http-interceptor.service.ts

import { HttpErrorResponse, HttpEvent, HttpHandler, HttpInterceptor, HttpRequest } from '@angular/common/http';
import { Injectable } from '@angular/core';
import { Observable, throwError } from 'rxjs';
import { catchError } from 'rxjs/operators';
import { ErrorOccurredMessage } from '../messages/error-occurred.message';
import { MessageBrokerService } from './message-broker.service';
import { LoggingService } from './logging-service';

@Injectable({
    providedIn: 'root'
})
export class HttpInterceptorService implements HttpInterceptor {
    constructor(private readonly messageService: MessageBrokerService,
                private readonly logging: LoggingService) { }

    intercept(req: HttpRequest<any>, next: HttpHandler):
        Observable<HttpEvent<any>> {
        return next.handle(req)
            .pipe(
                catchError((error) => this.handleError(error, this.messageService))
            );
    }

    private handleError(error: HttpErrorResponse, messageService: MessageBrokerService) {
        if (error && (typeof error.error === 'string')) {
            this.logging.logError('err: ' + error.error);
            messageService.sendMessage(new ErrorOccurredMessage(error.error));
        } else if (error) {
            if (error.status === 0) {
                this.logging.logError('Connection error.');
                messageService.sendMessage(new ErrorOccurredMessage('Connection error.'));
            } else {
                this.logging.logError('An error has occurred.');
                messageService.sendMessage(new ErrorOccurredMessage('An error has occurred.'));
            }
        }
        return throwError(error);
    }
}