// File: ymt_v3_api/go.mod
```go
module ymt_v3_api

go 1.18
```

// File: ymt_v3_api/client.go
```go
package ymt_v3_api

import (
	"bytes"
	"context"
	"crypto/rsa"
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"time"
)

// Client 是营销开放平台 SDK 的客户端，封装了认证、加密、签名等逻辑。
type Client struct {
	httpClient  *http.Client
	baseURL     string
	appID       string
	privateKey  *rsa.PrivateKey
	publicKey   *rsa.PublicKey
	encryptKey  []byte
	encryptType string // "AES" 或 "SM4"
}

// Option 是客户端配置选项函数。
type Option func(*Client)

// WithBaseURL 设置 API 基础地址。
func WithBaseURL(url string) Option {
	return func(c *Client) {
		c.baseURL = url
	}
}

// WithTimeout 设置 HTTP 请求超时时间。
func WithTimeout(d time.Duration) Option {
	return func(c *Client) {
		c.httpClient.Timeout = d
	}
}

// WithHTTPClient 设置自定义的 HTTP 客户端。
func WithHTTPClient(client *http.Client) Option {
	return func(c *Client) {
		c.httpClient = client
	}
}

// WithEncryptType 设置业务参数加密方式，支持 "AES" (默认) 或 "SM4"。
func WithEncryptType(t string) Option {
	return func(c *Client) {
		c.encryptType = t
	}
}

// NewClient 创建一个新的客户端实例。
// appID: 应用 ID
// privateKey: 应用私钥（PEM 格式字符串）
// publicKey: 平台公钥（PEM 格式字符串）
// encryptKey: 业务参数加解密密钥（字符串，AES 或 SM4 密钥）
func NewClient(appID, privateKey, publicKey, encryptKey string, opts ...Option) (*Client, error) {
	priv, err := parsePrivateKey(privateKey)
	if err != nil {
		return nil, fmt.Errorf("parse private key: %w", err)
	}
	pub, err := parsePublicKey(publicKey)
	if err != nil {
		return nil, fmt.Errorf("parse public key: %w", err)
	}

	c := &Client{
		httpClient: &http.Client{
			Timeout: 30 * time.Second,
		},
		baseURL:     "https://market.api.86698.cn", // 默认正式环境
		appID:       appID,
		privateKey:  priv,
		publicKey:   pub,
		encryptKey:  []byte(encryptKey),
		encryptType: "AES",
	}
	for _, opt := range opts {
		opt(c)
	}
	return c, nil
}

// doRequest 执行一次完整的 API 调用：加密业务参数、签名、发送请求、解密响应。
func (c *Client) doRequest(ctx context.Context, path string, bizReq interface{}, bizResp interface{}) error {
	// 1. 业务参数序列化为排序 JSON 并加密
	ciphertext, err := c.encryptPayload(bizReq)
	if err != nil {
		return fmt.Errorf("encrypt payload: %w", err)
	}

	// 2. 生成时间戳
	timestamp := time.Now().Format("2006-01-02 15:04:05")

	// 3. 签名
	sign, err := c.sign(c.appID, timestamp, ciphertext)
	if err != nil {
		return fmt.Errorf("sign: %w", err)
	}

	// 4. 构建请求体
	reqBody := cipherRequest{Ciphertext: ciphertext}
	bodyBytes, err := json.Marshal(reqBody)
	if err != nil {
		return fmt.Errorf("marshal request body: %w", err)
	}

	// 5. 创建 HTTP 请求
	url := c.baseURL + path
	req, err := http.NewRequestWithContext(ctx, http.MethodPost, url, bytes.NewReader(bodyBytes))
	if err != nil {
		return fmt.Errorf("new request: %w", err)
	}
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("Appid", c.appID)
	req.Header.Set("Timestamp", timestamp)
	req.Header.Set("Sign", sign)

	// 6. 发送请求
	resp, err := c.httpClient.Do(req)
	if err != nil {
		return fmt.Errorf("http do: %w", err)
	}
	defer resp.Body.Close()

	respBytes, err := io.ReadAll(resp.Body)
	if err != nil {
		return fmt.Errorf("read response body: %w", err)
	}

	// 7. 解析公共响应
	var apiResp apiResponse
	if err := json.Unmarshal(respBytes, &apiResp); err != nil {
		return fmt.Errorf("unmarshal api response: %w", err)
	}

	if apiResp.Code != 200 {
		return &APIError{
			Code:    apiResp.Code,
			Message: apiResp.Message,
			Reason:  apiResp.Reason,
		}
	}

	// 8. 解密业务响应
	if apiResp.Data == nil || apiResp.Data.Ciphertext == "" {
		// 某些接口可能直接返回 data 对象（如查询接口文档示例中 data 直接包含字段，但实际是 ciphertext 为空？）
		// 根据文档，成功时 data.ciphertext 存在，但查询接口示例中 data 直接是业务字段，没有 ciphertext 包裹。
