package service

import (
	"context"
	"fmt"
	"log/slog"
	"math"
	"strconv"
	"strings"
	"time"

	dbent "github.com/Wei-Shaw/sub2api/ent"
	"github.com/Wei-Shaw/sub2api/ent/paymentorder"
	"github.com/Wei-Shaw/sub2api/internal/payment"
	"github.com/Wei-Shaw/sub2api/internal/payment/provider"
	infraerrors "github.com/Wei-Shaw/sub2api/internal/pkg/errors"
)

// --- Order Creation ---

func (s *PaymentService) CreateOrder(ctx context.Context, req CreateOrderRequest) (*CreateOrderResponse, error) {
	if req.OrderType == "" {
		req.OrderType = payment.OrderTypeBalance
	}
	cfg, err := s.configService.GetPaymentConfig(ctx)
	if err != nil {
		return nil, fmt.Errorf("get payment config: %w", err)
	}
	if !cfg.Enabled {
		return nil, infraerrors.Forbidden("PAYMENT_DISABLED", "payment system is disabled")
	}
	plan, err := s.validateOrderInput(ctx, req, cfg)
	if err != nil {
		return nil, err
	}
	if err := s.checkCancelRateLimit(ctx, req.UserID, cfg); err != nil {
		return nil, err
	}
	user, err := s.userRepo.GetByID(ctx, req.UserID)
	if err != nil {
		return nil, fmt.Errorf("get user: %w", err)
	}
	if user.Status != payment.EntityStatusActive {
		return nil, infraerrors.Forbidden("USER_INACTIVE", "user account is disabled")
	}
	amount := req.Amount
	if plan != nil {
		amount = plan.Price
	}
	feeRate := s.getFeeRate(req.PaymentType)
	payAmountStr := payment.CalculatePayAmount(amount, feeRate)
	payAmount, _ := strconv.ParseFloat(payAmountStr, 64)
	order, err := s.createOrderInTx(ctx, req, user, plan, cfg, amount, feeRate, payAmount)
	if err != nil {
		return nil, err
	}
	resp, err := s.invokeProvider(ctx, order, req, cfg, payAmountStr, payAmount, plan)
	if err != nil {
		_, _ = s.entClient.PaymentOrder.UpdateOneID(order.ID).
			SetStatus(OrderStatusFailed).
			Save(ctx)
		return nil, err
	}
	return resp, nil
}

func (s *PaymentService) validateOrderInput(ctx context.Context, req CreateOrderRequest, cfg *PaymentConfig) (*dbent.SubscriptionPlan, error) {
	if req.OrderType == payment.OrderTypeBalance && cfg.BalanceDisabled {
		return nil, infraerrors.Forbidden("BALANCE_PAYMENT_DISABLED", "balance recharge has been disabled")
	}
	if req.OrderType == payment.OrderTypeSubscription {
		return s.validateSubOrder(ctx, req)
	}
	if math.IsNaN(req.Amount) || math.IsInf(req.Amount, 0) || req.Amount <= 0 {
		return nil, infraerrors.BadRequest("INVALID_AMOUNT", "amount must be a positive number")
	}
	if (cfg.MinAmount > 0 && req.Amount < cfg.MinAmount) || (cfg.MaxAmount > 0 && req.Amount > cfg.MaxAmount) {
		return nil, infraerrors.BadRequest("INVALID_AMOUNT", "amount out of range").
			WithMetadata(map[string]string{"min": fmt.Sprintf("%.2f", cfg.MinAmount), "max": fmt.Sprintf("%.2f", cfg.MaxAmount)})
	}
	return nil, nil
}

