module Hasura.Backends.Postgres.DDL.Field
  ( buildComputedFieldInfo
  )
where

import           Hasura.Prelude

import qualified Control.Monad.Validate                as MV
import qualified Data.HashSet                          as S
import qualified Data.Sequence                         as Seq
import qualified Language.GraphQL.Draft.Syntax         as G

import           Data.Text.Extended

import           Hasura.Backends.Postgres.DDL.Function
import           Hasura.Backends.Postgres.SQL.Types
import           Hasura.Base.Error
import           Hasura.RQL.Types.ComputedField
import           Hasura.RQL.Types.Function
import           Hasura.SQL.Backend
import           Hasura.SQL.Types
import           Hasura.Server.Utils


data ComputedFieldValidateError
  = CFVENotValidGraphQLName !ComputedFieldName
  | CFVEInvalidTableArgument !InvalidTableArgument
  | CFVEInvalidSessionArgument !InvalidSessionArgument
  | CFVENotBaseReturnType !PGScalarType
  | CFVEReturnTableNotFound !QualifiedTable
  | CFVENoInputArguments
  | CFVEFunctionVolatile
  deriving (Show, Eq)

data InvalidTableArgument
  = ITANotFound !FunctionArgName
  | ITANotComposite !FunctionTableArgument
  | ITANotTable !QualifiedTable !FunctionTableArgument
  deriving (Show, Eq)

data InvalidSessionArgument
  = ISANotFound !FunctionArgName
  | ISANotJSON !FunctionSessionArgument
  deriving (Show, Eq)

showError :: QualifiedFunction -> ComputedFieldValidateError -> Text
showError qf = \case
  CFVENotValidGraphQLName computedField ->
    computedField <<> " is not valid GraphQL name"
  CFVEInvalidTableArgument (ITANotFound argName) ->
    argName <<> " is not an input argument of the function " <>> qf
  CFVEInvalidTableArgument (ITANotComposite functionArg) ->
    showFunctionTableArgument functionArg <> " is not COMPOSITE type"
  CFVEInvalidTableArgument (ITANotTable ty functionArg) ->
    showFunctionTableArgument functionArg <> " of type " <> ty
    <<> " is not the table to which the computed field is being added"
  CFVEInvalidSessionArgument (ISANotFound argName) ->
    argName <<> " is not an input argument of the function " <>> qf
  CFVEInvalidSessionArgument (ISANotJSON functionArg) ->
    showFunctionSessionArgument functionArg <> " is not of type JSON"
  CFVENotBaseReturnType scalarType ->
    "the function " <> qf <<> " returning type " <> toSQLTxt scalarType
    <> " is not a BASE type"
  CFVEReturnTableNotFound table ->
    "the function " <> qf <<> " returning set of table " <> table
    <<> " is not tracked or not found in database"
  CFVENoInputArguments ->
    "the function " <> qf <<> " has no input arguments"
  CFVEFunctionVolatile ->
    "the function " <> qf <<> " is of type VOLATILE; cannot be added as a computed field"
  where
    showFunctionTableArgument = \case
      FTAFirst           -> "first argument of the function " <>> qf
      FTANamed argName _ -> argName <<> " argument of the function " <>> qf
    showFunctionSessionArgument = \case
      FunctionSessionArgument argName _ -> argName <<> " argument of the function " <>> qf

buildComputedFieldInfo
  :: forall pgKind m. (QErrM m)
  => S.HashSet QualifiedTable
  -- ^ the set of all tracked tables
  -> QualifiedTable
  -> ComputedFieldName
  -> ComputedFieldDefinition ('Postgres pgKind)
  -> PGRawFunctionInfo
  -> Maybe Text
  -> m (ComputedFieldInfo ('Postgres pgKind))
buildComputedFieldInfo trackedTables table computedField definition rawFunctionInfo comment =
  either (throw400 NotSupported . showErrors) pure =<< MV.runValidateT mkComputedFieldInfo
  where
    inputArgNames = rfiInputArgNames rawFunctionInfo
    ComputedFieldDefinition function maybeTableArg maybeSessionArg = definition
    functionReturnType = QualifiedPGType (rfiReturnTypeSchema rawFunctionInfo)
                         (rfiReturnTypeName rawFunctionInfo)
                         (rfiReturnTypeType rawFunctionInfo)

    computedFieldGraphQLName = G.mkName $ computedFieldNameToText computedField

    mkComputedFieldInfo
      :: MV.MonadValidate [ComputedFieldValidateError] n
      => n (ComputedFieldInfo ('Postgres pgKind))
    mkComputedFieldInfo = do
      -- Check if computed field name is a valid GraphQL name
      unless (isJust computedFieldGraphQLName) $
        MV.dispute $ pure $ CFVENotValidGraphQLName computedField

