adding some redux steps

step2-05/src/reducers/index.ts

@@ -0,0 +1,19 @@
+import { Store } from '../store';
+import { addTodo, remove, complete } from './pureFunctions';
+
+let index = 0;
+
+export function reducer(state: Store, payload: any): Store {
+  switch (payload.type) {
+    case 'addTodo':
+      return addTodo(state, payload.label);
+
+    case 'remove':
+      return remove(state, payload.id);
+
+    case 'complete':
+      return complete(state, payload.id);
+  }
+
+  return state;
+}