func (s *PaymentService) validateSubOrder(ctx context.Context, req CreateOrderRequest) (*dbent.SubscriptionPlan, error) {
	if req.PlanID == 0 {
		return nil, infraerrors.BadRequest("INVALID_INPUT", "subscription order requires a plan")
	}
	plan, err := s.configService.GetPlan(ctx, req.PlanID)
	if err != nil || !plan.ForSale {
		return nil, infraerrors.NotFound("PLAN_NOT_AVAILABLE", "plan not found or not for sale")
	}
	group, err := s.groupRepo.GetByID(ctx, plan.GroupID)
	if err != nil || group.Status != payment.EntityStatusActive {
		return nil, infraerrors.NotFound("GROUP_NOT_FOUND", "subscription group is no longer available")
	}
	if !group.IsSubscriptionType() {
		return nil, infraerrors.BadRequest("GROUP_TYPE_MISMATCH", "group is not a subscription type")
	}
	return plan, nil
}

func (s *PaymentService) createOrderInTx(ctx context.Context, req CreateOrderRequest, user *User, plan *dbent.SubscriptionPlan, cfg *PaymentConfig, amount, feeRate, payAmount float64) (*dbent.PaymentOrder, error) {
	tx, err := s.entClient.Tx(ctx)
	if err != nil {
		return nil, fmt.Errorf("begin transaction: %w", err)
	}
	defer func() { _ = tx.Rollback() }()
	if err := s.checkPendingLimit(ctx, tx, req.UserID, cfg.MaxPendingOrders); err != nil {
		return nil, err
	}
	if err := s.checkDailyLimit(ctx, tx, req.UserID, amount, cfg.DailyLimit); err != nil {
		return nil, err
	}
	tm := cfg.OrderTimeoutMin
	if tm <= 0 {
		tm = defaultOrderTimeoutMin
	}
	exp := time.Now().Add(time.Duration(tm) * time.Minute)
	b := tx.PaymentOrder.Create().
		SetUserID(req.UserID).
		SetUserEmail(user.Email).
		SetUserName(user.Username).
		SetNillableUserNotes(psNilIfEmpty(user.Notes)).
		SetAmount(amount).
		SetPayAmount(payAmount).
		SetFeeRate(feeRate).
		SetRechargeCode("").
		SetOutTradeNo(generateOutTradeNo()).
		SetPaymentType(req.PaymentType).
		SetPaymentTradeNo("").
		SetOrderType(req.OrderType).
		SetStatus(OrderStatusPending).
		SetExpiresAt(exp).
		SetClientIP(req.ClientIP).
		SetSrcHost(req.SrcHost)
	if req.SrcURL != "" {
		b.SetSrcURL(req.SrcURL)
	}
	if plan != nil {
		b.SetPlanID(plan.ID).SetSubscriptionGroupID(plan.GroupID).SetSubscriptionDays(psComputeValidityDays(plan.ValidityDays, plan.ValidityUnit))
	}
	order, err := b.Save(ctx)
	if err != nil {
		return nil, fmt.Errorf("create order: %w", err)
	}
	code := fmt.Sprintf("PAY-%d-%d", order.ID, time.Now().UnixNano()%100000)
	order, err = tx.PaymentOrder.UpdateOneID(order.ID).SetRechargeCode(code).Save(ctx)
	if err != nil {
		return nil, fmt.Errorf("set recharge code: %w", err)
	}
	if err := tx.Commit(); err != nil {
		return nil, fmt.Errorf("commit order transaction: %w", err)
	}
	return order, nil
}

func (s *PaymentService) checkPendingLimit(ctx context.Context, tx *dbent.Tx, userID int64, max int) error {
	if max <= 0 {
		max = defaultMaxPendingOrders
	}
	c, err := tx.PaymentOrder.Query().Where(paymentorder.UserIDEQ(userID), paymentorder.StatusEQ(OrderStatusPending)).Count(ctx)
	if err != nil {
		return fmt.Errorf("count pending orders: %w", err)
	}
	if c >= max {
		return infraerrors.TooManyRequests("TOO_MANY_PENDING", fmt.Sprintf("too many pending orders (max %d)", max)).
			WithMetadata(map[string]string{"max": strconv.Itoa(max)})
	}
	return nil
}