      -- Check if function is VOLATILE
      when (rfiFunctionType rawFunctionInfo == FTVOLATILE) $
        MV.dispute $ pure CFVEFunctionVolatile

      -- Validate and resolve return type
      returnType <-
        if rfiReturnsTable rawFunctionInfo then do
          let returnTable = typeToTable functionReturnType
          unless (returnTable `S.member` trackedTables) $ MV.dispute $ pure $
            CFVEReturnTableNotFound returnTable
          pure $ CFRSetofTable returnTable
        else do
          let scalarType = _qptName functionReturnType
          unless (isBaseType functionReturnType) $ MV.dispute $ pure $
            CFVENotBaseReturnType scalarType
          pure $ CFRScalar scalarType

      -- Validate and resolve table argument
      let inputArgs = mkFunctionArgs
            (rfiDefaultArgs   rawFunctionInfo)
            (rfiInputArgTypes rawFunctionInfo)
            inputArgNames
      tableArgument <- case maybeTableArg of
        Just argName ->
          case findWithIndex ((Just argName ==) . faName) inputArgs of
            Just (tableArg, index) -> do
              let functionTableArg = FTANamed argName index
              validateTableArgumentType functionTableArg $ faType tableArg
              pure functionTableArg
            Nothing ->
              MV.refute $ pure $ CFVEInvalidTableArgument $ ITANotFound argName
        Nothing -> do
          case inputArgs of
            []           -> MV.dispute $ pure CFVENoInputArguments
            (firstArg:_) ->
              validateTableArgumentType FTAFirst $ faType firstArg
          pure FTAFirst

      maybePGSessionArg <- sequence $ do
          argName <- maybeSessionArg
          return $ case findWithIndex ((Just argName ==) . faName) inputArgs of
            Just (sessionArg, index) -> do
              let functionSessionArg = FunctionSessionArgument argName index
              validateSessionArgumentType functionSessionArg $ faType sessionArg
              pure functionSessionArg
            Nothing ->
              MV.refute $ pure $ CFVEInvalidSessionArgument $ ISANotFound argName


      let inputArgSeq = Seq.fromList $
            dropTableAndSessionArgument tableArgument maybePGSessionArg inputArgs
          computedFieldFunction =
            ComputedFieldFunction function inputArgSeq tableArgument maybePGSessionArg $
            rfiDescription rawFunctionInfo

      pure $ ComputedFieldInfo @('Postgres pgKind) () computedField computedFieldFunction returnType comment

    validateTableArgumentType
      :: (MV.MonadValidate [ComputedFieldValidateError] n)
      => FunctionTableArgument
      -> QualifiedPGType
      -> n ()
    validateTableArgumentType tableArg qpt = do
      when (_qptType qpt /= PGKindComposite) $
        MV.dispute $ pure $ CFVEInvalidTableArgument $ ITANotComposite tableArg
      let typeTable = typeToTable qpt
      unless (table == typeTable) $
        MV.dispute $ pure $ CFVEInvalidTableArgument $ ITANotTable typeTable tableArg

    validateSessionArgumentType
      :: (MV.MonadValidate [ComputedFieldValidateError] n)
      => FunctionSessionArgument
      -> QualifiedPGType
      -> n ()
    validateSessionArgumentType sessionArg qpt = do
      unless (isJSONType $ _qptName qpt) $
        MV.dispute $ pure $ CFVEInvalidSessionArgument $ ISANotJSON sessionArg

    showErrors :: [ComputedFieldValidateError] -> Text
    showErrors allErrors =
      "the computed field " <> computedField <<> " cannot be added to table "
      <> table <<> " " <> reasonMessage
      where
        reasonMessage = makeReasonMessage allErrors (showError function)

    dropTableAndSessionArgument :: FunctionTableArgument
                                -> Maybe FunctionSessionArgument -> [FunctionArg ('Postgres pgKind)]
                                -> [FunctionArg ('Postgres pgKind)]
    dropTableAndSessionArgument tableArg sessionArg inputArgs =
      let withoutTable = case tableArg of
            FTAFirst  -> tail inputArgs
            FTANamed argName _ ->
              filter ((/=) (Just argName) . faName) inputArgs
          alsoWithoutSession = case sessionArg of
            Nothing -> withoutTable
            Just (FunctionSessionArgument name _) ->
              filter ((/=) (Just name) . faName) withoutTable
      in alsoWithoutSession