package store

import (
	"context"
	"database/sql"
	"fmt"
	"time"

	"github.com/cosmic-clash/cosmic-clash/server/domain"
)

const DueSeasonRolloversSQL = `SELECT s.season_id, r.player_id, r.rating, r.deviation,
    r.volatility, r.ranked_games
FROM seasons s
CROSS JOIN ratings r
LEFT JOIN ranked_season_rollovers rr ON rr.season_id = s.season_id AND rr.player_id = r.player_id
WHERE s.playlist = 'ranked' AND s.ends_at <= $1 AND rr.player_id IS NULL
ORDER BY s.ends_at, s.season_id, r.player_id
LIMIT $2`

const MarkSeasonRolledOverSQL = `UPDATE seasons SET rolled_over_at = $2
WHERE season_id = $1 AND rolled_over_at IS NULL
  AND NOT EXISTS (SELECT 1 FROM ratings r
                  LEFT JOIN ranked_season_rollovers rr ON rr.season_id = $1 AND rr.player_id = r.player_id
                  WHERE rr.player_id IS NULL)`

const MarkEmptySeasonsSQL = `UPDATE seasons s SET rolled_over_at = $1
WHERE s.playlist = 'ranked' AND s.ends_at <= $1 AND s.rolled_over_at IS NULL
  AND NOT EXISTS (SELECT 1 FROM ratings r
                  LEFT JOIN ranked_season_rollovers rr ON rr.season_id = s.season_id AND rr.player_id = r.player_id
                  WHERE rr.player_id IS NULL)`

type dueSeasonRollover struct {
	seasonID string
	playerID string
	profile  domain.RankedProfile
}

// RolloverDueSeasons processes a bounded batch. Each player update is its own
// exactly-once SERIALIZABLE transaction, so a worker crash can safely resume.
func RolloverDueSeasons(ctx context.Context, db *sql.DB, now time.Time, limit int) (int, error) {
	if db == nil || now.IsZero() || limit < 1 || limit > 1000 {
		return 0, fmt.Errorf("invalid season maintenance arguments")
	}
	// A season with no ranked profiles has no player row for DueSeasonRolloversSQL
	// to return. Mark it here so maintenance remains idempotent instead of
	// reconsidering the same empty season on every pass.
	if _, err := db.ExecContext(ctx, MarkEmptySeasonsSQL, now); err != nil {
		return 0, err
	}
	rows, err := db.QueryContext(ctx, DueSeasonRolloversSQL, now, limit)
	if err != nil {
		return 0, err
	}
	defer rows.Close()
	var due []dueSeasonRollover
	for rows.Next() {
		var item dueSeasonRollover
		if err := rows.Scan(&item.seasonID, &item.playerID, &item.profile.Value, &item.profile.RD, &item.profile.Volatility, &item.profile.RankedGames); err != nil {
			return 0, err
		}
		due = append(due, item)
	}
	if err := rows.Err(); err != nil {
		return 0, err
	}
	count := 0
	for _, item := range due {
		if _, applied, err := ApplyRankedSeasonRollover(ctx, db, item.playerID, item.seasonID, item.profile, now); err != nil {
			return count, err
		} else if applied {
			count++
		}
		if _, err := db.ExecContext(ctx, MarkSeasonRolledOverSQL, item.seasonID, now); err != nil {
			return count, err
		}
	}
	return count, nil
}