sub2api/backend/internal/service/payment_refund.go

package service

import (
	"context"
	"fmt"
	"log/slog"
	"math"
	"strconv"
	"strings"
	"time"

	dbent "github.com/Wei-Shaw/sub2api/ent"
	"github.com/Wei-Shaw/sub2api/ent/paymentorder"
	"github.com/Wei-Shaw/sub2api/internal/payment"
	infraerrors "github.com/Wei-Shaw/sub2api/internal/pkg/errors"
)

// --- Refund Flow ---

func (s *PaymentService) RequestRefund(ctx context.Context, oid, uid int64, reason string) error {
	o, err := s.validateRefundRequest(ctx, oid, uid)
	if err != nil {
		return err
	}
	u, err := s.userRepo.GetByID(ctx, o.UserID)
	if err != nil {
		return fmt.Errorf("get user: %w", err)
	}
	if u.Balance < o.Amount {
		return infraerrors.BadRequest("BALANCE_NOT_ENOUGH", "refund amount exceeds balance")
	}
	nr := strings.TrimSpace(reason)
	now := time.Now()
	by := fmt.Sprintf("%d", uid)
	c, err := s.entClient.PaymentOrder.Update().Where(paymentorder.IDEQ(oid), paymentorder.UserIDEQ(uid), paymentorder.StatusEQ(OrderStatusCompleted), paymentorder.OrderTypeEQ(payment.OrderTypeBalance)).SetStatus(OrderStatusRefundRequested).SetRefundRequestedAt(now).SetRefundRequestReason(nr).SetRefundRequestedBy(by).SetRefundAmount(o.Amount).Save(ctx)
	if err != nil {
		return fmt.Errorf("update: %w", err)
	}
	if c == 0 {
		return infraerrors.Conflict("CONFLICT", "order status changed")
	}
	s.writeAuditLog(ctx, oid, "REFUND_REQUESTED", fmt.Sprintf("user:%d", uid), map[string]any{"amount": o.Amount, "reason": nr})
	return nil
}

func (s *PaymentService) validateRefundRequest(ctx context.Context, oid, uid int64) (*dbent.PaymentOrder, error) {
	o, err := s.entClient.PaymentOrder.Get(ctx, oid)
	if err != nil {
		return nil, infraerrors.NotFound("NOT_FOUND", "order not found")
	}
	if o.UserID != uid {
		return nil, infraerrors.Forbidden("FORBIDDEN", "no permission")
	}
	if o.OrderType != payment.OrderTypeBalance {
		return nil, infraerrors.BadRequest("INVALID_ORDER_TYPE", "only balance orders can request refund")
	}
	if o.Status != OrderStatusCompleted {
		return nil, infraerrors.BadRequest("INVALID_STATUS", "only completed orders can request refund")
	}
	return o, nil
}

func (s *PaymentService) PrepareRefund(ctx context.Context, oid int64, amt float64, reason string, force, deduct bool) (*RefundPlan, *RefundResult, error) {
	o, err := s.entClient.PaymentOrder.Get(ctx, oid)
	if err != nil {
		return nil, nil, infraerrors.NotFound("NOT_FOUND", "order not found")
	}
	ok := []string{OrderStatusCompleted, OrderStatusRefundRequested, OrderStatusRefundFailed}
	if !psSliceContains(ok, o.Status) {
		return nil, nil, infraerrors.BadRequest("INVALID_STATUS", "order status does not allow refund")
	}
	if math.IsNaN(amt) || math.IsInf(amt, 0) {
		return nil, nil, infraerrors.BadRequest("INVALID_AMOUNT", "invalid refund amount")
	}
	if amt <= 0 {
		amt = o.Amount
	}
	if amt-o.Amount > amountToleranceCNY {
		return nil, nil, infraerrors.BadRequest("REFUND_AMOUNT_EXCEEDED", "refund amount exceeds recharge")
	}
	// Full refund: use actual pay_amount for gateway (includes fees)
	ga := amt
	if math.Abs(amt-o.Amount) <= amountToleranceCNY {
		ga = o.PayAmount
	}
	rr := strings.TrimSpace(reason)
	if rr == "" && o.RefundRequestReason != nil {
		rr = *o.RefundRequestReason
	}
	if rr == "" {
		rr = fmt.Sprintf("refund order:%d", o.ID)
	}
	p := &RefundPlan{OrderID: oid, Order: o, RefundAmount: amt, GatewayAmount: ga, Reason: rr, Force: force, DeductBalance: deduct, DeductionType: payment.DeductionTypeNone}
	if deduct {
		if er := s.prepDeduct(ctx, o, p, force); er != nil {
			return nil, er, nil
		}
	}
	return p, nil, nil
}

func (s *PaymentService) prepDeduct(ctx context.Context, o *dbent.PaymentOrder, p *RefundPlan, force bool) *RefundResult {
	if o.OrderType == payment.OrderTypeSubscription {
		p.DeductionType = payment.DeductionTypeSubscription
		return nil
	}
	u, err := s.userRepo.GetByID(ctx, o.UserID)
	if err != nil {
		if !force {
			return &RefundResult{Success: false, Warning: "cannot fetch user balance, use force", RequireForce: true}
		}
		return nil
	}
	p.DeductionType = payment.DeductionTypeBalance
	p.BalanceToDeduct = math.Min(p.RefundAmount, u.Balance)
	return nil
}

