import { HttpEvent, HttpHandler, HttpInterceptor, HttpRequest, HttpResponse } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable } from 'rxjs';
import { CacheApiService } from './cache-api.service';
import { catchError, tap } from 'rxjs/operators';

@Injectable()
export class HttpCacheInterceptor implements HttpInterceptor {
    constructor(private readonly _cacheApiService: CacheApiService) {}

    intercept(req: HttpRequest<unknown>, next: HttpHandler): Observable<HttpEvent<unknown>> {
        if (!this._cacheApiService.isCachable(req)) {
            return next.handle(req);
        }

        return this._cacheApiService.getCachedRequest(req).pipe(
            // tap(ok => {
            //     console.log('[CACHE-API] got from cache', ok);
            // }),
            catchError(cacheError => {
                // console.log('[CACHE-API] Cache fetch error', cacheError, req.url);
                return this.sendRequest(req, next);
            }),
        );
    }

    /**
     * Get server response observable by sending request to `next()`.
     * Will add the response to the cache on the way out.
     */
    sendRequest(request: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        return next.handle(request).pipe(
            tap(async event => {
                // There may be other events besides the response.
                if (event instanceof HttpResponse) {
                    await this._cacheApiService.cacheRequest(request, event);
                }
            }),
        );
    }
}