export default (state = {}, action) => {
  switch (action.type) {
    case "ADD_COMMENTS":
      return {
        ...state,
        [action.payload.articleId]: [
          ...state[action.payload.articleId],
          ...action.payload.comments
        ]
      };
    case "REMOVE_COMMENT":
      if (state[action.payload.articleId] == null) return state;
      return {
        ...state,
        [action.payload.articleId]: state[action.payload.articleId].filter(
          comment => comment.id !== action.payload.id
        )
      };
    case "SET_COMMENTS":
      return { [action.payload.articleId]: action.payload.comments };
    case "UPDATE_COMMENT": {
      const articleId = action.payload.articleId;
      let index = action.payload.index;
      if (!index) {
        const comment = state[articleId].find(
          c => c.id === action.payload.comment.id
        );
        index = state[articleId].indexOf(comment);
      }
      return {
        ...state,
        [articleId]: [
          ...state[articleId].slice(0, index),
          action.payload.comment,
          ...state[articleId].slice(index + 1)
        ]
      };
    }
    default:
      return state;
  }
};