module Hasura.GraphQL.Schema.OrderBy
  ( orderByExp
  ) where

import           Hasura.Prelude

import qualified Data.List.NonEmpty            as NE
import qualified Language.GraphQL.Draft.Syntax as G

import qualified Hasura.GraphQL.Parser         as P
import qualified Hasura.RQL.DML.Select         as RQL
import           Hasura.RQL.Types              as RQL
import           Hasura.SQL.DML                as SQL

import           Data.Text.Extended
import           Hasura.GraphQL.Parser         (InputFieldsParser, Kind (..), Parser,
                                                UnpreparedValue)
import           Hasura.GraphQL.Parser.Class
import           Hasura.GraphQL.Schema.Common
import           Hasura.GraphQL.Schema.Table
import           Hasura.SQL.Types


-- | Corresponds to an object type for an order by.
--
-- > input table_order_by {
-- >   col1: order_by
-- >   col2: order_by
-- >   .     .
-- >   .     .
-- >   coln: order_by
-- >   obj-rel: <remote-table>_order_by
-- > }
orderByExp
  :: forall m n r. (MonadSchema n m, MonadTableInfo r m, MonadRole r m)
  => QualifiedTable
  -> SelPermInfo
  -> m (Parser 'Input n [RQL.AnnOrderByItemG UnpreparedValue])
orderByExp table selectPermissions = memoizeOn 'orderByExp table $ do
  name <- qualifiedObjectToName table <&> (<> $$(G.litName "_order_by"))
  let description = G.Description $
        "Ordering options when selecting data from " <> table <<> "."
  tableFields  <- tableSelectFields table selectPermissions
  fieldParsers <- sequenceA . catMaybes <$> traverse mkField tableFields
  pure $ concat . catMaybes <$> P.object name (Just description) fieldParsers
  where
    mkField
      :: FieldInfo
      -> m (Maybe (InputFieldsParser n (Maybe [RQL.AnnOrderByItemG UnpreparedValue])))
    mkField fieldInfo = runMaybeT $
      case fieldInfo of
        FIColumn columnInfo -> do
          let fieldName = pgiName columnInfo
          pure $ P.fieldOptional fieldName Nothing orderByOperator
            <&> fmap (pure . mkOrderByItemG (RQL.AOCColumn columnInfo)) . join
        FIRelationship relationshipInfo -> do
          let remoteTable = riRTable relationshipInfo
          fieldName <- MaybeT $ pure $ G.mkName $ relNameToTxt $ riName relationshipInfo
          perms <- MaybeT $ tableSelectPermissions remoteTable
          let newPerms = fmapAnnBoolExp partialSQLExpToUnpreparedValue $ spiFilter perms
          case riType relationshipInfo of
            ObjRel -> do
              otherTableParser <- lift $ orderByExp remoteTable perms
              pure $ do
                otherTableOrderBy <- join <$> P.fieldOptional fieldName Nothing (P.nullable otherTableParser)
                pure $ fmap (map $ fmap $ RQL.AOCObjectRelation relationshipInfo newPerms) otherTableOrderBy
            ArrRel -> do
              let aggregateFieldName = fieldName <> $$(G.litName "_aggregate")
              aggregationParser <- lift $ orderByAggregation remoteTable perms
              pure $ do
                aggregationOrderBy <- join <$> P.fieldOptional aggregateFieldName Nothing (P.nullable aggregationParser)
                pure $ fmap (map $ fmap $ RQL.AOCArrayAggregation relationshipInfo newPerms) aggregationOrderBy
        FIComputedField _ -> empty
        FIRemoteRelationship _ -> empty



