feat: add custom transform functions for state persistence

store/persist.ts

@@ -1,8 +1,8 @@
-import { Err, Ok, type Operation, type Result } from "../deps.ts";
-import type { AnyState, Next } from "../types.ts";
+import { Err, Ok, Operation, Result } from "../deps.ts";
 import { select, updateStore } from "./fx.ts";
-import type { UpdaterCtx } from "./types.ts";
 
+import type { AnyState, Next } from "../types.ts";
+import type { UpdaterCtx } from "./types.ts";
 export const PERSIST_LOADER_ID = "@@starfx/persist";
 
 export interface PersistAdapter<S extends AnyState> {
@@ -17,6 +17,35 @@ export interface PersistProps<S extends AnyState> {
   key: string;
   reconciler: (original: S, rehydrated: Partial<S>) => S;
   rehydrate: () => Operation<Result<unknown>>;
+  transform?: TransformFunctions<S>;
+}
+interface TransformFunctions<S extends AnyState> {
+  in(s: Partial<S>): Partial<S>;
+  out(s: Partial<S>): Partial<S>;
+}
+
+export function createTransform<S extends AnyState>() {
+  const transformers: TransformFunctions<S> = {
+    in: function (currentState: Partial<S>): Partial<S> {
+      return currentState;
+    },
+    out: function (currentState: Partial<S>): Partial<S> {
+      return currentState;
+    },
+  };
+
+  const inTransformer = function (state: Partial<S>): Partial<S> {
+    return transformers.in(state);
+  };
+
+  const outTransformer = function (state: Partial<S>): Partial<S> {
+    return transformers.out(state);
+  };
+
+  return {
+    in: inTransformer,
+    out: outTransformer,
+  };
 }
 
 export function createLocalStorageAdapter<S extends AnyState>(): PersistAdapter<
@@ -51,7 +80,13 @@ export function shallowReconciler<S extends AnyState>(
 }
 
 export function createPersistor<S extends AnyState>(
-  { adapter, key = "starfx", reconciler = shallowReconciler, allowlist = [] }:
+  {
+    adapter,
+    key = "starfx",
+    reconciler = shallowReconciler,
+    allowlist = [],
+    transform,
+  }:
     & Pick<PersistProps<S>, "adapter">
     & Partial<PersistProps<S>>,
 ): PersistProps<S> {
@@ -60,9 +95,18 @@ export function createPersistor<S extends AnyState>(
     if (!persistedState.ok) {
       return Err(persistedState.error);
     }
+    let stateFromStorage = persistedState.value as Partial<S>;
+
+    if (transform) {
+      try {
+        stateFromStorage = transform.out(persistedState.value);
+      } catch (err: any) {
+        console.error("Persistor outbound transformer error:", err);
+      }
+    }
 
     const state = yield* select((s) => s);
-    const nextState = reconciler(state as S, persistedState.value);
+    const nextState = reconciler(state as S, stateFromStorage);
     yield* updateStore<S>(function (state) {
       Object.keys(nextState).forEach((key: keyof S) => {
         state[key] = nextState[key];
@@ -78,25 +122,39 @@ export function createPersistor<S extends AnyState>(
     allowlist,
     reconciler,
     rehydrate,
+    transform,
   };
 }
 
 export function persistStoreMdw<S extends AnyState>(
-  { allowlist, adapter, key }: PersistProps<S>,
+  { allowlist, adapter, key, transform }: PersistProps<S>,
 ) {
   return function* (_: UpdaterCtx<S>, next: Next) {
     yield* next();
     const state = yield* select((s: S) => s);
+
+    let transformedState: Partial<S> = state;
+    if (transform) {
+      try {
+        transformedState = transform.in(state);
+      } catch (err: any) {
+        console.error("Persistor inbound transformer error:", err);
+      }
+    }
+
     // empty allowlist list means save entire state
     if (allowlist.length === 0) {
-      yield* adapter.setItem(key, state);
+      yield* adapter.setItem(key, transformedState);
       return;
     }
 
     const allowedState = allowlist.reduce<Partial<S>>((acc, key) => {
-      acc[key] = state[key];
+      if (key in transformedState) {
+        acc[key] = transformedState[key] as S[keyof S];
+      }
       return acc;
     }, {});
+
     yield* adapter.setItem(key, allowedState);
   };
 }