added fallbacks

README.md

@@ -290,6 +290,28 @@ I18nModule.forRootAsync({
 });
 ```
 
+#### Using Fallbacks
+
+To configure multiple fallbacks use `fallbacks` option. You could handle a single language or multiple ones.
+
+> (note: In this example, the translations `en` `fr` and `pt-BR` are needed to work correctly.)
+
+```typescript
+I18nModule.forRoot({
+  fallbackLanguage: 'en',
+  fallbacks: {
+    'en-CA': 'fr',
+    'en-*': 'en',
+    'fr-*': 'fr',
+    'pt': 'pt-BR',
+  },
+  parser: I18nJsonParser,
+  parserOptions: {
+    path: path.join(__dirname, '/i18n/'),
+  },
+});
+```
+
 ### Translating with i18n module
 
 #### `I18nLang` decorator and `I18nService`

src/lib/interfaces/i18n-options.interface.ts

@@ -20,6 +20,7 @@ export type I18nOptionResolver =
 
 export interface I18nOptions {
   fallbackLanguage: string;
+  fallbacks?: { [key: string]: string };
   resolvers?: I18nOptionResolver[];
   parser: Type<I18nParser>;
   parserOptions: any;
@@ -30,6 +31,7 @@ export interface I18nOptionsFactory {
     | Promise<I18nOptionsWithoutResolvers>
     | I18nOptionsWithoutResolvers;
 }
+
 export interface I18nAsyncOptions extends Pick<ModuleMetadata, 'imports'> {
   name?: string;
   useExisting?: Type<I18nOptionsFactory>;

src/lib/services/i18n.service.ts

@@ -34,7 +34,7 @@ export class I18nService {
     private readonly languagesSubject: BehaviorSubject<string[]>,
     @Inject(I18N_TRANSLATIONS_SUBJECT)
     private readonly translationsSubject: BehaviorSubject<I18nTranslation>,
-  ) {}
+  ) { }
 
   public async translate(
     key: string,
@@ -53,6 +53,8 @@ export class I18nService {
         ? this.i18nOptions.fallbackLanguage
         : lang;
 
+    lang = await this.handleFallbacks(lang);
+
     const translationsByLanguage = (
       await this.translations.pipe(take(1)).toPromise()
     )[lang];
@@ -111,4 +113,22 @@ export class I18nService {
       this.languagesSubject.next(languages);
     }
   }
+
+  private async handleFallbacks(lang: string) {
+    const supportedLanguages = await this.getSupportedLanguages();
+    if (this.i18nOptions.fallbacks && !supportedLanguages.includes(lang)) {
+      const sanitizedLang =
+        lang.includes('-')
+          ? lang.substring(0, lang.indexOf('-')).concat('-*')
+          : lang;
+
+      for (const key in this.i18nOptions.fallbacks) {
+        if (key === lang || key === sanitizedLang) {
+          lang = this.i18nOptions.fallbacks[key];
+          break;
+        }
+      }
+    }
+    return lang;
+  }
 }

tests/i18n-async.spec.ts

@@ -75,3 +75,67 @@ describe('i18n module without trailing slash in path', () => {
     );
   });
 });
+
+describe('i18n async module with fallbacks', () => {
+  let i18nService: I18nService;
+
+  beforeAll(async () => {
+    const module = await Test.createTestingModule({
+      imports: [
+        I18nModule.forRootAsync({
+          useFactory: () => {
+            return {
+              fallbackLanguage: 'en',
+              fallbacks: {
+                'en-CA': 'fr',
+                'en-*': 'en',
+                'fr-*': 'fr',
+                'pt': 'pt-BR',
+              },
+              parserOptions: {
+                path: path.join(__dirname, '/i18n/'),
+              },
+            };
+          },
+          parser: I18nJsonParser,
+        }),
+      ],
+    }).compile();
+
+    i18nService = module.get(I18nService);
+  });
+
+  it('i18n service should be defined', async () => {
+    expect(i18nService).toBeTruthy();
+  });
+
+  it('i18n service should return correct translation', async () => {
+    expect(await i18nService.translate('test.HELLO')).toBe(
+      'Hello',
+    );
+    expect(await i18nService.translate('test.HELLO', { lang: 'en' })).toBe(
+      'Hello',
+    );
+    expect(await i18nService.translate('test.HELLO', { lang: 'en-US' })).toBe(
+      'Hello',
+    );
+    expect(await i18nService.translate('test.HELLO', { lang: 'en-CA' })).toBe(
+      'Bonjour',
+    );
+    expect(await i18nService.translate('test.HELLO', { lang: 'nl' })).toBe(
+      'Hallo',
+    );
+    expect(await i18nService.translate('test.HELLO', { lang: 'fr' })).toBe(
+      'Bonjour',
+    );
+    expect(await i18nService.translate('test.HELLO', { lang: 'fr-BE' })).toBe(
+      'Bonjour',
+    );
+    expect(await i18nService.translate('test.HELLO', { lang: 'pt' })).toBe(
+      'Olá',
+    );
+    expect(await i18nService.translate('test.HELLO', { lang: 'pt-BR' })).toBe(
+      'Olá',
+    );
+  });
+});