username validation

src/schemas/validators.py

@@ -1,11 +1,21 @@
 from typing import Any
 
 
-def ensure_password(value: Any) -> Any:
+def ensure_password(value: Any) -> str:
     if not isinstance(value, str):
         raise TypeError("Password must be a string")
+    value = value.strip()
     if len(value) < 8:
         raise ValueError("Password must be at least 8 characters")
-    if value.strip() == "":
+    elif value.strip() == "":
         raise ValueError("Password cannot be empty")
     return value
+
+
+def ensure_username(value: str) -> str:
+    value = value.strip()
+    if len(value) < 3:
+        raise ValueError("Username must be at least 3 characters")
+    elif value.lower() in ['admin', 'moderator', 'админ', 'модератор']:
+        raise ValueError("Login is already taken")
+    return value