From d96470a62a2a9b880755028078241058b2677133 Mon Sep 17 00:00:00 2001
From: Tobe O <thosakwe@gmail.com>
Date: Fri, 3 Aug 2018 21:23:45 -0400
Subject: [PATCH] Implement interface and union type querying

---
 angel_graphql/lib/src/graphql_http.dart |  9 +----
 graphql_schema/lib/src/object_type.dart | 18 ++++++++-
 graphql_server/lib/graphql_server.dart  | 53 +++++++++++++++++++++----
 3 files changed, 63 insertions(+), 17 deletions(-)

diff --git a/angel_graphql/lib/src/graphql_http.dart b/angel_graphql/lib/src/graphql_http.dart
index 0de6a02b..0f972b97 100644
--- a/angel_graphql/lib/src/graphql_http.dart
+++ b/angel_graphql/lib/src/graphql_http.dart
@@ -16,13 +16,6 @@ final Validator graphQlPostBody = new Validator({
   'variables': predicate((v) => v == null || v is Map),
 });
 
-Map<String, dynamic> _foldToStringDynamic(Map map) {
-  return map == null
-      ? null
-      : map.keys.fold<Map<String, dynamic>>(
-          <String, dynamic>{}, (out, k) => out..[k.toString()] = map[k]);
-}
-
 RequestHandler graphQLHttp(GraphQL graphQl) {
   return (req, res) async {
     try {
@@ -41,7 +34,7 @@ RequestHandler graphQLHttp(GraphQL graphQl) {
               text,
               sourceUrl: 'input',
               operationName: operationName,
-              variableValues: _foldToStringDynamic(variables),
+              variableValues: foldToStringDynamic(variables),
             ),
           };
         }
diff --git a/graphql_schema/lib/src/object_type.dart b/graphql_schema/lib/src/object_type.dart
index bf8e114a..baf59107 100644
--- a/graphql_schema/lib/src/object_type.dart
+++ b/graphql_schema/lib/src/object_type.dart
@@ -13,10 +13,12 @@ class GraphQLObjectType
   final List<GraphQLObjectType> _possibleTypes = [];
 
   /// A list of other types that this object type is known to implement.
-  List<GraphQLObjectType> get interfaces => new List<GraphQLObjectType>.unmodifiable(_interfaces);
+  List<GraphQLObjectType> get interfaces =>
+      new List<GraphQLObjectType>.unmodifiable(_interfaces);
 
   /// A list of other types that implement this interface.
-  List<GraphQLObjectType> get possibleTypes => new List<GraphQLObjectType>.unmodifiable(_possibleTypes);
+  List<GraphQLObjectType> get possibleTypes =>
+      new List<GraphQLObjectType>.unmodifiable(_possibleTypes);
 
   GraphQLObjectType(this.name, this.description, {this.isInterface: false});
 
@@ -88,6 +90,18 @@ class GraphQLObjectType
       return out..[k.toString()] = field.deserialize(value[k]);
     });
   }
+
+  bool isImplementationOf(GraphQLObjectType type) {
+    if (type == this) {
+      return true;
+    } else if (interfaces.contains(type)) {
+      return true;
+    } else if (interfaces.isNotEmpty) {
+      return interfaces.any((t) => t.isImplementationOf(type));
+    } else {
+      return false;
+    }
+  }
 }
 
 Map<String, dynamic> _foldToStringDynamic(Map map) {
diff --git a/graphql_server/lib/graphql_server.dart b/graphql_server/lib/graphql_server.dart
index 8410a12a..e911cd3b 100644
--- a/graphql_server/lib/graphql_server.dart
+++ b/graphql_server/lib/graphql_server.dart
@@ -5,6 +5,13 @@ import 'package:graphql_schema/graphql_schema.dart';
 
 import 'introspection.dart';
 
+Map<String, dynamic> foldToStringDynamic(Map map) {
+  return map == null
+      ? null
+      : map.keys.fold<Map<String, dynamic>>(
+          <String, dynamic>{}, (out, k) => out..[k.toString()] = map[k]);
+}
+
 class GraphQL {
   final List<GraphQLType> customTypes = [];
   GraphQLSchema _schema;
@@ -335,17 +342,48 @@ class GraphQL {
       }
     }
 
-    if (fieldType is GraphQLObjectType) {
-      var objectType = fieldType;
+    if (fieldType is GraphQLObjectType || fieldType is GraphQLUnionType) {
+      GraphQLObjectType objectType;
+
+      if (fieldType is GraphQLObjectType && !fieldType.isInterface) {
+        objectType = fieldType;
+      } else {
+        objectType = resolveAbstractType(fieldType, result);
+      }
+
       var subSelectionSet = mergeSelectionSets(fields);
       return await executeSelectionSet(
           document, subSelectionSet, objectType, result, variableValues);
     }
 
-    // TODO: Interface/union type
     throw new UnsupportedError('Unsupported type: $fieldType');
   }
 
+  GraphQLObjectType resolveAbstractType(GraphQLType type, result) {
+    List<GraphQLObjectType> possibleTypes;
+
+    if (type is GraphQLObjectType) {
+      possibleTypes = type.possibleTypes;
+    } else if (type is GraphQLUnionType) {
+      possibleTypes = type.possibleTypes;
+    } else {
+      throw new ArgumentError();
+    }
+
+    for (var t in possibleTypes) {
+      try {
+        var validation =
+            t.validate('@root', foldToStringDynamic(result as Map));
+
+        if (validation.successful) {
+          return t;
+        }
+      } catch (_) {}
+    }
+
+    throw new StateError('Cannot convert value $result to type $type.');
+  }
+
   SelectionSetContext mergeSelectionSets(List<SelectionContext> fields) {
     var selections = <SelectionContext>[];
 
@@ -451,13 +489,14 @@ class GraphQL {
   bool doesFragmentTypeApply(
       GraphQLObjectType objectType, TypeConditionContext fragmentType) {
     var type = convertType(new TypeContext(fragmentType.typeName, null));
-    // TODO: Handle interface type, union?
-
-    if (type is GraphQLObjectType) {
+    if (type is GraphQLObjectType && !type.isInterface) {
       for (var field in type.fields)
         if (!objectType.fields.any((f) => f.name == field.name)) return false;
-
       return true;
+    } else if (type is GraphQLObjectType && type.isInterface) {
+      return objectType.isImplementationOf(type);
+    } else if (type is GraphQLUnionType) {
+      return type.possibleTypes.any((t) => objectType.isImplementationOf(t));
     }
 
     return false;