package channel

import (
	"bytes"
	"context"
	"crypto"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"crypto/x509"
	"encoding/base64"
	"encoding/json"
	"encoding/pem"
	"errors"
	"fmt"
	"io"
	"math"
	"net/http"
	"os"
	"strings"
	"time"

	"wails-app/internal/config"
)

const (
	wechatAPIBase   = "https://api.mch.weixin.qq.com"
	wechatNativePay = "/v3/pay/transactions/native"
	wechatQueryByID = "/v3/pay/transactions/out-trade-no/"
)

// WechatChannel 微信支付 Native 扫码（APIv3）。
// 到账确认走查单接口（ADR-0002）；notify_url 仅透传给微信做预留挂点，
// 系统内没有回调端点。v1 未校验应答的微信平台签名（查询应答为明文 JSON），
// 商户私钥签名请求已启用。
type WechatChannel struct {
	appID      string
	mchID      string
	serialNo   string
	privateKey *rsa.PrivateKey
	notifyURL  string
	currency   string
	client     *http.Client
}

func NewWechatChannelFromConfig(cfg config.WechatPay) (*WechatChannel, error) {
	if !cfg.Enabled {
		return nil, errors.New("微信支付未启用")
	}
	if cfg.AppID == "" || cfg.MchID == "" || cfg.SerialNo == "" || cfg.PrivateKeyPath == "" {
		return nil, errors.New("微信支付商户配置不完整（app-id/mch-id/serial-no/private-key-path）")
	}
	pemBytes, err := os.ReadFile(cfg.PrivateKeyPath)
	if err != nil {
		return nil, fmt.Errorf("读取商户私钥失败: %w", err)
	}
	key, err := parsePrivateKey(pemBytes)
	if err != nil {
		return nil, err
	}
	currency := strings.ToUpper(strings.TrimSpace(cfg.Currency))
	if currency == "" {
		currency = "CNY"
	}
	return &WechatChannel{
		appID: cfg.AppID, mchID: cfg.MchID, serialNo: cfg.SerialNo,
		privateKey: key, notifyURL: cfg.NotifyURL, currency: currency,
		client: &http.Client{Timeout: 10 * time.Second},
	}, nil
}

func parsePrivateKey(pemBytes []byte) (*rsa.PrivateKey, error) {
	for {
		block, rest := pem.Decode(pemBytes)
		if block == nil {
			return nil, errors.New("商户私钥 PEM 解析失败")
		}
		if key, err := x509.ParsePKCS1PrivateKey(block.Bytes); err == nil {
			return key, nil
		}
		if key, err := x509.ParsePKCS8PrivateKey(block.Bytes); err == nil {
			if rsaKey, ok := key.(*rsa.PrivateKey); ok {
				return rsaKey, nil
			}
			return nil, errors.New("私钥不是 RSA 类型")
		}
		pemBytes = rest
	}
}

func (w *WechatChannel) Code() string { return ChannelWechat }

type wechatNativeResp struct {
	CodeURL string `json:"code_url"`
	Message string `json:"message"`
}

func (w *WechatChannel) CreateOrder(ctx context.Context, req CreateOrderRequest) (CreateOrderResult, error) {
	total, err := yuanToFen(req.Amount)
	if err != nil {
		return CreateOrderResult{}, err
	}
	body := map[string]interface{}{
		"appid":        w.appID,
		"mchid":        w.mchID,
		"description":  req.Description,
		"out_trade_no": req.OrderNo,
		"amount":       map[string]interface{}{"total": total, "currency": w.currency},
	}
	if w.notifyURL != "" {
		body["notify_url"] = w.notifyURL
	}
	var resp wechatNativeResp
	if err := w.call(ctx, http.MethodPost, wechatNativePay, body, &resp); err != nil {
		return CreateOrderResult{}, err
	}
	if resp.CodeURL == "" {
		return CreateOrderResult{}, fmt.Errorf("微信下单未返回 code_url: %s", resp.Message)
	}
	return CreateOrderResult{CodeURL: resp.CodeURL}, nil
}

