refactor: improve code structure and optimize key functions

backend/app/schemas/user.py

@@ -0,0 +1,41 @@
+import uuid
+from datetime import datetime
+from typing import Literal, Optional
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class UserBase(BaseModel):
+    username: str = Field(min_length=1)
+    role: Literal["PM", "CRA", "PV", "IMP"]
+    is_active: bool = True
+
+
+class UserCreate(UserBase):
+    password: str = Field(min_length=1)
+
+
+class UserRead(UserBase):
+    id: uuid.UUID
+    created_at: datetime
+
+    model_config = ConfigDict(from_attributes=True)
+
+
+class UserInDB(UserBase):
+    id: uuid.UUID
+    hashed_password: str
+    created_at: datetime
+
+    model_config = ConfigDict(from_attributes=True)
+
+
+class Token(BaseModel):
+    access_token: str
+    token_type: str = "bearer"
+
+
+class TokenPayload(BaseModel):
+    sub: uuid.UUID
+    role: str
+    exp: Optional[int] = None