		// 仔细看文档：获取券码响应成功时 data 里有 ciphertext；券码查询响应示例中 data 直接是业务字段，没有 ciphertext。
		// 但文档说“响应中的 data.ciphertext 使用与请求相同的加密方式和 key 进行解密”，可能查询接口也加密了，但示例展示了解密后的。
		// 为了兼容，如果 data.ciphertext 为空，尝试直接将 data 整体反序列化为业务响应。
		// 这里我们统一处理：如果 ciphertext 非空则解密，否则直接解析 data 字段。
		var resp struct {
			Data json.RawMessage `json:"data"`
		}
		if err := json.Unmarshal(respBytes, &resp); err != nil {
			return fmt.Errorf("unmarshal data field: %w", err)
		}
		return json.Unmarshal(resp.Data, bizResp)
	}

	if err := c.decryptPayload(apiResp.Data.Ciphertext, bizResp); err != nil {
		return fmt.Errorf("decrypt payload: %w", err)
	}
	return nil
}

// encryptPayload 将业务请求对象加密为 ciphertext 字符串。
func (c *Client) encryptPayload(payload interface{}) (string, error) {
	plaintext, err := toSortedJSON(payload)
	if err != nil {
		return "", err
	}
	switch c.encryptType {
	case "SM4":
		return sm4CbcEncrypt(plaintext, c.encryptKey)
	default:
		return aesEcbEncrypt(plaintext, c.encryptKey)
	}
}

// decryptPayload 将 ciphertext 解密并反序列化到目标对象。
func (c *Client) decryptPayload(ciphertext string, target interface{}) error {
	var plaintext []byte
	var err error
	switch c.encryptType {
	case "SM4":
		plaintext, err = sm4CbcDecrypt(ciphertext, c.encryptKey)
	default:
		plaintext, err = aesEcbDecrypt(ciphertext, c.encryptKey)
	}
	if err != nil {
		return err
	}
	return json.Unmarshal(plaintext, target)
}

// sign 生成请求签名。
func (c *Client) sign(appID, timestamp, ciphertext string) (string, error) {
	data := appID + timestamp + ciphertext
	return rsaSign([]byte(data), c.privateKey)
}

// verifySign 验证回调签名。
func (c *Client) verifySign(appID, timestamp, ciphertext, sign string) error {
	data := appID + timestamp + ciphertext
	return rsaVerify([]byte(data), sign, c.publicKey)
}

// cipherRequest 请求体结构
type cipherRequest struct {
	Ciphertext string `json:"ciphertext"`
}

// apiResponse 公共响应结构
type apiResponse struct {
	Code    int         `json:"code"`
	Message string      `json:"message"`
	Reason  string      `json:"reason,omitempty"`
	Data    *cipherData `json:"data,omitempty"`
}

type cipherData struct {
	Ciphertext string `json:"ciphertext"`
}
```

// File: ymt_v3_api/types.go
```go
package ymt_v3_api

// OrderKeyRequest 获取券码请求参数
type OrderKeyRequest struct {
	OutBizNo    string `json:"out_biz_no"`
	ActivityNo  string `json:"activity_no"`
	Account     string `json:"account,omitempty"`
	NotifyURL   string `json:"notify_url,omitempty"`
}

// OrderKeyResponse 获取券码响应参数
type OrderKeyResponse struct {
	OutBizNo        string  `json:"out_biz_no"`
	TradeNo         string  `json:"trade_no"`
	Key             string  `json:"key,omitempty"`
	URL             string  `json:"url,omitempty"`
	ValidBeginTime  string  `json:"valid_begin_time,omitempty"`
	ValidEndTime    string  `json:"valid_end_time,omitempty"`
	UsableNum       uint32  `json:"usable_num"`
	UsageNum        uint32  `json:"usage_num"`
	Status          uint32  `json:"status"`
	SettlementPrice float64 `json:"settlement_price,omitempty"`
	Account         string  `json:"account,omitempty"`
}

// QueryKeyRequest 券码查询请求参数
type QueryKeyRequest struct {
	OutBizNo string `json:"out_biz_no,omitempty"`
	TradeNo  string `json:"trade_no,omitempty"`
}

// QueryKeyResponse 券码查询响应参数（与获取券码一致）
type QueryKeyResponse = OrderKeyResponse

// DiscardKeyRequest 券码作废请求参数
type DiscardKeyRequest struct {
	OutBizNo string `json:"out_biz_no,omitempty"`
	TradeNo  string `json:"trade_no,omitempty"`
}

// DiscardKeyResponse 券码作废响应参数
type DiscardKeyResponse struct {
	OutBizNo string `json:"out_biz_no"`
