app-setup.service.ts

import { HttpService } from "../http/http.service";
import { Injectable, Inject } from "@angular/core";
import { Observable } from "jalhyd";
import { StorageService, LOCAL_STORAGE } from "ngx-webstorage-service";

/**
 * Stores app preferences
 */
@Injectable()
export class ApplicationSetupService extends Observable {

    private CONFIG_FILE_PATH = "app/config.json";
    private LOCAL_STORAGE_PREFIX = "nghyd_";

    /** ultimate fallback language (read from config) */
    private _fallbackLanguage = "fr";

    // default builtin values
    public displayPrecision = 0.001;
    public computePrecision = 0.0001;
    public newtonMaxIterations = 50;
    public enableNotifications = true;

    /**
     * just stores the current language preference, does not transmit it to I18nService, that is
     * not available here.
     *
     * @see ApplicationSetupComponent.currentLanguageCode() setter
     * @see I18nService.update() observer
     */
    public language = "fr";
    /** themes to group calculators, for displaying on the front page */
    public themes: any[];

    public warnBeforeTabClose: boolean;

    public constructor(
        private httpService: HttpService,
        @Inject(LOCAL_STORAGE) private storage: StorageService
    ) {
        super();
        // precedence: builtin values >> JSON config >> browser's language >> local storage
        const builtinLanguage = this.language;

        // related to @HostListener("window:beforeunload") in AppComponent
        this.warnBeforeTabClose = true;

        // load JSON config
        this.readValuesFromConfig().then((data) => {
            const configLanguage = this.language;
            this._fallbackLanguage = configLanguage;

            // guess browser's language
            this.language = navigator.language;
            const browserLanguage = this.language;

            // load saved preferences
            const loadedPrefKeys = this.readValuesFromLocalStorage();
            let storageLanguage: string;
            if (loadedPrefKeys.includes("language")) {
                storageLanguage = this.language;
            }

            // notify I18nService
            this.notifyObservers({
                action: "languagePreferenceChanged",
                languages: [ storageLanguage, browserLanguage, configLanguage, builtinLanguage ]
            });
        });
    }