[Redux] Extracting Presentational Components -- TodoApp

const TodoApp = ({
  todos,
  visibilityFilter
}) => {
  return (
      <div>
        <AddTodo 
           onAddTodo={ text =>
              store.dispatch({
                  type: ‘ADD_TODO‘,
                  id: nextTodoId++,
                  text
              })
           }
        />
        <TodoList 
          todos={getVisibleTodos(
              todos,
              visibilityFilter
          )}
          onTodoClick={
            (id)=>{
              store.dispatch({
                type: ‘TOGGLE_TODO‘,
                id
              })
            }
          }
        />
        <Footer 
           visibilityFilter = {visibilityFilter}
           onFilterClick={ (filter) => {
              store.dispatch({
                 type: ‘SET_VISIBILITY_FILTER‘,
                 filter
             });
           }}
        />
      </div>
    );
}

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

      return {
        ...state,
        completed: !state.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 } = Redux;
const todoApp = combineReducers({
  todos,
  visibilityFilter
});

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

const { Component } = React;

/*PC*/
const Todo = ({
  text,
  completed,
  onTodoClick
})=>{
  return (
    <li 
                onClick={onTodoClick}
                style={{
                  textDecoration:
                    completed ?
                      ‘line-through‘ :
                      ‘none‘
                }}>
              {text}
            </li>
  );
}


/*PC*/
const TodoList = ({
  todos,
  onTodoClick
}) => {
  return (
    <ul>
          {todos.map(todo =>
            <Todo 
             key={todo.id}
             {...todo}
             onClick={
                ()=>{
                  onTodoClick
                }
             } 
           />
          )}
        </ul>
  );
}

/**
 Functional compoment, persental compoment: doesn‘t need to know what to do, just show the interface, call the callback function.
*/
const AddTodo = ({
  onAddTodo
}) => {
  
  let input;
  return (
     <div>
          <input ref={node => {
          input = node;
        }} />
        <button onClick={() => {
          onAddTodo(input.value);
          input.value = ‘‘;
        }}>
          Add Todo
        </button>
     </div>
  );
}

/* Functional component */
const Footer = ({
  visibilityFilter,
  onFilterClick
}) => (
        <p>
          Show:
          {‘ ‘}
          <FilterLink
            filter=‘SHOW_ALL‘
            currentFilter={visibilityFilter}
            onFilterClick={onFilterClick}
          >
            All
          </FilterLink>
          {‘, ‘}
          <FilterLink
            filter=‘SHOW_ACTIVE‘
            currentFilter={visibilityFilter}
            onFilterClick={onFilterClick}
          >
            Active
          </FilterLink>
          {‘, ‘}
          <FilterLink
            filter=‘SHOW_COMPLETED‘
            currentFilter={visibilityFilter}
            onFilterClick={onFilterClick}
          >
            Completed
          </FilterLink>
        </p>
);

const FilterLink = ({
  filter,
  currentFilter,
  children,
  onFilterClick
}) => {
  if (filter === currentFilter) {
    return <span>{children}</span>;
  }

  return (
    <a href=‘#‘
       onClick={e => {
         e.preventDefault();
         onFilterClick(filter);
       }}
    >
      {children}
    </a>
  );
};

const getVisibleTodos = (
  todos,
  filter
) => {
  switch (filter) {
    case ‘SHOW_ALL‘:
      return todos;
    case ‘SHOW_COMPLETED‘:
      return todos.filter(
        t => t.completed
      );
    case ‘SHOW_ACTIVE‘:
      return todos.filter(
        t => !t.completed
      );
  }
}

let nextTodoId = 0;

const TodoApp = ({
  todos,
  visibilityFilter
}) => {
  return (
      <div>
        <AddTodo 
           onAddTodo={ text =>
              store.dispatch({
                  type: ‘ADD_TODO‘,
                  id: nextTodoId++,
                  text
              })
           }
        />
        <TodoList 
          todos={getVisibleTodos(
              todos,
              visibilityFilter
          )}
          onTodoClick={
            (id)=>{
              store.dispatch({
                type: ‘TOGGLE_TODO‘,
                id
              })
            }
          }
        />
        <Footer 
           visibilityFilter = {visibilityFilter}
           onFilterClick={ (filter) => {
              store.dispatch({
                 type: ‘SET_VISIBILITY_FILTER‘,
                 filter
             });
           }}
        />
      </div>
    );
}


const render = () => {
  ReactDOM.render(
    <TodoApp
      {...store.getState()}
    />,
    document.getElementById(‘root‘)
  );
};

store.subscribe(render);
render();