package processor

import (
	"context"
	"fmt"

	"github.com/google/uuid"

	"apskel-pos-be/internal/constants"
	"apskel-pos-be/internal/entities"
	"apskel-pos-be/internal/logger"
	"apskel-pos-be/internal/repository"
)

// ReversalOutcome is what a reversal took back, and what it could not.
type ReversalOutcome struct {
	Points         int64
	Coins          int64
	PointShortfall int64
	CoinShortfall  int64
}

// OnOrderRefunded is called after an order was voided or (partly) refunded and that
// has committed. It never fails the caller: a refund is never blocked by the loyalty
// balance (Q3), so errors are logged.
func (p *EarningProcessor) OnOrderRefunded(ctx context.Context, orderID uuid.UUID) {
	defer func() {
		if r := recover(); r != nil {
			logger.NonContext.Error(fmt.Sprintf("Earning reversal for order %s panicked", orderID), fmt.Errorf("%v", r))
		}
	}()
	if _, err := p.ReverseForOrder(ctx, orderID); err != nil {
		logger.NonContext.Error(fmt.Sprintf("Earning reversal for order %s failed", orderID), err)
	}
}

// ReverseForOrder takes back what an order earned, as far as it has been voided or
// refunded (docs/prd-point-coin.md F10):
//
//   - void: everything the order earned;
//   - refund: floor(earned × refunded / basis), never more than was earned, with the
//     refunded amount being the order's cumulative refund.
//
// Only the part not asked back yet is taken, so calling it again, or after each of
// several partial refunds, never takes more than the order earned. It draws from the
// lots the EARN created first, then from the others in K9 order, and takes what the
// balance has when it is short, recording the rest as shortfall (Q3).
func (p *EarningProcessor) ReverseForOrder(ctx context.Context, orderID uuid.UUID) (*ReversalOutcome, error) {
	order, err := p.orders.GetOrderForEarning(ctx, orderID)
	if err != nil {
		return nil, err
	}
	earns, err := p.orders.ListEarnTransactions(ctx, orderID)
	if err != nil {
		return nil, err
	}
	outcome := &ReversalOutcome{}
	if len(earns) == 0 {
		return outcome, nil
	}

	err = p.tx.WithTransaction(ctx, func(ctx context.Context) error {
		for _, earn := range earns {
			target := earningReversalTarget(order, earn)
			requested, err := p.orders.ReversalRequested(ctx, earn.ID)
			if err != nil {
				return err
			}
			amount := target - requested
			if amount <= 0 {
				continue
			}
			lots, err := p.orders.LotIDsCreatedBy(ctx, earn.ID)
			if err != nil {
				return err
			}

			reason := "REFUND"
			if order.IsVoid {
				reason = "VOID"
			}
			earnID := earn.ID
			res, err := p.wallet.DebitUpTo(ctx, WalletDebitInput{
				WalletEntry: WalletEntry{
					CustomerID:            earn.CustomerID,
					Currency:              earn.Currency,
					Type:                  constants.WalletTxTypeEarnReversal,
					Amount:                amount,
					ReferenceType:         constants.WalletRefTypeOrder,
					ReferenceID:           order.ID,
					ReversesTransactionID: &earnID,
					OutletID:              earn.OutletID,
					Description:           earningReversalDescription(order),
					Metadata: entities.Metadata{
						"reason":        reason,
						"refund_amount": order.RefundAmount,
						"target":        target,
					},
					// The target only grows with each refund, so each refund gets its own
					// key while a retry of the same one replays.
					IdempotencyKey: fmt.Sprintf("reverse:%s:%d", earn.ID, target),
				},
				PreferredLotIDs: lots,
			})
			if err != nil {
				return fmt.Errorf("reversing %s: %w", earn.Currency, err)
			}

			var taken int64
			if res.Transaction != nil {
				taken = -res.Transaction.Amount
			} else {
				// Nothing to take: the ledger has no row to carry the shortfall.
				logger.NonContext.WarnWithFields("Earning reversal found an empty balance; the whole amount is shortfall", map[string]interface{}{
					"order_id": order.ID.String(), "customer_id": earn.CustomerID.String(),
					"currency": earn.Currency, "shortfall": res.Shortfall,
				}, nil)
			}
			switch earn.Currency {
			case constants.WalletCurrencyPoint:
				outcome.Points += taken
				outcome.PointShortfall += res.Shortfall
			case constants.WalletCurrencyCoin:
				outcome.Coins += taken
				outcome.CoinShortfall += res.Shortfall
			}
		}
		return nil
	})
	if err != nil {
		return nil, err
	}
	return outcome, nil
}

// earningReversalTarget is how much of an EARN row should have been taken back in
// total, given the order's void flag and cumulative refund. It works in cents like
// CalculateEarning, with the basis frozen on the EARN row.
func earningReversalTarget(order *repository.EarningOrder, earn entities.WalletTransaction) int64 {
	earned := earn.Amount
	if order.IsVoid {
		return earned
	}
	refundCents := toCents(order.RefundAmount)
	if refundCents <= 0 {
		return 0
	}
	basis, _ := earn.Metadata["basis"].(float64)
	basisCents := toCents(basis)
	// A refund can include tax, which the basis does not, so it can reach past it.
	if basisCents <= 0 || refundCents >= basisCents {
		return earned
	}
	return earned * refundCents / basisCents
}

func earningReversalDescription(order *repository.EarningOrder) string {
	verb := "Refund"
	if order.IsVoid {
		verb = "Batal"
	}
	description := verb + " #" + order.OrderNumber
	if order.OutletName != "" {
		description += " di " + order.OutletName
	}
	return truncateRunes(description, walletDescriptionLimit)
}