package processor

import (
	"context"
	"errors"
	"fmt"
	"time"

	"github.com/google/uuid"

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

// ErrPointPaymentRejected wraps every reason a payment with EnakPoint is refused: the
// order, the customer, the outlet or the amount. The message says which.
var ErrPointPaymentRejected = errors.New("EnakPoint payment refused")

type pointPaymentSettings interface {
	Outlet(ctx context.Context, outletID uuid.UUID) (*models.OutletLoyaltySettings, error)
	PointValue(ctx context.Context, organizationID uuid.UUID) (int64, error)
}

type spendableReader interface {
	SpendableBalances(ctx context.Context, customerID uuid.UUID, asOf time.Time) (map[string]int64, error)
}

// PointPaymentInput is one payment of an order with EnakPoint.
type PointPaymentInput struct {
	OrderID         uuid.UUID
	PaymentMethodID uuid.UUID
	Points          int64
	// The cashier taking the payment at the POS; nil when the customer pays in the app.
	CashierID *uuid.UUID
	// Authorize proves the customer agreed, before anything is taken: at the POS it
	// redeems the payment code, in the app it checks the PIN (K8).
	Authorize func(ctx context.Context, customerID uuid.UUID) error
}

// PointPaymentResult is the payment made and where it left the order.
type PointPaymentResult struct {
	Payment *entities.Payment
	// True when this payment settled the order.
	Completed bool
	// Rupiah still to pay with another method.
	Remaining float64
}

// pointPaymentLimits applies the formula of docs/prd-point-coin.md F9, in cents:
//
//	cap        = min(remaining, total × max_payment_percent / 100 − already paid with EnakPoint)
//	max_points = min(balance, floor(cap / point_value))
type pointPaymentLimits struct {
	RemainingCents int64
	CapCents       int64
	MaxPoints      int64
}

func computePointPaymentLimits(total, totalPaid, paidWithPoints float64, maxPercent, pointValue, balance int64) pointPaymentLimits {
	remaining := toCents(total) - toCents(totalPaid)
	if remaining < 0 {
		remaining = 0
	}
	byPercent := toCents(total)*maxPercent/100 - toCents(paidWithPoints)
	capCents := min(remaining, byPercent)
	if capCents < 0 {
		capCents = 0
	}
	maxPoints := int64(0)
	if pointValue > 0 {
		maxPoints = min(balance, capCents/(pointValue*100))
	}
	if maxPoints < 0 {
		maxPoints = 0
	}
	return pointPaymentLimits{RemainingCents: remaining, CapCents: capCents, MaxPoints: maxPoints}
}

// PointPaymentProcessor pays orders with EnakPoint (docs/prd-point-coin.md F9).
type PointPaymentProcessor struct {
	repo      repository.PointPaymentRepository
	settings  pointPaymentSettings
	spendable spendableReader
	wallet    *WalletProcessor
	tx        TxRunner
	now       func() time.Time
}

func NewPointPaymentProcessor(repo repository.PointPaymentRepository, settings pointPaymentSettings, spendable spendableReader, wallet *WalletProcessor, tx TxRunner) *PointPaymentProcessor {
	return &PointPaymentProcessor{repo: repo, settings: settings, spendable: spendable, wallet: wallet, tx: tx, now: time.Now}
}

// Preview is GET /orders/:id/point-payment/preview: whether the order can be paid with
// EnakPoint, and at most how much.
func (p *PointPaymentProcessor) Preview(ctx context.Context, organizationID, orderID uuid.UUID) (*models.PointPaymentPreview, error) {
	order, err := p.repo.GetOrder(ctx, orderID, false)
	if err != nil {
		return nil, err
	}
	if order.OrganizationID != organizationID {
		return nil, repository.ErrPointPaymentOrderNotFound
	}
	preview := &models.PointPaymentPreview{OrderID: orderID, CustomerID: order.CustomerID}
	settings, err := p.settings.Outlet(ctx, order.OutletID)
	if err != nil {
		return nil, err
	}
	value, err := p.settings.PointValue(ctx, order.OrganizationID)
	if err != nil {
		return nil, err
	}
	preview.PointValue = value
	preview.MinPaymentPoints = settings.PointPayment.MinPaymentPoints
	preview.MaxPaymentPercent = settings.PointPayment.MaxPaymentPercent

