dustinspecker/redux-immutable-combine-reducers

'use strict'
import isPlainObj from 'is-plain-obj'
import Immutable from 'immutable'

/**
 * Returns a reducer function that always returns an Immutable.Map
 * @param {Object|Immutable.Map} reducers - keys or entries of functions
 * @return {Function} - a reducer function
 */
module.exports = function (reducers) {
  if (isPlainObj(reducers)) {
    Object.keys(reducers).forEach(key => {
      if (typeof reducers[key] !== 'function') {
        throw new Error('Expected an object with all keys being functions')
      }
    })

    return (state = Immutable.Map({}), action) =>
      Object.keys(reducers).reduce((nextstate, key) =>
        nextstate.set(key, reducers[key](state.get(key), action))
      , state)
  }

  if (Immutable.Map.isMap(reducers)) {
    reducers.keySeq().forEach(key => {
      if (typeof reducers.get(key) !== 'function') {
        throw new Error('Expected an Immutable.Map with all entries being functions')
      }
    })

    return (state = Immutable.Map({}), action) =>
      reducers.keySeq().reduce((nextstate, key) =>
        nextstate.set(key, reducers.get(key)(state.get(key), action))
      , state)
  }

  throw new TypeError('Expected an object or Immutable Map')
}