package repository

import (
	"context"
	"fmt"
	"time"

	"github.com/google/uuid"
	"gorm.io/gorm"
)

// DueLot is a lot whose expiry has passed and that still holds something.
type DueLot struct {
	ID         uuid.UUID
	CustomerID uuid.UUID
	Currency   string
	Remaining  int64
	ExpiresAt  time.Time
	// The description of the row that created the lot, for the EXPIRE row's.
	SourceDescription string
}

// WalletExpiryRepository finds what the expiry job has to do (docs/prd-point-coin.md
// F12). Balances only change through WalletProcessor.
type WalletExpiryRepository interface {
	// ListDueLots returns up to limit lots due at asOf, the longest overdue first. It
	// takes no lock: locking a lot before its wallet would deadlock against payments,
	// which lock the wallet first. WalletProcessor.ExpireLot locks and reads again.
	ListDueLots(ctx context.Context, asOf time.Time, limit int) ([]DueLot, error)
}

type walletExpiryRepository struct {
	db *gorm.DB
}

func NewWalletExpiryRepository(db *gorm.DB) WalletExpiryRepository {
	return &walletExpiryRepository{db: db}
}

func (r *walletExpiryRepository) ListDueLots(ctx context.Context, asOf time.Time, limit int) ([]DueLot, error) {
	var lots []DueLot
	err := DBFromContext(ctx, r.db).WithContext(ctx).Raw(`
		SELECT l.id, l.customer_id, l.currency, l.remaining_amount AS remaining, l.expires_at,
			t.description AS source_description
		FROM wallet_lots l
		JOIN wallet_transactions t ON t.id = l.source_transaction_id
		WHERE l.remaining_amount > 0 AND l.expires_at <= ?
		ORDER BY l.expires_at, l.id
		LIMIT ?`, asOf, limit).Scan(&lots).Error
	if err != nil {
		return nil, fmt.Errorf("failed to list due wallet lots: %w", err)
	}
	return lots, nil
}