Crussell/backend/handlers/payments/service.go

package payments

import (
	"context"
	"crussell/clock"
	"crussell/db"
	"crussell/internal/square"
	"database/sql"
	"errors"
	"fmt"
	"log"
	"log/slog"
	"math"
	"strings"
	"sync"
	"time"

	"github.com/jackc/pgx/v5"
)

type SavedCard struct {
	ID string `json:"id"`
	// SquareCustomerID is the user's provisioned Square customer profile id
	// (P14), persisted on the row the first time the user saves a card. It is
	// forwarded to CreatePayment as CustomerID on saved-card (ccof:) charges,
	// which Square requires for card-on-file payments. Empty for rows created
	// before provisioning was introduced.
	SquareCustomerID string `json:"square_customer_id,omitempty"`
	SquareCardID     string `json:"square_card_id"`
	Brand            string `json:"brand"`
	Last4            string `json:"last_4"`
	ExpMonth         int    `json:"exp_month"`
	ExpYear          int    `json:"exp_year"`
	Fingerprint      string `json:"fingerprint"`
	IsDefault        bool   `json:"is_default"`
}

type PaymentService struct{}

func NewPaymentService() *PaymentService {
	return &PaymentService{}
}

type PaymentRecord struct {
	ID              string
	BookingID       string
	PaymentType     string
	PaymentMethod   string
	VendorCode      *string
	InvoiceNumber   *int
	Status          string
	Amount          float64
	CardLast4       string
	IsVATApplicable bool
	VATRate         *float64
	VATAmount       *float64
	NetAmount       *float64
	UserSavedCardID *string
	SquarePaymentID *string
	IdempotencyKey  *string
	Fees            float64
	CreatedAt       time.Time
	UpdatedAt       time.Time
	CreatedBy       *string
	GiftCardID      *string
}

type RefundRecord struct {
	ID             string
	PaymentID      string
	BookingID      string
	Amount         float64
	SquareRefundID *string
	Status         string
	Reason         string
	Origin         string // 'manual' (admin handler) or 'cancellation' (cancellation loop)
	IdempotencyKey *string
	CreatedBy      *string
	CreatedAt      time.Time
}

type PaymentSummary struct {
	TotalAmount     float64
	PaidAmount      float64
	RefundedAmount  float64
	RemainingAmount float64
	TotalVATAmount  float64
	TotalNetAmount  float64
	Payments        []PaymentRecord
	Refunds         []RefundRecord
}

func (s *PaymentService) CalculateFees(amount int64, method string) float64 {
	if method == "online" {
		return float64((amount*14/1000)+25) / 100.0
	}
	return float64(amount*175/10000) / 100.0
}

func (s *PaymentService) CreatePaymentRecord(ctx context.Context, record PaymentRecord, giftCardID *string) (string, error) {
	return s.insertPaymentRecord(ctx, record, giftCardID, db.Conn)
}

// CreatePaymentRecordTx is identical to CreatePaymentRecord but accepts a
// pgx.Tx so the insert is part of an existing database transaction. This
// is used by CreateBookingPayment when inserting multiple split records
// from a single Square charge — wrapping both inserts in a transaction
// ensures atomicity (both succeed or both roll back).
func (s *PaymentService) CreatePaymentRecordTx(ctx context.Context, tx pgx.Tx, record PaymentRecord, giftCardID *string) (string, error) {
	return s.insertPaymentRecord(ctx, record, giftCardID, tx)
}

// insertPaymentRecord holds the common INSERT logic. The querier parameter
// accepts either *pgxpool.Pool or pgx.Tx so callers can choose transactional
// or non-transactional insertion.
type querier interface {
	QueryRow(ctx context.Context, sql string, args ...any) pgx.Row
}

func (s *PaymentService) insertPaymentRecord(ctx context.Context, record PaymentRecord, giftCardID *string, q querier) (string, error) {
	var bookingID *string
	if record.BookingID != "" {
		bookingID = &record.BookingID
	}

