package repository

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

	"github.com/google/uuid"
	"gorm.io/gorm"

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

// RedemptionPointSource is EnakPoint a redemption spent, traced back to the ledger row
// that first created it (D5): GAME_REWARD with the budget that paid for it, or EARN,
// ADJUSTMENT, MIGRATION with none.
type RedemptionPointSource struct {
	Points     int64
	SourceType string
	BudgetID   *uuid.UUID
}

// CustomerRedemption is a redemption as its customer lists it, with the voucher it was
// for and its code.
type CustomerRedemption struct {
	entities.VoucherRedemption
	VoucherName     string
	VoucherImageURL *string
	VoucherType     string
	Code            *string
	CodeExpiresAt   *time.Time
}

// VoucherRedemptionRepository stores redemptions and what they cost each budget
// (docs/rfc-enakgame.md §5.7, §7.4, §7.6).
type VoucherRedemptionRepository interface {
	// GetByKey returns a customer's redemption made with an Idempotency-Key, or nil.
	GetByKey(ctx context.Context, customerID uuid.UUID, idempotencyKey string) (*entities.VoucherRedemption, error)
	// CountForCustomer counts a customer's redemptions of a voucher that went through
	// or may still: COMPLETED and PENDING.
	CountForCustomer(ctx context.Context, customerID, voucherID uuid.UUID) (int64, error)
	CreateRedemption(ctx context.Context, redemption *entities.VoucherRedemption) error
	// ListCustomerRedemptions returns a page of a customer's redemptions, newest first,
	// and the total.
	ListCustomerRedemptions(ctx context.Context, customerID uuid.UUID, offset, limit int) ([]CustomerRedemption, int64, error)

	// PointSources follows the lots a debit drew from back to their root lots and
	// sums the EnakPoint per source type and budget (§7.6). Exchanges, transfers and
	// refunds are walked through, since their lots point at the lots they came from.
	PointSources(ctx context.Context, debitTransactionID uuid.UUID) ([]RedemptionPointSource, error)

	GetRedemption(ctx context.Context, id uuid.UUID) (*entities.VoucherRedemption, error)
	// MarkCompleted settles a PENDING redemption with the provider's voucher, and
	// reports false when it was no longer PENDING.
	MarkCompleted(ctx context.Context, id uuid.UUID, code, ref *string, at time.Time) (bool, error)
	// MarkFailed settles a PENDING redemption as failed, with the refund of its
	// EnakPoint, and reports false when it was no longer PENDING.
	MarkFailed(ctx context.Context, id, refundTransactionID uuid.UUID, reason string) (bool, error)
	// TouchPending counts one more unanswered call to the provider and returns the
	// count; 0 when the redemption is no longer PENDING.
	TouchPending(ctx context.Context, id uuid.UUID) (int, error)
	// ClaimStalePending takes at most limit PENDING redemptions untouched since before,
	// oldest first, and touches them, so another instance leaves them alone until they
	// go stale again.
	ClaimStalePending(ctx context.Context, before time.Time, limit int) ([]entities.VoucherRedemption, error)
	CreateCosts(ctx context.Context, costs []entities.VoucherRedemptionCost) error
	ListCosts(ctx context.Context, redemptionID uuid.UUID) ([]entities.VoucherRedemptionCost, error)
}

type voucherRedemptionRepository struct {
	db *gorm.DB
}

func NewVoucherRedemptionRepository(db *gorm.DB) VoucherRedemptionRepository {
	return &voucherRedemptionRepository{db: db}
}

func (r *voucherRedemptionRepository) GetByKey(ctx context.Context, customerID uuid.UUID, idempotencyKey string) (*entities.VoucherRedemption, error) {
	var redemption entities.VoucherRedemption
	err := DBFromContext(ctx, r.db).WithContext(ctx).
		Where("customer_id = ? AND idempotency_key = ?", customerID, idempotencyKey).First(&redemption).Error
	if errors.Is(err, gorm.ErrRecordNotFound) {
		return nil, nil
	}
	if err != nil {
		return nil, fmt.Errorf("failed to read voucher redemption: %w", err)
	}
	return &redemption, nil
}

func (r *voucherRedemptionRepository) CountForCustomer(ctx context.Context, customerID, voucherID uuid.UUID) (int64, error) {
	var count int64
	err := DBFromContext(ctx, r.db).WithContext(ctx).Model(&entities.VoucherRedemption{}).
		Where("customer_id = ? AND voucher_id = ? AND status IN ?", customerID, voucherID,
			[]string{constants.VoucherRedemptionCompleted, constants.VoucherRedemptionPending}).
		Count(&count).Error
	if err != nil {
		return 0, fmt.Errorf("failed to count voucher redemptions: %w", err)
	}
	return count, nil
}