	if reason := pointPaymentOrderProblem(order, settings); reason != "" {
		preview.Reason = reason
		return preview, nil
	}
	limits, balance, err := p.limits(ctx, order, settings, value)
	if err != nil {
		return nil, err
	}
	preview.PointBalance = balance
	preview.RemainingAmount = float64(limits.RemainingCents) / 100
	preview.MaxPoints = limits.MaxPoints
	preview.MaxAmount = limits.MaxPoints * value
	if limits.MaxPoints < settings.PointPayment.MinPaymentPoints {
		preview.Reason = "the customer cannot pay the minimum of EnakPoint on this order"
		return preview, nil
	}
	preview.Eligible = true
	return preview, nil
}

// Pay takes EnakPoint from the order's customer and records the payment. The payment
// row, the ledger PAYMENT row, the balance and the order change in one transaction
// with the order row and the wallet locked (F9 steps 1–6).
func (p *PointPaymentProcessor) Pay(ctx context.Context, in PointPaymentInput) (*PointPaymentResult, error) {
	reject := func(format string, args ...any) error {
		return fmt.Errorf("%w: %s", ErrPointPaymentRejected, fmt.Sprintf(format, args...))
	}
	if in.Points <= 0 {
		return nil, reject("the number of EnakPoint must be positive")
	}
	order, err := p.repo.GetOrder(ctx, in.OrderID, false)
	if err != nil {
		return nil, err
	}
	methodOrg, methodType, err := p.repo.GetPaymentMethod(ctx, in.PaymentMethodID)
	if err != nil {
		return nil, err
	}
	if methodType != string(constants.PaymentMethodTypePoint) || methodOrg != order.OrganizationID {
		return nil, reject("the payment method is not this organization's EnakPoint method")
	}
	settings, err := p.settings.Outlet(ctx, order.OutletID)
	if err != nil {
		return nil, err
	}
	if reason := pointPaymentOrderProblem(order, settings); reason != "" {
		return nil, reject("%s", reason)
	}
	if in.Points < settings.PointPayment.MinPaymentPoints {
		return nil, reject("at least %d EnakPoint must be used", settings.PointPayment.MinPaymentPoints)
	}
	customerID := *order.CustomerID

	// The customer agrees before anything is taken. A code is used up here even if the
	// payment then fails, and the customer shows a new one.
	if in.Authorize == nil {
		return nil, reject("the customer has not approved the payment")
	}
	if err := in.Authorize(ctx, customerID); err != nil {
		return nil, err
	}

	result := &PointPaymentResult{}
	err = p.tx.WithTransaction(ctx, func(ctx context.Context) error {
		// Lock the order, then the wallet, and read everything again: another payment
		// may have landed since the checks above.
		order, err := p.repo.GetOrder(ctx, in.OrderID, true)
		if err != nil {
			return err
		}
		if reason := pointPaymentOrderProblem(order, settings); reason != "" {
			return reject("%s", reason)
		}
		if err := p.wallet.LockWallet(ctx, customerID); err != nil {
			return err
		}
		value, err := p.settings.PointValue(ctx, order.OrganizationID)
		if err != nil {
			return err
		}
		limits, _, err := p.limits(ctx, order, settings, value)
		if err != nil {
			return err
		}
		if in.Points > limits.MaxPoints {
			return reject("at most %d EnakPoint can pay this order now", limits.MaxPoints)
		}
		amountCents := in.Points * value * 100
		// No change is ever given for EnakPoint (K7); the limits already keep it
		// within what is left, this only guards that.
		if amountCents > limits.RemainingCents {
			return reject("EnakPoint cannot pay more than what is left on the order")
		}

