import { Injectable } from '@angular/core';
import {
  HttpEvent,
  HttpInterceptor,
  HttpHandler,
  HttpRequest,
  HttpResponse
} from '@angular/common/http';
import { Observable, Subscriber } from 'rxjs';

import { HttpCacheService } from './http-cache.service';

@Injectable()
export class CacheInterceptor implements HttpInterceptor {
  private forceUpdate = false;

  constructor(private httpCacheService: HttpCacheService) {}

  configure(options?: { update?: boolean } | null): CacheInterceptor {
    const instance = new CacheInterceptor(this.httpCacheService);
    if (options && options.update) {
      instance.forceUpdate = true;
    }
    return instance;
  }

  intercept(
    request: HttpRequest<any>,
    next: HttpHandler
  ): Observable<HttpEvent<any>> {
    if (request.method !== 'GET') {
      return next.handle(request);
    }

    return new Observable((subscriber: Subscriber<HttpEvent<any>>) => {
      const cachedData = this.forceUpdate
        ? null
        : this.httpCacheService.getCacheData(request.urlWithParams);
      if (cachedData !== null) {
        subscriber.next(new HttpResponse(cachedData as Object));
        subscriber.complete();
      } else {
        next.handle(request).subscribe(
          event => {
            if (event instanceof HttpResponse) {
              this.httpCacheService.setCacheData(request.urlWithParams, event);
            }
            subscriber.next(event);
          },
          error => subscriber.error(error),
          () => subscriber.complete()
        );
      }
    });
  }
}