Add file utility functions for filename and path handling

Introduce helper functions to generate unique filenames, create date-based storage paths, and validate image content types. These utilities centralize and streamline file-related operations for consistency and reusability.

backend/app/utils/files.py

@@ -0,0 +1,28 @@
+import os
+import uuid
+from datetime import datetime
+
+from app.core.config import settings
+
+
+def generate_unique_filename(original_filename: str) -> str:
+    """Generate a unique filename preserving the original extension."""
+    name, ext = os.path.splitext(original_filename)
+    unique_id = uuid.uuid4().hex
+    return f"{unique_id}{ext}"
+
+
+def get_relative_storage_path(folder: str, filename: str) -> str:
+    """
+    Generate a relative storage path using date-based organization.
+
+    Example: "event-themes/2023/03/filename.jpg"
+    """
+    today = datetime.now()
+    year_month = today.strftime("%Y/%m")
+    return os.path.join(folder, year_month, filename)
+
+
+def validate_image_content_type(content_type: str) -> bool:
+    """Check if the content type is an allowed image type."""
+    return content_type in settings.ALLOWED_IMAGE_TYPES