Improve: i18n type gymnastics (#116)

Co-authored-by: Dreamacro <8615343+Dreamacro@users.noreply.github.com>

src/i18n/index.ts

@@ -1,3 +1,7 @@
+import { IsEqual } from 'type-fest'
+
+import Infer from '@lib/type'
+
 import en_US from './en_US'
 import zh_CN from './zh_CN'
 
@@ -8,6 +12,16 @@ export const Language = {
 
 export type Lang = keyof typeof Language
 
+type US = typeof Language.en_US
+type CN = typeof Language.zh_CN
+
+// type guard for US and CN
+type TrueGuard<T extends true> = T
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+type _equalGuard = TrueGuard<IsEqual<Infer<US>, Infer<CN>>>
+
+export type LocalizedType = US
+
 export const locales = Object.keys(Language)
 
 export function getDefaultLanguage (): Lang {

src/lib/type.ts

@@ -0,0 +1,5 @@
+type InferRecursion<K extends string, T> = T extends object ? { [P in keyof T]: P extends string ? InferRecursion<`${K}.${P}`, T[P]> : K }[keyof T] : K
+
+type Infer<T> = Extract<{ [K in keyof T]: K extends string ? InferRecursion<K, T[K]> : unknown }[keyof T], string>
+
+export default Infer

src/stores/jotai.ts

@@ -10,13 +10,14 @@ import { useCallback, useEffect, useMemo, useRef } from 'react'
 import useSWR from 'swr'
 import { Get } from 'type-fest'
 
-import { Language, locales, Lang, getDefaultLanguage } from '@i18n'
+import { Language, locales, Lang, getDefaultLanguage, LocalizedType } from '@i18n'
 import { partition } from '@lib/helper'
 import { useWarpImmerSetter, WritableDraft } from '@lib/jotai'
 import { isClashX, jsBridge } from '@lib/jsBridge'
 import { Snapshot } from '@lib/request'
 import * as API from '@lib/request'
 import { StreamReader } from '@lib/streamer'
+import Infer from '@lib/type'
 import * as Models from '@models'
 import { Log } from '@models/Log'
 
@@ -31,9 +32,9 @@ export function useI18n () {
     const lang = useMemo(() => defaultLang ?? getDefaultLanguage(), [defaultLang])
 
     const translation = useCallback(
-        function <Namespace extends keyof typeof Language['en_US']>(namespace: Namespace) {
-            function t<Path extends string> (path: Path) {
-                return get(Language[lang][namespace], path) as unknown as Get<typeof Language['en_US'][Namespace], Path>
+        function <Namespace extends keyof LocalizedType>(namespace: Namespace) {
+            function t<Path extends Infer<LocalizedType[Namespace]>> (path: Path) {
+                return get(Language[lang][namespace], path) as unknown as Get<LocalizedType[Namespace], Path>
             }
             return { t }
         },