import { createByKey, createGetByKey } from 'redux-xforms'
 
const hasFilterName = action => action.hasOwnProperty('filterName')
const mapActionToFilterName = action => action.filterName
 
// we can call this later with a reducer to get the transform
const createByFilter = createByKey(hasFilterName, mapActionToFilterName)
 
const createGetByFilter = createGetByKey(mapActionToFilterName)

const ACTION_TYPE = 'ACTION_TYPE'
const reducer = (state = { nested: null }, action) => {
  if (action.type === ACTION_TYPE) {
    return { nested: action.payload }
  }
  return state
}
 
const transformedReducer = createByFilter(reducer)
const getNestedState = createGetByFilter(state => state.nested)
 
// reducing actions:
const state = [ {}, {
  type: ACTION_TYPE,
  payload: 'some-payload',
  filterName: 'myFilterName',
} ].reduce(transformedReducer, undefined)
 
console.log(state)
// { myFilterName: { nested: 'some-payload' } }
 
console.log(getNestedState(state, { filterName: 'myFilterName' }))
// 'some-payload'

import { withInitialState, withFilter, updateSlice, isolateSlice } from 'redux-xforms'
import { compose } from 'redux'
 
const createByFilter = (predicate, mapActionToKey) => compose(
  withInitialState({}), // inject initial state as {}
  withFilter(predicate), // let through if action has filterName
  updateSlice(mapActionToKey), // update a single key in the state
  isolateSlice(mapActionToKey) // run the reducer on a single state slice
)
 
// we can transform (state, input -> state) selectors as well
const createGetByFilter = mapActionToFilterName => isolateSlice(mapActionToFilterName)