	var id string
	err := q.QueryRow(ctx, `
		INSERT INTO payments (
			booking_id, payment_type, payment_method, vendor_code, invoice_number,
			status, amount, is_vat_applicable, vat_rate, vat_amount, net_amount,
			user_saved_card_id, square_payment_id, idempotency_key, fees, created_at, updated_at, created_by,
			gift_card_id
		) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15, $16, $17, $18, $19)
		RETURNING id
	`,
		bookingID,
		record.PaymentType,
		record.PaymentMethod,
		record.VendorCode,
		record.InvoiceNumber,
		record.Status,
		record.Amount,
		record.IsVATApplicable,
		record.VATRate,
		record.VATAmount,
		record.NetAmount,
		record.UserSavedCardID,
		record.SquarePaymentID,
		record.IdempotencyKey,
		record.Fees,
		record.CreatedAt,
		record.UpdatedAt,
		record.CreatedBy,
		giftCardID,
	).Scan(&id)

	if err != nil {
		return "", err
	}
	return id, nil
}

func (s *PaymentService) CreateRefundRecord(ctx context.Context, record RefundRecord) (string, error) {
	var id string
	err := db.Conn.QueryRow(ctx, `
		INSERT INTO refunds (
			payment_id, booking_id, amount, square_refund_id, status, reason, idempotency_key, created_by, created_at, origin
		) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)
		RETURNING id
	`,
		record.PaymentID,
		record.BookingID,
		record.Amount,
		record.SquareRefundID,
		record.Status,
		record.Reason,
		record.IdempotencyKey,
		record.CreatedBy,
		record.CreatedAt,
		record.Origin,
	).Scan(&id)

	if err != nil {
		return "", err
	}
	return id, nil
}

func (s *PaymentService) GetBookingPaymentSummary(ctx context.Context, bookingID string) (*PaymentSummary, error) {
	summary := &PaymentSummary{
		Payments: []PaymentRecord{},
		Refunds:  []RefundRecord{},
	}

	var totalAmount float64
	err := db.Conn.QueryRow(ctx, `
		SELECT total_amount FROM bookings WHERE id = $1
	`, bookingID).Scan(&totalAmount)

	if err != nil && !errors.Is(err, pgx.ErrNoRows) {
		return nil, err
	}
	summary.TotalAmount = totalAmount

	rows, err := db.Conn.Query(ctx, `
		SELECT p.id, p.booking_id, p.payment_type, p.payment_method, p.vendor_code, p.invoice_number,
		       p.status, p.amount, COALESCE(usc.last_4, ''), p.is_vat_applicable, p.vat_rate, p.vat_amount, p.net_amount,
		       p.user_saved_card_id, p.square_payment_id, p.idempotency_key, p.fees, p.created_at, p.updated_at, p.created_by,
		       p.gift_card_id
		FROM payments p
		LEFT JOIN user_saved_cards usc ON p.user_saved_card_id = usc.id
		WHERE p.booking_id = $1
		ORDER BY p.created_at ASC
	`, bookingID)

	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var paidAmount, totalVATAmount, totalNetAmount float64
	for rows.Next() {
		var p PaymentRecord
		err := rows.Scan(
			&p.ID, &p.BookingID, &p.PaymentType, &p.PaymentMethod, &p.VendorCode, &p.InvoiceNumber,
			&p.Status, &p.Amount, &p.CardLast4, &p.IsVATApplicable, &p.VATRate, &p.VATAmount, &p.NetAmount,
			&p.UserSavedCardID, &p.SquarePaymentID, &p.IdempotencyKey, &p.Fees,
			&p.CreatedAt, &p.UpdatedAt, &p.CreatedBy, &p.GiftCardID,
		)
		if err != nil {
			return nil, err
		}
		summary.Payments = append(summary.Payments, p)
		if p.Status == "completed" {
			paidAmount += p.Amount
			if p.VATAmount != nil {
				totalVATAmount += *p.VATAmount
			}
			if p.NetAmount != nil {
				totalNetAmount += *p.NetAmount
			} else if p.VATAmount == nil {
				// Only fallback to gross amount if no VAT was applied at all.
				// When VAT is present, net_amount is always set by apply_vat_to_payment,
				// so this fallback only applies to non-VAT payments where net == gross.
				totalNetAmount += p.Amount
			}
		}
	}
	summary.PaidAmount = paidAmount
	summary.TotalVATAmount = totalVATAmount
	summary.TotalNetAmount = totalNetAmount

	refundRows, err := db.Conn.Query(ctx, `
		SELECT id, payment_id, booking_id, amount, square_refund_id, status, reason, idempotency_key, created_by, created_at, origin
		FROM refunds
		WHERE booking_id = $1 AND status = 'completed'
		ORDER BY created_at ASC
	`, bookingID)

