package processor

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"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"
)

// ErrVoucherRedemptionRejected wraps every reason a customer cannot redeem a voucher:
// the key, the voucher's status or dates, the stock, the per-customer limit, the
// EnakPoint balance. The message says which.
var ErrVoucherRedemptionRejected = errors.New("voucher redemption refused")

// catalogStockModes are the vouchers the catalog lists. An EXTERNAL one is listed only
// when its provider has an adapter.
var catalogStockModes = []string{constants.VoucherStockStatic, constants.VoucherStockCodePool, constants.VoucherStockExternal}

func redemptionRejected(format string, args ...any) error {
	return fmt.Errorf("%w: %s", ErrVoucherRedemptionRejected, fmt.Sprintf(format, args...))
}

// VoucherRedemptionProcessor redeems EnakPoint for vouchers and records what each
// redemption cost each budget (docs/rfc-enakgame.md §7.4, §7.6, D5).
type VoucherRedemptionProcessor struct {
	customers   gameCustomerReader
	vouchers    repository.VoucherRepository
	redemptions repository.VoucherRedemptionRepository
	pins        pinVerifier
	spendable   spendableReader
	wallet      *WalletProcessor
	providers   VoucherProviders
	tx          TxRunner
	now         func() time.Time
}

func NewVoucherRedemptionProcessor(customers gameCustomerReader, vouchers repository.VoucherRepository, redemptions repository.VoucherRedemptionRepository,
	pins pinVerifier, spendable spendableReader, wallet *WalletProcessor, providers VoucherProviders, tx TxRunner) *VoucherRedemptionProcessor {
	return &VoucherRedemptionProcessor{
		customers: customers, vouchers: vouchers, redemptions: redemptions, pins: pins, spendable: spendable,
		wallet: wallet, providers: providers, tx: tx, now: time.Now,
	}
}

// Redeem takes a voucher's point cost in EnakPoint and hands out the voucher, in one
// transaction (§7.4): the stock, the code, the debit, the redemption and its cost
// split all commit together or not at all. The PIN approves it (K8).
//
// An EXTERNAL voucher comes from its provider, which is never called inside a
// transaction (§7.5): the redemption is written PENDING with its debit first, the
// provider is asked, and its answer completes it, fails and refunds it, or, when
// there is no answer, leaves it PENDING for the recovery job.
//
// idempotencyKey is the client's Idempotency-Key: a retry with the same key returns
// the first redemption, with its code, and takes nothing more.
func (p *VoucherRedemptionProcessor) Redeem(ctx context.Context, customerID, voucherID uuid.UUID, pin, idempotencyKey string, info models.CustomerPinRequestInfo) (*models.VoucherRedeemResult, error) {
	key := strings.TrimSpace(idempotencyKey)
	if key == "" {
		return nil, redemptionRejected("the Idempotency-Key header is required")
	}
	if len(key) > gameSessionKeyLimit {
		return nil, redemptionRejected("the Idempotency-Key header must be at most %d characters", gameSessionKeyLimit)
	}
	customer, err := p.customers.GetCustomer(ctx, customerID)
	if err != nil {
		return nil, err
	}
	// A retry is answered before anything else is checked: the voucher may have run
	// out or ended since, but this redemption went through.
	if previous, err := p.redemptions.GetByKey(ctx, customerID, key); err != nil || previous != nil {
		if err != nil {
			return nil, err
		}
		return p.replay(ctx, previous, voucherID)
	}
	if !customer.IsActive {
		return nil, redemptionRejected("the customer is not active")
	}
	voucher, err := p.vouchers.GetVoucher(ctx, customer.OrganizationID, voucherID)
	if err != nil {
		return nil, err
	}
	// Refuse what cannot work before the PIN is checked, so it costs no attempt.
	if err := p.redeemable(voucher, p.now()); err != nil {
		return nil, err
	}
	if err := p.pins.VerifyPin(ctx, customerID, pin, PinActionRedeem, info); err != nil {
		return nil, err
	}

	var redemption *entities.VoucherRedemption
	var code *entities.VoucherCode
	replayed := false
	err = p.tx.WithTransaction(ctx, func(ctx context.Context) error {
		if err := p.wallet.LockWallet(ctx, customerID); err != nil {
			return err
		}
		// Under the lock, a request sent twice at once finds the first one here.
		previous, err := p.redemptions.GetByKey(ctx, customerID, key)
		if err != nil {
			return err
		}
		if previous != nil {
			redemption, replayed = previous, true
			return nil
		}
		if voucher, err = p.vouchers.GetVoucher(ctx, customer.OrganizationID, voucherID); err != nil {
			return err
		}
		now := p.now()
		if err := p.redeemable(voucher, now); err != nil {
			return err
		}
		if voucher.MaxPerCustomer != nil {
			// Counted under the wallet lock, so the customer's own redemptions at the
			// same time see each other.
			count, err := p.redemptions.CountForCustomer(ctx, customerID, voucher.ID)
			if err != nil {
				return err
			}
			if count >= int64(*voucher.MaxPerCustomer) {
				return redemptionRejected("this voucher can be redeemed at most %d times per customer", *voucher.MaxPerCustomer)
			}
		}

