Preferences Service

preferences.service.ts

import { Injectable } from '@angular/core';
import { LocalStorage } from '../storage/local.storage';

interface Preferences {
  myPreference: string;
}

@Injectable({ providedIn: 'root' })
export class PreferencesService {
  preferences: Preferences;

  private readonly LOCAL_STORAGE_KEY = 'preferences';

  constructor(private localStorage: LocalStorage) {
    const DEFAULT_PREFERENCES: Preferences = {
      myPreference: 'foo',
    };

    const storedPreferences = this.readFromLocalStorage();

    this.preferences = {
      ...DEFAULT_PREFERENCES,
      ...storedPreferences,
    };
  }

  update(preferences: Partial<Preferences>) {
    Object.assign(this.preferences, preferences);
    this.saveToLocalStorage();
  }

  set(preference: keyof Preferences, value: any) {
    this.preferences[preference] = value;
    this.saveToLocalStorage();
  }

  get(preference: keyof Preferences) {
    return this.preferences[preference];
  }

  private saveToLocalStorage() {
    const stringifiedPreferences = JSON.stringify(this.preferences);
    this.localStorage.setItem(this.LOCAL_STORAGE_KEY, stringifiedPreferences);
  }

  private readFromLocalStorage() {
    const stringifiedPreferences = this.localStorage.getItem(
      this.LOCAL_STORAGE_KEY
    );

    return JSON.parse(stringifiedPreferences);
  }
}