// Package crypto 提供可复用的安全原语：AES-256-GCM 字段加解密、argon2id 口令哈希。
// 密钥经 HKDF 从 config.EncryptionKey 派生（与 JWT 密钥分离）。
package crypto

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"crypto/subtle"
	"encoding/base64"
	"encoding/hex"
	"errors"
	"io"
	"strings"

	"opsxloki/config"

	"golang.org/x/crypto/argon2"
	"golang.org/x/crypto/hkdf"
)

const (
	keySaltPrefix = "lokideploy-v2-enc:" // HKDF info prefix for key derivation
)

// deriveEncryptionKey 使用HKDF从ENCRYPTION_KEY派生AES-256密钥
// 这样即使ENCRYPTION_KEY被复用，不同上下文的密钥也不同
func deriveEncryptionKey() ([]byte, error) {
	cfg := config.GetConfig()
	encKey := cfg.EncryptionKey

	// 支持hex或base64编码的密钥
	var masterKey []byte
	var err error
	if len(encKey) == 64 { // 可能是hex编码的32字节
		masterKey, err = hex.DecodeString(encKey)
		if err != nil {
			masterKey = []byte(encKey) // fallback: 直接使用原始字节
		}
	} else if len(encKey) > 32 { // 可能是base64编码
		masterKey, err = base64.StdEncoding.DecodeString(encKey)
		if err != nil {
			masterKey = []byte(encKey) // fallback: 直接使用原始字节
		}
	} else {
		masterKey = []byte(encKey)
	}

	// 使用HKDF-SHA256派生固定长度的AES密钥
	hkdfReader := hkdf.New(sha256.New, masterKey, nil, []byte(keySaltPrefix+"aes-gcm-256"))
	aesKey := make([]byte, 32)
	if _, err := io.ReadFull(hkdfReader, aesKey); err != nil {
		return nil, err
	}
	return aesKey, nil
}

func HashPassword(password string) (string, error) {
	salt := make([]byte, 16)
	if _, err := rand.Read(salt); err != nil {
		return "", err
	}
	hash := argon2.IDKey([]byte(password), salt, 3, 64*1024, 4, 32)
	combined := append(salt, hash...)
	return base64.StdEncoding.EncodeToString(combined), nil
}

func VerifyPassword(password, hashStr string) bool {
	combined, err := base64.StdEncoding.DecodeString(hashStr)
	if err != nil || len(combined) < 16 {
		return false
	}
	salt := combined[:16]
	hash := combined[16:]
	newHash := argon2.IDKey([]byte(password), salt, 3, 64*1024, 4, 32)
	return subtle.ConstantTimeCompare(hash, newHash) == 1
}

func Encrypt(plaintext string) (string, error) {
	if plaintext == "" {
		return "", nil
	}

	key, err := deriveEncryptionKey()
	if err != nil {
		return "", err
	}

	block, err := aes.NewCipher(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
}

func Decrypt(ciphertext string) (string, error) {
	if ciphertext == "" {
		return "", nil
	}

	key, err := deriveEncryptionKey()
	if err != nil {
		return "", err
	}

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

	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}
	if len(data) < gcm.NonceSize() {
		return "", errors.New("ciphertext too short")
	}
	nonce, ciphertextBytes := data[:gcm.NonceSize()], data[gcm.NonceSize():]
	plaintext, err := gcm.Open(nil, nonce, ciphertextBytes, nil)
	if err != nil {
		return "", err
	}
	return string(plaintext), nil
}

// EncryptField 加密敏感字段，返回 ENC: 前缀标记格式。
// 加密失败时返回错误（绝不返回明文或哨兵串），调用方必须处理该错误，
// 否则可能把垃圾值当凭证落库。
func EncryptField(plaintext string) (string, error) {
	if plaintext == "" {
		return "", nil
	}
	enc, err := Encrypt(plaintext)
	if err != nil {
		return "", err
	}
	return "ENC:" + enc, nil
}

// DecryptField 解密 ENC: 前缀标记的字段
func DecryptField(encrypted string) string {
	if encrypted == "" {
		return ""
	}
	if strings.HasPrefix(encrypted, "ENC:") {
		plain, err := Decrypt(encrypted[4:])
		if err != nil {
			return ""
		}
		return plain
	}
	// 未加密的数据直接返回（向后兼容）
	return encrypted
}

// IsEncryptedField 检查字段是否已加密
func IsEncryptedField(value string) bool {
	return strings.HasPrefix(value, "ENC:")
}