	if err != nil {
		return nil, err
	}
	defer refundRows.Close()

	var refundedAmount float64
	for refundRows.Next() {
		var r RefundRecord
		err := refundRows.Scan(
			&r.ID, &r.PaymentID, &r.BookingID, &r.Amount, &r.SquareRefundID,
			&r.Status, &r.Reason, &r.IdempotencyKey, &r.CreatedBy, &r.CreatedAt, &r.Origin,
		)
		if err != nil {
			return nil, err
		}
		summary.Refunds = append(summary.Refunds, r)
		refundedAmount += r.Amount
	}
	summary.RefundedAmount = refundedAmount
	summary.RemainingAmount = totalAmount - paidAmount + refundedAmount

	return summary, nil
}

func (s *PaymentService) CheckIdempotency(ctx context.Context, bookingID, idempotencyKey string) (*PaymentRecord, error) {
	var p PaymentRecord
	err := db.Conn.QueryRow(ctx, `
		SELECT id, booking_id, payment_type, payment_method, vendor_code, invoice_number,
		       status, amount, is_vat_applicable, vat_rate, vat_amount, net_amount,
		       user_saved_card_id, square_payment_id, idempotency_key, fees, created_at, updated_at, created_by,
		       gift_card_id
		FROM payments
		WHERE booking_id = $1 AND idempotency_key = $2
	`, bookingID, idempotencyKey).Scan(
		&p.ID, &p.BookingID, &p.PaymentType, &p.PaymentMethod, &p.VendorCode, &p.InvoiceNumber,
		&p.Status, &p.Amount, &p.IsVATApplicable, &p.VATRate, &p.VATAmount, &p.NetAmount,
		&p.UserSavedCardID, &p.SquarePaymentID, &p.IdempotencyKey, &p.Fees,
		&p.CreatedAt, &p.UpdatedAt, &p.CreatedBy, &p.GiftCardID,
	)

	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, nil
		}
		return nil, err
	}
	return &p, nil
}

func (s *PaymentService) CheckIdempotencyByKey(ctx context.Context, idempotencyKey string) (*PaymentRecord, error) {
	var p PaymentRecord
	// booking_id and gift_card_id are NULL for gift-card purchases — scan into
	// NullString to avoid "cannot scan NULL into *string".
	var bookingID, giftCardID sql.NullString
	err := db.Conn.QueryRow(ctx, `
		SELECT id, booking_id, payment_type, payment_method, vendor_code, invoice_number,
		       status, amount, is_vat_applicable, vat_rate, vat_amount, net_amount,
		       user_saved_card_id, square_payment_id, idempotency_key, fees, created_at, updated_at, created_by,
		       gift_card_id
		FROM payments
		WHERE idempotency_key = $1
	`, idempotencyKey).Scan(
		&p.ID, &bookingID, &p.PaymentType, &p.PaymentMethod, &p.VendorCode, &p.InvoiceNumber,
		&p.Status, &p.Amount, &p.IsVATApplicable, &p.VATRate, &p.VATAmount, &p.NetAmount,
		&p.UserSavedCardID, &p.SquarePaymentID, &p.IdempotencyKey, &p.Fees,
		&p.CreatedAt, &p.UpdatedAt, &p.CreatedBy, &giftCardID,
	)
	p.BookingID = bookingID.String
	if giftCardID.Valid {
		p.GiftCardID = &giftCardID.String
	}

	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, nil
		}
		return nil, err
	}
	return &p, nil
}

func (s *PaymentService) GetPaymentByID(ctx context.Context, paymentID string) (*PaymentRecord, error) {
	var p PaymentRecord
	// booking_id / vendor_code / gift_card_id / invoice_number are nullable
	// (e.g. gift-card purchases have no booking). Scan into Null* and map so a
	// NULL value doesn't 500 the scan (N-3: the same fix class as
	// CheckIdempotencyByKey).
	var bookingID, vendorCode, giftCardID sql.NullString
	var invoiceNumber sql.NullInt64
	err := db.Conn.QueryRow(ctx, `
		SELECT id, booking_id, payment_type, payment_method, vendor_code, invoice_number,
		       status, amount, is_vat_applicable, vat_rate, vat_amount, net_amount,
		       user_saved_card_id, square_payment_id, idempotency_key, fees, created_at, updated_at, created_by,
		       gift_card_id
		FROM payments
		WHERE id = $1
	`, paymentID).Scan(
		&p.ID, &bookingID, &p.PaymentType, &p.PaymentMethod, &vendorCode, &invoiceNumber,
		&p.Status, &p.Amount, &p.IsVATApplicable, &p.VATRate, &p.VATAmount, &p.NetAmount,
		&p.UserSavedCardID, &p.SquarePaymentID, &p.IdempotencyKey, &p.Fees,
		&p.CreatedAt, &p.UpdatedAt, &p.CreatedBy, &giftCardID,
	)

