الگوی Singleton در برنامه React

export class LocalisationService {
    private static instance: LocalisationService
}

private constructor() {
    this.languages = {
      [LanguageCode.EN]: {
        shortName: LanguageCode.EN,
        longName: LanguageName.ENGLISH,
      },
      [LanguageCode.DE]: {
        shortName: LanguageCode.DE,
        longName: LanguageName.DEUTSCH,
      },
      [LanguageCode.FR]: {
        shortName: LanguageCode.FR,
        longName: LanguageName.FRANCAIS,
      },
    }
}

public static getInstance(): LocalizationService {
  if (!LocalizationService.instance) {
    LocalizationService.instance = new LocalizationService()
  }

  return LocalizationService.instance
}

export enum LanguageCode {
  EN = "en",
  DE = "de",
  FR = "fr",
}

export enum LanguageName {
  ENGLISH = "English",
  DEUTSCH = "Deutsch",
  FRANCAIS = "Français",
}
export interface Language {
  shortName: LanguageCode
  longName: LanguageName
}

import { LanguageCode, LocalizationService } from "services"

const localizationService = LocalizationService.getInstance()

export enum LanguageCode {
  EN = "en",
  DE = "de",
  FR = "fr",
}

export enum LanguageName {
  ENGLISH = "English",
  DEUTSCH = "Deutsch",
  FRANCAIS = "Français",
}
export interface Language {
  shortName: LanguageCode
  longName: LanguageName
}

/**
 * Represents the localization service, responsible for managing language-related tasks.
 * This class follows the Singleton pattern to ensure only one instance is used throughout the application.
 */
export class LocalizationService {
  private static instance: LocalizationService
  private readonly languages: { [key: string]: Language }

  /**
   * Initializes a new instance of the LocalizationService class.
   * The constructor is private to prevent instantiation from outside the class.
   */
  private constructor() {
    this.languages = {
      [LanguageCode.EN]: {
        shortName: LanguageCode.EN,
        longName: LanguageName.ENGLISH,
      },
      [LanguageCode.DE]: {
        shortName: LanguageCode.DE,
        longName: LanguageName.DEUTSCH,
      },
      [LanguageCode.FR]: {
        shortName: LanguageCode.FR,
        longName: LanguageName.FRANCAIS,
      },
    }
  }

  /**
   * Retrieves the single instance of the LocalizationService class.
   * If an instance does not exist, it creates a new one.
   * @returns {LocalizationService} The single instance of the LocalizationService class.
   */
  public static getInstance(): LocalizationService {
    if (!LocalizationService.instance) {
      LocalizationService.instance = new LocalizationService()
    }

    return LocalizationService.instance
  }

  /**
   * Retrieves an array of all available languages.
   * @returns {Language[]} An array containing all available languages.
   */
  public getAllLanguages(): Language[] {
    return Object.values(this.languages)
  }

  /**
   * Retrieves a language by its short name.
   * @param {LanguageCode} shortName - The short name of the language to retrieve.
   * @returns {Language | undefined} The language with the specified short name, or undefined if not found.
   */
  public getLanguageByShortName(shortName: LanguageCode): Language | undefined {
    return this.languages[shortName]
  }

  /**
   * Retrieves an array of all languages except the one specified by the key.
   * @param {LanguageCode} key - The key of the language to exclude from the result.
   * @returns {Language[]} An array containing all languages except the one specified by the key.
   */
  public getLanguagesExcept(key: LanguageCode): Language[] {
    return this.getAllLanguages().filter((language) => language.shortName !== key)
  }
}