drizzle/src/drizzle-middleware.js

import * as DrizzleActions from './drizzleStatus/constants'
import * as AccountsActions from './accounts/constants'
import * as ContractActions from './contracts/constants'

export const drizzleMiddleware = drizzleInstance => store => next => action => {
  const { type } = action

  if (type === DrizzleActions.DRIZZLE_INITIALIZING) {
    drizzleInstance = action.drizzle
  }

  if (
    type === AccountsActions.ACCOUNTS_FETCHED &&
    drizzleInstance &&
    drizzleInstance.contractList.length
  ) {
    const newAccount = action.accounts[0]
    const oldAccount = drizzleInstance.contractList[0].options.from

    // Update `from` fields with newAccount
    if (oldAccount !== newAccount) {
      drizzleInstance.contractList.forEach(contract => {
        contract.options.from = newAccount
      })
    }
  }

  if (type === ContractActions.ADD_CONTRACT && drizzleInstance) {
    try {
      const { contractConfig, events } = action
      drizzleInstance.addContract(contractConfig, events)
    } catch (error) {
      console.error('Attempt to add a duplicate contract.\n', error)

      // Notify user via
      const notificationAction = {
        type: ContractActions.ERROR_ADD_CONTRACT,
        error,
        attemptedAction: action
      }
      store.dispatch(notificationAction)

      // Don't propogate current action
      return
    }
  }
  return next(action)
}

const initializedMiddleware = drizzleMiddleware(undefined)
export default initializedMiddleware