from pydantic import BaseModel, Field, field_validator
from typing import List, Union

# Pydantic Model for Response Validation
class ContinentStats(BaseModel):
    continent: str = Field(..., title="Continent Name", example="Asia")
    Total_Countries: int = Field(..., title="Total Number of Countries", example=48)
    Total_Population: int = Field(..., title="Total Population", example=4600000000)
    Average_Population: float = Field(..., title="Average Population Per Country", example=96000000)
    Total_Area: int = Field(..., title="Total Land Area (sq km)", example=44679000)
    max_population: int = Field(..., title="Highest Country Population", example=1400000000)
    min_population: int = Field(..., title="Lowest Country Population", example=100000)
    Population_Density: float = Field(..., title="Population Density (people/sq km)", example=103)

    @field_validator("Total_Countries", "Total_Population", "Total_Area", "max_population", "min_population")
    @classmethod
    def must_be_positive(cls, value):
        if value < 0:
            raise ValueError("Value must be non-negative")
        return value