add custom DateTime scalar type

schema.graphqls

@@ -1,3 +1,5 @@
+scalar DateTime
+
 # The Interchange system schema.
 # Note how Passio ID and parking ID are abstracted away
 # from the endpoints.

src/MergedResolvers.ts

@@ -1,4 +1,4 @@
-import { Coordinates, Eta, OrderedStop, Resolvers } from "./generated/graphql";
+import { Resolvers } from "./generated/graphql";
 import { ServerContext } from "./ServerContext";
 import { QueryResolvers } from "./resolvers/QueryResolvers";
 import { SystemResolvers } from "./resolvers/SystemResolvers";
@@ -9,6 +9,7 @@ import { ShuttleResolvers } from "./resolvers/ShuttleResolvers";
 import { RouteResolvers } from "./resolvers/RouteResolvers";
 import { MutationResolvers } from "./resolvers/MutationResolvers";
 import { ParkingSystemResolvers } from "./resolvers/ParkingSystemResolvers";
+import { DateTime } from "./scalars/DateTime";
 
 export const MergedResolvers: Resolvers<ServerContext> = {
   ...QueryResolvers,
@@ -20,4 +21,5 @@ export const MergedResolvers: Resolvers<ServerContext> = {
   ...OrderedStopResolvers,
   ...EtaResolvers,
   ...MutationResolvers,
+  DateTime: DateTime,
 };

src/scalars/DateTime.ts

@@ -0,0 +1,28 @@
+import { GraphQLScalarType } from "graphql/type";
+import { Kind } from "graphql/language";
+
+// See Apollo documentation: https://www.apollographql.com/docs/apollo-server/schema/custom-scalars#providing-custom-scalars-to-apollo-server
+export const DateTime = new GraphQLScalarType({
+  name: 'DateTime',
+  description: 'DateTime custom scalar type',
+  serialize(value) {
+    if (value instanceof Date) {
+      return value.getTime();
+    } else if (value instanceof Number) {
+      return value;
+    }
+    throw Error('GraphQL Date Scalar serializer expected a `Date` object or number');
+  },
+  parseValue(value) {
+    if (typeof value === 'number') {
+      return new Date(value);
+    }
+    throw new Error('GraphQL Date Scalar parser expected a `number`');
+  },
+  parseLiteral(ast) {
+    if (ast.kind === Kind.INT) {
+      return new Date(parseInt(ast.value, 10));
+    }
+    return null;
+  },
+})