package paymentconfig

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/base64"
	"errors"
	"io"
)

// Encryptor 密钥加密器接口
type Encryptor interface {
	Encrypt(plaintext string) (string, error)
	Decrypt(ciphertext string) (string, error)
}

// AESEncryptor AES 加密器
type AESEncryptor struct {
	key []byte
}

// NewAESEncryptor 创建 AES 加密器
// key 必须是 16、24 或 32 字节（对应 AES-128、AES-192、AES-256）
func NewAESEncryptor(key string) (*AESEncryptor, error) {
	keyBytes := []byte(key)
	if len(keyBytes) != 16 && len(keyBytes) != 24 && len(keyBytes) != 32 {
		return nil, errors.New("invalid key length: must be 16, 24, or 32 bytes")
	}
	return &AESEncryptor{key: keyBytes}, nil
}

// Encrypt 加密明文（使用 AES-GCM）
func (e *AESEncryptor) Encrypt(plaintext string) (string, error) {
	if plaintext == "" {
		return "", nil
	}

	block, err := aes.NewCipher(e.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 解密密文（使用 AES-GCM）
func (e *AESEncryptor) Decrypt(ciphertext string) (string, error) {
	if ciphertext == "" {
		return "", nil
	}

	ciphertextBytes, err := base64.StdEncoding.DecodeString(ciphertext)
	if err != nil {
		return "", err
	}

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

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

	nonceSize := gcm.NonceSize()
	if len(ciphertextBytes) < nonceSize {
		return "", errors.New("ciphertext too short")
	}

	nonce, ciphertextBytes := ciphertextBytes[:nonceSize], ciphertextBytes[nonceSize:]
	plaintext, err := gcm.Open(nil, nonce, ciphertextBytes, nil)
	if err != nil {
		return "", err
	}

	return string(plaintext), nil
}

// MockEncryptor 模拟加密器（用于测试）
type MockEncryptor struct{}

func (e *MockEncryptor) Encrypt(plaintext string) (string, error) {
	return plaintext, nil
}

func (e *MockEncryptor) Decrypt(ciphertext string) (string, error) {
	return ciphertext, nil
}
