add resolver for previous stop

src/resolvers.ts

@@ -155,6 +155,28 @@ export const resolvers: Resolvers<ServerContext> = {
       const nextStopObject = await contextValue.repository.getStopById(nextOrderedStop.stopId);
       if (!nextStopObject) return null;
 
+      return {
+        route: parent.route,
+        stop: {
+          coordinates: nextStopObject.coordinates as Coordinates,
+          id: nextStopObject.id,
+          name: nextStopObject.name,
+        }
+      }
+    },
+    previousStop: async (parent, args, contextValue, info): Promise<OrderedStop | null> => {
+      const routeId = parent.route.id;
+      const stopId = parent.stop.id;
+
+      const currentOrderedStop = await contextValue.repository.getOrderedStopByRouteAndStopId(routeId, stopId);
+      if (!currentOrderedStop) return null;
+
+      const previousOrderedStop = currentOrderedStop.previousStop;
+      if (!previousOrderedStop) return null;
+
+      const nextStopObject = await contextValue.repository.getStopById(previousOrderedStop.stopId);
+      if (!nextStopObject) return null;
+
       return {
         route: parent.route,
         stop: {