func (s *PaymentService) checkDailyLimit(ctx context.Context, tx *dbent.Tx, userID int64, amount, limit float64) error {
	if limit <= 0 {
		return nil
	}
	ts := psStartOfDayUTC(time.Now())
	orders, err := tx.PaymentOrder.Query().Where(paymentorder.UserIDEQ(userID), paymentorder.StatusIn(OrderStatusPaid, OrderStatusRecharging, OrderStatusCompleted), paymentorder.PaidAtGTE(ts)).All(ctx)
	if err != nil {
		return fmt.Errorf("query daily usage: %w", err)
	}
	var used float64
	for _, o := range orders {
		used += o.Amount
	}
	if used+amount > limit {
		return infraerrors.TooManyRequests("DAILY_LIMIT_EXCEEDED", fmt.Sprintf("daily recharge limit reached, remaining: %.2f", math.Max(0, limit-used)))
	}
	return nil
}

func (s *PaymentService) invokeProvider(ctx context.Context, order *dbent.PaymentOrder, req CreateOrderRequest, cfg *PaymentConfig, payAmountStr string, payAmount float64, plan *dbent.SubscriptionPlan) (*CreateOrderResponse, error) {
	// Select an instance across all providers that support the requested payment type.
	// This enables cross-provider load balancing (e.g. EasyPay + Alipay direct for "alipay").
	sel, err := s.loadBalancer.SelectInstance(ctx, "", req.PaymentType, payment.Strategy(cfg.LoadBalanceStrategy), payAmount)
	if err != nil {
		return nil, infraerrors.ServiceUnavailable("PAYMENT_GATEWAY_ERROR", fmt.Sprintf("payment method (%s) is not configured", req.PaymentType))
	}
	if sel == nil {
		return nil, infraerrors.TooManyRequests("NO_AVAILABLE_INSTANCE", "no available payment instance")
	}
	prov, err := provider.CreateProvider(sel.ProviderKey, sel.InstanceID, sel.Config)
	if err != nil {
		return nil, infraerrors.ServiceUnavailable("PAYMENT_GATEWAY_ERROR", "payment method is temporarily unavailable")
	}
	subject := s.buildPaymentSubject(plan, payAmountStr, cfg)
	outTradeNo := order.OutTradeNo
	pr, err := prov.CreatePayment(ctx, payment.CreatePaymentRequest{OrderID: outTradeNo, Amount: payAmountStr, PaymentType: req.PaymentType, Subject: subject, ClientIP: req.ClientIP, IsMobile: req.IsMobile, InstanceSubMethods: sel.SupportedTypes})
	if err != nil {
		slog.Error("[PaymentService] CreatePayment failed", "provider", sel.ProviderKey, "instance", sel.InstanceID, "error", err)
		return nil, infraerrors.ServiceUnavailable("PAYMENT_GATEWAY_ERROR", fmt.Sprintf("payment gateway error: %s", err.Error()))
	}
	_, err = s.entClient.PaymentOrder.UpdateOneID(order.ID).SetNillablePaymentTradeNo(psNilIfEmpty(pr.TradeNo)).SetNillablePayURL(psNilIfEmpty(pr.PayURL)).SetNillableQrCode(psNilIfEmpty(pr.QRCode)).SetNillableProviderInstanceID(psNilIfEmpty(sel.InstanceID)).Save(ctx)
	if err != nil {
		return nil, fmt.Errorf("update order with payment details: %w", err)
	}
	s.writeAuditLog(ctx, order.ID, "ORDER_CREATED", fmt.Sprintf("user:%d", req.UserID), map[string]any{"amount": req.Amount, "paymentType": req.PaymentType, "orderType": req.OrderType})
	return &CreateOrderResponse{OrderID: order.ID, Amount: order.Amount, PayAmount: payAmount, FeeRate: order.FeeRate, Status: OrderStatusPending, PaymentType: req.PaymentType, PayURL: pr.PayURL, QRCode: pr.QRCode, ClientSecret: pr.ClientSecret, ExpiresAt: order.ExpiresAt, PaymentMode: sel.PaymentMode}, nil
}

func (s *PaymentService) buildPaymentSubject(plan *dbent.SubscriptionPlan, payAmountStr string, cfg *PaymentConfig) string {
	if plan != nil {
		if plan.ProductName != "" {
			return plan.ProductName
		}
		return "Sub2API Subscription " + plan.Name
	}
	pf := strings.TrimSpace(cfg.ProductNamePrefix)
	sf := strings.TrimSpace(cfg.ProductNameSuffix)
	if pf != "" || sf != "" {
		return strings.TrimSpace(pf + " " + payAmountStr + " " + sf)
	}
	return "Sub2API " + payAmountStr + " CNY"
}

