{-# language OverloadedStrings #-}

module Rel8.Statement.Using
  ( ppFrom
  , ppUsing
  )
where

-- base
import Prelude

-- opaleye
import qualified Opaleye.Internal.Tag as Opaleye

-- pretty
import Text.PrettyPrint ( Doc, (<+>), parens, text )

-- rel8
import Rel8.Query ( Query )
import Rel8.Schema.Table ( TableSchema(..), ppTable )
import Rel8.Statement.Select ( Optimized(..), ppPrimSelect )

-- transformers
import Control.Monad.Trans.State.Strict (State)


ppFrom :: Query a -> State Opaleye.Tag (Maybe (Doc, a))
ppFrom = ppJoin "FROM"


ppUsing :: Query a -> State Opaleye.Tag (Maybe (Doc, a))
ppUsing = ppJoin "USING"


ppJoin :: String -> Query a -> State Opaleye.Tag (Maybe (Doc, a))
ppJoin clause join = do
  (ofrom, a) <- ppPrimSelect join
  pure $ do
    doc <- case ofrom of
      Empty -> Nothing
      Unit -> Just mempty
      Optimized doc -> Just $ text clause <+> parens doc <+> ppTable alias
    pure (doc, a)
  where
    alias = TableSchema {name = "T1", columns = ()}