	TradeNo  string `json:"trade_no"`
	Status   uint32 `json:"status"`
}

// BatchOrderRequest 批量发卡请求参数
type BatchOrderRequest struct {
	OutBizNo   string `json:"out_biz_no"`
	ActivityNo string `json:"activity_no"`
	Number     int32  `json:"number"`
	NotifyURL  string `json:"notify_url,omitempty"`
}

// BatchOrderResponse 批量发卡响应参数
type BatchOrderResponse struct {
	OutBizNo string `json:"out_biz_no"`
	TradeNo  string `json:"trade_no"`
	Status   string `json:"status"`
}

// BatchQueryRequest 批量查询请求参数
type BatchQueryRequest struct {
	OutBizNo string `json:"out_biz_no,omitempty"`
	TradeNo  string `json:"trade_no,omitempty"`
}

// BatchQueryResponse 批量查询响应参数
type BatchQueryResponse struct {
	OutBizNo    string `json:"out_biz_no"`
	TradeNo     string `json:"trade_no"`
	Status      string `json:"status"`
	DownloadURL string `json:"download_url,omitempty"`
	ZipPassword string `json:"zip_password,omitempty"`
}
```

// File: ymt_v3_api/crypto.go
```go
package ymt_v3_api

import (
	"bytes"
	"crypto"
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"crypto/x509"
	"encoding/base64"
	"encoding/json"
	"encoding/pem"
	"errors"
	"fmt"
	"sort"
	"strings"
)

// ---------- AES-ECB 实现 ----------

// aesEcbEncrypt 使用 AES-ECB 模式加密，结果进行 Base64 编码。
func aesEcbEncrypt(plaintext []byte, key []byte) (string, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}
	plaintext = pkcs7Padding(plaintext, block.BlockSize())
	ciphertext := make([]byte, len(plaintext))
	// ECB 模式：逐块加密
	for i := 0; i < len(plaintext); i += block.BlockSize() {
		block.Encrypt(ciphertext[i:i+block.BlockSize()], plaintext[i:i+block.BlockSize()])
	}
	return base64.StdEncoding.EncodeToString(ciphertext), nil
}

// aesEcbDecrypt 解密 Base64 编码的 AES-ECB 密文。
func aesEcbDecrypt(ciphertext string, key []byte) ([]byte, error) {
	data, err := base64.StdEncoding.DecodeString(ciphertext)
	if err != nil {
		return nil, err
	}
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}
	if len(data)%block.BlockSize() != 0 {
		return nil, errors.New("ciphertext is not a multiple of the block size")
	}
	plaintext := make([]byte, len(data))
	for i := 0; i < len(data); i += block.BlockSize() {
		block.Decrypt(plaintext[i:i+block.BlockSize()], data[i:i+block.BlockSize()])
	}
	return pkcs7Unpadding(plaintext)
}

func pkcs7Padding(data []byte, blockSize int) []byte {
	padding := blockSize - len(data)%blockSize
	padtext := bytes.Repeat([]byte{byte(padding)}, padding)
	return append(data, padtext...)
}

func pkcs7Unpadding(data []byte) ([]byte, error) {
	length := len(data)
	if length == 0 {
		return nil, errors.New("invalid padding size")
	}
	unpadding := int(data[length-1])
	if unpadding > length {
		return nil, errors.New("invalid padding")
	}
	return data[:(length - unpadding)], nil
}

// ---------- SM4-CBC 实现 ----------

// sm4CbcEncrypt 使用 SM4-CBC 模式加密，IV 为 16 字节全 0，结果 Base64 编码。
func sm4CbcEncrypt(plaintext []byte, key []byte) (string, error) {
	block, err := newSM4Cipher(key)
	if err != nil {
		return "", err
	}
	plaintext = pkcs7Padding(plaintext, block.BlockSize())
	iv := make([]byte, block.BlockSize()) // 默认全 0 IV
	ciphertext := make([]byte, len(plaintext))
	mode := cipher.NewCBCEncrypter(block, iv)
	mode.CryptBlocks(ciphertext, plaintext)
	return base64.StdEncoding.EncodeToString(ciphertext), nil
}

// sm4CbcDecrypt 解密 Base64 编码的 SM4-CBC 密文。
func sm4CbcDecrypt(ciphertext string, key []byte) ([]byte, error) {
	data, err := base64.StdEncoding.DecodeString(ciphertext)
	if err != nil {
		return nil, err
	}
	block, err := newSM4Cipher(key)
	if err != nil {
		return nil, err
	}
	if len(data)%block.BlockSize() != 0 {