// --- Order Queries ---

func (s *PaymentService) GetOrder(ctx context.Context, orderID, userID int64) (*dbent.PaymentOrder, error) {
	o, err := s.entClient.PaymentOrder.Get(ctx, orderID)
	if err != nil {
		return nil, infraerrors.NotFound("NOT_FOUND", "order not found")
	}
	if o.UserID != userID {
		return nil, infraerrors.Forbidden("FORBIDDEN", "no permission for this order")
	}
	return o, nil
}

func (s *PaymentService) GetOrderByID(ctx context.Context, orderID int64) (*dbent.PaymentOrder, error) {
	o, err := s.entClient.PaymentOrder.Get(ctx, orderID)
	if err != nil {
		return nil, infraerrors.NotFound("NOT_FOUND", "order not found")
	}
	return o, nil
}

func (s *PaymentService) GetUserOrders(ctx context.Context, userID int64, p OrderListParams) ([]*dbent.PaymentOrder, int, error) {
	q := s.entClient.PaymentOrder.Query().Where(paymentorder.UserIDEQ(userID))
	if p.Status != "" {
		q = q.Where(paymentorder.StatusEQ(p.Status))
	}
	if p.OrderType != "" {
		q = q.Where(paymentorder.OrderTypeEQ(p.OrderType))
	}
	if p.PaymentType != "" {
		q = q.Where(paymentorder.PaymentTypeEQ(p.PaymentType))
	}
	total, err := q.Clone().Count(ctx)
	if err != nil {
		return nil, 0, fmt.Errorf("count user orders: %w", err)
	}
	ps, pg := applyPagination(p.PageSize, p.Page)
	orders, err := q.Order(dbent.Desc(paymentorder.FieldCreatedAt)).Limit(ps).Offset((pg - 1) * ps).All(ctx)
	if err != nil {
		return nil, 0, fmt.Errorf("query user orders: %w", err)
	}
	return orders, total, nil
}

// AdminListOrders returns a paginated list of orders. If userID > 0, filters by user.
func (s *PaymentService) AdminListOrders(ctx context.Context, userID int64, p OrderListParams) ([]*dbent.PaymentOrder, int, error) {
	q := s.entClient.PaymentOrder.Query()
	if userID > 0 {
		q = q.Where(paymentorder.UserIDEQ(userID))
	}
	if p.Status != "" {
		q = q.Where(paymentorder.StatusEQ(p.Status))
	}
	if p.OrderType != "" {
		q = q.Where(paymentorder.OrderTypeEQ(p.OrderType))
	}
	if p.PaymentType != "" {
		q = q.Where(paymentorder.PaymentTypeEQ(p.PaymentType))
	}
	if p.Keyword != "" {
		q = q.Where(paymentorder.Or(
			paymentorder.OutTradeNoContainsFold(p.Keyword),
			paymentorder.UserEmailContainsFold(p.Keyword),
			paymentorder.UserNameContainsFold(p.Keyword),
		))
	}
	total, err := q.Clone().Count(ctx)
	if err != nil {
		return nil, 0, fmt.Errorf("count admin orders: %w", err)
	}
	ps, pg := applyPagination(p.PageSize, p.Page)
	orders, err := q.Order(dbent.Desc(paymentorder.FieldCreatedAt)).Limit(ps).Offset((pg - 1) * ps).All(ctx)
	if err != nil {
		return nil, 0, fmt.Errorf("query admin orders: %w", err)
	}
	return orders, total, nil
}
