import { HttpClient, HttpEvent, HttpHandler, HttpRequest } from '@angular/common/http';
import { Inject, Injectable, InjectionToken, Optional } from '@angular/core';
import { Observable } from 'rxjs';

import { HttpRequestOptions } from '../model/internal/http-requests';

export const HTTP_SERVICE_INTERCEPTORS = new InjectionToken<HttpServiceInterceptor>('HTTP_SERVICE_INTERCEPTORS');

export interface HttpServiceHandler {
    handle(req: HttpRequest<any>, options: Partial<HttpRequestOptions>): Observable<HttpEvent<any>>;
}

export interface HttpServiceInterceptor {
    intercept(req: HttpRequest<any>, options: Partial<HttpRequestOptions>, next: HttpServiceHandler): Observable<HttpEvent<any>>;
}

@Injectable()
export class HttpService {

    private handler: HttpServiceHandler;

    constructor(
        protected httpHandler: HttpHandler,
        @Optional() @Inject(HTTP_SERVICE_INTERCEPTORS) interceptors: HttpServiceInterceptor[] | null
    ) {
        let handler: HttpServiceHandler = {
            handle: (req, options) => httpHandler.handle(req)
        };
        if (interceptors) {
            handler = interceptors.reduceRight((next, interceptor) => ({
                handle: (req, options) => interceptor.intercept(req, options, next)
            }), handler);
        }
        this.handler = handler;
    }

    public client(options: HttpRequestOptions = {}): HttpClient {
        return new HttpClient({
            handle: (req) => this.handler.handle(req, options)
        });
    }
}