checking in docs for github.io page

docs/playground/src/redux-utils/action.ts

@@ -0,0 +1,14 @@
+import { Action } from 'redux';
+
+type ActionWithPayload<T, P> = Action<T> & P;
+
+export function action<T extends string>(type: T): Action<T>;
+export function action<T extends string, P>(type: T, payload: P): ActionWithPayload<T, P>;
+export function action<T extends string, P>(type: T, payload?: P) {
+  return { type, ...payload };
+}
+
+export type GenericActionMapping<A> = { [somekey in keyof A]: (...args: any) => Action<any> | ActionWithPayload<any, any> };
+export type GenericActionTypes<A extends GenericActionMapping<A>> = ReturnType<A[keyof A]>['type'];
+export type GenericAction<A extends GenericActionMapping<A>> = ReturnType<A[GenericActionTypes<A>]>;
+export type GenericActionLookup<A extends GenericActionMapping<A>> = { [a in GenericActionTypes<A>]: ReturnType<A[a]> };

docs/playground/src/redux-utils/reducer.ts

@@ -0,0 +1,34 @@
+import { Reducer } from 'redux';
+import { Draft, produce } from 'immer';
+import { GenericActionLookup, GenericActionMapping } from './action';
+
+export type ImmerReducer<T, A> = (state: Draft<T>, action?: A) => T;
+export type HandlerMap<T, A extends GenericActionMapping<A>> = {
+  [actionType in keyof A]?: ImmerReducer<T, GenericActionLookup<A>[actionType]>
+};
+
+function isHandlerFunction<T, A extends GenericActionMapping<A>>(
+  handlerOrMap: HandlerMap<T, A> | ImmerReducer<T, A>
+): handlerOrMap is ImmerReducer<T, A> {
+  if (typeof handlerOrMap === 'function') {
+    return true;
+  }
+
+  return false;
+}
+
+export function createGenericReducer<T, A extends GenericActionMapping<A>, AM = keyof GenericActionMapping<A>>(
+  initialState: T,
+  handlerOrMap: HandlerMap<T, A> | ImmerReducer<T, GenericActionLookup<A>[AM]>
+): Reducer<T> {
+  return function reducer(state = initialState, action: GenericActionLookup<A>[AM]): T {
+    if (isHandlerFunction(handlerOrMap)) {
+      return produce(state, draft => handlerOrMap(draft, action as GenericActionLookup<A>[AM]));
+    } else if (handlerOrMap.hasOwnProperty(action.type)) {
+      const handler = (handlerOrMap as any)[action.type] as ImmerReducer<T, GenericActionLookup<A>[AM]>;
+      return produce(state, draft => handler(draft, action));
+    } else {
+      return state;
+    }
+  };
+}