fix(Store): Compose provided metareducers for a feature state

Closes #701

modules/store/spec/utils.spec.ts

@@ -1,4 +1,4 @@
-import { omit } from '../src/utils';
+import { omit, createFeatureReducer } from '../src/utils';
 import { combineReducers, compose } from '@ngrx/store';
 
 describe(`Store utils`, () => {
@@ -60,7 +60,7 @@ describe(`Store utils`, () => {
     const precision = (n: number) => parseFloat(n.toPrecision(12));
     const addPtTwo = (n: number) => n + 0.2;
 
-    it(`should should compose functions`, () => {
+    it(`should compose functions`, () => {
       const addPrecision = compose(precision, addPtTwo);
       const addPrecisionCubed = compose(cube, addPrecision);
 
@@ -73,4 +73,21 @@ describe(`Store utils`, () => {
       expect(id(1)).toBe(1);
     });
   });
+
+  describe('createFeatureReducer()', () => {
+    it('should compose a reducer from the provided meta reducers', () => {
+      const metaReducer = jasmine
+        .createSpy('metaReducer')
+        .and.callFake(red => (s: any, a: any) => red(s, a));
+      const reducer = (state: any, action: any) => state;
+
+      const featureReducer = createFeatureReducer(reducer, [metaReducer]);
+
+      const initialState = 1;
+      const state = featureReducer(initialState, undefined);
+
+      expect(metaReducer).toHaveBeenCalled();
+      expect(state).toBe(initialState);
+    });
+  });
 });

modules/store/src/reducer_manager.ts

@@ -6,10 +6,11 @@ import {
   ActionReducer,
   ActionReducerMap,
   ActionReducerFactory,
+  MetaReducer,
   StoreFeature,
 } from './models';
 import { INITIAL_STATE, INITIAL_REDUCERS, REDUCER_FACTORY } from './tokens';
-import { omit, createReducerFactory } from './utils';
+import { omit, createReducerFactory, createFeatureReducer } from './utils';
 import { ActionsSubject } from './actions_subject';
 
 export abstract class ReducerObservable extends Observable<
@@ -40,7 +41,11 @@ export class ReducerManager extends BehaviorSubject<ActionReducer<any, any>>
   }: StoreFeature<any, any>) {
     const reducer =
       typeof reducers === 'function'
-        ? (state: any, action: any) => reducers(state || initialState, action)
+        ? (state: any, action: any) =>
+            createFeatureReducer(reducers, metaReducers)(
+              state || initialState,
+              action
+            )
         : createReducerFactory(reducerFactory, metaReducers)(
             reducers,
             initialState

modules/store/src/utils.ts

@@ -96,3 +96,14 @@ export function createReducerFactory<T, V extends Action = Action>(
 
   return reducerFactory;
 }
+
+export function createFeatureReducer<T, V extends Action = Action>(
+  reducer: ActionReducer<T, V>,
+  metaReducers?: MetaReducer<T, V>[]
+): ActionReducer<T, V> {
+  if (Array.isArray(metaReducers) && metaReducers.length > 0) {
+    return compose<ActionReducer<T, V>>(...metaReducers)(reducer);
+  }
+
+  return reducer;
+}