{-# OPTIONS_GHC -fno-warn-orphans #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}

-- |
-- Module      : Database.Relational.Query.Monad.Assign
-- Copyright   : 2013 Kei Hibino
-- License     : BSD3
--
-- Maintainer  : ex8k.hibino@gmail.com
-- Stability   : experimental
-- Portability : unknown
--
-- This module contains definitions about restrict context with assignment monad type.
module Database.Relational.Query.Monad.Assign (
  -- * Monad to restrict target records with assignment.
  Assign, AssignStatement,
  -- updateStatement,
  extract,
  ) where

import Database.Relational.Query.Internal.Sub (QueryRestriction)
import Database.Relational.Query.Component (Config, Assignments)
import Database.Relational.Query.Context (Flat)
import Database.Relational.Query.Table (Table)
import Database.Relational.Query.Projection (Projection)
import Database.Relational.Query.Monad.Restrict (Restrict)
import qualified Database.Relational.Query.Monad.Restrict as Restrict
import Database.Relational.Query.Monad.Trans.Assigning (Assignings, extractAssignments)

-- | Target update monad type used from update statement and merge statement.
type Assign r = Assignings r Restrict

-- | AssignStatement type synonym.
--   Specifying assignments and restrictions like update statement.
--   Projection record type must be
--   the same as 'Target' type parameter 'r'.
type AssignStatement r a = Projection Flat r -> Assign r a

-- -- | 'return' of 'Update'
-- updateStatement :: a -> Assignings r (Restrictings Identity) a
-- updateStatement =  assignings . restrictings . Identity

-- | Run 'Assign'.
extract :: Assign r a -> Config -> ((a, Table r -> Assignments), QueryRestriction Flat)
extract =  Restrict.extract . extractAssignments