Rematch Retyped

typedModel.ts

type TypedDispatcher<R> = R extends (state: any, payload?: infer P, meta?: infer M) => any
  ? (payload?: P, meta?: M) => Action<P, M>
  : R extends (state: any, payload: infer P, meta?: infer M) => any
    ? (payload: P, meta?: M) => Action<P, M>
    : R extends (state: any, payload: infer P, meta: infer M) => any
      ? (payload: P, meta: M) => Action<P, M>
      : null;

type StripUnknown<T> = T extends (payload?: unknown, meta?: unknown) => Action<unknown, unknown>
  ? () => Action<never, never>
  : T extends (payload?: infer P, meta?: unknown) => Action<infer P, unknown>
    ? (payload?: P) => Action<P | undefined, never>
    : T extends (payload: infer P, meta?: unknown) => Action<infer P, unknown>
      ? (payload: P) => Action<P, never>
      : T;

type Effects<S, R> = {
  [ effectName: string ]: (
    this: { [K in keyof R]: StripUnknown<TypedDispatcher<R[K]>> }, payload: any, rootState: S) => void;
};

type Reducers<S> = { [ reducerName: string ]: (state: S, payload?: any, meta?: any) => S };

function typedModel<S, R extends Reducers<S>, E extends Effects<S, R>>(
  name: string, state: S, reducers: R, effects: E | ((dispatch: RematchDispatch) => E)) {
  return { state, reducers, effects };
}