Crussell/backend/handlers/payments/giftcard_limits.go

package payments

import (
	"context"

	"crussell/db"
)

// Gift-card purchase/transaction limits (owner decisions).
//
//   - Every admin gift-card value operation (CreateGiftCard, TopUpGiftCard,
//     TransferGiftCard) is capped at £250 per transaction — tighter than the
//     £10,000 ceiling ValidateAmount enforces on other payment entry points.
//   - A customer (BuyGiftCard) may buy at most £500 of online gift cards per
//     UTC day.
//   - An admin may create/top-up/transfer at most £5,000 of gift-card value
//     per UTC day.
//
// till.go uses the same £250 transaction cap (maxAdminGiftCardTransactionPence)
// for its gift-card creates/topups — this shared constant is the single source
// of the owner decision.
const (
	// maxAdminGiftCardTransactionPence caps a single admin gift-card
	// create/top-up/transfer at £250 (25,000 pence).
	maxAdminGiftCardTransactionPence = 25_000
	// maxUserGiftCardDailyPence caps one user's online gift-card purchases at
	// £500 (50,000 pence) per UTC day.
	maxUserGiftCardDailyPence = 500_00
	// maxAdminGiftCardDailyPence caps the gift-card value an admin can
	// create/top-up/transfer in one UTC day at £5,000 (500,000 pence).
	maxAdminGiftCardDailyPence = 500_000
)

// userGiftCardSpentToday returns the total value (in pounds) the user has
// spent on ONLINE gift-card purchases so far today, returned as a float64 so
// the caller can convert to pence with math.Round, matching the repo's
// currency convention.
//
// Signal: gift_card_transactions rows written by BuyGiftCard — the ONLY
// customer-facing online purchase path. Every BuyGiftCard purchase (self and
// friend) inserts a row with transaction_type='purchase', reference_type='api'
// and user_id = the buyer (see giftcards.go). Admin-created cards
// (CreateGiftCard/TopUpGiftCard) also write reference_type='api' but with the
// ADMIN's user id, and till sales write reference_type='till_sale', so neither
// can match a customer. The payments-based alternative (payments rows with
// payment_type='gift_card') does NOT exist in this schema — the payment_type
// enum is ('deposit','full','tip','balance','partial') and BuyGiftCard writes
// payment_type='full' — so the transactions audit log is the correct signal.
//
// "Today" is the UTC day boundary (created_at >= CURRENT_DATE), matching the
// repo's existing time convention: the DB session runs in timezone=UTC and
// completion.go uses the same CURRENT_DATE boundary for its daily loyalty
// stamp cap.
func userGiftCardSpentToday(ctx context.Context, q db.Querier, userID string) (float64, error) {
	var spent float64
	err := q.QueryRow(ctx, `
		SELECT COALESCE(SUM(amount), 0)
		FROM gift_card_transactions
		WHERE user_id = $1
		  AND transaction_type = 'purchase'
		  AND reference_type = 'api'
		  AND created_at >= CURRENT_DATE
	`, userID).Scan(&spent)
	if err != nil {
		return 0, err
	}
	return spent, nil
}

// adminGiftCardValueToday returns the total gift-card value (in pounds) the
// admin has created, topped up, or transferred today (UTC day boundary,
// created_at >= CURRENT_DATE), returned as a float64 for pence conversion.
//
// Signal (chosen to be double-count free across the three admin operations):
//
//  1. Cards the admin created today — SUM(total_funds_added). total_funds_added
//     is cumulative, so a card created today already reflects any same-day
//     top-up or transfer INTO it, and its creation amount.
//  2. API top-ups executed by this admin today on cards created BEFORE today
//     (cards created today are excluded — term 1 already includes their
//     funding via total_funds_added, so counting the top-up row again would
//     double-count). This is the gift_card_transactions rows
//     (reference_type='api', user_id=admin) written by CreateGiftCard
//     ('purchase') and TopUpGiftCard ('topup', or 'purchase' on an inventory
//     card's first top-up).
//
// Transfers INTO pre-existing cards leave no attributable audit row
// (TransferGiftCard deliberately writes no gift_card_transactions entry), so
// they are not directly counted; a transfer also creates no NEW gift-card
// liability, so the daily cap still measures all value this admin has newly
// issued today. Till sales (CreateTillSale) write reference_type='till_sale'
// and are attributed to the CUSTOMER (user_id), so they are excluded here —
// the admin daily cap covers the admin API surface only.
func adminGiftCardValueToday(ctx context.Context, q db.Querier, adminID string) (float64, error) {
	var value float64
	err := q.QueryRow(ctx, `
		SELECT
			COALESCE((
				SELECT SUM(gc.total_funds_added)
				FROM gift_cards gc
				WHERE gc.created_by = $1 AND gc.created_at >= CURRENT_DATE
			), 0)
		  + COALESCE((
				SELECT SUM(gct.amount)
				FROM gift_card_transactions gct
				WHERE gct.user_id = $1
				  AND gct.reference_type = 'api'
				  AND gct.transaction_type IN ('purchase', 'topup')
				  AND gct.created_at >= CURRENT_DATE
				  AND gct.gift_card_id NOT IN (
						SELECT gc2.id FROM gift_cards gc2
						WHERE gc2.created_by = $1 AND gc2.created_at >= CURRENT_DATE
				  )
			), 0)
	`, adminID).Scan(&value)
	if err != nil {
		return 0, err
	}
	return value, nil
}