AHABHGK

1interface Action<T = any> {
2  type: T,
3}
4interface AnyAction extends Action {
5  [key: string]: any,
6}
7type Reducer<S = any, A extends Action = AnyAction> = (
8  state: S | undefined,
9  action: A
10) => S
11interface Store<S, A extends Action = AnyAction> {
12  getState(): S,
13  dispatch(action: A): A,
14  subscribe(listener: () => void): () => void,
15}
16const createStore = <S, A extends Action>(reducer: Reducer<S, A>, initialState: S): Store<S, A> => {
17  const action$ = new Subject<A>()
18  let currentState = initialState
19  const store$ = action$.pipe(
20    startWith(initialState as unknown as A),
21    scan(reducer),
22    tap((state) => currentState = state),
23  )
24
25  return {
26    getState: () => currentState,
27    dispatch: (action) => {
28      action$.next(action)
29      return action
30    },
31    subscribe: (listener) => {
32      const subscription = store$.subscribe(listener)
33      return () => {
34        subscription.unsubscribe()
35      }
36    }
37  }
38}
39
40const incrAction = {
41  type: 'incr'
42}
43const decrAction = {
44  type: 'decr'
45}
46const initialState = { num: 0 }
47
48type CountActions = typeof incrAction | typeof decrAction
49
50const re = (state = initialState, action: CountActions) => {
51  switch (action.type) {
52    case 'incr':
53      return { num: state.num + 1 }
54    case 'decr':
55      return { num: state.num - 1 }
56    default:
57      return state
58  }
59}
60
61const store = createStore(re, initialState)
62store.subscribe(console.log)
63store.dispatch(incrAction)