use withMutations for better efficiency about redux-immutable HOT 3 CLOSED

import {reduce, forEach, mapValues, keys, identity} from 'lodash';
import reducerMap from './reducerMap';
import composeReducers from './composeReducers';

function combineImmutableReducersBase(reducers) {
  if (!keys(reducers).length) return identity;
  return (state, action) => state.withMutations(mutableState => reduce(
    reducers,
    (nextState, domainHandler, domain) => nextState.update(domain, value => domainHandler(value, action)),
    mutableState));
}

export default function combineImmutableReducers(reducers) {
  let actionMap = {};
  let otherReducers = {};
  forEach(reducers, (domainHandler, domain) => {
    if (domainHandler.actionMap) {
      // invert from domain -> action name -> action handler 
      //          to action name -> domain -> action handler
      forEach(domainHandler.actionMap, (actionHandler, actionName) => {
        (actionMap[actionName] || (actionMap[actionName] = {}))[domain] = actionHandler;
      });
    }
    else {
      otherReducers[domain] = domainHandler;
    }
  });

  return composeReducers(
    reducerMap(mapValues(actionMap, combineImmutableReducersBase)),
    combineImmutableReducersBase(otherReducers)
  );
}