Added frontend. Working on user management

src/file-processor/app/database/connection.py

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+"""
+MongoDB database connection management.
+
+This module handles MongoDB connection with fail-fast approach.
+The application will terminate if MongoDB is not accessible at startup.
+"""
+
+import sys
+from typing import Optional
+from pymongo import MongoClient
+from pymongo.database import Database
+from pymongo.errors import ConnectionFailure, ServerSelectionTimeoutError
+
+from ..config.settings import get_mongodb_url, get_mongodb_database_name
+
+# Global variables for singleton pattern
+_client: Optional[MongoClient] = None
+_database: Optional[Database] = None
+
+
+def create_mongodb_client() -> MongoClient:
+  """
+  Create MongoDB client with connection validation.
+
+  Returns:
+      MongoClient: Connected MongoDB client
+
+  Raises:
+      SystemExit: If connection fails (fail-fast approach)
+  """
+  mongodb_url = get_mongodb_url()
+  
+  try:
+    # Create client with short timeout for fail-fast behavior
+    client = MongoClient(
+      mongodb_url,
+      serverSelectionTimeoutMS=5000,  # 5 seconds timeout
+      connectTimeoutMS=5000,
+      socketTimeoutMS=5000
+    )
+    
+    # Test connection by running admin command
+    client.admin.command('ping')
+    
+    print(f"Successfully connected to MongoDB at {mongodb_url}")
+    return client
+  
+  except (ConnectionFailure, ServerSelectionTimeoutError) as e:
+    print(f"ERROR: Failed to connect to MongoDB at {mongodb_url}")
+    print(f"Connection error: {str(e)}")
+    print("MongoDB is required for this application. Please ensure MongoDB is running and accessible.")
+    sys.exit(1)
+  except Exception as e:
+    print(f"ERROR: Unexpected error connecting to MongoDB: {str(e)}")
+    sys.exit(1)
+
+
+def get_database() -> Database:
+  """
+  Get MongoDB database instance (singleton pattern).
+
+  Returns:
+      Database: MongoDB database instance
+
+  This function implements singleton pattern to ensure only one
+  database connection is created throughout the application lifecycle.
+  """
+  global _client, _database
+  
+  if _database is None:
+    if _client is None:
+      _client = create_mongodb_client()
+    
+    database_name = get_mongodb_database_name()
+    _database = _client[database_name]
+    print(f"Connected to database: {database_name}")
+  
+  return _database
+
+
+def close_database_connection():
+  """
+  Close MongoDB database connection.
+
+  This function should be called during application shutdown
+  to properly close the database connection.
+  """
+  global _client, _database
+  
+  if _client is not None:
+    _client.close()
+    _client = None
+    _database = None
+    print("MongoDB connection closed")
+
+
+def get_mongodb_client() -> Optional[MongoClient]:
+  """
+  Get the raw MongoDB client instance.
+
+  Returns:
+      MongoClient or None: MongoDB client instance if connected
+
+  This is primarily for testing purposes or advanced use cases
+  where direct client access is needed.
+  """
+  return _client
+
+
+def test_database_connection() -> bool:
+  """
+  Test if database connection is working.
+
+  Returns:
+      bool: True if connection is working, False otherwise
+
+  This function can be used for health checks.
+  """
+  try:
+    db = get_database()
+    # Simple operation to test connection
+    db.command('ping')
+    return True
+  except Exception:
+    return False