Asymmetrik/ngx-starter

import { HttpBackend, HttpEvent, HttpRequest, HttpResponse } from '@angular/common/http';
import { Injectable, inject } from '@angular/core';

import { AsyncSubject, Observable } from 'rxjs';

import { Config } from './config.model';

@Injectable({
    providedIn: 'root'
})
export class ConfigService {
    readonly #http = inject(HttpBackend);

    readonly #configSubject$ = new AsyncSubject<Config | null>();

    constructor() {
        this.reloadConfig();
    }

    /**
     * Get the shared config observable
     */
    public getConfig(): Observable<Config | null> {
        return this.#configSubject$;
    }

    /**
     * Refresh the latest config and fire it to the subject. This should not need
     * to be invoked frequently because the config rarely changes.
     *
     * We are using HttpBackend to avoid the interceptors since this call is invoked
     * as part of the app initialization process.
     */
    public reloadConfig() {
        const request = new HttpRequest<Config>('GET', 'api/config', {});

        this.#http.handle(request).subscribe({
            next: (httpEvent: HttpEvent<Config>) => {
                if (httpEvent instanceof HttpResponse) {
                    let newConfig = null;
                    const response: HttpResponse<Config> = httpEvent;

                    if (response.status >= 200 && response.status < 300) {
                        newConfig = response.body;
                    }

                    this.#configSubject$.next(newConfig);
                    this.#configSubject$.complete();
                }
            },
            error: () => {
                this.#configSubject$.next(null);
                this.#configSubject$.complete();
            }
        });
    }
}