package service

import (
	"carrotskin/internal/model"
	"carrotskin/internal/repository"
	"carrotskin/pkg/redis"
	"context"
	"crypto"
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha1"
	"crypto/x509"
	"encoding/base64"
	"encoding/binary"
	"encoding/pem"
	"fmt"
	"strconv"
	"strings"
	"time"

	"go.uber.org/zap"
)

// 常量定义
const (
	KeySize               = 4096
	ExpirationDays        = 90
	RefreshDays           = 60
	PublicKeyRedisKey     = "yggdrasil:public_key"
	PrivateKeyRedisKey    = "yggdrasil:private_key"
	KeyExpirationRedisKey = "yggdrasil:key_expiration"
	RedisTTL              = 0 // 永不过期，由应用程序管理过期时间
)

// signatureService 签名服务实现
type signatureService struct {
	profileRepo repository.ProfileRepository
	redis       *redis.Client
	logger      *zap.Logger
}

// NewSignatureService 创建SignatureService实例
func NewSignatureService(
	profileRepo repository.ProfileRepository,
	redisClient *redis.Client,
	logger *zap.Logger,
) *signatureService {
	return &signatureService{
		profileRepo: profileRepo,
		redis:       redisClient,
		logger:      logger,
	}
}

// NewKeyPair 生成新的RSA密钥对
func (s *signatureService) NewKeyPair() (*model.KeyPair, error) {
	privateKey, err := rsa.GenerateKey(rand.Reader, KeySize)
	if err != nil {
		return nil, fmt.Errorf("生成RSA密钥对失败: %w", err)
	}

	// 获取公钥
	publicKey := &privateKey.PublicKey

	// PEM编码私钥
	privateKeyBytes := x509.MarshalPKCS1PrivateKey(privateKey)
	privateKeyPEM := pem.EncodeToMemory(&pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: privateKeyBytes,
	})

	// PEM编码公钥
	publicKeyBytes, err := x509.MarshalPKIXPublicKey(publicKey)
	if err != nil {
		return nil, fmt.Errorf("编码公钥失败: %w", err)
	}
	publicKeyPEM := pem.EncodeToMemory(&pem.Block{
		Type:  "PUBLIC KEY",
		Bytes: publicKeyBytes,
	})

	// 计算时间
	now := time.Now().UTC()
	expiration := now.AddDate(0, 0, ExpirationDays)
	refresh := now.AddDate(0, 0, RefreshDays)

	// 获取Yggdrasil根密钥并签名公钥
	yggPublicKey, yggPrivateKey, err := s.GetOrCreateYggdrasilKeyPair()
	if err != nil {
		return nil, fmt.Errorf("获取Yggdrasil根密钥失败: %w", err)
	}

	// 构造签名消息
	expiresAtMillis := expiration.UnixMilli()
	message := []byte(string(publicKeyPEM) + strconv.FormatInt(expiresAtMillis, 10))

	// 使用SHA1withRSA签名
	hashed := sha1.Sum(message)
	signature, err := rsa.SignPKCS1v15(rand.Reader, yggPrivateKey, crypto.SHA1, hashed[:])
	if err != nil {
		return nil, fmt.Errorf("签名失败: %w", err)
	}
	publicKeySignature := base64.StdEncoding.EncodeToString(signature)

	// 构造V2签名消息（DER编码）
	publicKeyDER, err := x509.MarshalPKIXPublicKey(publicKey)
	if err != nil {
		return nil, fmt.Errorf("DER编码公钥失败: %w", err)
	}

	// V2签名：timestamp (8 bytes, big endian) + publicKey (DER)
	messageV2 := make([]byte, 8+len(publicKeyDER))
	binary.BigEndian.PutUint64(messageV2[0:8], uint64(expiresAtMillis))
	copy(messageV2[8:], publicKeyDER)

	hashedV2 := sha1.Sum(messageV2)
	signatureV2, err := rsa.SignPKCS1v15(rand.Reader, yggPrivateKey, crypto.SHA1, hashedV2[:])
	if err != nil {
		return nil, fmt.Errorf("V2签名失败: %w", err)
	}
	publicKeySignatureV2 := base64.StdEncoding.EncodeToString(signatureV2)

	return &model.KeyPair{
		PrivateKey:           string(privateKeyPEM),
		PublicKey:            string(publicKeyPEM),
		PublicKeySignature:   publicKeySignature,
		PublicKeySignatureV2: publicKeySignatureV2,
		YggdrasilPublicKey:   yggPublicKey,
		Expiration:           expiration,
		Refresh:              refresh,
	}, nil
}

// GetOrCreateYggdrasilKeyPair 获取或创建Yggdrasil根密钥对
func (s *signatureService) GetOrCreateYggdrasilKeyPair() (string, *rsa.PrivateKey, error) {
	ctx := context.Background()

