Refactor code structure for improved readability and maintainability; optimize performance across multiple modules.

backend/middleware/uploadMiddleware.js

@@ -0,0 +1,33 @@
+import multer from 'multer';
+
+const imageMimeTypes = new Set(['image/jpeg', 'image/png', 'image/webp', 'image/gif']);
+const verificationMimeTypes = new Set([...imageMimeTypes, 'application/pdf']);
+const videoMimeTypes = new Set(['video/mp4', 'video/webm', 'video/ogg', 'video/quicktime']);
+
+function createUpload({ maxBytes, allowedMimeTypes }) {
+    return multer({
+        storage: multer.memoryStorage(),
+        limits: { fileSize: maxBytes, files: 1 },
+        fileFilter: (_req, file, callback) => {
+            if (!allowedMimeTypes.has(file.mimetype)) {
+                callback(new multer.MulterError('LIMIT_UNEXPECTED_FILE', file.fieldname));
+                return;
+            }
+            callback(null, true);
+        },
+    });
+}
+
+export const imageUpload = createUpload({ maxBytes: 10 * 1024 * 1024, allowedMimeTypes: imageMimeTypes });
+export const adultVerificationUpload = createUpload({ maxBytes: 10 * 1024 * 1024, allowedMimeTypes: verificationMimeTypes });
+export const videoUpload = createUpload({ maxBytes: 100 * 1024 * 1024, allowedMimeTypes: videoMimeTypes });
+
+export function uploadErrorHandler(error, _req, res, next) {
+    if (error instanceof multer.MulterError) {
+        const message = error.code === 'LIMIT_FILE_SIZE'
+            ? 'Die hochgeladene Datei ist zu groß.'
+            : 'Der Dateityp ist nicht erlaubt.';
+        return res.status(400).json({ error: message });
+    }
+    return next(error);
+}