{-# LANGUAGE CPP #-}
{-# LANGUAGE TypeFamilies #-}
module Database.Persist.Class.PersistUnique
    ( PersistUnique (..)
    ) where

import qualified Prelude
import Prelude hiding ((++), show)
import Data.Monoid (mappend)
import Data.Time (Day, TimeOfDay, UTCTime)
import Data.Time.LocalTime (ZonedTime, zonedTimeToUTC, zonedTimeToLocalTime, zonedTimeZone)
import Data.ByteString.Char8 (ByteString, unpack)
import Control.Applicative
import Data.Typeable (Typeable)
import Data.Int (Int8, Int16, Int32, Int64)
import Data.Word (Word8, Word16, Word32, Word64)

import Text.Blaze.Html
import Text.Blaze.Html.Renderer.Text (renderHtml)

import qualified Data.Text as T
import qualified Data.Text.Lazy as TL
import qualified Data.ByteString.Lazy as L

import qualified Control.Exception as E
import Control.Monad.Trans.Error (Error (..))

import Data.Bits (bitSize)
import Control.Monad (liftM, (<=<))
import Control.Arrow (second)

import qualified Data.Text.Encoding as T
import qualified Data.Text.Encoding.Error as T
import Web.PathPieces (PathPiece (..))
import qualified Data.Text.Read

import Data.Aeson (Value)
import Data.Aeson.Types (Parser)
import qualified Data.Aeson as A
import qualified Data.Attoparsec.Number as AN
import qualified Data.Vector as V

import qualified Data.Set as S
import qualified Data.Map as M
import qualified Data.HashMap.Strict as HM

import qualified Data.Text.Encoding as TE
import qualified Data.ByteString.Base64 as B64

import Data.Aeson (toJSON)
import Data.Aeson.Encode (fromValue)
import Data.Text.Lazy (toStrict)
import Data.Text.Lazy.Builder (toLazyText)

import Control.Monad.Trans.Control (MonadBaseControl)
import Control.Monad.Trans.Class (lift)
import Control.Monad.IO.Class (MonadIO, liftIO)
import Data.Monoid (Monoid)

import Data.Conduit.Internal (Pipe, ConduitM)
import Control.Monad.Logger (LoggingT)
import Control.Monad.Trans.Identity ( IdentityT)
import Control.Monad.Trans.List     ( ListT    )
import Control.Monad.Trans.Maybe    ( MaybeT   )
import Control.Monad.Trans.Error    ( ErrorT   )
import Control.Monad.Trans.Reader   ( ReaderT  )
import Control.Monad.Trans.Cont     ( ContT  )
import Control.Monad.Trans.State    ( StateT   )
import Control.Monad.Trans.Writer   ( WriterT  )
import Control.Monad.Trans.RWS      ( RWST     )
import Control.Monad.Trans.Resource ( ResourceT)

import qualified Control.Monad.Trans.RWS.Strict    as Strict ( RWST   )
import qualified Control.Monad.Trans.State.Strict  as Strict ( StateT )
import qualified Control.Monad.Trans.Writer.Strict as Strict ( WriterT )
import Database.Persist.Class.PersistStore
import Database.Persist.Class.PersistEntity

-- | Queries against unique keys (other than the id).
--
-- Please read the general Persistent documentation to learn how to create
-- Unique keys.
-- SQL backends automatically create uniqueness constraints, but for MongoDB you must place a unique index on the field.
class PersistStore m => PersistUnique m where
    -- | Get a record by unique key, if available. Returns also the identifier.
    getBy :: (PersistEntityBackend val ~ PersistMonadBackend m, PersistEntity val) => Unique val -> m (Maybe (Entity val))

    -- | Delete a specific record by unique key. Does nothing if no record
    -- matches.
    deleteBy :: (PersistEntityBackend val ~ PersistMonadBackend m, PersistEntity val) => Unique val -> m ()

    -- | Like 'insert', but returns 'Nothing' when the record
    -- couldn't be inserted because of a uniqueness constraint.
    insertUnique :: (PersistEntityBackend val ~ PersistMonadBackend m, PersistEntity val) => val -> m (Maybe (Key val))
    insertUnique datum = do
        isUnique <- checkUnique datum
        if isUnique then Just `liftM` insert datum else return Nothing

#define DEF(T) { getBy = lift . getBy; deleteBy = lift . deleteBy; insertUnique = lift . insertUnique }
#define GO(T) instance (PersistUnique m) => PersistUnique (T m) where DEF(T)
#define GOX(X, T) instance (X, PersistUnique m) => PersistUnique (T m) where DEF(T)

GO(LoggingT)
GO(IdentityT)
GO(ListT)
GO(MaybeT)
GOX(Error e, ErrorT e)
GO(ReaderT r)
GO(ContT r)
GO(StateT s)
GO(ResourceT)
GO(Pipe l i o u)
GOX(Monoid w, WriterT w)
GOX(Monoid w, RWST r w s)
GOX(Monoid w, Strict.RWST r w s)
GO(Strict.StateT s)
GOX(Monoid w, Strict.WriterT w)

#undef DEF
#undef GO
#undef GOX

-- | Check whether there are any conflicts for unique keys with this entity and
-- existing entities in the database.
--
-- Returns 'True' if the entity would be unique, and could thus safely be
-- 'insert'ed; returns 'False' on a conflict.
checkUnique :: (PersistEntityBackend val ~ PersistMonadBackend m, PersistEntity val, PersistUnique m) => val -> m Bool
checkUnique val =
    go $ persistUniqueKeys val
  where
    go [] = return True
    go (x:xs) = do
        y <- getBy x
        case y of
            Nothing -> go xs
            Just _ -> return False