		redemptionID := uuid.New()
		switch voucher.StockMode {
		case constants.VoucherStockStatic:
			taken, err := p.vouchers.TakeStock(ctx, voucher.ID)
			if err != nil {
				return err
			}
			if !taken {
				return redemptionRejected("the voucher is out of stock")
			}
		case constants.VoucherStockCodePool:
			if code, err = p.vouchers.ClaimCode(ctx, voucher.ID, redemptionID, now); err != nil {
				return err
			}
			if code == nil {
				return redemptionRejected("the voucher is out of stock")
			}
		}
		external := voucher.StockMode == constants.VoucherStockExternal

		debit, err := p.wallet.Debit(ctx, WalletDebitInput{WalletEntry: WalletEntry{
			CustomerID:     customerID,
			Currency:       constants.WalletCurrencyPoint,
			Type:           constants.WalletTxTypeRewardRedeem,
			Amount:         voucher.PointCost,
			ReferenceType:  constants.WalletRefTypeRewardRedemption,
			ReferenceID:    redemptionID,
			Description:    truncateDescription("Tukar voucher " + voucher.Name),
			Metadata:       entities.Metadata{"voucher_id": voucher.ID.String(), "face_value": voucher.FaceValue},
			IdempotencyKey: "redeem:" + redemptionID.String(),
		}})
		if errors.Is(err, repository.ErrWalletInsufficientBalance) {
			return redemptionRejected("not enough EnakPoint")
		}
		if err != nil {
			return err
		}

		redemption = &entities.VoucherRedemption{
			ID:                 redemptionID,
			OrganizationID:     customer.OrganizationID,
			CustomerID:         customerID,
			VoucherID:          voucher.ID,
			IdempotencyKey:     key,
			Status:             constants.VoucherRedemptionCompleted,
			FaceValue:          voucher.FaceValue,
			PointCost:          voucher.PointCost,
			DebitTransactionID: debit.Transaction.ID,
			CompletedAt:        &now,
		}
		if external {
			// Its cost is split once the provider has issued it.
			redemption.Status, redemption.CompletedAt = constants.VoucherRedemptionPending, nil
		}
		if code != nil {
			redemption.VoucherCodeID = &code.ID
		}
		if err := p.redemptions.CreateRedemption(ctx, redemption); err != nil {
			return err
		}
		if external {
			return nil
		}
		return p.recordCost(ctx, redemption)
	})
	if err != nil {
		return nil, err
	}
	if replayed {
		return p.replay(ctx, redemption, voucherID)
	}
	if redemption.Status == constants.VoucherRedemptionPending {
		if redemption, err = p.issueExternal(ctx, redemption, voucher, false); err != nil {
			return nil, err
		}
	}
	return p.result(ctx, redemption, voucher, code, false)
}

// recordCost splits a completed redemption's face value over where its EnakPoint
// came from and freezes the split (§7.6). Only the part from EnakGame rewards names
// a budget; the rest is kept for reporting.
func (p *VoucherRedemptionProcessor) recordCost(ctx context.Context, redemption *entities.VoucherRedemption) error {
	sources, err := p.redemptions.PointSources(ctx, redemption.DebitTransactionID)
	if err != nil {
		return err
	}
	var traced int64
	for _, s := range sources {
		traced += s.Points
	}
	if traced != redemption.PointCost {
		return fmt.Errorf("redemption %s: traced %d EnakPoint back to their source, not %d", redemption.ID, traced, redemption.PointCost)
	}
	parts := SplitVoucherCost(redemption.FaceValue, sources)
	costs := make([]entities.VoucherRedemptionCost, 0, len(parts))
	for _, part := range parts {
		costs = append(costs, entities.VoucherRedemptionCost{
			RedemptionID: redemption.ID, BudgetID: part.BudgetID, SourceType: part.SourceType,
			Points: part.Points, Cost: part.Cost, RecognizedAt: *redemption.CompletedAt,
		})
	}
	return p.redemptions.CreateCosts(ctx, costs)
}