		return nil, errors.New("ciphertext is not a multiple of the block size")
	}
	iv := make([]byte, block.BlockSize())
	plaintext := make([]byte, len(data))
	mode := cipher.NewCBCDecrypter(block, iv)
	mode.CryptBlocks(plaintext, data)
	return pkcs7Unpadding(plaintext)
}

// ---------- SM4 算法实现（简化版，符合 GB/T 32907-2016） ----------

var sBox = [256]byte{
	0xd6, 0x90, 0xe9, 0xfe, 0xcc, 0xe1, 0x3d, 0xb7, 0x16, 0xb6, 0x14, 0xc2, 0x28, 0xfb, 0x2c, 0x05,
	0x2b, 0x67, 0x9a, 0x76, 0x2a, 0xbe, 0x04, 0xc3, 0xaa, 0x44, 0x13, 0x26, 0x49, 0x86, 0x06, 0x99,
	0x9c, 0x42, 0x50, 0xf4, 0x91, 0xef, 0x98, 0x7a, 0x33, 0x54, 0x0b, 0x43, 0xed, 0xcf, 0xac, 0x62,
	0xe4, 0xb3, 0x1c, 0xa9, 0xc9, 0x08, 0xe8, 0x95, 0x80, 0xdf, 0x94, 0xfa, 0x75, 0x8f, 0x3f, 0xa6,
	0x47, 0x07, 0xa7, 0xfc, 0xf3, 0x73, 0x17, 0xba, 0x83, 0x59, 0x3c, 0x19, 0xe6, 0x85, 0x4f, 0xa8,
	0x68, 0x6b, 0x81, 0xb2, 0x71, 0x64, 0xda, 0x8b, 0xf8, 0xeb, 0x0f, 0x4b, 0x70, 0x56, 0x9d, 0x35,
	0x1e, 0x24, 0x0e, 0x5e, 0x63, 0x58, 0xd1, 0xa2, 0x25, 0x22, 0x7c, 0x3b, 0x01, 0x21, 0x78, 0x87,
	0xd4, 0x00, 0x46, 0x57, 0x9f, 0xd3, 0x27, 0x52, 0x4c, 0x36, 0x02, 0xe7, 0xa0, 0xc4, 0xc8, 0x9e,
	0xea, 0xbf, 0x8a, 0xd2, 0x40, 0xc7, 0x38, 0xb5, 0xa3, 0xf7, 0xf2, 0xce, 0xf9, 0x61, 0x15, 0xa1,
	0xe0, 0xae, 0x5d, 0xa4, 0x9b, 0x34, 0x1a, 0x55, 0xad, 0x93, 0x32, 0x30, 0xf5, 0x8c, 0xb1, 0xe3,
	0x1d, 0xf6, 0xe2, 0x2e, 0x82, 0x66, 0xca, 0x60, 0xc0, 0x29, 0x23, 0xab, 0x0d, 0x53, 0x4e, 0x6f,
	0xd5, 0xdb, 0x37, 0x45, 0xde, 0xfd, 0x8e, 0x2f, 0x03, 0xff, 0x6a, 0x72, 0x6d, 0x6c, 0x5b, 0x51,
	0x8d, 0x1b, 0xaf, 0x92, 0xbb, 0xdd, 0xbc, 0x7f, 0x11, 0xd9, 0x5c, 0x41, 0x1f, 0x10, 0x5a, 0xd8,
	0x0a, 0xc1, 0x31, 0x88, 0xa5, 0xcd, 0x7b, 0xbd, 0x2d, 0x74, 0xd0, 0x12, 0xb8, 0xe5, 0xb4, 0xb0,
	0x89, 0x69, 0x97, 0x4a, 0x0c, 0x96, 0x77, 0x7e, 0x65, 0xb9, 0xf1, 0x09, 0xc5, 0x6e, 0xc6, 0x84,
	0x18, 0xf0, 0x7d, 0xec, 0x3a, 0xdc, 0x4d, 0x20, 0x79, 0xee, 0x5f, 0x3e, 0xd7, 0xcb, 0x39, 0x48,
}

var fk = [4]uint32{0xa3b1bac6, 0x56aa3350, 0x677d9197, 0xb27022dc}
var ck = [32]uint32{
	0x00070e15, 0x1c232a31, 0x383f464d, 0x545b6269,
	0x70777e85, 0x8c939aa1, 0xa8afb6bd, 0xc4cbd2d9,
	0xe0e7eef5, 0xfc030a11, 0x181f262d, 0x343b4249,
	0x50575e65, 0x6c737a81, 0x888f969d, 0xa4abb2b9,
	0xc0c7ced5, 0xdce3eaf1, 0xf8ff060d, 0x141b2229,
	0x30373e45, 0x4c535a61, 0x686f767d, 0x848b9299,
	0xa0a7aeb5, 0xbcc3cad1, 0xd8dfe6ed, 0xf4fb0209,
	0x10171e25, 0x2c333a41, 0x484f565d, 0x646b7279,
}

type sm4Cipher struct {
	enc []uint32
	dec []uint32
}

func newSM4Cipher(key []byte) (cipher.Block, error) {
	if len(key) != 16 {
		return nil, errors.New("SM4 key must be 16 bytes")
	}
	c := &sm4Cipher{}
	c.enc = make([]uint32, 32)
	c.dec = make([]uint32, 32)
	c.expandKey(key)
	return c, nil
}

func (c *sm4Cipher) BlockSize() int { return 16 }

func (c *sm4Cipher) Encrypt(dst, src []byte) {
	if len(src) < 16 || len(dst) < 16 {
		panic("sm4: invalid buffer")
	}
	x := bytesToUint32s(src)
	for i := 0; i < 32; i++ {
		x = sm4Round(x, c.enc[i])
	}
	putUint32s(dst, x)
}

func (c *sm4Cipher) Decrypt(dst, src []byte) {
	if len(src) < 16 || len(dst) < 16 {
		panic("sm4: invalid buffer")
	}
	x := bytesToUint32s(src)
	for i := 0; i < 32; i++ {
		x = sm4Round(x, c.dec[i])
	}
	putUint32s(dst, x)
}

func (c *sm4Cipher) expandKey(key []byte) {
	mk := bytesToUint32s(key)
	k := make([]uint32, 36)
	k[0] = mk[0] ^ fk[0]
	k[1] = mk[1] ^ fk[1]
	k[2] = mk[2] ^ fk[2]
	k[3] = mk[3] ^ fk[3]
	for i := 0; i < 32; i++ {
		k[i+4] = k[i] ^ sm4T(k[i+1]^k[i+2]^k[i+3]^ck[i])
		c.enc[i] = k[i+4]
		c.dec[31-i] = k[i+4]
	}
}

func sm4Round(x []uint32, rk uint32) []uint32 {
	return []uint32{
		x[1],