func (s *PaymentService) ExecuteRefund(ctx context.Context, p *RefundPlan) (*RefundResult, error) {
	c, err := s.entClient.PaymentOrder.Update().Where(paymentorder.IDEQ(p.OrderID), paymentorder.StatusIn(OrderStatusCompleted, OrderStatusRefundRequested, OrderStatusRefundFailed)).SetStatus(OrderStatusRefunding).Save(ctx)
	if err != nil {
		return nil, fmt.Errorf("lock: %w", err)
	}
	if c == 0 {
		return nil, infraerrors.Conflict("CONFLICT", "order status changed")
	}
	if p.DeductionType == payment.DeductionTypeBalance && p.BalanceToDeduct > 0 {
		// Skip balance deduction on retry if previous attempt already deducted
		// but failed to roll back (REFUND_ROLLBACK_FAILED in audit log).
		if !s.hasAuditLog(ctx, p.OrderID, "REFUND_ROLLBACK_FAILED") {
			if err := s.userRepo.DeductBalance(ctx, p.Order.UserID, p.BalanceToDeduct); err != nil {
				s.restoreStatus(ctx, p)
				return nil, fmt.Errorf("deduction: %w", err)
			}
		} else {
			slog.Warn("skipping balance deduction on retry (previous rollback failed)", "orderID", p.OrderID)
			p.BalanceToDeduct = 0
		}
	}
	if err := s.gwRefund(ctx, p); err != nil {
		return s.handleGwFail(ctx, p, err)
	}
	return s.markRefundOk(ctx, p)
}

func (s *PaymentService) gwRefund(ctx context.Context, p *RefundPlan) error {
	if p.Order.PaymentTradeNo == "" {
		s.writeAuditLog(ctx, p.Order.ID, "REFUND_NO_TRADE_NO", "admin", map[string]any{"detail": "skipped"})
		return nil
	}

	// Use the exact provider instance that created this order, not a random one
	// from the registry. Each instance has its own merchant credentials.
	prov, err := s.getRefundProvider(ctx, p.Order)
	if err != nil {
		return fmt.Errorf("get refund provider: %w", err)
	}
	_, err = prov.Refund(ctx, payment.RefundRequest{
		TradeNo: p.Order.PaymentTradeNo,
		OrderID: p.Order.OutTradeNo,
		Amount:  strconv.FormatFloat(p.GatewayAmount, 'f', 2, 64),
		Reason:  p.Reason,
	})
	return err
}

// getRefundProvider creates a provider using the order's original instance config.
// Delegates to getOrderProvider which handles instance lookup and fallback.
func (s *PaymentService) getRefundProvider(ctx context.Context, o *dbent.PaymentOrder) (payment.Provider, error) {
	return s.getOrderProvider(ctx, o)
}

func (s *PaymentService) handleGwFail(ctx context.Context, p *RefundPlan, gErr error) (*RefundResult, error) {
	if s.RollbackRefund(ctx, p, gErr) {
		s.restoreStatus(ctx, p)
		s.writeAuditLog(ctx, p.OrderID, "REFUND_GATEWAY_FAILED", "admin", map[string]any{"detail": psErrMsg(gErr)})
		return &RefundResult{Success: false, Warning: "gateway failed: " + psErrMsg(gErr) + ", rolled back"}, nil
	}
	now := time.Now()
	_, _ = s.entClient.PaymentOrder.UpdateOneID(p.OrderID).SetStatus(OrderStatusRefundFailed).SetFailedAt(now).SetFailedReason(psErrMsg(gErr)).Save(ctx)
	s.writeAuditLog(ctx, p.OrderID, "REFUND_FAILED", "admin", map[string]any{"detail": psErrMsg(gErr)})
	return nil, infraerrors.InternalServer("REFUND_FAILED", psErrMsg(gErr))
}

func (s *PaymentService) markRefundOk(ctx context.Context, p *RefundPlan) (*RefundResult, error) {
	fs := OrderStatusRefunded
	if p.RefundAmount < p.Order.Amount {
		fs = OrderStatusPartiallyRefunded
	}
	now := time.Now()
	_, err := s.entClient.PaymentOrder.UpdateOneID(p.OrderID).SetStatus(fs).SetRefundAmount(p.RefundAmount).SetRefundReason(p.Reason).SetRefundAt(now).SetForceRefund(p.Force).Save(ctx)
	if err != nil {
		return nil, fmt.Errorf("mark refund: %w", err)
	}
	s.writeAuditLog(ctx, p.OrderID, "REFUND_SUCCESS", "admin", map[string]any{"refundAmount": p.RefundAmount, "reason": p.Reason, "balanceDeducted": p.BalanceToDeduct, "force": p.Force})
	return &RefundResult{Success: true, BalanceDeducted: p.BalanceToDeduct, SubDaysDeducted: p.SubDaysToDeduct}, nil
}

func (s *PaymentService) RollbackRefund(ctx context.Context, p *RefundPlan, gErr error) bool {
	if p.DeductionType == payment.DeductionTypeBalance && p.BalanceToDeduct > 0 {
		if err := s.userRepo.UpdateBalance(ctx, p.Order.UserID, p.BalanceToDeduct); err != nil {
			slog.Error("[CRITICAL] rollback failed", "orderID", p.OrderID, "amount", p.BalanceToDeduct, "error", err)
			s.writeAuditLog(ctx, p.OrderID, "REFUND_ROLLBACK_FAILED", "admin", map[string]any{"gatewayError": psErrMsg(gErr), "rollbackError": psErrMsg(err), "balanceDeducted": p.BalanceToDeduct})
			return false
		}
	}
	return true
}

func (s *PaymentService) restoreStatus(ctx context.Context, p *RefundPlan) {
	rs := OrderStatusCompleted
	if p.Order.Status == OrderStatusRefundRequested {
		rs = OrderStatusRefundRequested
	}
	_, _ = s.entClient.PaymentOrder.UpdateOneID(p.OrderID).SetStatus(rs).Save(ctx)
}