-- local definitions

type OrderInfo = (SQL.OrderType, SQL.NullsOrder)


orderByAggregation
  :: forall m n r. (MonadSchema n m, MonadTableInfo r m, MonadRole r m)
  => QualifiedTable
  -> SelPermInfo
  -> m (Parser 'Input n [OrderByItemG RQL.AnnAggregateOrderBy])
orderByAggregation table selectPermissions = do
  -- WIP NOTE
  -- there is heavy duplication between this and Select.tableAggregationFields
  -- it might be worth putting some of it in common, just to avoid issues when
  -- we change one but not the other?
  tableName  <- qualifiedObjectToName table
  allColumns <- tableSelectColumns table selectPermissions
  let numColumns  = onlyNumCols allColumns
      compColumns = onlyComparableCols allColumns
      numFields   = catMaybes <$> traverse mkField numColumns
      compFields  = catMaybes <$> traverse mkField compColumns
      aggFields   = fmap (concat . catMaybes . concat) $ sequenceA $ catMaybes
        [ -- count
          Just $ P.fieldOptional $$(G.litName "count") Nothing orderByOperator
            <&> pure . fmap (pure . mkOrderByItemG RQL.AAOCount) . join
        , -- operators on numeric columns
          if null numColumns then Nothing else Just $
          for numericAggOperators \operator ->
            parseOperator operator tableName numFields
        , -- operators on comparable columns
          if null compColumns then Nothing else Just $
          for comparisonAggOperators \operator ->
            parseOperator operator tableName compFields
        ]
  let objectName  = tableName <> $$(G.litName "_aggregate_order_by")
      description = G.Description $ "order by aggregate values of table " <>> table
  pure $ P.object objectName (Just description) aggFields
  where
    mkField :: PGColumnInfo -> InputFieldsParser n (Maybe (PGColumnInfo, OrderInfo))
    mkField columnInfo =
      P.fieldOptional (pgiName columnInfo) (pgiDescription columnInfo) orderByOperator
        <&> fmap (columnInfo,) . join

    parseOperator
      :: G.Name
      -> G.Name
      -> InputFieldsParser n [(PGColumnInfo, OrderInfo)]
      -> InputFieldsParser n (Maybe [OrderByItemG RQL.AnnAggregateOrderBy])
    parseOperator operator tableName columns =
      let opText     = G.unName operator
          objectName = tableName <> $$(G.litName "_") <> operator <> $$(G.litName "_order_by")
          objectDesc = Just $ G.Description $ "order by " <> opText <> "() on columns of table " <>> table
      in  P.fieldOptional operator Nothing (P.object objectName objectDesc columns)
        `mapField` map (\(col, info) -> mkOrderByItemG (RQL.AAOOp opText col) info)



orderByOperator :: MonadParse m => Parser 'Both m (Maybe OrderInfo)
orderByOperator =
  P.nullable $ P.enum $$(G.litName "order_by") (Just "column ordering options") $ NE.fromList
    [ ( define $$(G.litName "asc") "in ascending order, nulls last"
      , (SQL.OTAsc, SQL.NLast)
      )
    , ( define $$(G.litName "asc_nulls_first") "in ascending order, nulls first"
      , (SQL.OTAsc, SQL.NFirst)
      )
    , ( define $$(G.litName "asc_nulls_last") "in ascending order, nulls last"
      , (SQL.OTAsc, SQL.NLast)
      )
    , ( define $$(G.litName "desc") "in descending order, nulls first"
      , (SQL.OTDesc, SQL.NFirst)
      )
    , ( define $$(G.litName "desc_nulls_first") "in descending order, nulls first"
      , (SQL.OTDesc, SQL.NFirst)
      )
    , ( define $$(G.litName "desc_nulls_last") "in descending order, nulls last"
      , (SQL.OTDesc, SQL.NLast)
      )
    ]
  where
    define name desc = P.mkDefinition name (Just desc) P.EnumValueInfo



-- local helpers

mkOrderByItemG :: a -> OrderInfo -> OrderByItemG a
mkOrderByItemG column (orderType, nullsOrder) =
  OrderByItemG { obiType   = Just $ RQL.OrderType orderType
               , obiColumn = column
               , obiNulls  = Just $ RQL.NullsOrder nullsOrder
               }

aliasToName :: G.Name -> FieldName
aliasToName = FieldName . G.unName