[React + Functional Programming ADT] Create Redux Middleware to Dispatch Actions with the Async ADT

We would like the ability to group a series of actions to be dispatched with single dispatching functions used as handlers in various parts of our game. The only issue with that, is that animations and other design elements in our game require us to provide some temporal space between each of those actions in the series being fired.

This is something we can achieve by reaching for the Async ADT provided by the crocks library. In order to allow for Asyncs in our Redux flow we are going to need to create some middleware that can identify when an Async is provided as an action, and then handle it appropriately .

Here we have dispatched three action on game start:

const mapDispatch = dispatch => ({
  answer: unit,
  restart: unit,
  start: () => dispatch([
    startGame(),
    hideAllCards(),
    startTurn()
  ]),
})

Now that we want is after we call 'startGame', we should give players 5 second to remember each cards, then we dispatch 'hideAllCards' & 'startTurn' actions.

We can use Async ADT for this:

import Async from 'crocks/Async'

const mapDispatch = dispatch => ({
  answer: unit,
  restart: unit,
  start: () => dispatch([
    startGame(),
    Async.resolveAfter(5000, hideAllCards()),
    Async.resolveAfter(5600, startTurn()),
  ]),
})

It is not enough for the program to working yet, because Redux by default expect sync opreation, not async opreation, to take async operation, we need async middleware:

import Async from 'crocks/Async'
import compose from 'crocks/helpers/compose'
import isSameType from 'crocks/predicates/isSameType'

export const errAction = payload => ({
  type: 'ASYNC_ERROR', payload, error: true
})

export default function asyncMiddleware({dispatch}) {
  return next => action => 
    isSameType(Async, action) ? 
      action.fork(compose(next, errAction),  dispatch) : //fork(reject, resolve)
      next(action)
}

Last apply the middleware:

import { createStore, applyMiddleware, compose } from 'redux'

import asyncMiddleware from './middleware/async'
import multiMiddleware from './middleware/multi'

import reducer from './reducers'
import { initialState } from './model/initialize'

const middleware = applyMiddleware(
  asyncMiddleware,
  multiMiddleware
)

const composeEnhancers =
  window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose

export default createStore(
  reducer,
  initialState(),
  composeEnhancers(middleware)
)