package bookings

import (
	"context"
	"errors"
	"sort"
	"time"

	"github.com/jackc/pgx/v5"

	"bookra/apps/backend/internal/db"
)

// PromoteWaitlist confirms the earliest waitlisted bookings on a class session
// while free capacity remains. It returns the promoted records so callers can
// notify customers. A missing session is treated as nothing to promote.
func PromoteWaitlist(ctx context.Context, repo db.Repository, tenantID, sessionID string) ([]db.BookingRecord, error) {
	session, err := repo.GetClassSessionByID(ctx, sessionID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, nil
		}
		return nil, err
	}

	bookings, err := repo.ListBookingsByTenantBetween(ctx, tenantID, session.StartsAt.Add(-time.Second), session.EndsAt.Add(time.Second))
	if err != nil {
		return nil, err
	}

	confirmed := 0
	var waitlisted []db.BookingRecord
	for _, booking := range bookings {
		if booking.ClassSessionID == nil || *booking.ClassSessionID != sessionID {
			continue
		}
		switch booking.Status {
		case "confirmed":
			confirmed++
		case "waitlisted":
			waitlisted = append(waitlisted, booking)
		}
	}
	if len(waitlisted) == 0 {
		return nil, nil
	}
	sort.SliceStable(waitlisted, func(i, j int) bool {
		return waitlisted[i].CreatedAt.Before(waitlisted[j].CreatedAt)
	})

	var promoted []db.BookingRecord
	for _, booking := range waitlisted {
		if session.Capacity > 0 && confirmed >= int(session.Capacity) {
			break
		}
		if err := repo.UpdateBookingStatus(ctx, booking.ID, "confirmed"); err != nil {
			return promoted, err
		}
		_ = repo.ResolveWaitlistEntry(ctx, tenantID, sessionID, booking.CustomerEmail)
		confirmed++
		promoted = append(promoted, booking)
	}
	return promoted, nil
}