package fqapi

import (
	"bytes"
	"compress/gzip"
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha512"
	"encoding/base64"
	"fmt"
	"io"
)

// FIXED_STRING 固定字符串（base64解码后的值）
var FIXED_STRING = []byte{
	0x4D, 0xD4, 0xC2, 0xE6, 0xB8, 0x31, 0x62, 0x09,
	0x0E, 0x52, 0xB3, 0xC7, 0xA6, 0x73, 0x3B, 0xA4,
	0x1C, 0xB2, 0x46, 0x2B, 0x82, 0x9A, 0xB5, 0x8A,
	0x19, 0x6B, 0x39, 0xDB, 0x57, 0x17, 0x75, 0x24,
	0xF4, 0x9B, 0xAF, 0x7F, 0x08, 0xE8, 0xD6, 0x8D,
	0x26, 0xA7, 0x2E, 0x37, 0xC1, 0xA9, 0x5A, 0x2F,
	0x1F, 0x05, 0xA5, 0x18, 0x92, 0xAE, 0xF2, 0x94,
	0x97, 0x32, 0xB6, 0x2A, 0x38, 0xAA, 0xDD, 0x58,
}

// sha512Hash 计算SHA512哈希值
func sha512Hash(data []byte) []byte {
	hash := sha512.Sum512(data)
	return hash[:]
}

// generateRandomBytes 生成指定长度的随机字节
func generateRandomBytes(size int) []byte {
	bytes := make([]byte, size)
	rand.Read(bytes)
	return bytes
}

// gzipCompress 使用gzip压缩数据
func gzipCompress(data []byte) ([]byte, error) {
	buf := new(bytes.Buffer)
	writer := gzip.NewWriter(buf)
	_, err := writer.Write(data)
	if err != nil {
		return nil, err
	}
	err = writer.Close()
	if err != nil {
		return nil, err
	}

	return buf.Bytes(), nil
}

// gzipDecompress 使用gzip解压缩数据
func gzipDecompress(data []byte) ([]byte, error) {
	reader, err := gzip.NewReader(bytes.NewReader(data))
	if err != nil {
		return nil, err
	}
	defer reader.Close()

	result, err := io.ReadAll(reader)
	if err != nil {
		return nil, err
	}

	return result, nil
}

// encryptData 使用AES-CBC模式加密数据
func encryptData(data []byte, key []byte, iv []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

	// PKCS7填充
	padding := aes.BlockSize - len(data)%aes.BlockSize
	padText := bytes.Repeat([]byte{byte(padding)}, padding)
	paddedData := append(data, padText...)

	ciphertext := make([]byte, len(paddedData))
	mode := cipher.NewCBCEncrypter(block, iv)
	mode.CryptBlocks(ciphertext, paddedData)

	return ciphertext, nil
}

// decryptData 使用AES-CBC模式解密数据
func decryptData(data []byte, key []byte, iv []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

	mode := cipher.NewCBCDecrypter(block, iv)
	decrypted := make([]byte, len(data))
	mode.CryptBlocks(decrypted, data)

	// 移除PKCS7填充
	padding := int(decrypted[len(decrypted)-1])
	return decrypted[:len(decrypted)-padding], nil
}

// TTEncrypt 加密函数
func TTEncrypt(data []byte) ([]byte, error) {
	// 生成随机值
	randomValue := generateRandomBytes(32)

	// 计算SHA512哈希值
	hashValue := sha512Hash(append(sha512Hash(randomValue), FIXED_STRING...))

	// 提取key和iv
	key := hashValue[:16]
	iv := hashValue[16:32]

	// 压缩数据并计算哈希值
	compressedData, err := gzipCompress(data)
	if err != nil {
		return nil, err
	}
	hashedData := append(sha512Hash(compressedData), compressedData...)

	// 加密数据
	encryptedData, err := encryptData(hashedData, key, iv)
	if err != nil {
		return nil, err
	}

	// 返回结果
	header := []byte{116, 99, 5, 16, 0, 0}
	result := append(header, randomValue...)
	result = append(result, encryptedData...)

	return result, nil
}

// TTDecrypt 解密函数
func TTDecrypt(encryptedData []byte) ([]byte, error) {
	// 提取固定头、随机值和加密数据
	// header := encryptedData[:6]
	randomValue := encryptedData[6:38]
	encryptedPayload := encryptedData[38:]

	// 计算SHA512哈希值
	hashValue := sha512Hash(append(sha512Hash(randomValue), FIXED_STRING...))

	// 提取key和iv
	key := hashValue[:16]
	iv := hashValue[16:32]

	// 解密数据
	decryptedData, err := decryptData(encryptedPayload, key, iv)
	if err != nil {
		return nil, err
	}

	// 分离哈希值和压缩数据
	hashLength := 64
	hashedValue := decryptedData[:hashLength]
	compressedData := decryptedData[hashLength:]

	// 验证哈希值
	expectedHash := sha512Hash(compressedData)
	for i := 0; i < hashLength; i++ {
		if hashedValue[i] != expectedHash[i] {
			return nil, fmt.Errorf("hash verification failed")
		}
	}

	// 解压缩数据
	originalData, err := gzipDecompress(compressedData)
	if err != nil {
		return nil, err
	}

	return originalData, nil
}

// Encrypt 导出的加密函数
func Encrypt(data []byte) string {
	result, _ := TTEncrypt(data)
	return base64.StdEncoding.EncodeToString(result)
}

// Decrypt 导出的解密函数
func Decrypt(encryptedStr string) ([]byte, error) {
	encryptedData, err := base64.StdEncoding.DecodeString(encryptedStr)
	if err != nil {
		return nil, err
	}
	return TTDecrypt(encryptedData)
}