Refactor code structure and dependencies

src/middlewares/graphql.middleware.ts

@@ -0,0 +1,26 @@
+import { Injectable, NestMiddleware } from '@nestjs/common';
+import { Request, Response, NextFunction } from 'express';
+
+@Injectable()
+export class GraphQLValidationMiddleware implements NestMiddleware {
+  use(req: Request, res: Response, next: NextFunction) {
+    // Only handle POST requests
+    if (req.method === 'POST' && req.headers['content-type'] === 'application/json') {
+      const { query, mutation, subscription } = req.body;
+
+      // If none of these are present, return a custom error response
+      if (!query && !mutation && !subscription) {
+        return res.status(400).json({
+          errors: [
+            {
+              message: 'Must provide a valid GraphQL query, mutation, or subscription.',
+            },
+          ],
+        });
+      }
+    }
+
+    // Continue to the next middleware or GraphQL handler
+    next();
+  }
+}