	if err != nil {
		return nil, err
	}
	p.BookingID = bookingID.String
	if vendorCode.Valid {
		p.VendorCode = &vendorCode.String
	}
	if giftCardID.Valid {
		p.GiftCardID = &giftCardID.String
	}
	if invoiceNumber.Valid {
		n := int(invoiceNumber.Int64)
		p.InvoiceNumber = &n
	}
	return &p, nil
}

// GetAlreadyRefundedAmount returns the total refunded amount (in pence) for a
// payment, counting both 'completed' and 'pending' refunds. Pending refunds are
// counted because a Square call may already be in flight for them — excluding
// them would let a concurrent refund over-refund the payment. 'failed' refunds
// are excluded: they were definitively rejected by Square and must not block
// future refund attempts.
func (s *PaymentService) GetAlreadyRefundedAmount(ctx context.Context, paymentID string) (int64, error) {
	var amount float64
	err := db.Conn.QueryRow(ctx, `
		SELECT COALESCE(SUM(amount), 0) FROM refunds
		WHERE payment_id = $1 AND status IN ('completed', 'pending')
	`, paymentID).Scan(&amount)

	if err != nil {
		return 0, err
	}
	return int64(math.Round(amount * 100)), nil
}

// HasCompletedPayment reports whether the booking has a completed non-tip
// payment. 'tip' is deliberately excluded: a tip-only booking (no deposit/full
// payment) must NOT be treated as "already paid" for the purposes of allowing a
// tip. Note buildSplitRecords' overflow-tip records are also invisible here —
// intended (a tip is never evidence of payment), but a caller must not assume
// this covers every payment_type.
func (s *PaymentService) HasCompletedPayment(ctx context.Context, bookingID string) (bool, error) {
	var count int
	err := db.Conn.QueryRow(ctx, `
		SELECT COUNT(*) FROM payments
		WHERE booking_id = $1 AND status = 'completed' AND payment_type IN ('full', 'deposit', 'balance', 'partial')
	`, bookingID).Scan(&count)
	if err != nil {
		return false, err
	}
	return count > 0, nil
}

func (s *PaymentService) GetBookingStatus(ctx context.Context, bookingID string) (string, error) {
	var status string
	err := db.Conn.QueryRow(ctx, `SELECT status FROM bookings WHERE id = $1`, bookingID).Scan(&status)
	if err != nil {
		return "", err
	}
	return status, nil
}

// BookingPaymentInfo holds booking-level data needed for payment split decisions.
type BookingPaymentInfo struct {
	StartTime   time.Time
	TotalAmount float64
	TotalPaid   float64
	Status      string
}

// GetBookingPaymentInfo fetches the booking start time, total service amount, and
// total net paid (completed payments minus completed/pending refunds) for a
// booking. Refunds are subtracted so cancellation refunds never double-refund
// money that has already been returned (e.g. via a manual admin refund).
func (s *PaymentService) GetBookingPaymentInfo(ctx context.Context, bookingID string) (*BookingPaymentInfo, error) {
	var info BookingPaymentInfo
	err := db.Conn.QueryRow(ctx, `
		SELECT b.start_time, b.status,
			COALESCE(b.total_amount, 0),
			COALESCE(pt.total_paid, 0) - COALESCE(rr.total_refunded, 0)
		FROM bookings b
		LEFT JOIN (
			SELECT booking_id, SUM(amount) AS total_paid
			FROM payments WHERE booking_id = $1 AND status = 'completed' AND payment_method NOT IN ('discount', 'on_the_house') GROUP BY booking_id
		) pt ON b.id = pt.booking_id
		LEFT JOIN (
			SELECT p.booking_id, SUM(r.amount) AS total_refunded
			FROM refunds r
			JOIN payments p ON r.payment_id = p.id
			WHERE p.booking_id = $1 AND r.status IN ('completed', 'pending')
			GROUP BY p.booking_id
		) rr ON b.id = rr.booking_id
		WHERE b.id = $1
	`, bookingID).Scan(&info.StartTime, &info.Status, &info.TotalAmount, &info.TotalPaid)
	if err != nil {
		return nil, err
	}
	return &info, nil
}

