from __future__ import annotations

from dataclasses import dataclass

from sqlalchemy import desc, select
from sqlalchemy.orm import Session

from fan_passport import models
from fan_passport.errors import ValidationError


ALLOWED_LEADERBOARD_METRICS = {
    "points_total",
    "collection_points",
    "quiz_points",
    "prediction_points",
    "challenge_points",
    "achievement_points",
}


@dataclass(frozen=True)
class LeaderboardRow:
    rank: int
    user_id: str
    display_name: str
    country_code: str | None
    metric: str
    score: int


class LeaderboardService:
    def __init__(self, session: Session):
        self.session = session

    def get_leaderboard(
        self,
        *,
        metric: str = "points_total",
        limit: int = 50,
        country_code: str | None = None,
    ) -> list[LeaderboardRow]:
        if metric not in ALLOWED_LEADERBOARD_METRICS:
            raise ValidationError(
                "Unsupported leaderboard metric.",
                details={"metric": metric, "supported": sorted(ALLOWED_LEADERBOARD_METRICS)},
            )

        limit = max(1, min(limit, 100))
        metric_column = getattr(models.UserProfile, metric)
        stmt = select(models.UserProfile).order_by(desc(metric_column), models.UserProfile.created_at).limit(
            limit
        )
        if country_code:
            stmt = stmt.where(models.UserProfile.country_code == country_code.upper())

        profiles = self.session.scalars(stmt).all()
        return [
            LeaderboardRow(
                rank=index + 1,
                user_id=profile.id,
                display_name=profile.display_name,
                country_code=profile.country_code,
                metric=metric,
                score=int(getattr(profile, metric)),
            )
            for index, profile in enumerate(profiles)
        ]