actions.js

import {
  makeAsyncActionCreator as makeAsyncActionCreatorOrig,
  makeActionCreator as makeActionCreatorOrig,
  composeReducers,
  makeAsyncReducer,
  makeReducer,
} from 'redux-toolbelt'

const makeAsyncActionCreator = makeAsyncActionCreatorOrig.withDefaults({ prefix: 'document/' })
const makeActionCreator = makeActionCreatorOrig.withDefaults({ prefix: 'document/' })

export const addPage = makeActionCreator('addPage')
export const clonePage = makeActionCreator('clonePage')
export const splitPage = makeActionCreator('splitPage')
export const movePage = makeActionCreator('movePage')
export const removePage = makeActionCreator('removePage')
// ... many more actions here

reducers.js

const permissions = makeReducer(/* ... */)
const animations = composeReducers(/* ... */)
const sounds = composeReducers(/* ... */)
const metadata = makeAsyncReducer(/* ... */)
const pages = composeReducers(/* ... */)
const activePageIndex = makeReducer(/* ... */)

//... more intermediate reducers here

export const document = composeReducers(
  {
    permissions,
    metadata,
    content: {
      pages: composeReducers({
        pages,
        activePageIndex,
      }),
      animations,
      sounds,
    },
    viewState: composeReducers({
      lastPageId: makeReducer(
        [addPage, clonePage, splitPage], 
        (state, { payload: page }) => page.id)
      ),
      /* ... more ... */
    }),
  },
  createReducer(removePage, (state, { payload: id }) => {
    if(id !== state.viewState.lastPageId){
      return state
    }
    return dotProp.set(state, 'viewState.lastPageId', state.content.pages[0].id)
  })
)