func (s *PaymentService) GetBookingUserID(ctx context.Context, bookingID string) (string, error) {
	var userID string
	err := db.Conn.QueryRow(ctx, `SELECT user_id FROM bookings WHERE id = $1`, bookingID).Scan(&userID)
	if err != nil {
		return "", err
	}
	return userID, nil
}

func (s *PaymentService) GetBookingRemainingBalanceCents(ctx context.Context, bookingID string) (int64, error) {
	var remainingCents int64
	err := db.Conn.QueryRow(ctx, `
	WITH booking_total AS (
		SELECT total_amount AS total_pounds FROM bookings WHERE id = $1
	),
		paid_total AS (
			SELECT COALESCE(SUM(amount), 0) AS paid_pounds
			FROM payments
			WHERE booking_id = $1 AND status = 'completed'
			  -- A tip is money paid beyond the booking total — it does not
			  -- reduce the balance owed, so it must not count as "paid".
			  AND payment_type <> 'tip'
		)
		SELECT GREATEST(0, ROUND((bt.total_pounds - pt.paid_pounds) * 100))::bigint
		FROM booking_total bt, paid_total pt
	`, bookingID).Scan(&remainingCents)
	if err != nil {
		return 0, err
	}
	return remainingCents, nil
}

func (s *PaymentService) GetUserPaymentMethods(ctx context.Context, userID string) ([]SavedCard, error) {
	rows, err := db.Conn.Query(ctx, `
		SELECT id, COALESCE(square_card_id, ''), brand, last_4, exp_month, exp_year, fingerprint, is_default, COALESCE(square_customer_id, '')
		FROM user_saved_cards
		WHERE user_id = $1 AND deleted_at IS NULL
		ORDER BY is_default DESC, created_at DESC
	`, userID)

	if err != nil {
		return nil, err
	}
	defer rows.Close()

	var cards []SavedCard
	for rows.Next() {
		var c SavedCard
		err := rows.Scan(&c.ID, &c.SquareCardID, &c.Brand, &c.Last4, &c.ExpMonth, &c.ExpYear, &c.Fingerprint, &c.IsDefault, &c.SquareCustomerID)
		if err != nil {
			return nil, err
		}
		cards = append(cards, c)
	}

	if cards == nil {
		cards = []SavedCard{}
	}

	return cards, nil
}

func (s *PaymentService) DeletePaymentMethod(ctx context.Context, cardID, userID string) error {
	// Load the Square card id and disable the card at Square BEFORE the local
	// soft-delete (R8). Without this the card stays ENABLED at Square and keeps
	// accepting ccof: charges even though the user deleted it locally — the
	// account-deletion path already calls DeleteCardOnFile; this mirrors it for
	// single-card deletes. The Square call is best-effort: a local delete must
	// never be blocked by a Square failure. A NOT_FOUND answer means Square no
	// longer has the card (nothing to disable); any other error is logged and
	// ignored so the local delete proceeds regardless.
	var sqCardID sql.NullString
	err := db.Conn.QueryRow(ctx, `
		SELECT square_card_id FROM user_saved_cards
		WHERE id = $1 AND user_id = $2
	`, cardID, userID).Scan(&sqCardID)
	if err != nil && !errors.Is(err, pgx.ErrNoRows) {
		return err
	}
	// ErrNoRows: the card is not owned by this user — the soft-delete below is
	// a silent no-op (matching the pre-R8 behaviour), so skip the Square call.
	if sqCardID.Valid && sqCardID.String != "" {
		if err := SquareClient.DeleteCardOnFile(ctx, sqCardID.String); err != nil {
			msg := strings.ToUpper(err.Error())
			if square.ErrorCode(err) == "NOT_FOUND" || strings.Contains(msg, "NOT_FOUND") || strings.Contains(msg, "NOT FOUND") {
				// Square already removed/disabled the card — nothing to do.
			} else {
				// TokenPrefix redacts the ccof: card token — the full ID must
				// never reach logs.
				slog.Warn("failed to disable Square card on local delete — card may remain enabled at Square", "square_card_id", square.TokenPrefix(sqCardID.String), "err", err)
			}
		}
	}

