package service

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

// SecretCodec 使用应用主密钥加密落库的第三方密钥，避免明文存储。
type SecretCodec struct {
	gcm cipher.AEAD
}

func NewSecretCodec(masterKey string) (*SecretCodec, error) {
	if masterKey == "" {
		return nil, errors.New("数据加密主密钥不能为空")
	}
	sum := sha256.Sum256([]byte(masterKey))
	block, err := aes.NewCipher(sum[:])
	if err != nil {
		return nil, err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, err
	}
	return &SecretCodec{gcm: gcm}, nil
}

func (c *SecretCodec) Encrypt(plain string) (string, error) {
	nonce := make([]byte, c.gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", err
	}
	sealed := c.gcm.Seal(nil, nonce, []byte(plain), nil)
	return base64.RawURLEncoding.EncodeToString(append(nonce, sealed...)), nil
}

func (c *SecretCodec) Decrypt(ciphertext string) (string, error) {
	raw, err := base64.RawURLEncoding.DecodeString(ciphertext)
	if err != nil {
		return "", errors.New("密钥密文格式错误")
	}
	if len(raw) < c.gcm.NonceSize() {
		return "", errors.New("密钥密文长度错误")
	}
	plain, err := c.gcm.Open(nil, raw[:c.gcm.NonceSize()], raw[c.gcm.NonceSize():], nil)
	if err != nil {
		return "", errors.New("密钥解密失败")
	}
	return string(plain), nil
}