import datetime
from collections.abc import Sequence
from dataclasses import dataclass

from sqlalchemy import Date, DateTime, Float, Integer, String, UniqueConstraint, select
from sqlalchemy.orm import DeclarativeBase, Mapped, Session, mapped_column
from sqlalchemy.sql import func


class Base(DeclarativeBase):
    pass


class WeatherForecast(Base):
    __tablename__ = "weather_forecast"
    __table_args__ = (
        UniqueConstraint("city", "forecast_date", name="unique_city_forecast_date"),
    )

    id: Mapped[int] = mapped_column(Integer, primary_key=True, autoincrement=True)
    city: Mapped[str] = mapped_column(String, nullable=False)
    forecast_date: Mapped[datetime.date] = mapped_column(Date, nullable=False)
    temp_min: Mapped[float] = mapped_column(Float, nullable=False)
    temp_max: Mapped[float] = mapped_column(Float, nullable=False)
    humidity: Mapped[int] = mapped_column(Integer, nullable=False)
    wind_speed: Mapped[float] = mapped_column(Float, nullable=False)
    description: Mapped[str | None] = mapped_column(String, nullable=True)
    created_at: Mapped[datetime.datetime] = mapped_column(
        DateTime, default=func.now(), nullable=False
    )

    def __repr__(self) -> str:
        return (
            f"WeatherForecast(id={self.id!r}, city={self.city!r}, "
            f"forecast_date={self.forecast_date!r}, temp_min={self.temp_min!r}, "
            f"temp_max={self.temp_max!r}, humidity={self.humidity!r}, "
            f"wind_speed={self.wind_speed!r}, description={self.description!r})"
        )


@dataclass(frozen=True)
class DailyForecast:
    city: str
    forecast_date: datetime.date
    temp_min: float
    temp_max: float
    humidity: int
    wind_speed: float
    description: str


def save_forecasts(session: Session, forecasts: Sequence[DailyForecast]) -> int:
    if not forecasts:
        return 0

    known: dict[str, set[datetime.date]] = {}
    for city in {f.city for f in forecasts}:
        known[city] = set(
            session.scalars(
                select(WeatherForecast.forecast_date).where(
                    WeatherForecast.city == city
                )
            ).all()
        )

    add = [
        WeatherForecast(
            city=f.city,
            forecast_date=f.forecast_date,
            temp_min=f.temp_min,
            temp_max=f.temp_max,
            humidity=f.humidity,
            wind_speed=f.wind_speed,
            description=f.description,
        )
        for f in forecasts
        if f.forecast_date not in known[f.city]
    ]
    session.add_all(add)
    session.commit()
    return len(add)