beginning on selectors

src/Updux.ts

@@ -26,10 +26,10 @@ type ResolveAction<
     ? ActionArg
     : ActionArg extends (...args: any) => any
     ? ActionCreatorWithPreparedPayload<
-          Parameters<ActionArg>,
+        Parameters<ActionArg>,
-          ReturnType<ActionArg>,
+        ReturnType<ActionArg>,
-          ActionType
+        ActionType
-      >
+    >
     : ActionCreatorWithoutPayload<ActionType>;
 
 type ResolveActions<
@@ -37,10 +37,10 @@ type ResolveActions<
         [key: string]: any;
     },
 > = {
-    [ActionType in keyof A]: ActionType extends string
+        [ActionType in keyof A]: ActionType extends string
         ? ResolveAction<ActionType, A[ActionType]>
         : never;
-};
+    };
 
 export type Mutation<A extends Action<any> = Action<any>, S = any> = (
     payload: A extends {
@@ -51,12 +51,22 @@ export type Mutation<A extends Action<any> = Action<any>, S = any> = (
     action: A,
 ) => (state: S) => S | void;
 
+export type AggregateSelectors<S> = S;
+
+type SelectorForState<S> = (state: S) => unknown;
+type SelectorsForState<S> = {
+    [key: string]: SelectorForState<S>;
+};
+
 export default class Updux<
     T_LocalState = Record<any, any>,
     T_LocalActions extends {
         [actionType: string]: any;
     } = {},
     T_Subduxes extends Record<string, Dux> = {},
+    T_LocalSelectors extends SelectorsForState<
+        AggregateState<T_LocalState, T_Subduxes>
+    > = {},
 > {
     #localInitial: T_LocalState;
     #localActions: T_LocalActions;
@@ -70,11 +80,19 @@ export default class Updux<
 
     #initial: AggregateState<T_LocalState, T_Subduxes>;
 
+    #localSelectors: Record<
+        string,
+        (state: AggregateState<T_LocalState, T_Subduxes>) => any
+    >;
+
+    #selectors: AggregateSelectors<T_LocalSelectors>;
+
     constructor(
         config: Partial<{
             initial: T_LocalState;
             actions: T_LocalActions;
             subduxes: T_Subduxes;
+            selectors: T_LocalSelectors;
         }>,
     ) {
         // TODO check that we can't alter the initial after the fact
@@ -85,6 +103,7 @@ export default class Updux<
         this.#actions = buildActions(this.#localActions, this.#subduxes);
 
         this.#initial = buildInitial(this.#localInitial, this.#subduxes);
+        this.#localSelectors = config.selectors;
     }
 
     get actions() {
@@ -110,6 +129,10 @@ export default class Updux<
         return store;
     }
 
+    get selectors(): T_LocalSelectors {
+        return this.#localSelectors as any;
+    }
+
     // TODO memoize this sucker
     get reducer() {
         return buildReducer(

src/selectors.test.ts

@@ -0,0 +1,27 @@
+import { test, expect } from 'vitest';
+
+import Updux, { createAction } from './index.js';
+
+test('basic selectors', () => {
+    type State = { x: number };
+
+    const foo = new Updux({
+        initial: {
+            x: 1,
+        },
+        selectors: {
+            getX: ({ x }: State) => x,
+        },
+        subduxes: {
+            bar: new Updux({
+                initial: { y: 2 },
+                selectors: {
+                    getY: ({ y }: { y: number }) => y,
+                },
+            }),
+        },
+    });
+
+    expect(foo.selectors.getY({ bar: { y: 3 } } as typeof foo.initial)).toBe(3);
+    expect(foo.selectors.getX({ x: 4 } as typeof foo.initial)).toBe(4);
+});