import {
  ApplicationRef,
  Inject,
  Injectable,
} from '@angular/core';
import { isPromiseLike } from '@rxap/utilities';
import {
  BehaviorSubject,
  firstValueFrom,
  isObservable,
  Observable,
  of,
} from 'rxjs';
import {
  filter,
  switchMap,
  take,
  tap,
} from 'rxjs/operators';

export interface LifeCycleHook {
  promise: PromiseLike<any>;
}

@Injectable({
  providedIn: 'root',
})
export class LifeCycleService {

  private static hooks = new Map<string, LifeCycleHook>();
  public isReady$ = new BehaviorSubject(false);

  constructor(@Inject(ApplicationRef) public readonly appRef: ApplicationRef) {

    LifeCycleService.AddHook('stable', firstValueFrom(appRef.isStable.pipe(
      tap(isStable => console.log('app state:', isStable ? 'stable' : 'unstable')),
      filter(Boolean),
      take(1),
      tap(() => console.log('app is ready')),
    )));

    Promise.all(Array.from(LifeCycleService.hooks.values()).map(hook => hook.promise))
           .then(() => this.isReady$.next(true));

  }

  public static AddHook(name: string, promise: PromiseLike<any>): void {
    LifeCycleService.hooks.set(name, { promise });
  }

  public whenReady<T>(thenOrFunction: Observable<T> | PromiseLike<T> | (() => Observable<T>) | (() => PromiseLike<T>) | (() => T)): Observable<T> {

    return this.isReady$.pipe(
      filter(Boolean),
      take(1),
      switchMap(() => {

        if (typeof thenOrFunction === 'function') {

          const then = thenOrFunction();

          if (isPromiseLike(then) || isObservable(then)) {
            return then;
          } else {
            return of(then);
          }

        } else {
          return thenOrFunction;
        }

      }),
    );

  }

}