from __future__ import annotations

from typing import Union, Optional
from pydantic import BaseModel, PositiveInt, field_validator, Field


class User(BaseModel):
    name: str
    surname: str
    age: int
    registered: bool

class UserNone(BaseModel):
    # preferred variant
    name: str
    surname: str
    age: int | None
    registered: bool = False

class UserUnion(BaseModel):
    name: str
    surname: str
    age: Union[int, None] = None
    registered: bool = False

class UserOptional(BaseModel):
    name: str
    surname: str
    age: Optional[int] # default value is None
    registered: bool = False

class UserPositiveInt(BaseModel):
    name: str
    surname: str
    age: Union[PositiveInt, None] = None
    registered: bool = False

class UserFieldValidator(BaseModel):
    name: str
    surname: str
    age: PositiveInt | None
    registered: bool = False

    @field_validator("age")
    def validate_age(cls, value):
        if value < 18:
            raise ValueError("age must be at least 18")
        return value


class UserMaxLength(BaseModel):
    name: str = Field(..., max_length=10)
    surname: str = Field(..., max_length=10)
    age: PositiveInt | None
    registered: bool = False

    @field_validator("age")
    def check_age(cls, value):
        if value < 18:
            raise ValueError("You are too young to register")
        return value