package security

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

// Encryption 加密工具
type Encryption struct {
	key []byte
}

// NewEncryption 创建加密工具（密钥长度必须是16, 24或32字节）
func NewEncryption(key string) (*Encryption, error) {
	if len(key) != 16 && len(key) != 24 && len(key) != 32 {
		return nil, errors.New("key length must be 16, 24 or 32 bytes")
	}
	return &Encryption{key: []byte(key)}, nil
}

// Encrypt 使用AES-256-GCM加密
func (e *Encryption) 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 使用AES-256-GCM解密
func (e *Encryption) Decrypt(ciphertext string) (string, error) {
	data, 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(data) < nonceSize {
		return "", errors.New("ciphertext too short")
	}

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

	return string(plaintext), nil
}

// MaskEmail 邮箱脱敏
func MaskEmail(email string) string {
	if email == "" {
		return ""
	}
	
	prefix := email[:3]
	suffix := email[strings.Index(email, "@"):]
	return prefix + "***" + suffix
}

// MaskPhone 手机号脱敏
func MaskPhone(phone string) string {
	if len(phone) != 11 {
		return phone
	}
	return phone[:3] + "****" + phone[7:]
}