feat: move i18n type utils to lib and describe (#33)

src/lib/index.ts

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+export * from './types';

src/lib/types.ts

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+/** 
+ * @example type Output = Split<'a.b1' | 'a.b2', '.'>;
+ * // ["a", "b1"] | ["a", "b2"]
+*/
+type Split<S extends string, D extends string> =
+  S extends `${infer A}${D}${infer B}` ? [A, ...Split<B, D>] : [S];
+
+/** 
+ * @example type Output = NestedObject<["a", "b1"] | ["a", "b2"]>;
+ * // { a: { b1: string; }; } | { a: { b2: string; }; }
+*/
+type NestedObject<T extends string[]> =
+  T extends [infer Head, ...infer Tail] ?
+    Head extends string ?
+      { [key in Head]: NestedObject<Tail extends string[] ? Tail : []> } : never :
+    string;
+
+/** 
+ * @example type Output = UnionToIntersection<{ a: { b1: string; }; } | { a: { b2: string; }; }>;
+ * // { a: { b1: string; }; } & { a: { b2: string; }; }
+*/
+type UnionToIntersection<U> =
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  (U extends any ? (k: U) => void : never) extends (k: infer I) => void ? I : never;
+
+/** 
+ * @example type Output = CreateTree<'a.b1' | 'a.b2', '.'>;
+ * // { a: { b1: string; }; } & { a: { b2: string; }; }
+*/
+export type CreateTree<T> =
+  UnionToIntersection<T extends infer U ?
+    U extends string ?
+      NestedObject<Split<U, '.'>> : never : never>;