type wechatQueryResp struct {
	TradeState    string `json:"trade_state"`
	TransactionID string `json:"transaction_id"`
	OutTradeNo    string `json:"out_trade_no"`
}

func (w *WechatChannel) QueryOrder(ctx context.Context, orderNo string) (QueryOrderResult, error) {
	path := wechatQueryByID + orderNo + "?mchid=" + w.mchID
	var resp wechatQueryResp
	if err := w.call(ctx, http.MethodGet, path, nil, &resp); err != nil {
		return QueryOrderResult{}, err
	}
	switch resp.TradeState {
	case "SUCCESS":
		return QueryOrderResult{Status: QueryPaid, TransactionID: resp.TransactionID}, nil
	case "CLOSED", "REVOKED", "PAYERROR":
		return QueryOrderResult{Status: QueryClosed}, nil
	default: // NOTPAY, USERPAYING 等
		return QueryOrderResult{Status: QueryPending}, nil
	}
}

// call 发起微信 APIv3 请求并用商户私钥签名（WECHATPAY2-SHA256withRSA）。
func (w *WechatChannel) call(ctx context.Context, method, path string, body interface{}, out interface{}) error {
	var bodyBytes []byte
	if body != nil {
		var err error
		bodyBytes, err = json.Marshal(body)
		if err != nil {
			return err
		}
	}
	req, err := http.NewRequestWithContext(ctx, method, wechatAPIBase+path, bytes.NewReader(bodyBytes))
	if err != nil {
		return err
	}
	authorization, err := w.authorizationHeader(method, path, bodyBytes)
	if err != nil {
		return err
	}
	req.Header.Set("Authorization", authorization)
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Accept", "application/json")
	req.Header.Set("User-Agent", "smart-parking-exit-kiosk")

	resp, err := w.client.Do(req)
	if err != nil {
		return fmt.Errorf("微信支付请求失败: %w", err)
	}
	defer resp.Body.Close()
	respBytes, err := io.ReadAll(io.LimitReader(resp.Body, 1<<20))
	if err != nil {
		return err
	}
	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("微信支付接口错误 HTTP %d: %s", resp.StatusCode, truncate(respBytes, 300))
	}
	if out != nil && len(respBytes) > 0 {
		if err := json.Unmarshal(respBytes, out); err != nil {
			return fmt.Errorf("微信支付应答解析失败: %w", err)
		}
	}
	return nil
}

func (w *WechatChannel) authorizationHeader(method, path string, body []byte) (string, error) {
	timestamp := fmt.Sprintf("%d", time.Now().Unix())
	nonce, err := randomNonce()
	if err != nil {
		return "", err
	}
	message := strings.Join([]string{method, path, timestamp, nonce, string(body)}, "\n") + "\n"
	digest := sha256.Sum256([]byte(message))
	signature, err := rsa.SignPKCS1v15(rand.Reader, w.privateKey, crypto.SHA256, digest[:])
	if err != nil {
		return "", fmt.Errorf("微信支付签名失败: %w", err)
	}
	return fmt.Sprintf(`WECHATPAY2-SHA256withRSA mchid="%s",nonce_str="%s",signature="%s",timestamp="%s",serial_no="%s"`,
		w.mchID, nonce, base64.StdEncoding.EncodeToString(signature), timestamp, w.serialNo), nil
}

func randomNonce() (string, error) {
	buf := make([]byte, 16)
	if _, err := rand.Read(buf); err != nil {
		return "", err
	}
	return base64.RawURLEncoding.EncodeToString(buf), nil
}

// yuanToFen 金额（元）转分，超出两位小数视为非法。
func yuanToFen(amount float64) (int64, error) {
	if math.IsNaN(amount) || math.IsInf(amount, 0) || amount < 0 {
		return 0, errors.New("支付金额必须是有限的非负数")
	}
	fen := math.Round(amount * 100)
	if math.Abs(fen-amount*100) > 0.51 {
		return 0, fmt.Errorf("支付金额精度超限: %.4f", amount)
	}
	return int64(fen), nil
}

func truncate(b []byte, n int) string {
	if len(b) <= n {
		return string(b)
	}
	return string(b[:n]) + "..."
}