	tx, err := db.Conn.Begin(ctx)
	if err != nil {
		log.Printf("Failed to begin transaction: %v", err)
		return err
	}
	defer func() {
		if err := tx.Rollback(ctx); err != nil && !errors.Is(err, pgx.ErrTxClosed) {
			slog.Error("failed to rollback transaction", "err", err)
		}
	}()

	retainedUntil := clock.Now().Add(7 * 365 * 24 * time.Hour)
	_, err = tx.Exec(ctx, `
		UPDATE user_saved_cards
		SET deleted_at = NOW(), deleted_by = $1, retained_until = $2
		WHERE id = $3 AND user_id = $1
	`, userID, retainedUntil, cardID)
	if err != nil {
		return err
	}

	if err := tx.Commit(ctx); err != nil {
		log.Printf("Failed to commit transaction: %v", err)
		return err
	}

	return nil
}

func (s *PaymentService) CreatePaymentMethodFromToken(ctx context.Context, userID, cardToken string) (*SavedCard, error) {
	// PCI-DSS: raw PANs are never accepted. The client must supply a Square
	// Web Payments nonce (cnon:xxx), which the backend tokenizes via the
	// Cards API — the full PAN exists only inside Square's vault.
	//
	// P14: this endpoint saves a card, so lazily ensure the user has a Square
	// customer profile BEFORE the card is tokenized — if provisioning fails the
	// card cannot be saved, so abort with a clear error instead of creating an
	// orphan card at Square. One-off (non-save) payments never call this.
	squareCustomerID, err := s.ensureSquareCustomer(ctx, userID)
	if err != nil {
		return nil, err
	}

	cardOnFile, err := SquareClient.CreateCardOnFile(ctx, userID, cardToken, squareCustomerID)
	if err != nil {
		return nil, fmt.Errorf("failed to tokenize card: %w", err)
	}

	var savedCardID string
	var isDefault bool
	// ON CONFLICT (user_id, square_card_id): a response-lost retry re-tokenizes
	// the same card for the SAME user (CreateCardOnFile's deterministic key
	// returns the same ccof: id), so the per-user UNIQUE constraint would
	// otherwise 500 on the duplicate. Upsert instead so the retry returns the
	// existing saved card (N-8). The conflict target is scoped per user — a
	// card tokenized by user B that user A already saved is a brand-new row for
	// B, never a mutation of A's row.
	err = db.Conn.QueryRow(ctx, `
		INSERT INTO user_saved_cards (user_id, square_card_id, brand, last_4, exp_month, exp_year, fingerprint, square_customer_id, is_default)
		SELECT $1, $2, $3, $4, $5, $6, $7, $8,
			NOT EXISTS(SELECT 1 FROM user_saved_cards WHERE user_id = $1 AND deleted_at IS NULL)
		ON CONFLICT (user_id, square_card_id) DO UPDATE SET
			brand = EXCLUDED.brand,
			last_4 = EXCLUDED.last_4,
			exp_month = EXCLUDED.exp_month,
			exp_year = EXCLUDED.exp_year,
			fingerprint = EXCLUDED.fingerprint,
			square_customer_id = EXCLUDED.square_customer_id,
			deleted_at = NULL,
			retained_until = NULL
		WHERE user_saved_cards.user_id = EXCLUDED.user_id
		RETURNING id, is_default
	`, userID, cardOnFile.CardID, cardOnFile.Brand, cardOnFile.Last4, cardOnFile.ExpMonth, cardOnFile.ExpYear, cardOnFile.Fingerprint, squareCustomerID).Scan(&savedCardID, &isDefault)
	if err != nil {
		return nil, fmt.Errorf("failed to save card: %w", err)
	}

	return &SavedCard{
		ID:               savedCardID,
		SquareCustomerID: squareCustomerID,
		SquareCardID:     cardOnFile.CardID,
		Brand:            cardOnFile.Brand,
		Last4:            cardOnFile.Last4,
		ExpMonth:         cardOnFile.ExpMonth,
		ExpYear:          cardOnFile.ExpYear,
		Fingerprint:      cardOnFile.Fingerprint,
		IsDefault:        isDefault,
	}, nil
}

