-- | Definition of the DbImport typeclass.
module TSN.DbImport
where

import Control.Monad.IO.Class ( MonadIO )
import Database.Groundhog.Core ( PersistBackend )

import TSN.XmlImport ( XmlImport(..) )

-- | The type that will be returned from every file import attempt.
--
data ImportResult =
  ImportFailed String -- ^ Failure with an error message.
    | ImportSkipped String -- ^ We processed the file, but didn't import it.
                           --   The reason is contained in the second field.
    | ImportSucceeded      -- ^ We did import records.
    | ImportUnsupported String -- ^ We didn't know how to process this file.
                               --   The second field should contain info.

-- | Instances of this type know how to insert themselves into a
--   Groundhog database.
--
class DbImport a where
  -- | Import an instance of type @a@.
  dbimport :: (PersistBackend m) => a -> m ImportResult

  -- | This must migrate *all* stuffs that can potentially be
  -- created/used by the type @a@.
  dbmigrate :: (MonadIO m, PersistBackend m) => a -> m ()

dbimport_generic :: (XmlImport a, MonadIO m, PersistBackend m)
                 => a
                 -> m ImportResult
dbimport_generic x = insert_xml x >> return ImportSucceeded