create-messages-reducer.js

import MESSAGE_TYPE from './message-type';

const handleMessage = (state, message) =>
  typeof message === 'function'
    ? message(state)
    : Object.assign({}, state, message);

// createMessagesReducer : STATE_NAME -> INITIAL_STATE -> (state, action) -> state
export default stateName => initialState => (state = initialState, action) =>
  action.stateName === stateName && action.type.indexOf(MESSAGE_TYPE) === 0
    ? Object.assign({}, state, handleMessage(state, action.message))
    : state;