From dd996570c2829e929ae59d3517a9fb82ad1f1ff3 Mon Sep 17 00:00:00 2001
From: Eugen Wissner <belka@caraus.de>
Date: Sun, 15 Aug 2021 15:41:15 +0200
Subject: [PATCH] Add new executor module

---
 graphql.cabal                    |  1 +
 src/Language/GraphQL/Executor.hs | 82 ++++++++++++++++++++++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100644 src/Language/GraphQL/Executor.hs

diff --git a/graphql.cabal b/graphql.cabal
index b67f4ae..98f4365 100644
--- a/graphql.cabal
+++ b/graphql.cabal
@@ -38,6 +38,7 @@ library
       Language.GraphQL.Error
       Language.GraphQL.Execute
       Language.GraphQL.Execute.Coerce
+      Language.GraphQL.Executor
       Language.GraphQL.Execute.OrderedMap
       Language.GraphQL.Type
       Language.GraphQL.Type.In
diff --git a/src/Language/GraphQL/Executor.hs b/src/Language/GraphQL/Executor.hs
new file mode 100644
index 0000000..97447f5
--- /dev/null
+++ b/src/Language/GraphQL/Executor.hs
@@ -0,0 +1,82 @@
+{- This Source Code Form is subject to the terms of the Mozilla Public License,
+   v. 2.0. If a copy of the MPL was not distributed with this file, You can
+   obtain one at https://mozilla.org/MPL/2.0/. -}
+
+{-# LANGUAGE LambdaCase #-}
+
+module Language.GraphQL.Executor
+   ( Error(..)
+   , Operation(..)
+   , QueryError(..)
+   , Response(..)
+   , Segment(..)
+   , executeRequest
+   ) where
+
+import qualified Language.GraphQL.AST.Document as Full
+import qualified Data.Aeson as Aeson
+import Data.Foldable (find)
+import qualified Data.Text as Text
+import qualified Language.GraphQL.Type.Internal as Type.Internal
+
+data Segment = Segment String | Index Int
+
+data Error = Error
+   { message :: String
+   , locations :: [Full.Location]
+   , path :: [Segment]
+   }
+
+data Response = Response
+   { data' :: Aeson.Object
+   , errors :: [Error]
+   }
+
+data QueryError
+   = OperationNameRequired
+   | OperationNotFound
+
+-- operationName selectionSet location
+data Operation = Operation
+    Full.OperationType
+    (Maybe String)
+    [Full.VariableDefinition]
+    Full.SelectionSet
+    Full.Location
+
+document :: Full.Document -> [Operation]
+document = foldr filterOperation []
+  where
+    filterOperation (Full.ExecutableDefinition executableDefinition) accumulator
+        | Full.DefinitionOperation operationDefinition' <- executableDefinition =
+           operationDefinition operationDefinition' : accumulator
+    filterOperation _ accumulator = accumulator -- Fragment.
+
+operationDefinition :: Full.OperationDefinition -> Operation
+operationDefinition = \case
+    Full.OperationDefinition operationType operationName variables _ selectionSet operationLocation ->
+        let maybeOperationName = Text.unpack <$> operationName
+         in Operation operationType maybeOperationName variables selectionSet operationLocation
+    Full.SelectionSet selectionSet operationLocation ->
+        Operation Full.Query Nothing [] selectionSet operationLocation
+
+executeRequest :: Type.Internal.Schema IO
+    -> Full.Document
+    -> Maybe String
+    -> Aeson.Object
+    -> Aeson.Object
+    -> IO Response
+executeRequest _schema sourceDocument operationName _variableValues _initialValue =
+   let transformedDocument = document sourceDocument
+       _operation = getOperation transformedDocument operationName
+    in pure $ Response mempty mempty
+
+getOperation :: [Operation] -> Maybe String -> Either QueryError Operation
+getOperation [operation] Nothing = Right operation
+getOperation operations (Just givenOperationName) =
+    maybe (Left OperationNotFound) Right $ find findOperationByName operations
+  where
+    findOperationByName (Operation _ (Just operationName) _ _ _) =
+        givenOperationName == operationName
+    findOperationByName _ = False
+getOperation _ _ = Left OperationNameRequired