-- | Planning T-SQL queries and subscriptions.

module Hasura.Backends.MSSQL.Plan where
  -- TODO: Re-add the export list after cleaning up the module
  -- ( planQuery
  -- , planSubscription
  -- ) where

import           Hasura.Prelude                hiding (first)

import qualified Data.Aeson                    as J
import           Data.ByteString.Lazy          (toStrict)
import qualified Data.HashMap.Strict           as HM
import qualified Data.HashMap.Strict.InsOrd    as OMap
import qualified Data.HashSet                  as Set
import qualified Data.Text                     as T
import qualified Database.ODBC.SQLServer       as ODBC
import qualified Language.GraphQL.Draft.Syntax as G

import           Control.Monad.Validate
import           Data.Text.Extended

import qualified Hasura.GraphQL.Parser         as GraphQL
import qualified Hasura.RQL.Types.Column       as RQL

import           Hasura.Backends.MSSQL.FromIr
import           Hasura.Backends.MSSQL.Types
import           Hasura.Base.Error
import           Hasura.RQL.IR
import           Hasura.SQL.Backend
import           Hasura.Session


--------------------------------------------------------------------------------
-- Top-level planner

planQuery
  :: MonadError QErr m
  => SessionVariables
  -> QueryDB 'MSSQL (Const Void) (GraphQL.UnpreparedValue 'MSSQL)
  -> m Select
planQuery sessionVariables queryDB = do
  rootField <- traverse (prepareValueQuery sessionVariables) queryDB
  sel <-
    runValidate (runFromIr (fromRootField rootField))
    `onLeft` (throw400 NotSupported . tshow)
  pure $
    sel
      { selectFor =
          case selectFor sel of
            NoFor           -> NoFor
            JsonFor forJson ->
              JsonFor forJson {jsonRoot =
                                 case jsonRoot forJson of
                                   NoRoot -> Root "root"
                                   -- Keep whatever's there if already
                                   -- specified. In the case of an
                                   -- aggregate query, the root will
                                   -- be specified "aggregate", for
                                   -- example.
                                   keep   -> keep
                              }
      }

-- | Prepare a value without any query planning; we just execute the
-- query with the values embedded.
prepareValueQuery
  :: MonadError QErr m
  => SessionVariables
  -> GraphQL.UnpreparedValue 'MSSQL
  -> m Expression
prepareValueQuery sessionVariables =
  {- History note:
      This function used to be called 'planNoPlan', and was used for building sql
      expressions for queries. That evolved differently, but this function is now
      left as a *suggestion* for implementing support for mutations.
      -}
  \case
    GraphQL.UVLiteral x -> pure x
    GraphQL.UVSession -> pure $ ValueExpression $ ODBC.ByteStringValue $ toStrict $ J.encode sessionVariables
    GraphQL.UVParameter _ RQL.ColumnValue{..} -> pure $ ValueExpression cvValue
    GraphQL.UVSessionVar _typ sessionVariable -> do
      value <- getSessionVariableValue sessionVariable sessionVariables
        `onNothing` throw400 NotFound ("missing session variable: " <>> sessionVariable)
      pure $ ValueExpression $ ODBC.TextValue value

planSubscription
  :: MonadError QErr m
  => OMap.InsOrdHashMap G.Name (QueryDB 'MSSQL (Const Void) (GraphQL.UnpreparedValue 'MSSQL))
  -> SessionVariables
  -> m (Reselect, PrepareState)
planSubscription unpreparedMap sessionVariables = do
  let (rootFieldMap, prepareState) =
        runState
          (traverse
            (traverse (prepareValueSubscription (getSessionVariablesSet sessionVariables)))
            unpreparedMap)
          emptyPrepareState
  selectMap <-
    runValidate (runFromIr (traverse fromRootField rootFieldMap))
    `onLeft` (throw400 NotSupported . tshow)
  pure (collapseMap selectMap, prepareState)

