module CQRSExample.Instances
       (
       ) where

import           Data.CQRS.Command (Eventable(..))

import           CQRSExample.Aggregates
import           CQRSExample.Events

instance Eventable Task Event where
  applyEvent mTask (TaskEvent taskEvent) = go taskEvent
      where
        go (TaskAdded title) =
            case mTask of
              Nothing -> Just $ newTask title
              Just _  -> error "Cannot add task which already exists"
        go TaskCompleted = fmap (\task -> task { taskStatus = TaskStatusComplete }) mTask
        go TaskReopened = fmap (\task -> task { taskStatus = TaskStatusOpen }) mTask
        go TaskArchived = fmap (\task -> task { taskStatus = TaskStatusArchived }) mTask