { BehaviorSubject } from 'rxjs';
import { IStore } from './IStore';
import { proxyToBehaviorSubject } from './proxyToBehaviorSubject';
import { onFirstSubscription } from './onFirstSubscription';

export class ValueStore<Value> implements IStore<Value> {
  state$: BehaviorSubject<Value>;

  get state() {
    return this.state$.value;
  }

  constructor(value: Value) {
    const subject$ = new BehaviorSubject<Value>(value);
    this.state$ = proxyToBehaviorSubject(
      subject$.pipe(
        onFirstSubscription(
          () => this.onSubscribe(),
          () => this.onUnsubscribe()
        )
      ),
      subject$
    );
  }

  setState(value: Value) {
    this.state$.next(value);
  }

  /**
   * This callback is called when the first subscriber subscribes to this store.
   * It may be called multiple times during the lifetime of the store.
   * You can use it to perform side-effects like subscribing to other
   * observables.
   */
  onSubscribe() {}

  /**
   * This callback is called when the last subscriber unsubscribes from this store.
   * It may be called multiple times during the lifetime of the store.
   * You can use it to cleanup side-effects created during onSubscribe.
   */
  onUnsubscribe() {}
}