  -- Plan a query without prepare/exec.
  -- planNoPlanMap ::
  --      OMap.InsOrdHashMap G.Name (SubscriptionRootFieldMSSQL (GraphQL.UnpreparedValue 'MSSQL))
  --   -> Either PrepareError Reselect
  -- planNoPlanMap _unpreparedMap =
  -- let rootFieldMap = runIdentity $
  --       traverse (traverseQueryRootField (pure . prepareValueNoPlan)) unpreparedMap
  -- selectMap <-
  --   first
  --     FromIrError
  --     (runValidate (runFromIr (traverse fromRootField rootFieldMap)))
  -- pure (collapseMap selectMap)

--------------------------------------------------------------------------------
-- Converting a root field into a T-SQL select statement

-- | Collapse a set of selects into a single select that projects
-- these as subselects.
collapseMap :: OMap.InsOrdHashMap G.Name Select
            -> Reselect
collapseMap selects =
  Reselect
    { reselectFor =
        JsonFor ForJson {jsonCardinality = JsonSingleton, jsonRoot = NoRoot}
    , reselectWhere = Where mempty
    , reselectProjections =
        map projectSelect (OMap.toList selects)
    }
  where
    projectSelect :: (G.Name, Select) -> Projection
    projectSelect (name, sel) =
      ExpressionProjection
        (Aliased
           { aliasedThing = SelectExpression sel
           , aliasedAlias = G.unName name
           })

--------------------------------------------------------------------------------
-- Session variables

globalSessionExpression :: Expression
globalSessionExpression =
  ValueExpression (ODBC.TextValue "current_setting('hasura.user')::json")


--------------------------------------------------------------------------------
-- Resolving values

data PrepareError
  = FromIrError (NonEmpty Error)

data PrepareState = PrepareState
  { positionalArguments :: ![RQL.ColumnValue 'MSSQL]
  , namedArguments      :: !(HashMap G.Name (RQL.ColumnValue 'MSSQL))
  , sessionVariables    :: !(Set.HashSet SessionVariable)
  }

emptyPrepareState :: PrepareState
emptyPrepareState = PrepareState
  { positionalArguments = mempty
  , namedArguments = mempty
  , sessionVariables = mempty
  }


-- | Prepare a value for multiplexed queries.
prepareValueSubscription
  :: Set.HashSet SessionVariable
  -> GraphQL.UnpreparedValue 'MSSQL
  -> State PrepareState Expression
prepareValueSubscription globalVariables =
  \case
    GraphQL.UVLiteral x -> pure x

    GraphQL.UVSession -> do
      modify' (\s -> s {sessionVariables = sessionVariables s <> globalVariables})
      pure $ resultVarExp (RootPath `FieldPath` "session")

    GraphQL.UVSessionVar _typ text -> do
      modify' (\s -> s {sessionVariables = text `Set.insert` sessionVariables s})
      pure $ resultVarExp (sessionDot $ toTxt text)

    GraphQL.UVParameter mVariableInfo columnValue ->
      case fmap GraphQL.getName mVariableInfo of
        Nothing -> do
          currentIndex <- (toInteger . length) <$> gets positionalArguments
          modify' (\s -> s {
            positionalArguments = positionalArguments s <> [columnValue] })
          pure (resultVarExp (syntheticIx currentIndex))
        Just name -> do
          modify
            (\s ->
               s
                 { namedArguments =
                     HM.insert name columnValue (namedArguments s)
                 })
          pure $ resultVarExp (queryDot $ G.unName name)

    where
      resultVarExp :: JsonPath -> Expression
      resultVarExp =
        JsonValueExpression $
          ColumnExpression $
            FieldName
              { fieldNameEntity = rowAlias
              , fieldName = resultVarsAlias
              }

      queryDot :: Text -> JsonPath
      queryDot name = RootPath `FieldPath` "query" `FieldPath` name

      syntheticIx :: Integer -> JsonPath
      syntheticIx i = (RootPath `FieldPath` "synthetic" `IndexPath` i)

      sessionDot :: Text -> JsonPath
      sessionDot name = RootPath `FieldPath` "session" `FieldPath` name


resultIdAlias :: T.Text
resultIdAlias = "result_id"

resultVarsAlias :: T.Text
resultVarsAlias = "result_vars"

resultAlias :: T.Text
resultAlias = "result"

rowAlias :: T.Text
rowAlias = "row"