import { Injectable, Inject, PLATFORM_ID } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent, HttpResponse } from '@angular/common/http';
import { Observable, of } from 'rxjs';
import { tap } from 'rxjs/operators';
import { TransferState, makeStateKey, StateKey } from '@angular/platform-browser';
import { isPlatformServer } from '@angular/common';

@Injectable({
  providedIn: 'root'
})
export class HttpInterceptorService implements HttpInterceptor {
  constructor(private transferState: TransferState, @Inject(PLATFORM_ID) private platformId: any) {}

  public intercept(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {

    //console.info("intercept transferstate");
    if (request.method !== 'GET') {
      return next.handle(request);
    }

    const key: StateKey<string> = makeStateKey<string>(request.url);

    const storedResponse = this.transferState.get<any>(key, null);
    //console.info(key, storedResponse);
    if (storedResponse) {
      const response = new HttpResponse({body: storedResponse, status: 200});
      if (!isPlatformServer(this.platformId)) {
        //console.info("browser remove: ", key);
        this.transferState.remove(key);
      }
      return of(response);
    } else {
      if (isPlatformServer(this.platformId)) {
        return next.handle(request).pipe(tap((event) => {
          //console.info("server add: ", key);
          this.transferState.set(key, (<HttpResponse<any>>event).body);
        }));
      } else {
        return next.handle(request);
      }
    }
  }
}