		x[2],
		x[3],
		x[0] ^ sm4T(x[1]^x[2]^x[3]^rk),
	}
}

func sm4T(x uint32) uint32 {
	return sm4L(sm4Tau(x))
}

func sm4Tau(a uint32) uint32 {
	return uint32(sBox[a>>24])<<24 |
		uint32(sBox[a>>16&0xff])<<16 |
		uint32(sBox[a>>8&0xff])<<8 |
		uint32(sBox[a&0xff])
}

func sm4L(b uint32) uint32 {
	return b ^ rotl(b, 2) ^ rotl(b, 10) ^ rotl(b, 18) ^ rotl(b, 24)
}

func rotl(x uint32, n uint) uint32 {
	return (x << n) | (x >> (32 - n))
}

func bytesToUint32s(b []byte) []uint32 {
	return []uint32{
		uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3]),
		uint32(b[4])<<24 | uint32(b[5])<<16 | uint32(b[6])<<8 | uint32(b[7]),
		uint32(b[8])<<24 | uint32(b[9])<<16 | uint32(b[10])<<8 | uint32(b[11]),
		uint32(b[12])<<24 | uint32(b[13])<<16 | uint32(b[14])<<8 | uint32(b[15]),
	}
}

func putUint32s(dst []byte, x []uint32) {
	_ = dst[15]
	dst[0] = byte(x[0] >> 24)
	dst[1] = byte(x[0] >> 16)
	dst[2] = byte(x[0] >> 8)
	dst[3] = byte(x[0])
	dst[4] = byte(x[1] >> 24)
	dst[5] = byte(x[1] >> 16)
	dst[6] = byte(x[1] >> 8)
	dst[7] = byte(x[1])
	dst[8] = byte(x[2] >> 24)
	dst[9] = byte(x[2] >> 16)
	dst[10] = byte(x[2] >> 8)
	dst[11] = byte(x[2])
	dst[12] = byte(x[3] >> 24)
	dst[13] = byte(x[3] >> 16)
	dst[14] = byte(x[3] >> 8)
	dst[15] = byte(x[3])
}

// ---------- RSA 签名与验签 ----------

// rsaSign 使用 RSA 私钥对数据进行 SHA256 签名，返回 Base64 编码的签名。
func rsaSign(data []byte, priv *rsa.PrivateKey) (string, error) {
	hashed := sha256.Sum256(data)
	sig, err := rsa.SignPKCS1v15(rand.Reader, priv, crypto.SHA256, hashed[:])
	if err != nil {
		return "", err
	}
	return base64.StdEncoding.EncodeToString(sig), nil
}

// rsaVerify 使用 RSA 公钥验证 Base64 编码的签名。
func rsaVerify(data []byte, sign string, pub *rsa.PublicKey) error {
	sig, err := base64.StdEncoding.DecodeString(sign)
	if err != nil {
		return err
	}
	hashed := sha256.Sum256(data)
	return rsa.VerifyPKCS1v15(pub, crypto.SHA256, hashed[:], sig)
}

// ---------- 密钥解析 ----------

func parsePrivateKey(pemStr string) (*rsa.PrivateKey, error) {
	block, _ := pem.Decode([]byte(pemStr))
	if block == nil {
		return nil, errors.New("failed to decode PEM block")
	}
	priv, err := x509.ParsePKCS8PrivateKey(block.Bytes)
	if err != nil {
		priv, err = x509.ParsePKCS1PrivateKey(block.Bytes)
		if err != nil {
			return nil, err
		}
	}
	rsaPriv, ok := priv.(*rsa.PrivateKey)
	if !ok {
		return nil, errors.New("not an RSA private key")
	}
	return rsaPriv, nil
}

func parsePublicKey(pemStr string) (*rsa.PublicKey, error) {
	block, _ := pem.Decode([]byte(pemStr))
	if block == nil {
		return nil, errors.New("failed to decode PEM block")
	}
	pub, err := x509.ParsePKIXPublicKey(block.Bytes)
	if err != nil {
		return nil, err
	}
	rsaPub, ok := pub.(*rsa.PublicKey)
	if !ok {
		return nil, errors.New("not an RSA public key")
	}
	return rsaPub, nil
}

// ---------- 业务参数排序 JSON ----------

// toSortedJSON 将结构体转为按 key 排序的 JSON 字符串，并忽略零值字段。
func toSortedJSON(v interface{}) ([]byte, error) {
	// 先通过 json.Marshal 得到 map，利用 omitempty 忽略零值
	raw, err := json.Marshal(v)
	if err != nil {
		return nil, err
	}
	var m map[string]interface{}
	if err := json.Unmarshal(raw, &m); err != nil {
		return nil, err
	}
	// 过滤掉值为 nil 的键（json.Unmarshal 会将 null 转为 nil）
	for k, val := range m {
		if val == nil {
			delete(m, k)
		}
	}
	// 按 key 排序
	keys := make([]string, 0, len(m))
	for k := range m {
		keys = append(keys, k)
	}
	sort.Strings(keys)
	// 构建有序的 JSON
	var buf bytes.Buffer
	buf.WriteByte('{')
	for i, k := range keys {
		if i > 0 {
			buf.WriteByte(',')
		}
		keyJSON, _ := json.Marshal(k)
		valJSON, _ := json.Marshal(m[k])
		buf.Write(keyJSON)
