combineReducers

const todo = (state, action) => {
  switch (action.type) {
      case 'ADD_TODO':    
      return {
            id: action.id,
            completed:false,
            text: action.text,
        };
      case 'TOGGLE_TODO':
       if(state.id !== action.id){
          return state;
        }
        return {
          ...state,
          completed: !todo.completed
      }
      default:
        return state;
  }
}


const todos = (state = [], action) => {
  switch (action.type) {
    case 'ADD_TODO':
      return [
        ...state,
    todo(undefined, action)
      ];
    case 'TOGGLE_TODO':
      return state.map(t => todo(t,action))
    default:
      return state;
  }
};

const visibilityFilter = (
  state = 'SHOW_ALL',
  action
) => {
  switch (action.type){
    case 'SET_VISIBILITY_FILTER':
      return action.filter;
    default:
      return state;
  }
}


const combineReducers = (reduce) => {
  return (state = {}, action) => {
    return Object.keys(reducers).reduce(
      (nextState, key) => {
        nextState[key] = reducers[key](
          state[key],
          action
        );
        return nextState;
      },
      {}
    )
  }
}

//const {combineReducers} = Redux;
const todoApp = combineReducers({
  todos, // same as todos: todos
  visibilityFilter
})

// const todoApp = (state = {}, action) => {
//   return {
//     todos: todos(
//       state.todos,
//       action
//     ),
//     visibiltyFilter: visibilityFilter (
//     state.visibilityFilter,
//     action
//     )
//   };
// };




const togggleAction = {
  type: 'TOGGLE_TODO',
  id:1
}

const preState = [{
  id:1,
  completed:false,
  text: 'Learn Redux'
},
  {
  id:0,
  completed:false,
  text: 'Getting it'
}]


const {createStore} = Redux;
const store = createStore(todoApp);




console.log("Initial state==",store.getState());
store.dispatch({type:'ADD_TODO', id:4, text:'hello'})
console.log('current state', store.getState());
store.dispatch({type:'ADD_TODO', id:5, text:'sleeppy'})
store.dispatch({type:'SET_VISIBILITY_FILTER', filter: 'SHOW_COMPLETED'})
console.log('current state--->', store.getState());