feat: add persist middleware

src/middleware.ts

@@ -1,10 +1,10 @@
 import {
-  State,
   GetState,
-  SetState,
-  StoreApi,
   PartialState,
+  SetState,
+  State,
   StateCreator,
+  StoreApi,
 } from './vanilla'
 
 export const redux = <S extends State, A extends { type: unknown }>(
@@ -116,3 +116,35 @@ export const combine = <
       api as StoreApi<PrimaryState>
     )
   )
+
+type StateStorage = {
+  getItem: (key: string) => string | null | Promise<string | null>
+  setItem: (key: string, value: string) => void | Promise<void>
+}
+
+export const persist = <S extends State>(
+  name: string,
+  config: StateCreator<S>,
+  storage: StateStorage = localStorage
+) => (set: SetState<S>, get: GetState<S>, api: StoreApi<S>): S => {
+  const state = config(
+    (payload) => {
+      set(payload)
+
+      storage.setItem(name, JSON.stringify(get()))
+    },
+    get,
+    api
+  )
+
+  ;(async () => {
+    try {
+      const storedState = await storage.getItem(name)
+      if (storedState) set(JSON.parse(storedState))
+    } catch (e) {
+      console.error(new Error(`Unable to get to stored state in "${name}"`))
+    }
+  })()
+
+  return state
+}