// Package wecom 提供企业微信外部系统 Adapter。
package wecom

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

	"github.com/break/junhong_cmp_fiber/pkg/errors"
)

var credentialAAD = []byte("junhong-wecom-credential-v1")

// CredentialCipher 使用 AES-256-GCM 加解密企业微信敏感凭据。
type CredentialCipher struct {
	aead cipher.AEAD
}

// NewCredentialCipher 从 32 字节 Base64 密钥创建凭据加密器。
func NewCredentialCipher(encodedKey string) (*CredentialCipher, error) {
	key, err := base64.StdEncoding.DecodeString(encodedKey)
	if err != nil || len(key) != 32 {
		return nil, errors.New(errors.CodeWeComCredentialInvalid, "企业微信凭据加密密钥必须是 32 字节 Base64")
	}
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, errors.Wrap(errors.CodeWeComCredentialInvalid, err, "初始化企业微信凭据加密器失败")
	}
	aead, err := cipher.NewGCM(block)
	if err != nil {
		return nil, errors.Wrap(errors.CodeWeComCredentialInvalid, err, "初始化企业微信凭据加密模式失败")
	}
	return &CredentialCipher{aead: aead}, nil
}

// Encrypt 加密单个敏感凭据，返回 nonce 与密文组合。
func (c *CredentialCipher) Encrypt(plaintext string) ([]byte, error) {
	if c == nil || c.aead == nil || plaintext == "" {
		return nil, errors.New(errors.CodeWeComCredentialInvalid)
	}
	nonce := make([]byte, c.aead.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return nil, errors.Wrap(errors.CodeInternalError, err, "生成企业微信凭据随机数失败")
	}
	return c.aead.Seal(nonce, nonce, []byte(plaintext), credentialAAD), nil
}

// Decrypt 解密单个企业微信敏感凭据。
func (c *CredentialCipher) Decrypt(ciphertext []byte) (string, error) {
	if c == nil || c.aead == nil || len(ciphertext) <= c.aead.NonceSize() {
		return "", errors.New(errors.CodeWeComCredentialInvalid)
	}
	nonce := ciphertext[:c.aead.NonceSize()]
	plaintext, err := c.aead.Open(nil, nonce, ciphertext[c.aead.NonceSize():], credentialAAD)
	if err != nil {
		return "", errors.Wrap(errors.CodeWeComCredentialInvalid, err, "解密企业微信凭据失败")
	}
	return string(plaintext), nil
}