// ensureSquareCustomer lazily provisions a Square customer profile for the
// user (P14). A customer is only ever minted when a card is being SAVED — the
// saved-card row is the persistence point, and the id is reused for every
// subsequent card save by the same user. Square dedups on a deterministic
// idempotency key derived from the email, so a response-lost retry returns the
// same customer instead of minting a duplicate.
//
// R7: the created id is written back to the user's saved-card rows (when any
// exist) AND cached in a package-level map, so a second ensureSquareCustomer
// call in the same request flow (e.g. the handler's save-card branch followed
// by SaveCardForUser) never re-hits the DB and never re-mints a customer. The
// cache is process-local and dev-friendly; the row write makes it durable for
// the next process/request.
func (s *PaymentService) ensureSquareCustomer(ctx context.Context, userID string) (string, error) {
	if v, ok := squareCustomerCache.Load(userID); ok {
		return v.(string), nil
	}

	var customerID sql.NullString
	err := db.Conn.QueryRow(ctx, `
		SELECT square_customer_id FROM user_saved_cards
		WHERE user_id = $1 AND square_customer_id IS NOT NULL AND square_customer_id <> ''
		ORDER BY created_at DESC
		LIMIT 1
	`, userID).Scan(&customerID)
	if err == nil && customerID.Valid {
		squareCustomerCache.Store(userID, customerID.String)
		return customerID.String, nil
	}
	if err != nil && !errors.Is(err, pgx.ErrNoRows) {
		return "", fmt.Errorf("failed to look up Square customer id: %w", err)
	}

	var name, email string
	if err := db.Conn.QueryRow(ctx, `
		SELECT fn, email FROM users WHERE id = $1
	`, userID).Scan(&name, &email); err != nil {
		return "", fmt.Errorf("failed to load user for Square customer provisioning: %w", err)
	}

	customer, err := SquareClient.CreateCustomer(ctx, name, email)
	if err != nil {
		return "", fmt.Errorf("failed to create Square customer for card save: %w", err)
	}

	// Persist the minted id so the NEXT process/request reuses it instead of
	// re-running CreateCustomer (the cache above only serves this process).
	// Best-effort: the cache covers the immediate double-ensure within one
	// request, and the save-card INSERT below carries the id anyway.
	if _, upErr := db.Conn.Exec(ctx, `
		UPDATE user_saved_cards SET square_customer_id = $1
		WHERE user_id = $2 AND square_customer_id IS NULL
	`, customer.ID, userID); upErr != nil {
		log.Printf("Failed to persist Square customer id for user %s (non-fatal): %v", userID, upErr)
	}
	squareCustomerCache.Store(userID, customer.ID)
	return customer.ID, nil
}

// EnsureSquareCustomer lazily provisions (or reuses) the user's Square customer
// profile, persisting its id on the saved-card row for reuse. Exported for
// handlers that must pass the customer id to CreateCardOnFile in save-card
// flows (P14): Square creates the card against that customer, and subsequent
// saved-card (ccof:) charges carry it as CreatePaymentReq.CustomerID.
func (s *PaymentService) EnsureSquareCustomer(ctx context.Context, userID string) (string, error) {
	return s.ensureSquareCustomer(ctx, userID)
}

// EnsureSquareCustomerForSavedCard returns the Square customer id for a
// saved-card row, lazily provisioning + persisting one when the row predates
// P14 (square_customer_id empty). A ccof: source can NEVER be charged without
// a CustomerID — Square rejects the payment — so every saved-card charge path
// calls this before CreatePayment. Provisioning failure aborts the charge.
func (s *PaymentService) EnsureSquareCustomerForSavedCard(ctx context.Context, savedCardID, userID string) (string, error) {
	var customerID sql.NullString
	if err := db.Conn.QueryRow(ctx, `
		SELECT square_customer_id FROM user_saved_cards
		WHERE id = $1 AND user_id = $2
	`, savedCardID, userID).Scan(&customerID); err != nil {
		return "", err
	}
	if customerID.Valid && customerID.String != "" {
		return customerID.String, nil
	}
	provisioned, err := s.EnsureSquareCustomer(ctx, userID)
	if err != nil {
		return "", err
	}
	if _, upErr := db.Conn.Exec(ctx, `
		UPDATE user_saved_cards SET square_customer_id = $1
		WHERE id = $2 AND user_id = $3
	`, provisioned, savedCardID, userID); upErr != nil {
		return "", upErr
	}
	return provisioned, nil
}