		pointsUsed := in.Points
		frozenValue := float64(value)
		payment := &entities.Payment{
			ID:              uuid.New(),
			OrderID:         order.ID,
			PaymentMethodID: in.PaymentMethodID,
			Amount:          float64(amountCents) / 100,
			Status:          entities.PaymentTransactionStatusCompleted,
			PointsUsed:      &pointsUsed,
			PointValue:      &frozenValue,
			Metadata:        entities.Metadata{"points_used": pointsUsed, "point_value": value},
		}
		if err := p.repo.InsertPayment(ctx, payment); err != nil {
			return err
		}

		outletID := order.OutletID
		if _, err := p.wallet.Debit(ctx, WalletDebitInput{WalletEntry: WalletEntry{
			CustomerID:     customerID,
			Currency:       constants.WalletCurrencyPoint,
			Type:           constants.WalletTxTypePayment,
			Amount:         in.Points,
			ReferenceType:  constants.WalletRefTypePayment,
			ReferenceID:    payment.ID,
			OutletID:       &outletID,
			CreatedByUser:  in.CashierID,
			Description:    pointPaymentDescription(order, amountCents),
			Metadata:       entities.Metadata{"point_value": value, "amount": payment.Amount},
			IdempotencyKey: "payment:" + payment.ID.String(),
		}}); err != nil {
			if errors.Is(err, repository.ErrWalletInsufficientBalance) {
				return reject("the customer does not have enough EnakPoint")
			}
			return err
		}

		remainingCents := limits.RemainingCents - amountCents
		completed := remainingCents == 0
		if err := p.repo.UpdateOrderAfterPayment(ctx, order.ID, float64(remainingCents)/100, completed); err != nil {
			return err
		}
		result.Payment = payment
		result.Completed = completed
		result.Remaining = float64(remainingCents) / 100
		return nil
	})
	if err != nil {
		return nil, err
	}
	return result, nil
}

func (p *PointPaymentProcessor) limits(ctx context.Context, order *repository.PointPaymentOrder, settings *models.OutletLoyaltySettings, value int64) (pointPaymentLimits, int64, error) {
	totalPaid, err := p.repo.TotalPaid(ctx, order.ID)
	if err != nil {
		return pointPaymentLimits{}, 0, err
	}
	paidWithPoints, err := p.repo.PaidWithPoints(ctx, order.ID)
	if err != nil {
		return pointPaymentLimits{}, 0, err
	}
	balances, err := p.spendable.SpendableBalances(ctx, *order.CustomerID, p.now())
	if err != nil {
		return pointPaymentLimits{}, 0, err
	}
	balance := balances[constants.WalletCurrencyPoint]
	return computePointPaymentLimits(order.TotalAmount, totalPaid, paidWithPoints, settings.PointPayment.MaxPaymentPercent, value, balance), balance, nil
}

// pointPaymentOrderProblem says why an order cannot be paid with EnakPoint at all, or
// "" when it can.
func pointPaymentOrderProblem(order *repository.PointPaymentOrder, settings *models.OutletLoyaltySettings) string {
	switch {
	case order.IsVoid:
		return "the order is void"
	case order.PaymentStatus == string(entities.PaymentStatusCompleted):
		return "the order is already paid"
	case !settings.PointPayment.AcceptPayment:
		return "this outlet does not accept EnakPoint"
	case order.CustomerID == nil || order.CustomerIsDefault == nil:
		return "the order has no customer"
	case *order.CustomerIsDefault:
		return "a walk-in order cannot be paid with EnakPoint"
	case order.CustomerIsActive == nil || !*order.CustomerIsActive:
		return "the customer is not active"
	}
	return ""
}

func pointPaymentDescription(order *repository.PointPaymentOrder, amountCents int64) string {
	description := "Bayar #" + order.OrderNumber
	if order.OutletName != "" {
		description += " di " + order.OutletName
	}
	description += " (Rp " + formatRupiah(amountCents/100) + ")"
	return truncateRunes(description, walletDescriptionLimit)
}

// formatRupiah writes 50000 as 50.000.
func formatRupiah(n int64) string {
	s := fmt.Sprintf("%d", n)
	out := make([]byte, 0, len(s)+len(s)/3)
	for i, c := range []byte(s) {
		if i > 0 && (len(s)-i)%3 == 0 {
			out = append(out, '.')
		}
		out = append(out, c)
	}
	return string(out)
}