.js

import { combineReducers } from 'redux';
import {
    SELECT_REDDIT , INVALIDATE_REDDIT ,
    REQUEST_POSTS , RECEIVE_POSTS ,
} from '../actions';

const selectedReddit = (
    state = 'reactjs' ,
    action ,
) => {
    switch ( action.type ) {
        case SELECT_REDDIT:
            return action.reddit;
        default:
            return state;
    }
};

const posts = (
    state = {
        isFetching : false ,
        didInvalidate : false ,
        items : [] ,
    } ,
    action ,
) => {
    switch ( action.type ) {
        case INVALIDATE_REDDIT:
            return {
                ...state ,
                didInvalidate : true ,
            };
        case REQUEST_POSTS:
            return {
                ...state ,
                isFetching : true ,
                didInvalidate : false ,
            };
        case RECEIVE_POSTS:
            return {
                ...state ,
                isFetching : false ,
                didInvalidate : false ,
                items : action.posts ,
                lastUpdated : action.receivedAt ,
            };
        default:
            return state;
    }
};

const postsByReddit = (
    state = {} ,
    action ,
) => {
    switch ( action.type ) {
        case INVALIDATE_REDDIT:
        case RECEIVE_POSTS:
        case REQUEST_POSTS:
            return {
                ...state ,
                [action.reddit] : posts(
                    state[action.reddit] ,
                    action ,
                ) ,
            };
        default:
            return state;
    }
};

const rootReducer = combineReducers(({
    postsByReddit ,
    selectedReddit ,
}));

export default rootReducer;