From 80d18703c476841deb95e0d979453e0d25a1fc31 Mon Sep 17 00:00:00 2001
From: Yanick Champoux <yanick@babyl.ca>
Date: Mon, 6 Mar 2023 10:09:39 -0500
Subject: [PATCH] wip

---
 docs/tutorial.md     |  8 ++++----
 package.json         |  1 +
 src/Updux.ts         | 26 +++++++++++++++++++++++++-
 src/tutorial.test.ts | 22 +++++++++++++++++++++-
 4 files changed, 51 insertions(+), 6 deletions(-)

diff --git a/docs/tutorial.md b/docs/tutorial.md
index 6ab9599..387200e 100644
--- a/docs/tutorial.md
+++ b/docs/tutorial.md
@@ -72,10 +72,10 @@ Mutations are the reducing functions associated to actions. They
 are defined via the `mutation` method:
 
 ```js
-todosDux.mutation( addTodo, description => ({next_id: id, todos}) => ({
-    next_id: 1 + id,
-    todos: [...todos, { description, id, done: false }]
-}));
+    dux.mutation(addTodo, (state, description) => {
+        state.todos.unshift({ description, id: state.nextId, done: false });
+        state.nextId++;
+    });
 ```
 ## Effects
 
diff --git a/package.json b/package.json
index 5f5155c..2a05480 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,7 @@
 {
     "type": "module",
     "dependencies": {
+        "@yanick/updeep-remeda": "^2.1.0",
         "immer": "^9.0.15",
         "json-schema-shorthand": "^2.0.0",
         "redux": "^4.2.0",
diff --git a/src/Updux.ts b/src/Updux.ts
index 56b9e4c..59c1456 100644
--- a/src/Updux.ts
+++ b/src/Updux.ts
@@ -2,8 +2,20 @@ import {
     createStore as reduxCreateStore,
     applyMiddleware,
     DeepPartial,
+    Action,
 } from 'redux';
-import { configureStore, Reducer } from '@reduxjs/toolkit';
+import { configureStore, Reducer, createAction } from '@reduxjs/toolkit';
+import { withPayload } from './actions';
+
+type ActionCreator = ReturnType<typeof createAction>;
+
+type AggregateState<L> = L;
+
+type Mutation<A extends ActionCreator = ActionCreator, S = any> = (
+    state: S,
+    payload: ReturnType<A>['payload'],
+    action: ReturnType<A>,
+) => S | void;
 
 export default class Updux<
     T_LocalState = Record<any, any>,
@@ -11,6 +23,10 @@ export default class Updux<
 > {
     #localInitial: T_LocalState;
     #localActions: T_LocalActions;
+    #localMutations: Record<
+        string,
+        Mutation<ActionCreator, AggregateState<T_LocalState>>
+    > = {};
 
     constructor(
         config: Partial<{
@@ -45,4 +61,12 @@ export default class Updux<
 
         return store;
     }
+
+    // TODO force the actionCreator to be one of the actions?
+    mutation<A extends ActionCreator>(
+        actionCreator: A,
+        mutation: Mutation<A, AggregateState<T_LocalState>>,
+    ) {
+        this.#localMutations[actionCreator.type] = mutation;
+    }
 }
diff --git a/src/tutorial.test.ts b/src/tutorial.test.ts
index d1992af..753e746 100644
--- a/src/tutorial.test.ts
+++ b/src/tutorial.test.ts
@@ -1,4 +1,5 @@
 import Updux, { createAction, withPayload } from './index.js';
+import u from '@yanick/updeep-remeda';
 
 const expectType = <T>(value: T) => value;
 
@@ -23,7 +24,7 @@ test('initial state', () => {
     expect(store.getState()).toEqual(initial);
 });
 
-test.only('actions', () => {
+test('actions', () => {
     const addTodo = createAction('addTodo', withPayload<string>());
     const todoDone = createAction('todoDone');
 
@@ -39,3 +40,22 @@ test.only('actions', () => {
         payload: 'write tutorial',
     });
 });
+
+test('mutation', () => {
+    const addTodo = createAction('addTodo', withPayload<string>());
+
+    type Todo = {
+        description: string;
+        id: number;
+        done: boolean;
+    };
+
+    const dux = new Updux({
+        initial: { nextId: 0, todos: [] as Todo[] },
+    });
+
+    dux.mutation(addTodo, (state, description) => {
+        state.todos.unshift({ description, id: state.nextId, done: false });
+        state.nextId++;
+    });
+});