From c361687103648dff60aa594f57a44d05fa59cfee Mon Sep 17 00:00:00 2001
From: Jakub Grzywacz <kontakt@jakubgrzywacz.pl>
Date: Mon, 11 Nov 2024 18:18:36 +0100
Subject: [PATCH] feat: introduce createLanguageDetector (#29)

Introduce createLanguageDetector to provide greater flexibility with language detection. This change means the current detector (ReactNativeLanguageDetector) will be deprecated in favor of the more adaptable option.
---
 README.md               | 19 ++++++++--
 example/App.tsx         |  6 ++-
 src/languageDetector.ts | 84 +++++++++++++++++++++++++++++++++--------
 3 files changed, 89 insertions(+), 20 deletions(-)

diff --git a/README.md b/README.md
index 1a14f65..366f9b2 100644
--- a/README.md
+++ b/README.md
@@ -129,19 +129,32 @@ setLanguage("en-US");
 ## i18next
 
 This library is fully compatible with [i18next](https://www.i18next.com/).
-To use it with i18next, you need to use `ReactNativeLanguageDetector` before init function:
 
+To use it with i18next, create a language detector by using `createLanguageDetector` with the specified `options`:
 ```ts
-import { ReactNativeLanguageDetector } from 'react-native-localization-settings';
+import { createLanguageDetector } from 'react-native-localization-settings';
+
+const languageDetector = createLanguageDetector({});
 
 i18next
-  .use(ReactNativeLanguageDetector)
+  .use(languageDetector)
   .use(initReactI18next)
   .init({
     // ...
   });
 ```
 
+### Options
+
+```ts
+type LanguageDetectorOptions = {
+  cacheCurrentLanguage?: boolean; // default: false - sets current detected language
+  async?: boolean;                // default: false - uses getLanguageAsync (set to true on old architecture)
+};
+```
+
+### Changing language
+
 Then, if you want to create custom in-app language selector, you should be able to change the language (along with the
 settings per-app language) using standard i18next function:
 
diff --git a/example/App.tsx b/example/App.tsx
index b6bedde..55b79a0 100644
--- a/example/App.tsx
+++ b/example/App.tsx
@@ -3,13 +3,15 @@ import { StyleSheet, View, Text, Button } from 'react-native';
 import i18next from 'i18next';
 import { initReactI18next, useTranslation } from 'react-i18next';
 import {
+  createLanguageDetector,
   getLanguage,
   getLanguageAsync,
-  ReactNativeLanguageDetector,
 } from 'react-native-localization-settings';
 
+const languageDetector = createLanguageDetector();
+
 i18next
-  .use(ReactNativeLanguageDetector)
+  .use(languageDetector)
   .use(initReactI18next)
   .init({
     resources: {
diff --git a/src/languageDetector.ts b/src/languageDetector.ts
index e9ec0ba..6686aef 100644
--- a/src/languageDetector.ts
+++ b/src/languageDetector.ts
@@ -1,25 +1,79 @@
-import { getLanguage, setLanguage } from './api';
+import { getLanguage, getLanguageAsync, setLanguage } from './api';
+
+interface I18nLanguageDetectorModule {
+  type: 'languageDetector';
+  init?(): void;
+  detect(): string | readonly string[] | undefined;
+  cacheUserLanguage?(lang: string): void;
+}
+interface I18nLanguageDetectorAsyncModule {
+  type: 'languageDetector';
+  async: true;
+  init?(): void;
+  detect(
+    callback: (lng: string | readonly string[] | undefined) => void | undefined
+  ): void | Promise<string | readonly string[] | undefined>;
+  cacheUserLanguage?(lng: string): void | Promise<void>;
+}
+
+type LanguageDetectorOptions = {
+  cacheCurrentLanguage?: boolean;
+  async?: boolean;
+};
+
+/**
+ * @deprecated Use createLanguageDetector instead
+ */
+export const ReactNativeLanguageDetector: I18nLanguageDetectorModule = {
+  type: 'languageDetector',
+  init: () => {},
+  detect: () => getLanguage(),
+  cacheUserLanguage: (lang: string) => setLanguage(lang),
+};
 
 /**
- * i18next language detector
+ * I18next language detector generator
+ * @param options - detector options
+ * @returns I18nLanguageDetectorModule | I18nLanguageDetectorAsyncModule
  * @example
  * Usage:
+ * const languageDetector = createLanguageDetector(options);
  * i18next
- *   .use(ReactNativeLanguageDetector)
+ *   .use(languageDetector)
  *   .init({
  *     ...
  *   });
  */
-export const ReactNativeLanguageDetector: I18nLanguageDetectorModule = {
-  type: 'languageDetector',
-  init: () => {},
-  detect: () => getLanguage(),
-  cacheUserLanguage: (lng: string) => setLanguage(lng),
-};
+export const createLanguageDetector = (
+  options?: LanguageDetectorOptions
+): I18nLanguageDetectorModule | I18nLanguageDetectorAsyncModule => {
+  const { cacheCurrentLanguage = false } = options || {};
+  let skipNextCache = false;
 
-interface I18nLanguageDetectorModule {
-  type: 'languageDetector';
-  init?(): void;
-  detect(): string | readonly string[] | undefined;
-  cacheUserLanguage?(lng: string): void;
-}
+  let languageDetector:
+    | I18nLanguageDetectorModule
+    | I18nLanguageDetectorAsyncModule = {
+    type: 'languageDetector',
+    init: () => {
+      skipNextCache = true;
+    },
+    detect: () => getLanguage(),
+    cacheUserLanguage: (lang: string) => {
+      if (cacheCurrentLanguage === false && skipNextCache) {
+        skipNextCache = false;
+        return;
+      }
+      setLanguage(lang);
+    },
+  };
+  if (options?.async) {
+    languageDetector = {
+      ...languageDetector,
+      async: true,
+      detect: (callback) => {
+        getLanguageAsync().then(callback);
+      },
+    };
+  }
+  return languageDetector;
+};