func (r *voucherRedemptionRepository) CreateRedemption(ctx context.Context, redemption *entities.VoucherRedemption) error {
	if err := DBFromContext(ctx, r.db).WithContext(ctx).Create(redemption).Error; err != nil {
		return fmt.Errorf("failed to create voucher redemption: %w", err)
	}
	return nil
}

func (r *voucherRedemptionRepository) ListCustomerRedemptions(ctx context.Context, customerID uuid.UUID, offset, limit int) ([]CustomerRedemption, int64, error) {
	db := DBFromContext(ctx, r.db).WithContext(ctx)
	var total int64
	if err := db.Model(&entities.VoucherRedemption{}).Where("customer_id = ?", customerID).Count(&total).Error; err != nil {
		return nil, 0, fmt.Errorf("failed to count voucher redemptions: %w", err)
	}
	var redemptions []entities.VoucherRedemption
	err := db.Where("customer_id = ?", customerID).Order("created_at DESC, id").Offset(offset).Limit(limit).Find(&redemptions).Error
	if err != nil {
		return nil, 0, fmt.Errorf("failed to list voucher redemptions: %w", err)
	}
	voucherIDs, codeIDs := []uuid.UUID{}, []uuid.UUID{}
	for _, red := range redemptions {
		voucherIDs = append(voucherIDs, red.VoucherID)
		if red.VoucherCodeID != nil {
			codeIDs = append(codeIDs, *red.VoucherCodeID)
		}
	}
	vouchers := map[uuid.UUID]entities.Voucher{}
	if len(voucherIDs) > 0 {
		var rows []entities.Voucher
		if err := db.Where("id IN ?", voucherIDs).Find(&rows).Error; err != nil {
			return nil, 0, fmt.Errorf("failed to read redeemed vouchers: %w", err)
		}
		for _, v := range rows {
			vouchers[v.ID] = v
		}
	}
	codes := map[uuid.UUID]entities.VoucherCode{}
	if len(codeIDs) > 0 {
		var rows []entities.VoucherCode
		if err := db.Where("id IN ?", codeIDs).Find(&rows).Error; err != nil {
			return nil, 0, fmt.Errorf("failed to read redeemed codes: %w", err)
		}
		for _, c := range rows {
			codes[c.ID] = c
		}
	}
	out := make([]CustomerRedemption, 0, len(redemptions))
	for _, red := range redemptions {
		v := vouchers[red.VoucherID]
		item := CustomerRedemption{VoucherRedemption: red, VoucherName: v.Name, VoucherImageURL: v.ImageURL, VoucherType: v.VoucherType, Code: red.ExternalCode}
		if red.VoucherCodeID != nil {
			if c, ok := codes[*red.VoucherCodeID]; ok {
				code := c.Code
				item.Code, item.CodeExpiresAt = &code, c.ExpiresAt
			}
		}
		out = append(out, item)
	}
	return out, total, nil
}

func (r *voucherRedemptionRepository) PointSources(ctx context.Context, debitTransactionID uuid.UUID) ([]RedemptionPointSource, error) {
	var rows []struct {
		Points     int64
		SourceType string
		BudgetID   *string
	}
	err := DBFromContext(ctx, r.db).WithContext(ctx).Raw(`
		WITH RECURSIVE chain AS (
			SELECT a.lot_id AS spent_lot, a.amount AS points, l.origin_lot_id, l.source_transaction_id
			FROM wallet_lot_allocations a
			JOIN wallet_lots l ON l.id = a.lot_id
			WHERE a.transaction_id = ?
		  UNION ALL
			SELECT c.spent_lot, c.points, p.origin_lot_id, p.source_transaction_id
			FROM chain c
			JOIN wallet_lots p ON p.id = c.origin_lot_id
		)
		SELECT SUM(c.points) AS points, t.type AS source_type, gsr.budget_id::text AS budget_id
		FROM chain c
		JOIN wallet_transactions t ON t.id = c.source_transaction_id
		LEFT JOIN game_session_rewards gsr ON gsr.wallet_transaction_id = t.id
		WHERE c.origin_lot_id IS NULL
		GROUP BY t.type, gsr.budget_id
		ORDER BY t.type, gsr.budget_id`, debitTransactionID).Scan(&rows).Error
	if err != nil {
		return nil, fmt.Errorf("failed to trace redeemed EnakPoint: %w", err)
	}
	out := make([]RedemptionPointSource, 0, len(rows))
	for _, row := range rows {
		s := RedemptionPointSource{Points: row.Points, SourceType: row.SourceType}
		if row.BudgetID != nil {
			id, err := uuid.Parse(*row.BudgetID)
			if err != nil {
				return nil, fmt.Errorf("bad budget id %q: %w", *row.BudgetID, err)
			}
			s.BudgetID = &id
		}
		out = append(out, s)
	}
	return out, nil
}

