text: import { RECEIVE_TWEETS, TOGGLE_TWEET, ADD_TWEET } from '../actions/tweets'
  
  export default function tweets (state = {}, action) {
    switch(action.type) {
      case RECEIVE_TWEETS :
        return {
          ...state,
          ...action.tweets
        }
  
      case TOGGLE_TWEET :
        return {
          ...state,
          [action.id]: {
            ...state[action.id],
            likes: action.hasLiked === true
              ? state[action.id].likes.filter((uid) => uid !== action.authedUser)
              : state[action.id].likes.concat([action.authedUser])
          }
        }
  
      case ADD_TWEET :
        const { tweet } = action
        let replyingTo = {}
        //has parent tweet to reply
        if (tweet.replyingTo !== null) {
          replyingTo = {
            [tweet.replyingTo]: {
              ...state[tweet.replyingTo],
              replies: state[tweet.replyingTo].replies.concat([tweet.id])
            }
          }
        }
        return {
          ...state,
          [action.tweet.id]: action.tweet,
          ...replyingTo,
        }
  
      default :
        return state
    }
  }