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