package crypto

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

func defaultKey() []byte {
	key := os.Getenv("ENCRYPT_KEY")
	if key == "" {
		key = "opencatd-default-key-change-me"
	}
	h := sha256.Sum256([]byte(key))
	return h[:] // 32 bytes
}

// Encrypt encrypts plaintext using AES-GCM with the default key
func Encrypt(plaintext string) (string, error) {
	enc, err := NewEncryptor(defaultKey())
	if err != nil {
		return "", err
	}
	return enc.Encrypt(plaintext)
}

// Decrypt decrypts ciphertext using AES-GCM with the default key
func Decrypt(encoded string) (string, error) {
	enc, err := NewEncryptor(defaultKey())
	if err != nil {
		return "", err
	}
	return enc.Decrypt(encoded)
}

// Sha256Hex is a convenience wrapper for SHA-256 hex hashing
func Sha256Hex(data string) string {
	h := sha256.Sum256([]byte(data))
	return hex.EncodeToString(h[:])
}

// Encryptor AES-GCM 加密器
type Encryptor struct {
	key []byte
}

// NewEncryptor 创建加密器（key 为 16/24/32 字节）
func NewEncryptor(key []byte) (*Encryptor, error) {
	switch len(key) {
	case 16, 24, 32:
	default:
		return nil, errors.New("crypto: invalid key length, must be 16, 24, or 32 bytes")
	}
	return &Encryptor{key: key}, nil
}

// Encrypt AES-GCM 加密，返回 base64 编码的密文
func (e *Encryptor) Encrypt(plaintext string) (string, error) {
	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 AES-GCM 解密
func (e *Encryptor) Decrypt(encoded string) (string, error) {
	data, err := base64.StdEncoding.DecodeString(encoded)
	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(data) < nonceSize {
		return "", errors.New("ciphertext too short")
	}
	nonce, ciphertext := data[:nonceSize], data[nonceSize:]
	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return "", err
	}
	return string(plaintext), nil
}