func (r *voucherRedemptionRepository) CreateCosts(ctx context.Context, costs []entities.VoucherRedemptionCost) error {
	if len(costs) == 0 {
		return nil
	}
	if err := DBFromContext(ctx, r.db).WithContext(ctx).Create(&costs).Error; err != nil {
		return fmt.Errorf("failed to record redemption costs: %w", err)
	}
	return nil
}

func (r *voucherRedemptionRepository) ListCosts(ctx context.Context, redemptionID uuid.UUID) ([]entities.VoucherRedemptionCost, error) {
	var costs []entities.VoucherRedemptionCost
	err := DBFromContext(ctx, r.db).WithContext(ctx).Where("redemption_id = ?", redemptionID).
		Order("cost DESC, source_type").Find(&costs).Error
	if err != nil {
		return nil, fmt.Errorf("failed to list redemption costs: %w", err)
	}
	return costs, nil
}

func (r *voucherRedemptionRepository) GetRedemption(ctx context.Context, id uuid.UUID) (*entities.VoucherRedemption, error) {
	var redemption entities.VoucherRedemption
	if err := DBFromContext(ctx, r.db).WithContext(ctx).Where("id = ?", id).First(&redemption).Error; err != nil {
		return nil, fmt.Errorf("failed to read voucher redemption: %w", err)
	}
	return &redemption, nil
}

func (r *voucherRedemptionRepository) MarkCompleted(ctx context.Context, id uuid.UUID, code, ref *string, at time.Time) (bool, error) {
	result := DBFromContext(ctx, r.db).WithContext(ctx).Exec(`
		UPDATE voucher_redemptions SET status = ?, external_code = ?, external_ref = ?, completed_at = ?,
			attempts = attempts + 1, updated_at = NOW()
		WHERE id = ? AND status = ?`,
		constants.VoucherRedemptionCompleted, code, ref, at, id, constants.VoucherRedemptionPending)
	if result.Error != nil {
		return false, fmt.Errorf("failed to complete voucher redemption: %w", result.Error)
	}
	return result.RowsAffected == 1, nil
}

func (r *voucherRedemptionRepository) MarkFailed(ctx context.Context, id, refundTransactionID uuid.UUID, reason string) (bool, error) {
	if len(reason) > 255 {
		reason = reason[:255]
	}
	result := DBFromContext(ctx, r.db).WithContext(ctx).Exec(`
		UPDATE voucher_redemptions SET status = ?, refund_transaction_id = ?, failure_reason = ?,
			attempts = attempts + 1, updated_at = NOW()
		WHERE id = ? AND status = ?`,
		constants.VoucherRedemptionFailed, refundTransactionID, reason, id, constants.VoucherRedemptionPending)
	if result.Error != nil {
		return false, fmt.Errorf("failed to fail voucher redemption: %w", result.Error)
	}
	return result.RowsAffected == 1, nil
}

func (r *voucherRedemptionRepository) TouchPending(ctx context.Context, id uuid.UUID) (int, error) {
	var attempts []int
	err := DBFromContext(ctx, r.db).WithContext(ctx).Raw(`
		UPDATE voucher_redemptions SET attempts = attempts + 1, updated_at = NOW()
		WHERE id = ? AND status = ? RETURNING attempts`, id, constants.VoucherRedemptionPending).Scan(&attempts).Error
	if err != nil {
		return 0, fmt.Errorf("failed to touch voucher redemption: %w", err)
	}
	if len(attempts) == 0 {
		return 0, nil
	}
	return attempts[0], nil
}

func (r *voucherRedemptionRepository) ClaimStalePending(ctx context.Context, before time.Time, limit int) ([]entities.VoucherRedemption, error) {
	var claimed []entities.VoucherRedemption
	err := DBFromContext(ctx, r.db).WithContext(ctx).Raw(`
		UPDATE voucher_redemptions SET updated_at = NOW()
		WHERE id IN (
			SELECT id FROM voucher_redemptions
			WHERE status = ? AND updated_at <= ?
			ORDER BY updated_at, id
			LIMIT ?
			FOR UPDATE SKIP LOCKED)
		RETURNING *`, constants.VoucherRedemptionPending, before, limit).Scan(&claimed).Error
	if err != nil {
		return nil, fmt.Errorf("failed to claim pending voucher redemptions: %w", err)
	}
	return claimed, nil
}