-- |
-- Module      : Database.Relational.Query.Monad.BaseType
-- Copyright   : 2015-2017 Kei Hibino
-- License     : BSD3
--
-- Maintainer  : ex8k.hibino@gmail.com
-- Stability   : experimental
-- Portability : unknown
--
-- This module defines base monad type to build queries.
module Database.Relational.Query.Monad.BaseType
       ( -- * Base monad type to build queries
         ConfigureQuery, configureQuery,
         qualifyQuery, askConfig,

         -- * Relation type
         Relation, unsafeTypeRelation, untypeRelation, relationWidth,

         dump,
         sqlFromRelationWith, sqlFromRelation,

         rightPh, leftPh,
       ) where

import Data.Functor.Identity (Identity, runIdentity)
import Control.Applicative ((<$>))

import Database.Record.Persistable (PersistableRecordWidth, unsafePersistableRecordWidth)

import Database.Relational.Query.Internal.Config (Config, defaultConfig)
import Database.Relational.Query.Internal.SQL (StringSQL, showStringSQL)

import Database.Relational.Query.Sub (Qualified, SubQuery, showSQL, width)
import qualified Database.Relational.Query.Monad.Trans.Qualify as Qualify
import Database.Relational.Query.Monad.Trans.Qualify (Qualify, qualify, evalQualifyPrime)
import Database.Relational.Query.Monad.Trans.Config (QueryConfig, runQueryConfig, askQueryConfig)

-- | Thin monad type for untyped structure.
type ConfigureQuery = Qualify (QueryConfig Identity)

-- | Run 'ConfigureQuery' monad with initial state to get only result.
configureQuery :: ConfigureQuery q -> Config -> q
configureQuery cq c = runIdentity $ runQueryConfig (evalQualifyPrime cq) c

-- | Get qualifyed table form query.
qualifyQuery :: a -> ConfigureQuery (Qualified a)
qualifyQuery =  Qualify.qualifyQuery

-- | Read configuration.
askConfig :: ConfigureQuery Config
askConfig =  qualify askQueryConfig


-- | Relation type with place-holder parameter 'p' and query result type 'r'.
newtype Relation p r = SubQuery (ConfigureQuery SubQuery)

-- | Unsafely type qualified subquery into record typed relation type.
unsafeTypeRelation :: ConfigureQuery SubQuery -> Relation p r
unsafeTypeRelation = SubQuery

-- | Sub-query Qualify monad from relation.
untypeRelation :: Relation p r -> ConfigureQuery SubQuery
untypeRelation (SubQuery qsub) = qsub

-- | 'PersistableRecordWidth' of 'Relation' type.
relationWidth :: Relation p r ->  PersistableRecordWidth r
relationWidth rel =
  unsafePersistableRecordWidth . width $ configureQuery (untypeRelation rel) defaultConfig
  ---                               Assume that width is independent from Config structure

unsafeCastPlaceHolder :: Relation a r -> Relation b r
unsafeCastPlaceHolder (SubQuery qsub) = SubQuery qsub

-- | Simplify placeholder type applying left identity element.
rightPh :: Relation ((), p) r -> Relation p r
rightPh =  unsafeCastPlaceHolder

-- | Simplify placeholder type applying right identity element.
leftPh :: Relation (p, ()) r -> Relation p r
leftPh =  unsafeCastPlaceHolder

-- | Generate SQL string from 'Relation' with configuration.
sqlFromRelationWith :: Relation p r -> Config -> StringSQL
sqlFromRelationWith =  configureQuery . (showSQL <$>) . untypeRelation

-- | SQL string from 'Relation'.
sqlFromRelation :: Relation p r -> StringSQL
sqlFromRelation =  (`sqlFromRelationWith` defaultConfig)

-- | Dump internal structure tree.
dump :: Relation p r -> String
dump =  show . (`configureQuery` defaultConfig) . untypeRelation

instance Show (Relation p r) where
  show = showStringSQL . sqlFromRelation
