{-# LANGUAGE StrictData #-}

module Hasura.GraphQL.Parser.Column
  ( PGColumnValue(..)
  , column
  , mkScalarTypeName

  , UnpreparedValue(..)

  , Opaque
  , openOpaque
  , mkParameter
  ) where

import           Hasura.Prelude

import qualified Data.HashMap.Strict.Extended          as M
import qualified Database.PG.Query                     as Q

import           Language.GraphQL.Draft.Syntax         (Description (..), Name (..),
                                                        Nullability (..), Value (..), litName,
                                                        mkName)

import qualified Hasura.RQL.Types.Column               as RQL
import qualified Hasura.RQL.Types.CustomTypes          as RQL

import           Data.Text.Extended
import           Hasura.GraphQL.Parser.Class
import           Hasura.GraphQL.Parser.Internal.Parser
import           Hasura.GraphQL.Parser.Schema
import           Hasura.RQL.Types.Column               hiding (EnumValue (..), EnumValueInfo (..))
import           Hasura.RQL.Types.Error
import           Hasura.SQL.DML
import           Hasura.SQL.Types
import           Hasura.SQL.Value
import           Hasura.Session                        (SessionVariable)

-- -------------------------------------------------------------------------------------------------

data Opaque a = Opaque
  { _opVariable :: Maybe VariableInfo
  -- ^ The variable this value came from, if any.
  , _opValue    :: a
  } -- Note: we intentionally don’t derive any instances here, since that would
    -- defeat the opaqueness!

openOpaque :: MonadParse m => Opaque a -> m a
openOpaque (Opaque Nothing  value) = pure value
openOpaque (Opaque (Just _) value) = markNotReusable $> value

data UnpreparedValue
  -- | A SQL value that can be parameterized over.
  = UVParameter PGColumnValue
                (Maybe VariableInfo)
                -- ^ The GraphQL variable this value came from, if any.
  -- | A literal SQL expression that /cannot/ be parameterized over.
  | UVLiteral SQLExp
  -- | The entire session variables JSON object.
  | UVSession
  -- | A single session variable.
  | UVSessionVar (PGType PGScalarType) SessionVariable

data PGColumnValue = PGColumnValue
  { pcvType  :: PGColumnType
  , pcvValue :: WithScalarType PGScalarValue
  }

mkParameter :: Opaque PGColumnValue -> UnpreparedValue
mkParameter (Opaque variable value) = UVParameter value variable

-- -------------------------------------------------------------------------------------------------

column
  :: (MonadSchema n m, MonadError QErr m)
  => PGColumnType
  -> Nullability
  -> m (Parser 'Both n (Opaque PGColumnValue))
column columnType (Nullability isNullable) =
  -- TODO(PDV): It might be worth memoizing this function even though it isn’t
  -- recursive simply for performance reasons, since it’s likely to be hammered
  -- during schema generation. Need to profile to see whether or not it’s a win.
  opaque . fmap (PGColumnValue columnType) <$> case columnType of
    PGColumnScalar scalarType -> withScalarType scalarType <$> case scalarType of
      PGInteger -> pure (PGValInteger <$> int)
      PGBoolean -> pure (PGValBoolean <$> boolean)
      PGFloat   -> pure (PGValDouble  <$> float)
      PGText    -> pure (PGValText    <$> string)
      PGVarchar -> pure (PGValVarchar <$> string)
      PGJSON    -> pure (PGValJSON  . Q.JSON  <$> json)
      PGJSONB   -> pure (PGValJSONB . Q.JSONB <$> jsonb)

      -- For all other scalars, we convert the value to JSON and use the
      -- FromJSON instance. The major upside is that this avoids having to write
      -- a new parsers for each custom type: if the JSON parser is sound, so
      -- will this one, and it avoids the risk of having two separate ways of
      -- parsing a value in the codebase, which could lead to inconsistencies.
      _  -> do
        name <- mkScalarTypeName scalarType
        let schemaType = NonNullable $ TNamed $ mkDefinition name Nothing TIScalar
        pure $ Parser
          { pType = schemaType
          , pParser =
              valueToJSON (toGraphQLType schemaType) >=>
              either (parseErrorWith ParseFailed . qeError) pure . runAesonParser (parsePGValue scalarType)
          }
    PGColumnEnumReference (EnumReference tableName enumValues) ->
      case nonEmpty (M.toList enumValues) of
        Just enumValuesList -> do
          name <- qualifiedObjectToName tableName <&> (<> $$(litName "_enum"))
          pure $ withScalarType PGText $ enum name Nothing (mkEnumValue <$> enumValuesList)
        Nothing -> throw400 ValidationFailed "empty enum values"
  where
    -- Sadly, this combinator is not sound in general, so we can’t export it
    -- for general-purpose use. If we did, someone could write this:
    --
    --   mkParameter <$> opaque do
    --     n <- int
    --     pure (mkIntColumnValue (n + 1))
    --
    -- Now we’d end up with a UVParameter that has a variable in it, so we’d
    -- parameterize over it. But when we’d reuse the plan, we wouldn’t know to
    -- increment the value by 1, so we’d use the wrong value!
    --
    -- We could theoretically solve this by retaining a reference to the parser
    -- itself and re-parsing each new value, using the saved parser, which
    -- would admittedly be neat. But it’s more complicated, and it isn’t clear
    -- that it would actually be useful, so for now we don’t support it.
    opaque :: MonadParse m => Parser 'Both m a -> Parser 'Both m (Opaque a)
    opaque parser = parser
      { pParser = \case
          GraphQLValue (VVariable var@Variable{ vInfo, vValue }) -> do
            typeCheck False (toGraphQLType $ pType parser) var
            Opaque (Just vInfo) <$> pParser parser (absurd <$> vValue)
          value -> Opaque Nothing <$> pParser parser value
      }

    withScalarType scalarType = fmap (WithScalarType scalarType) . possiblyNullable scalarType
    possiblyNullable scalarType
      | isNullable = fmap (fromMaybe $ PGNull scalarType) . nullable
      | otherwise  = id

    mkEnumValue (RQL.EnumValue value, RQL.EnumValueInfo description) =
      ( mkDefinition value (Description <$> description) EnumValueInfo
      , PGValText $ unName value
      )

mkScalarTypeName :: MonadError QErr m => PGScalarType -> m Name
mkScalarTypeName PGInteger  = pure RQL.intScalar
mkScalarTypeName PGBoolean  = pure RQL.boolScalar
mkScalarTypeName PGFloat    = pure RQL.floatScalar
mkScalarTypeName PGText     = pure RQL.stringScalar
mkScalarTypeName PGVarchar  = pure RQL.stringScalar
mkScalarTypeName scalarType = mkName (toSQLTxt scalarType) `onNothing` throw400 ValidationFailed
  ("cannot use SQL type " <> scalarType <<> " in the GraphQL schema because its name is not a "
  <> "valid GraphQL identifier")