		buf.WriteByte(':')
		buf.Write(valJSON)
	}
	buf.WriteByte('}')
	return buf.Bytes(), nil
}

// ---------- 回调验签辅助 ----------

// VerifyCallbackSign 验证回调请求的签名。
// body: 回调请求的原始 body（JSON 字符串）
// appID: 应用 ID
// timestamp: 回调 Header 中的 Timestamp
// sign: 回调 Header 中的 Sign
func (c *Client) VerifyCallbackSign(body []byte, appID, timestamp, sign string) error {
	// 1. 解析 body 中的 data 字段
	var resp struct {
		Data json.RawMessage `json:"data"`
	}
	if err := json.Unmarshal(body, &resp); err != nil {
		return fmt.Errorf("unmarshal callback body: %w", err)
	}
	// 2. 将 data 转为排序 JSON
	var dataMap map[string]interface{}
	if err := json.Unmarshal(resp.Data, &dataMap); err != nil {
		return fmt.Errorf("unmarshal data: %w", err)
	}
	// 过滤零值
	for k, v := range dataMap {
		if v == nil || isZeroValue(v) {
			delete(dataMap, k)
		}
	}
	plainBytes, err := json.Marshal(dataMap) // map 序列化自动排序
	if err != nil {
		return err
	}
	// 3. 加密得到 ciphertext
	var ciphertext string
	switch c.encryptType {
	case "SM4":
		ciphertext, err = sm4CbcEncrypt(plainBytes, c.encryptKey)
	default:
		ciphertext, err = aesEcbEncrypt(plainBytes, c.encryptKey)
	}
	if err != nil {
		return err
	}
	// 4. 拼接签名字符串并验签
	return c.verifySign(appID, timestamp, ciphertext, sign)
}

func isZeroValue(v interface{}) bool {
	switch val := v.(type) {
	case string:
		return val == ""
	case float64:
		return val == 0
	case bool:
		return !val
	default:
		return false
	}
}

// 为了兼容旧版 Go，添加 strings 包的引用（实际未使用，但防止 import 被移除）
var _ = strings.TrimSpace
```

// File: ymt_v3_api/errors.go
```go
package ymt_v3_api

import "fmt"

// APIError 表示 API 返回的错误信息。
type APIError struct {
	Code    int    `json:"code"`
	Message string `json:"message"`
	Reason  string `json:"reason,omitempty"`
}

func (e *APIError) Error() string {
	if e.Reason != "" {
		return fmt.Sprintf("API error [%d]: %s (reason: %s)", e.Code, e.Message, e.Reason)
	}
	return fmt.Sprintf("API error [%d]: %s", e.Code, e.Message)
}

// 公共错误码常量
const (
	ErrCodeSystemError          = 500
	ErrCodeInvalidPayload       = 400
	ErrCodeMissingParam         = 400
	ErrCodeInvalidTimestamp     = 400
	ErrCodeDecryptFailed        = 400
	ErrCodeAppNotFound          = 401
	ErrCodeInvalidSignature     = 401
	ErrCodeExpiredTimestamp     = 401
	ErrCodeDuplicateRequest     = 429
	ErrCodeActivityNotAuth      = 401
	ErrCodeMerchantNotExist     = 401
	ErrCodeMerchantNotAuth      = 401
	ErrCodeMerchantAppIncomplete = 401
	ErrCodeMerchantAppNotAuth   = 401
	ErrCodeActivityExpire       = 403
	ErrCodeActivityOutOfStock   = 403
	ErrCodeActivityNotExist     = 404
	ErrCodeMerchantOrderNotExist = 404
	ErrCodeKeyNotExist          = 404
	ErrCodeParamFail            = 400
	ErrCodeParamDecryptFail     = 400
)
```

// File: ymt_v3_api/api_key.go
```go
package ymt_v3_api

import "context"

// OrderKey 获取券码
// 请求路由：POST /openapi/v1/key/order
func (c *Client) OrderKey(ctx context.Context, req *OrderKeyRequest) (*OrderKeyResponse, error) {
	var resp OrderKeyResponse
	if err := c.doRequest(ctx, "/openapi/v1/key/order", req, &resp); err != nil {
		return nil, err
	}
	return &resp, nil
}

// QueryKey 券码查询
// 请求路由：POST /openapi/v1/key/query
func (c *Client) QueryKey(ctx context.Context, req *QueryKeyRequest) (*QueryKeyResponse, error) {
	var resp QueryKeyResponse
	if err := c.doRequest(ctx, "/openapi/v1/key/query", req, &resp); err != nil {
		return nil, err
	}
	return &resp, nil
}

// DiscardKey 券码作废
// 请求路由：POST /openapi/v1/key/discard
func (c *Client) DiscardKey(ctx context.Context, req *DiscardKeyRequest) (*DiscardKeyResponse, error) {
	var resp DiscardKeyResponse
