//
// Copyright (C) 2024 veypi <i@veypi.com>
// 2025-03-04 16:08:06
// Distributed under terms of the MIT license.
//

package crypto

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"io"

	"golang.org/x/crypto/bcrypt"
)

// HashPassword 使用bcrypt哈希密码
func HashPassword(password string, cost int) (string, error) {
	bytes, err := bcrypt.GenerateFromPassword([]byte(password), cost)
	if err != nil {
		return "", fmt.Errorf("failed to hash password: %w", err)
	}
	return string(bytes), nil
}

// VerifyPassword 验证密码
func VerifyPassword(password, hash string) bool {
	err := bcrypt.CompareHashAndPassword([]byte(hash), []byte(password))
	return err == nil
}

// GenerateRandomString 生成随机字符串
func GenerateRandomString(length int) (string, error) {
	bytes := make([]byte, length)
	if _, err := rand.Read(bytes); err != nil {
		return "", err
	}
	return base64.URLEncoding.EncodeToString(bytes)[:length], nil
}

// GenerateSecret 生成密钥
func GenerateSecret(length int) string {
	const charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
	bytes := make([]byte, length)
	rand.Read(bytes)
	for i, b := range bytes {
		bytes[i] = charset[b%byte(len(charset))]
	}
	return string(bytes)
}

// GenerateClientID 生成OAuth客户端ID
func GenerateClientID() string {
	return "vc_" + GenerateSecret(28)
}

// GenerateClientSecret 生成OAuth客户端密钥
func GenerateClientSecret() string {
	return GenerateSecret(64)
}

// deriveKey 从密钥字符串派生32字节AES密钥
func deriveKey(key string) []byte {
	hash := sha256.Sum256([]byte(key))
	return hash[:]
}

// Encrypt 使用AES-GCM加密数据
// key: 加密密钥（会被派生为32字节）
// plaintext: 明文数据
// 返回: base64编码的密文（包含nonce）
func Encrypt(key, plaintext string) (string, error) {
	if key == "" || plaintext == "" {
		return "", fmt.Errorf("key and plaintext cannot be empty")
	}

	block, err := aes.NewCipher(deriveKey(key))
	if err != nil {
		return "", err
	}

	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}

	nonce := make([]byte, gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", err
	}

	ciphertext := gcm.Seal(nonce, nonce, []byte(plaintext), nil)
	return base64.StdEncoding.EncodeToString(ciphertext), nil
}

// Decrypt 使用AES-GCM解密数据
// key: 解密密钥
// ciphertext: base64编码的密文（包含nonce）
// 返回: 明文数据
func Decrypt(key, ciphertext string) (string, error) {
	if key == "" || ciphertext == "" {
		return "", fmt.Errorf("key and ciphertext cannot be empty")
	}

	data, err := base64.StdEncoding.DecodeString(ciphertext)
	if err != nil {
		return "", fmt.Errorf("failed to decode ciphertext: %w", err)
	}

	block, err := aes.NewCipher(deriveKey(key))
	if err != nil {
		return "", err
	}

	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}

	nonceSize := gcm.NonceSize()
	if len(data) < nonceSize {
		return "", fmt.Errorf("ciphertext too short")
	}

	nonce, encrypted := data[:nonceSize], data[nonceSize:]
	plaintext, err := gcm.Open(nil, nonce, encrypted, nil)
	if err != nil {
		return "", fmt.Errorf("failed to decrypt: %w", err)
	}

	return string(plaintext), nil
}
