import { Injectable, Inject, PLATFORM_ID } from '@angular/core';
import { HttpEvent, HttpInterceptor, HttpHandler, HttpRequest, HttpResponse, HttpErrorResponse, HttpEventType } from '@angular/common/http';

import { Observable } from 'rxjs/Observable';

import { TransferState } from '@angular/platform-browser';
import { isPlatformServer } from '@angular/common';

import { ORIGIN_URL } from './shared/constants/baseurl.constants';

@Injectable()
export class CustomHttpInterceptor implements HttpInterceptor {

    private isServer = isPlatformServer(this.platformId);

    constructor(
        @Inject(PLATFORM_ID) private platformId,
        protected transferState: TransferState,
        @Inject(ORIGIN_URL) private baseUrl: string) { }

    intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
        let modifiedRequest: any;
        let url: string;

        let isLocalRequest: boolean = !req.url.startsWith('http');
        if (isLocalRequest) {

            url = this.baseUrl + req.url;

            // Skip cache check if the request method isn't GET.
            if (req.method == 'GET') {
                const cachedResponse = this.getFromCache(url);

                if (cachedResponse) {
                    // A cached response exists. Serve it instead of forwarding
                    // the request to the next handler.

                    let modifiedResponse = new HttpResponse<any>({ headers: cachedResponse.headers, body: cachedResponse.body, status: cachedResponse.status, statusText: cachedResponse.statusText, url: cachedResponse.url });
                    return Observable.of(modifiedResponse);
                }
            }

            // Clone the request to add the new header.
            modifiedRequest = req.clone({ headers: req.headers, url: url, body: req.body });
        }

        return next.handle(isLocalRequest ? modifiedRequest : req)
            .do((event: HttpEvent<any>) => {
                if (event instanceof HttpResponse) {
                    if (this.isServer) {
                        this.setCache(url, event);
                    }
                }
            });
    }

    private setCache(key, data) {
        return this.transferState.set(key, data);
    }

    private getFromCache(key): HttpResponse<any> | null {
        return this.transferState.get(key, null as any);
    }
}

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