package channel

import (
	"context"
	"errors"
	"fmt"
	"net/http"
	"time"

	"github.com/wechatpay-apiv3/wechatpay-go/core"
	"github.com/wechatpay-apiv3/wechatpay-go/core/auth/verifiers"
	"github.com/wechatpay-apiv3/wechatpay-go/core/downloader"
	"github.com/wechatpay-apiv3/wechatpay-go/core/notify"
	"github.com/wechatpay-apiv3/wechatpay-go/core/option"
	"github.com/wechatpay-apiv3/wechatpay-go/services/payments"
	"github.com/wechatpay-apiv3/wechatpay-go/services/payments/native"
	"github.com/wechatpay-apiv3/wechatpay-go/utils"

	"github.com/wangjia/pay/internal/model"
	"github.com/wangjia/pay/internal/util"
)

// wechatChannel 微信支付 V3 · Native（扫码）实现。
// PC 网站场景微信只提供 Native 扫码（无支付宝那种网页跳转收银台），所以：
//   - PreCreate → Native 下单，返回 code_url（前端经 /qrcode 渲染成二维码）
//   - PagePay   → 不适用，返回错误引导改用扫码
//   - VerifyNotify / Query → 回调解密验签 / 主动查单
type wechatChannel struct {
	mchID   string
	appID   string
	client  *core.Client
	native  *native.NativeApiService
	handler *notify.Handler
}

func newWechat(m *model.Merchant) (Channel, error) {
	if m.MchID == "" || m.WxAppID == "" || m.WxPrivateKey == "" || m.CertSerial == "" || m.APIv3Key == "" {
		return nil, fmt.Errorf("商户 %s 的微信凭证不完整（mch_id/wx_app_id/cert_serial/wx_private_key/apiv3_key）", m.Code)
	}

	mchPrivateKey, err := utils.LoadPrivateKey(m.WxPrivateKey)
	if err != nil {
		return nil, fmt.Errorf("加载微信商户私钥失败: %w", err)
	}

	// 初始化时自动下载并周期性更新微信支付平台证书（需公网可达微信 API）。
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	client, err := core.NewClient(ctx, option.WithWechatPayAutoAuthCipher(
		m.MchID, m.CertSerial, mchPrivateKey, m.APIv3Key,
	))
	if err != nil {
		return nil, fmt.Errorf("初始化微信支付客户端失败: %w", err)
	}

	// 回调处理器：用平台证书验签 + APIv3 密钥解密。
	certVisitor := downloader.MgrInstance().GetCertificateVisitor(m.MchID)
	handler, err := notify.NewRSANotifyHandler(m.APIv3Key, verifiers.NewSHA256WithRSAVerifier(certVisitor))
	if err != nil {
		return nil, fmt.Errorf("初始化微信回调处理器失败: %w", err)
	}

	return &wechatChannel{
		mchID:   m.MchID,
		appID:   m.WxAppID,
		client:  client,
		native:  &native.NativeApiService{Client: client},
		handler: handler,
	}, nil
}

func (w *wechatChannel) Name() string { return "wechat" }

// PagePay 微信无网页跳转收银台（PC 网站走 Native 扫码），改用 PreCreate。
func (w *wechatChannel) PagePay(context.Context, CreateReq) (string, error) {
	return "", errors.New("微信支付无网页跳转收银台，请用扫码下单（CreateQR / PreCreate）")
}

// PreCreate Native 下单，返回 code_url 供渲染二维码。
func (w *wechatChannel) PreCreate(ctx context.Context, req CreateReq) (string, error) {
	cents, err := util.AmountToCents(req.Amount)
	if err != nil {
		return "", fmt.Errorf("金额换算失败: %w", err)
	}
	resp, _, err := w.native.Prepay(ctx, native.PrepayRequest{
		Appid:       core.String(w.appID),
		Mchid:       core.String(w.mchID),
		Description: core.String(req.Subject),
		OutTradeNo:  core.String(req.OutTradeNo),
		NotifyUrl:   core.String(req.NotifyURL),
		Amount: &native.Amount{
			Total:    core.Int64(cents),
			Currency: core.String("CNY"),
		},
	})
	if err != nil {
		return "", fmt.Errorf("微信 Native 下单失败: %w", err)
	}
	if resp.CodeUrl == nil || *resp.CodeUrl == "" {
		return "", errors.New("微信 Native 下单未返回 code_url")
	}
	return *resp.CodeUrl, nil
}

// VerifyNotify 解密验签微信异步回调，解析成统一结果。
func (w *wechatChannel) VerifyNotify(ctx context.Context, r *http.Request) (*NotifyResult, error) {
	tx := new(payments.Transaction)
	if _, err := w.handler.ParseNotifyRequest(ctx, r, tx); err != nil {
		return nil, fmt.Errorf("微信回调验签/解密失败: %w", err)
	}
	return txToNotifyResult(tx), nil
}

// Query 主动查单（out_trade_no 维度）。
func (w *wechatChannel) Query(ctx context.Context, outTradeNo string) (*QueryResult, error) {
	tx, _, err := w.native.QueryOrderByOutTradeNo(ctx, native.QueryOrderByOutTradeNoRequest{
		OutTradeNo: core.String(outTradeNo),
		Mchid:      core.String(w.mchID),
	})
	if err != nil {
		// 交易不存在等：视为未找到，交由上层决定（与支付宝实现一致）。
		return &QueryResult{Found: false}, nil
	}
	res := txToNotifyResult(tx)
	return &QueryResult{
		Found:      true,
		OutTradeNo: res.OutTradeNo,
		TradeNo:    res.TradeNo,
		Amount:     res.Amount,
		Paid:       res.Paid,
	}, nil
}

// txToNotifyResult 把微信交易对象归一化成本服务的统一结构（金额分→元字符串）。
func txToNotifyResult(tx *payments.Transaction) *NotifyResult {
	res := &NotifyResult{}
	if tx.OutTradeNo != nil {
		res.OutTradeNo = *tx.OutTradeNo
	}
	if tx.TransactionId != nil {
		res.TradeNo = *tx.TransactionId
	}
	if tx.Amount != nil && tx.Amount.Total != nil {
		res.Amount = util.CentsToAmount(*tx.Amount.Total)
	}
	if tx.Payer != nil && tx.Payer.Openid != nil {
		res.BuyerLogonID = *tx.Payer.Openid
	}
	// 交易状态：SUCCESS 视为已支付（其余 NOTPAY/CLOSED/REFUND 等均非成功）。
	res.Paid = tx.TradeState != nil && *tx.TradeState == "SUCCESS"
	return res
}