// replay answers a retry with the redemption it repeats.
func (p *VoucherRedemptionProcessor) replay(ctx context.Context, redemption *entities.VoucherRedemption, voucherID uuid.UUID) (*models.VoucherRedeemResult, error) {
	if redemption.VoucherID != voucherID {
		return nil, redemptionRejected("this Idempotency-Key was already used to redeem another voucher")
	}
	voucher, err := p.vouchers.GetVoucher(ctx, redemption.OrganizationID, redemption.VoucherID)
	if err != nil {
		return nil, err
	}
	var code *entities.VoucherCode
	if redemption.VoucherCodeID != nil {
		if code, err = p.vouchers.GetCode(ctx, *redemption.VoucherCodeID); err != nil {
			return nil, err
		}
	}
	return p.result(ctx, redemption, voucher, code, true)
}

func (p *VoucherRedemptionProcessor) result(ctx context.Context, r *entities.VoucherRedemption, v *entities.Voucher, code *entities.VoucherCode, replayed bool) (*models.VoucherRedeemResult, error) {
	balances, err := p.spendable.SpendableBalances(ctx, r.CustomerID, p.now())
	if err != nil {
		return nil, err
	}
	item := repository.CustomerRedemption{VoucherRedemption: *r, VoucherName: v.Name, VoucherImageURL: v.ImageURL, VoucherType: v.VoucherType, Code: r.ExternalCode}
	if code != nil {
		c := code.Code
		item.Code, item.CodeExpiresAt = &c, code.ExpiresAt
	}
	return &models.VoucherRedeemResult{
		CustomerVoucherRedemption: customerRedemptionModel(item),
		PointBalance:              balances[constants.WalletCurrencyPoint],
		Replayed:                  replayed,
	}, nil
}

// Catalog returns the vouchers the customer can redeem now, with how many are left.
func (p *VoucherRedemptionProcessor) Catalog(ctx context.Context, customerID uuid.UUID) ([]models.CustomerVoucher, error) {
	customer, err := p.customers.GetCustomer(ctx, customerID)
	if err != nil {
		return nil, err
	}
	vouchers, err := p.vouchers.ListCatalog(ctx, customer.OrganizationID, p.now(), catalogStockModes)
	if err != nil {
		return nil, err
	}
	out := make([]models.CustomerVoucher, 0, len(vouchers))
	for _, v := range vouchers {
		if v.StockMode == constants.VoucherStockExternal {
			if _, ok := p.providerOf(&v.Voucher); !ok {
				continue
			}
		}
		out = append(out, models.CustomerVoucher{
			ID: v.ID, Name: v.Name, Description: v.Description, ImageURL: v.ImageURL, VoucherType: v.VoucherType,
			FaceValue: v.FaceValue, PointCost: v.PointCost, MaxPerCustomer: v.MaxPerCustomer, ValidUntil: v.ValidUntil,
			Terms: []byte(v.Terms), Available: v.Available,
		})
	}
	return out, nil
}

// ListRedemptions returns a page of the customer's redemptions, newest first, with
// their codes.
func (p *VoucherRedemptionProcessor) ListRedemptions(ctx context.Context, customerID uuid.UUID, page, limit int) (*models.PaginatedResponse[models.CustomerVoucherRedemption], error) {
	page, limit = enakGamePage(page, limit)
	rows, total, err := p.redemptions.ListCustomerRedemptions(ctx, customerID, (page-1)*limit, limit)
	if err != nil {
		return nil, err
	}
	items := make([]models.CustomerVoucherRedemption, 0, len(rows))
	for _, row := range rows {
		items = append(items, customerRedemptionModel(row))
	}
	return &models.PaginatedResponse[models.CustomerVoucherRedemption]{Data: items, Pagination: enakGamePagination(page, limit, total)}, nil
}

// redeemable says why a voucher cannot be redeemed now, or nil.
func (p *VoucherRedemptionProcessor) redeemable(v *entities.Voucher, now time.Time) error {
	if v.StockMode == constants.VoucherStockExternal {
		if _, ok := p.providerOf(v); !ok {
			return redemptionRejected("the voucher is not available yet")
		}
	}
	return redeemableNow(v, now)
}

func redeemableNow(v *entities.Voucher, now time.Time) error {
	switch {
	case v.Status != constants.VoucherStatusActive:
		return redemptionRejected("the voucher is not available")
	case v.ValidFrom != nil && now.Before(*v.ValidFrom):
		return redemptionRejected("the voucher cannot be redeemed yet")
	case v.ValidUntil != nil && !now.Before(*v.ValidUntil):
		return redemptionRejected("the voucher has ended")
	}
	return nil
}

func customerRedemptionModel(r repository.CustomerRedemption) models.CustomerVoucherRedemption {
	return models.CustomerVoucherRedemption{
		ID: r.ID, VoucherID: r.VoucherID, VoucherName: r.VoucherName, VoucherImageURL: r.VoucherImageURL,
		VoucherType: r.VoucherType, Status: r.Status, FaceValue: r.FaceValue, PointCost: r.PointCost,
		Code: r.Code, CodeExpiresAt: r.CodeExpiresAt, CompletedAt: r.CompletedAt, CreatedAt: r.CreatedAt,
	}
}