package pay

import (
	"context"
	"crypto/md5"
	"encoding/hex"
	"encoding/xml"
	"fmt"
	"math/rand"
	"sort"
	"strings"
	"time"

	"github.com/cloudprint/cloudprint-backend/config"
	"github.com/iGoogle-ink/gopay"
)

// RandomString generates a random string with given length
func RandomString(length int) string {
	const charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	b := make([]byte, length)
	for i := range b {
		b[i] = charset[rand.Intn(len(charset))]
	}
	return string(b)
}

type WeChatPay struct {
	client *gopay.WxPayClient
	config *config.WeChatConfig
}

type UnifiedOrderResponse struct {
	ReturnCode    string `xml:"return_code"`
	ReturnMsg     string `xml:"return_msg"`
	ResultCode    string `xml:"result_code"`
	PrepayID      string `xml:"prepay_id,omitempty"`
	CodeURL       string `xml:"code_url,omitempty"`
	MWebURL       string `xml:"mweb_url,omitempty"`
	ErrCode       string `xml:"err_code,omitempty"`
	ErrMsg        string `xml:"err_msg,omitempty"`
	TransactionID string `xml:"transaction_id,omitempty"`
	TradeState    string `xml:"trade_state,omitempty"`
	TotalFee      int    `xml:"total_fee,omitempty"`
}

type PayCallback struct {
	ReturnCode    string `xml:"return_code"`
	ReturnMsg     string `xml:"return_msg"`
	AppID         string `xml:"appid"`
	MchID         string `xml:"mch_id"`
	NonceStr      string `xml:"nonce_str"`
	Sign          string `xml:"sign"`
	ResultCode    string `xml:"result_code"`
	TransactionID string `xml:"transaction_id"`
	OutTradeNo    string `xml:"out_trade_no"`
	TotalFee      int    `xml:"total_fee"`
	TimeEnd       string `xml:"time_end"`
}

func NewWeChatPay(cfg *config.WeChatConfig) *WeChatPay {
	client := gopay.NewWxPayClient(cfg.AppID, cfg.MchID, cfg.ApiKey, cfg.NotifyURL)
	if cfg.CertPath != "" {
		client.SetCertFilePath(cfg.CertPath)
	}
	return &WeChatPay{
		client: client,
		config: cfg,
	}
}

func (p *WeChatPay) createSign(params map[string]string) string {
	keys := make([]string, 0, len(params))
	for k := range params {
		keys = append(keys, k)
	}
	sort.Strings(keys)

	var signParts []string
	for _, k := range keys {
		if params[k] != "" && k != "sign" {
			signParts = append(signParts, fmt.Sprintf("%s=%s", k, params[k]))
		}
	}
	signStr := strings.Join(signParts, "&")
	signStr += "&key=" + p.config.ApiKey

	md5Hash := md5.New()
	md5Hash.Write([]byte(signStr))
	return strings.ToUpper(hex.EncodeToString(md5Hash.Sum(nil)))
}

func (p *WeChatPay) UnifiedOrder(ctx context.Context, orderNo string, amount float64, description, openID, clientIP string) (*UnifiedOrderResponse, error) {
	nonceStr := RandomString(32)
	totalFee := int(amount * 100) // Convert to fen

	// Build request body
	body := gopay.UnifiedOrder{
		AppID:          p.config.AppID,
		MchID:          p.config.MchID,
		NonceStr:       nonceStr,
		Body:           description,
		OutTradeNo:     orderNo,
		TotalFee:       totalFee,
		SpbillCreateIP: clientIP,
		NotifyURL:      p.config.NotifyURL,
		TradeType:      "JSAPI",
		OpenID:         openID,
	}

	// Use go-pay client to call unified order
	resp, err := p.client.UnifiedOrder(ctx, body)
	if err != nil {
		return nil, fmt.Errorf("unified order failed: %w", err)
	}

	result := &UnifiedOrderResponse{
		ReturnCode: resp.GetString("return_code"),
		ReturnMsg:  resp.GetString("return_msg"),
		ResultCode: resp.GetString("result_code"),
		PrepayID:   resp.GetString("prepay_id"),
		CodeURL:    resp.GetString("code_url"),
		MWebURL:    resp.GetString("mweb_url"),
		ErrCode:    resp.GetString("err_code"),
		ErrMsg:     resp.GetString("err_msg"),
	}

	return result, nil
}

func (p *WeChatPay) QueryOrder(ctx context.Context, orderNo string) (string, int, error) {
	nonceStr := RandomString(32)

	body := gopay.QueryOrder{
		AppID:      p.config.AppID,
		MchID:      p.config.MchID,
		NonceStr:   nonceStr,
		OutTradeNo: orderNo,
	}

	resp, err := p.client.QueryOrder(ctx, body)
	if err != nil {
		return "", 0, err
	}

	tradeState := resp.GetString("trade_state")
	totalFee := resp.GetInt("total_fee")

	return tradeState, totalFee, nil
}

func (p *WeChatPay) ParseCallback(body []byte) (*PayCallback, error) {
	var callback PayCallback
	if err := xml.Unmarshal(body, &callback); err != nil {
		return nil, fmt.Errorf("failed to parse callback: %w", err)
	}
	return &callback, nil
}

func (p *WeChatPay) ValidateCallback(callback *PayCallback) bool {
	params := map[string]string{
		"return_code":    callback.ReturnCode,
		"return_msg":     callback.ReturnMsg,
		"appid":          callback.AppID,
		"mch_id":         callback.MchID,
		"nonce_str":      callback.NonceStr,
		"result_code":    callback.ResultCode,
		"transaction_id": callback.TransactionID,
		"out_trade_no":   callback.OutTradeNo,
		"total_fee":      fmt.Sprintf("%d", callback.TotalFee),
		"time_end":       callback.TimeEnd,
	}

	expectedSign := p.createSign(params)
	return callback.Sign == expectedSign
}

func (p *WeChatPay) GenerateJSAPIPayParams(prepayID string) (map[string]string, error) {
	nonceStr := RandomString(32)
	timestamp := fmt.Sprintf("%d", time.Now().Unix())

	params := map[string]string{
		"appId":     p.config.AppID,
		"timeStamp": timestamp,
		"nonceStr":  nonceStr,
		"package":   "prepay_id=" + prepayID,
		"signType":  "MD5",
	}

	paySign := p.createSign(map[string]string{
		"appId":     p.config.AppID,
		"timeStamp": timestamp,
		"nonceStr":  nonceStr,
		"package":   "prepay_id=" + prepayID,
		"signType":  "MD5",
	})

	params["paySign"] = paySign
	return params, nil
}