package processor

import (
	"context"
	"fmt"
	"time"

	"github.com/google/uuid"

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

// Why an order earned nothing.
const (
	EarningSkipNotPaid          = "NOT_PAID"
	EarningSkipVoid             = "VOID"
	EarningSkipNoCustomer       = "NO_CUSTOMER"
	EarningSkipDefaultCustomer  = "DEFAULT_CUSTOMER"
	EarningSkipInactiveCustomer = "INACTIVE_CUSTOMER"
	EarningSkipNothingToEarn    = "NOTHING_TO_EARN"
)

// EarningOutcome is what earning did for one order.
type EarningOutcome struct {
	Points int64
	Coins  int64
	// Set when the order earned nothing, to say why.
	Skipped string
}

type outletSettingsReader interface {
	Outlet(ctx context.Context, outletID uuid.UUID) (*models.OutletLoyaltySettings, error)
}

// EarningProcessor credits EnakPoint and EnakCoin for paid orders
// (docs/prd-point-coin.md F3).
type EarningProcessor struct {
	orders   repository.EarningRepository
	settings outletSettingsReader
	wallet   *WalletProcessor
	tx       TxRunner
}

func NewEarningProcessor(orders repository.EarningRepository, settings outletSettingsReader, wallet *WalletProcessor, tx TxRunner) *EarningProcessor {
	return &EarningProcessor{orders: orders, settings: settings, wallet: wallet, tx: tx}
}

// OnOrderPaid is called once an order has become fully paid and the payment has
// committed. It never fails the caller: a failed earning is logged and picked up later
// by EarnMissing, and the idempotency keys make that retry safe.
func (p *EarningProcessor) OnOrderPaid(ctx context.Context, orderID uuid.UUID) {
	defer func() {
		if r := recover(); r != nil {
			logger.NonContext.Error(fmt.Sprintf("Earning for order %s panicked; it will be retried", orderID), fmt.Errorf("%v", r))
		}
	}()
	if _, err := p.EarnForOrder(ctx, orderID); err != nil {
		logger.NonContext.Error(fmt.Sprintf("Earning for order %s failed; it will be retried", orderID), err)
	}
}

// EarnForOrder credits what a paid order earns. Calling it again for the same order
// credits nothing more.
func (p *EarningProcessor) EarnForOrder(ctx context.Context, orderID uuid.UUID) (*EarningOutcome, error) {
	order, err := p.orders.GetOrderForEarning(ctx, orderID)
	if err != nil {
		return nil, err
	}
	if skip := earningSkipReason(order); skip != "" {
		return &EarningOutcome{Skipped: skip}, nil
	}

	settings, err := p.settings.Outlet(ctx, order.OutletID)
	if err != nil {
		return nil, err
	}
	pointPaid, err := p.orders.PointPaidAmount(ctx, orderID)
	if err != nil {
		return nil, err
	}
	result := CalculateEarning(&entities.Order{Subtotal: order.Subtotal, DiscountAmount: order.DiscountAmount}, pointPaid, *settings)
	if result.Point.Amount == 0 && result.Coin.Amount == 0 {
		return &EarningOutcome{Skipped: EarningSkipNothingToEarn}, nil
	}

	outcome := &EarningOutcome{}
	err = p.tx.WithTransaction(ctx, func(ctx context.Context) error {
		for _, c := range []struct {
			currency string
			line     EarningLine
			total    *int64
		}{
			{constants.WalletCurrencyPoint, result.Point, &outcome.Points},
			{constants.WalletCurrencyCoin, result.Coin, &outcome.Coins},
		} {
			if c.line.Amount == 0 {
				continue
			}
			outletID := order.OutletID
			res, err := p.wallet.Credit(ctx, WalletCreditInput{WalletEntry: WalletEntry{
				CustomerID:     *order.CustomerID,
				Currency:       c.currency,
				Type:           constants.WalletTxTypeEarn,
				Amount:         c.line.Amount,
				ReferenceType:  constants.WalletRefTypeOrder,
				ReferenceID:    order.ID,
				OutletID:       &outletID,
				Description:    earningDescription(order),
				Metadata:       result.Metadata(c.line),
				IdempotencyKey: fmt.Sprintf("earn:%s:%s", order.ID, c.currency),
				// Lots never expire until the expiry model is decided (F12, note N4).
			}})
			if err != nil {
				return fmt.Errorf("crediting %s: %w", c.currency, err)
			}
			*c.total = res.Transaction.Amount
		}
		return nil
	})
	if err != nil {
		return nil, err
	}
	return outcome, nil
}

// EarnMissing is the safety net behind OnOrderPaid: it looks for orders paid since the
// given time that should have earned and have no EARN row, and earns for them. It
// returns how many orders it looked at and how many now earned. One order failing does
// not stop the others.
func (p *EarningProcessor) EarnMissing(ctx context.Context, since time.Time, maxOrders int) (checked, earned int, err error) {
	const page = 200
	var after *repository.EarningCursor
	for checked < maxOrders {
		batch, err := p.orders.ListPaidOrdersWithoutEarning(ctx, since, after, page)
		if err != nil {
			return checked, earned, err
		}
		if len(batch) == 0 {
			break
		}
		for _, candidate := range batch {
			checked++
			outcome, err := p.EarnForOrder(ctx, candidate.ID)
			if err != nil {
				logger.NonContext.Error(fmt.Sprintf("Earning retry for order %s failed", candidate.ID), err)
				continue
			}
			if outcome.Skipped == "" {
				earned++
			}
		}
		last := batch[len(batch)-1]
		after = &last
	}
	return checked, earned, nil
}

func earningSkipReason(order *repository.EarningOrder) string {
	switch {
	case order.PaymentStatus != string(entities.PaymentStatusCompleted):
		return EarningSkipNotPaid
	case order.IsVoid:
		return EarningSkipVoid
	case order.CustomerID == nil || order.CustomerIsDefault == nil:
		return EarningSkipNoCustomer
	case *order.CustomerIsDefault:
		return EarningSkipDefaultCustomer
	case order.CustomerIsActive == nil || !*order.CustomerIsActive:
		return EarningSkipInactiveCustomer
	}
	return ""
}

func earningDescription(order *repository.EarningOrder) string {
	description := "Belanja #" + order.OrderNumber
	if order.OutletName != "" {
		description += " di " + order.OutletName
	}
	return truncateRunes(description, walletDescriptionLimit)
}