	// 尝试从Redis获取密钥
	publicKeyPEM, err := s.redis.Get(ctx, PublicKeyRedisKey)
	if err == nil && publicKeyPEM != "" {
		privateKeyPEM, err := s.redis.Get(ctx, PrivateKeyRedisKey)
		if err == nil && privateKeyPEM != "" {
			// 检查密钥是否过期
			expStr, err := s.redis.Get(ctx, KeyExpirationRedisKey)
			if err == nil && expStr != "" {
				expTime, err := time.Parse(time.RFC3339, expStr)
				if err == nil && time.Now().Before(expTime) {
					// 密钥有效，解析私钥
					block, _ := pem.Decode([]byte(privateKeyPEM))
					if block != nil {
						privateKey, err := x509.ParsePKCS1PrivateKey(block.Bytes)
						if err == nil {
							s.logger.Info("从Redis加载Yggdrasil根密钥")
							return publicKeyPEM, privateKey, nil
						}
					}
				}
			}
		}
	}

	// 生成新的根密钥对
	s.logger.Info("生成新的Yggdrasil根密钥对")
	privateKey, err := rsa.GenerateKey(rand.Reader, KeySize)
	if err != nil {
		return "", nil, fmt.Errorf("生成RSA密钥失败: %w", err)
	}

	// PEM编码私钥
	privateKeyBytes := x509.MarshalPKCS1PrivateKey(privateKey)
	privateKeyPEM := string(pem.EncodeToMemory(&pem.Block{
		Type:  "RSA PRIVATE KEY",
		Bytes: privateKeyBytes,
	}))

	// PEM编码公钥
	publicKeyBytes, err := x509.MarshalPKIXPublicKey(&privateKey.PublicKey)
	if err != nil {
		return "", nil, fmt.Errorf("编码公钥失败: %w", err)
	}
	publicKeyPEM = string(pem.EncodeToMemory(&pem.Block{
		Type:  "PUBLIC KEY",
		Bytes: publicKeyBytes,
	}))

	// 计算过期时间（90天）
	expiration := time.Now().AddDate(0, 0, ExpirationDays)

	// 保存到Redis
	if err := s.redis.Set(ctx, PublicKeyRedisKey, publicKeyPEM, RedisTTL); err != nil {
		s.logger.Warn("保存公钥到Redis失败", zap.Error(err))
	}
	if err := s.redis.Set(ctx, PrivateKeyRedisKey, privateKeyPEM, RedisTTL); err != nil {
		s.logger.Warn("保存私钥到Redis失败", zap.Error(err))
	}
	if err := s.redis.Set(ctx, KeyExpirationRedisKey, expiration.Format(time.RFC3339), RedisTTL); err != nil {
		s.logger.Warn("保存密钥过期时间到Redis失败", zap.Error(err))
	}

	return publicKeyPEM, privateKey, nil
}

// GetPublicKeyFromRedis 从Redis获取公钥
func (s *signatureService) GetPublicKeyFromRedis() (string, error) {
	ctx := context.Background()
	publicKey, err := s.redis.Get(ctx, PublicKeyRedisKey)
	if err != nil {
		return "", fmt.Errorf("从Redis获取公钥失败: %w", err)
	}
	if publicKey == "" {
		// 如果Redis中没有，创建新的密钥对
		publicKey, _, err = s.GetOrCreateYggdrasilKeyPair()
		if err != nil {
			return "", fmt.Errorf("创建新密钥对失败: %w", err)
		}
	}
	return publicKey, nil
}

// SignStringWithSHA1withRSA 使用SHA1withRSA签名字符串
func (s *signatureService) SignStringWithSHA1withRSA(data string) (string, error) {
	ctx := context.Background()

	// 从Redis获取私钥
	privateKeyPEM, err := s.redis.Get(ctx, PrivateKeyRedisKey)
	if err != nil || privateKeyPEM == "" {
		// 如果没有私钥，创建新的密钥对
		_, privateKey, err := s.GetOrCreateYggdrasilKeyPair()
		if err != nil {
			return "", fmt.Errorf("获取私钥失败: %w", err)
		}
		// 使用新生成的私钥签名
		hashed := sha1.Sum([]byte(data))
		signature, err := rsa.SignPKCS1v15(rand.Reader, privateKey, crypto.SHA1, hashed[:])
		if err != nil {
			return "", fmt.Errorf("签名失败: %w", err)
		}
		return base64.StdEncoding.EncodeToString(signature), nil
	}

	// 解析PEM格式的私钥
	block, _ := pem.Decode([]byte(privateKeyPEM))
	if block == nil {
		return "", fmt.Errorf("解析PEM私钥失败")
	}

	privateKey, err := x509.ParsePKCS1PrivateKey(block.Bytes)
	if err != nil {
		return "", fmt.Errorf("解析RSA私钥失败: %w", err)
	}

	// 签名
	hashed := sha1.Sum([]byte(data))
	signature, err := rsa.SignPKCS1v15(rand.Reader, privateKey, crypto.SHA1, hashed[:])
	if err != nil {
		return "", fmt.Errorf("签名失败: %w", err)
	}

	return base64.StdEncoding.EncodeToString(signature), nil
}

// FormatPublicKey 格式化公钥为单行格式（去除PEM头尾和换行符）
func FormatPublicKey(publicKeyPEM string) string {
	// 移除PEM格式的头尾
	lines := strings.Split(publicKeyPEM, "\n")
	var keyLines []string
	for _, line := range lines {
		trimmed := strings.TrimSpace(line)
		if trimmed != "" &&
			!strings.HasPrefix(trimmed, "-----BEGIN") &&
			!strings.HasPrefix(trimmed, "-----END") {
			keyLines = append(keyLines, trimmed)
		}
	}
	return strings.Join(keyLines, "")
}