feat(db): add account existence check before insertion

prevent duplicate accounts by checking if an account with the same username and stream already exists for the user before inserting a new one. returns a 409 conflict error if duplicate is detected.

ktvmanager/lib/database.py

@@ -148,9 +148,14 @@ def add_account(user_id: int) -> Response:
         user_id: The ID of the user.
 
     Returns:
-        A Flask JSON response confirming the account was added.
+        A Flask JSON response confirming the account was added or an error message.
     """
     data = request.form
+    
+    # Check if account already exists
+    if account_exists(user_id, data["username"], data["stream"]):
+        return jsonify({"error": "Account already exists for this user"}), 409
+    
     res = single_account_check(data, get_latest_urls_from_dns())
     encrypted_password = encrypt_password(data["password"])
     query = "INSERT INTO userAccounts (username, stream, streamURL, expiaryDate, password, userID, maxConnections) VALUES (%s, %s, %s, %s, %s, %s, %s)"
@@ -167,6 +172,23 @@ def add_account(user_id: int) -> Response:
     return jsonify(result)
 
 
+def account_exists(user_id: int, username: str, stream: str) -> bool:
+    """Check if an account with the same username and stream already exists for the user.
+
+    Args:
+        user_id: The ID of the user.
+        username: The username of the account.
+        stream: The stream of the account.
+
+    Returns:
+        True if the account exists, False otherwise.
+    """
+    query = "SELECT COUNT(*) as count FROM userAccounts WHERE userID = %s AND username = %s AND stream = %s"
+    params = (user_id, username, stream)
+    result = _execute_query(query, params)
+    return result[0]["count"] > 0
+
+
 def update_expiry_date(username: str, stream: str, expiry_date: str) -> None:
     """Updates the expiry date of an account.