// SaveCardForUser persists a tokenized card as a saved card for the user.
// squareCustomerID is the user's provisioned Square customer profile id
// (P14) — the caller has already ensured it via EnsureSquareCustomer, so this
// method NEVER re-provisions (R7: a second ensureSquareCustomer would re-query
// the DB and, on a first-save flow, re-run CreateCustomer).
func (s *PaymentService) SaveCardForUser(ctx context.Context, userID, squareCustomerID, squareCardID, brand, last4 string, expMonth, expYear int, fingerprint string) (string, error) {
	var id string
	// ON CONFLICT (user_id, square_card_id) DO NOTHING: resolveChargeSource
	// runs CreateCardOnFile (deterministic sha256 key) + SaveCardForUser on a
	// same-key retry of a save_card=true charge. Square returns the SAME ccof:
	// id on the retry, so a plain INSERT would violate the per-user UNIQUE
	// constraint (N-8). Upsert instead so the retry returns the existing row;
	// a distinct card id is a brand-new row, never a mutation of another
	// user's card.
	err := db.Conn.QueryRow(ctx, `
		INSERT INTO user_saved_cards (
			user_id, square_card_id, square_customer_id, brand, last_4, exp_month, exp_year, fingerprint, is_default, created_at
		) VALUES ($1, $2, $3, $4, $5, $6, $7, $8, false, NOW())
		ON CONFLICT (user_id, square_card_id) DO NOTHING
		RETURNING id
	`, userID, squareCardID, squareCustomerID, brand, last4, expMonth, expYear, fingerprint).Scan(&id)

	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			if err := db.Conn.QueryRow(ctx, `
				SELECT id FROM user_saved_cards
				WHERE user_id = $1 AND square_card_id = $2 AND deleted_at IS NULL
			`, userID, squareCardID).Scan(&id); err != nil {
				return "", err
			}
			return id, nil
		}
		return "", err
	}
	return id, nil
}

func (s *PaymentService) GetCardByID(ctx context.Context, cardID, userID string) (*SavedCard, error) {
	return s.GetCardByIDQuerier(ctx, db.Conn, cardID, userID)
}

// GetCardByIDQuerier is identical to GetCardByID but accepts a db.Querier
// so the lookup can be performed inside a transaction. Callers inside an
// existing transaction should pass their tx variable instead of db.Conn.
func (s *PaymentService) GetCardByIDQuerier(ctx context.Context, q db.Querier, cardID, userID string) (*SavedCard, error) {
	var c SavedCard
	err := q.QueryRow(ctx, `
		SELECT id, COALESCE(square_card_id, ''), brand, last_4, exp_month, exp_year, fingerprint, is_default, COALESCE(square_customer_id, '')
		FROM user_saved_cards
		WHERE id = $1 AND user_id = $2 AND deleted_at IS NULL
	`, cardID, userID).Scan(&c.ID, &c.SquareCardID, &c.Brand, &c.Last4, &c.ExpMonth, &c.ExpYear, &c.Fingerprint, &c.IsDefault, &c.SquareCustomerID)

	if err != nil {
		return nil, err
	}
	return &c, nil
}

// squareCustomerCache is a package-level process-local cache of
// userID → Square customer id, populated on the first successful provisioning
// (R7). It prevents a second ensureSquareCustomer call in the same request
// flow (or a rapid retry) from re-running the DB query and re-minting a
// customer. The durable record remains the user_saved_cards row.
var squareCustomerCache sync.Map

// InvalidateSquareCustomerCache drops a user's cached Square customer id,
// e.g. after GDPR erasure deletes the customer at Square and NULLs the DB
// columns. Without it, the process-local cache would keep serving the erased
// user's stale customer id on a later save-card flow — reusing a deleted
// Square customer id (fail-closed at Square, but incorrect) and letting the
// erased identity resurface in memory. Called by the erasure handlers
// (handlers/user, handlers/scheduling) after the local anonymization commits.
func InvalidateSquareCustomerCache(userID string) {
	squareCustomerCache.Delete(userID)
}

var SquareClient square.SquareClient