	if err := c.doRequest(ctx, "/openapi/v1/key/discard", req, &resp); err != nil {
		return nil, err
	}
	return &resp, nil
}

// BatchOrderKey 批量发卡
// 请求路由：POST /openapi/v1/key/batch_order
func (c *Client) BatchOrderKey(ctx context.Context, req *BatchOrderRequest) (*BatchOrderResponse, error) {
	var resp BatchOrderResponse
	if err := c.doRequest(ctx, "/openapi/v1/key/batch_order", req, &resp); err != nil {
		return nil, err
	}
	return &resp, nil
}

// BatchQueryKey 批量查询
// 请求路由：POST /openapi/v1/key/batch_query
func (c *Client) BatchQueryKey(ctx context.Context, req *BatchQueryRequest) (*BatchQueryResponse, error) {
	var resp BatchQueryResponse
	if err := c.doRequest(ctx, "/openapi/v1/key/batch_query", req, &resp); err != nil {
		return nil, err
	}
	return &resp, nil
}
```

// File: ymt_v3_api/example_test.go
```go
package ymt_v3_api

import (
	"context"
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"encoding/json"
	"encoding/pem"
	"net/http"
	"net/http/httptest"
	"testing"
	"time"
)

// 生成测试用的 RSA 密钥对和 AES 密钥
func generateTestKeys() (appID, privateKeyPEM, publicKeyPEM, aesKey string, err error) {
	appID = "test_app_id"
	priv, err := rsa.GenerateKey(rand.Reader, 2048)
	if err != nil {
		return
	}
	privBytes, err := x509.MarshalPKCS8PrivateKey(priv)
	if err != nil {
		return
	}
	privateKeyPEM = string(pem.EncodeToMemory(&pem.Block{Type: "PRIVATE KEY", Bytes: privBytes}))

	pubBytes, err := x509.MarshalPKIXPublicKey(&priv.PublicKey)
	if err != nil {
		return
	}
	publicKeyPEM = string(pem.EncodeToMemory(&pem.Block{Type: "PUBLIC KEY", Bytes: pubBytes}))

	aesKey = "1234567890123456" // 16 字节
	return
}

// 启动一个模拟服务器，返回加密的成功响应
func setupMockServer(t *testing.T, client *Client, bizResp interface{}) *httptest.Server {
	t.Helper()
	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// 验证必要 Header
		if r.Header.Get("Appid") == "" || r.Header.Get("Timestamp") == "" || r.Header.Get("Sign") == "" {
			w.WriteHeader(http.StatusBadRequest)
			json.NewEncoder(w).Encode(apiResponse{Code: 400, Message: "missing header"})
			return
		}
		// 解密请求体，验证 ciphertext 存在
		var reqBody cipherRequest
		if err := json.NewDecoder(r.Body).Decode(&reqBody); err != nil || reqBody.Ciphertext == "" {
			w.WriteHeader(http.StatusBadRequest)
			json.NewEncoder(w).Encode(apiResponse{Code: 400, Message: "invalid body"})
			return
		}
		// 构造加密响应
		ciphertext, err := client.encryptPayload(bizResp)
		if err != nil {
			w.WriteHeader(http.StatusInternalServerError)
			return
		}
		resp := apiResponse{
			Code:    200,
			Message: "成功",
			Data:    &cipherData{Ciphertext: ciphertext},
		}
		w.Header().Set("Content-Type", "application/json")
		json.NewEncoder(w).Encode(resp)
	}))
	return server
}

func TestOrderKey(t *testing.T) {
	appID, privPEM, pubPEM, aesKey, err := generateTestKeys()
	if err != nil {
		t.Fatal(err)
	}
	client, err := NewClient(appID, privPEM, pubPEM, aesKey, WithEncryptType("AES"))
	if err != nil {
		t.Fatal(err)
	}
	expectedResp := &OrderKeyResponse{
		OutBizNo:        "order_001",
		TradeNo:         "7251449503000383488",
		Key:             "aZKdU9BymzR6qGRzJM",
		ValidBeginTime:  "2026-06-22 15:30:00",
		ValidEndTime:    "2026-12-31 23:59:59",
		UsableNum:       1,
		UsageNum:        0,
		Status:          1,
		SettlementPrice: 9.9,
		Account:         "18666666666",
	}
	server := setupMockServer(t, client, expectedResp)
	defer server.Close()
	client.baseURL = server.URL

	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
	defer cancel()

	req := &OrderKeyRequest{
		OutBizNo:   "order_001",
		ActivityNo: "ACT20260622001",
		Account:    "18666666666",
		NotifyURL:  "https://notify.example.com/openapi",
	}
	resp, err := client.OrderKey(ctx, req)
	if err != nil {
		t.Fatalf("OrderKey failed: %v", err)
	}
	if resp.TradeNo != expectedResp.TradeNo {
		t.Errorf("expected trade_no %s, got %s", expectedResp.TradeNo, resp.TradeNo)
	}
	if resp.Key != expectedResp.Key {
		t.Errorf("expected key %s, got %s", expectedResp.Key, resp.Key)
	}
}

func TestQueryKey(t *testing.T) {
	appID, privPEM, pubPEM, aesKey, err := generateTestKeys()
	if err != nil {
		t.Fatal(err)
	}
	client, err := NewClient(appID, privPEM, pubPEM, aesKey)
	if err != nil {
		t.Fatal(err)
	}
	expectedResp := &QueryKeyResponse{
		OutBizNo: "order_001",
		TradeNo:  "7251449503000383488",
		Status:   1,
	}
	server := setupMockServer(t, client, expectedResp)
	defer server.Close()
	client.baseURL = server.URL

	ctx := context.Background()
	req := &QueryKeyRequest{OutBizNo: "order_001"}
	resp, err := client.QueryKey(ctx, req)
	if err != nil {
		t.Fatalf("QueryKey failed: %v", err)
	}
	if resp.OutBizNo != expectedResp.OutBizNo {
		t.Errorf("expected out_biz_no %s, got %s", expectedResp.OutBizNo, resp.OutBizNo)
	}
}

func TestDiscardKey(t *testing.T) {
	appID, privPEM, pubPEM, aesKey, err := generateTestKeys()
	if err != nil {
		t.Fatal(err)
	}
	client, err := NewClient(appID, privPEM, pubPEM, aesKey)
	if err != nil {
		t.Fatal(err)
	}
	expectedResp := &DiscardKeyResponse{
		OutBizNo: "order_001",
		TradeNo:  "7251449503000383488",
		Status:   3,
	}
	server := setupMockServer(t, client, expectedResp)
	defer server.Close()
	client.baseURL = server.URL

	ctx := context.Background()
	req := &DiscardKeyRequest{TradeNo: "7251449503000383488"}
	resp, err := client.DiscardKey(ctx, req)
	if err != nil {
		t.Fatalf("DiscardKey failed: %v", err)
	}
	if resp.Status != 3 {
		t.Errorf("expected status 3, got %d", resp.Status)
	}
}

func TestBatchOrderKey(t *testing.T) {
	appID, privPEM, pubPEM, aesKey, err := generateTestKeys()
	if err != nil {
		t.Fatal(err)
	}
	client, err := NewClient(appID, privPEM, pubPEM, aesKey)
	if err != nil {
		t.Fatal(err)
	}
	expectedResp := &BatchOrderResponse{
		OutBizNo: "batch_001",
		TradeNo:  "7251449503000383499",
		Status:   "processing",
	}
	server := setupMockServer(t, client, expectedResp)
	defer server.Close()
	client.baseURL = server.URL

	ctx := context.Background()
	req := &BatchOrderRequest{
		OutBizNo:   "batch_001",
		ActivityNo: "ACT20260622001",
		Number:     100,
	}
	resp, err := client.BatchOrderKey(ctx, req)
	if err != nil {
		t.Fatalf("BatchOrderKey failed: %v", err)
	}
	if resp.Status != "processing" {
		t.Errorf("expected status processing, got %s", resp.Status)
	}
}

func TestBatchQueryKey(t *testing.T) {
	appID, privPEM, pubPEM, aesKey, err := generateTestKeys()
	if err != nil {
		t.Fatal(err)
	}
	client, err := NewClient(appID, privPEM, pubPEM, aesKey)
	if err != nil {
		t.Fatal(err)
	}
	expectedResp := &BatchQueryResponse{
		OutBizNo:    "batch_001",
		TradeNo:     "7251449503000383499",
		Status:      "success",
		DownloadURL: "https://oss.example.com/openapi_7251449503000383499.zip",
		ZipPassword: "123456",
	}
	server := setupMockServer(t, client, expectedResp)
	defer server.Close()
	client.baseURL = server.URL

	ctx := context.Background()
	req := &BatchQueryRequest{TradeNo: "7251449503000383499"}
	resp, err := client.BatchQueryKey(ctx, req)
	if err != nil {
		t.Fatalf("BatchQueryKey failed: %v", err)
	}
	if resp.DownloadURL != expectedResp.DownloadURL {
		t.Errorf("expected download_url %s, got %s", expectedResp.DownloadURL, resp.DownloadURL)
	}
}
```