backend/internal/service/sensitive_service.go

package service

import (
	"context"
	"encoding/json"
	"fmt"
	"log"
	"regexp"
	"strings"
	"sync"
	"time"
	"unicode/utf8"

	"carrot_bbs/internal/model"
	redisclient "carrot_bbs/internal/pkg/redis"

	"gorm.io/gorm"
)

// ==================== DFA 敏感词过滤实现 ====================

// SensitiveNode 敏感词树节点
type SensitiveNode struct {
	// 子节点映射
	Children map[rune]*SensitiveNode
	// 是否为敏感词结尾
	IsEnd bool
	// 敏感词信息（仅在 IsEnd 为 true 时有效）
	Word     string
	Level    model.SensitiveWordLevel
	Category model.SensitiveWordCategory
}

// NewSensitiveNode 创建新的敏感词节点
func NewSensitiveNode() *SensitiveNode {
	return &SensitiveNode{
		Children: make(map[rune]*SensitiveNode),
		IsEnd:    false,
	}
}

// SensitiveWordTree 敏感词树
type SensitiveWordTree struct {
	root       *SensitiveNode
	wordCount  int
	mu         sync.RWMutex
	lastReload time.Time
}

// NewSensitiveWordTree 创建新的敏感词树
func NewSensitiveWordTree() *SensitiveWordTree {
	return &SensitiveWordTree{
		root:       NewSensitiveNode(),
		wordCount:  0,
		lastReload: time.Now(),
	}
}

// AddWord 添加敏感词到树中
func (t *SensitiveWordTree) AddWord(word string, level model.SensitiveWordLevel, category model.SensitiveWordCategory) {
	if word == "" {
		return
	}

	t.mu.Lock()
	defer t.mu.Unlock()

	node := t.root
	// 转换为小写进行匹配（不区分大小写）
	lowerWord := strings.ToLower(word)
	runes := []rune(lowerWord)

	for _, r := range runes {
		child, exists := node.Children[r]
		if !exists {
			child = NewSensitiveNode()
			node.Children[r] = child
		}
		node = child
	}

	// 如果不是已存在的敏感词，则计数+1
	if !node.IsEnd {
		t.wordCount++
	}

	node.IsEnd = true
	node.Word = word
	node.Level = level
	node.Category = category
}

// RemoveWord 从树中移除敏感词
func (t *SensitiveWordTree) RemoveWord(word string) {
	if word == "" {
		return
	}

	t.mu.Lock()
	defer t.mu.Unlock()

	lowerWord := strings.ToLower(word)
	runes := []rune(lowerWord)

	// 查找节点
	node := t.root
	for _, r := range runes {
		child, exists := node.Children[r]
		if !exists {
			return // 敏感词不存在
		}
		node = child
	}

	if node.IsEnd {
		node.IsEnd = false
		node.Word = ""
		t.wordCount--
	}
}

// Check 检查文本是否包含敏感词，返回是否包含及敏感词列表
func (t *SensitiveWordTree) Check(text string) (bool, []string) {
	if text == "" {
		return false, nil
	}

	t.mu.RLock()
	defer t.mu.RUnlock()

	var foundWords []string
	runes := []rune(strings.ToLower(text))
	length := len(runes)

	// 用于标记已找到的敏感词位置，避免重复计算
	marked := make([]bool, length)

	for i := 0; i < length; i++ {
		// 从当前位置开始搜索
		node := t.root
		matchEnd := -1
		matchWord := ""

		for j := i; j < length; j++ {
			child, exists := node.Children[runes[j]]
			if !exists {
				break
			}
			node = child

			if node.IsEnd {
				matchEnd = j
				matchWord = node.Word
			}
		}

		// 标记找到的敏感词位置
		if matchEnd >= 0 && !marked[i] {
			for k := i; k <= matchEnd; k++ {
				marked[k] = true
			}
			foundWords = append(foundWords, matchWord)
		}
	}

	return len(foundWords) > 0, foundWords
}

// Replace 替换文本中的敏感词
func (t *SensitiveWordTree) Replace(text string, repl string) string {
	if text == "" {
		return text
	}

	t.mu.RLock()
	defer t.mu.RUnlock()

	runes := []rune(text)
	length := len(runes)
	result := make([]rune, 0, length)

	// 用于标记已替换的位置
	marked := make([]bool, length)

	for i := 0; i < length; i++ {
		if marked[i] {
			continue
		}

		// 从当前位置开始搜索
		node := t.root
		matchEnd := -1

		for j := i; j < length; j++ {
			child, exists := node.Children[runes[j]]
			if !exists {
				break
			}
			node = child

			if node.IsEnd {
				matchEnd = j
			}
		}

		if matchEnd >= 0 {
			// 标记已替换的位置
			for k := i; k <= matchEnd; k++ {
				marked[k] = true
			}
			// 追加替换符
			replRunes := []rune(repl)
			result = append(result, replRunes...)
			// 跳过已匹配的字符
			i = matchEnd
		} else {
			// 追加原字符
			result = append(result, runes[i])
		}
	}

	return string(result)
}

// WordCount 获取敏感词数量
func (t *SensitiveWordTree) WordCount() int {
	t.mu.RLock()
	defer t.mu.RUnlock()
	return t.wordCount
}

// ==================== 敏感词服务实现 ====================

// SensitiveService 敏感词服务接口
type SensitiveService interface {
	// Check 检查文本是否包含敏感词
	Check(ctx context.Context, text string) (bool, []string)
	// Replace 替换敏感词
	Replace(ctx context.Context, text string, repl string) string
	// AddWord 添加敏感词
	AddWord(ctx context.Context, word string, category string, level int) error
	// RemoveWord 移除敏感词
	RemoveWord(ctx context.Context, word string) error
	// Reload 重新加载敏感词库
	Reload(ctx context.Context) error
	// GetWordCount 获取敏感词数量
	GetWordCount(ctx context.Context) int
}

// sensitiveServiceImpl 敏感词服务实现
type sensitiveServiceImpl struct {
	tree       *SensitiveWordTree
	db         *gorm.DB
	redis      *redisclient.Client
	config     *SensitiveConfig
	mu         sync.RWMutex
	replaceStr string
}

// SensitiveConfig 敏感词服务配置
type SensitiveConfig struct {
	Enabled    bool   `mapstructure:"enabled" yaml:"enabled"`
	ReplaceStr string `mapstructure:"replace_str" yaml:"replace_str"`
	// 最小匹配长度
	MinMatchLen int `mapstructure:"min_match_len" yaml:"min_match_len"`
	// 是否从数据库加载
	LoadFromDB bool `mapstructure:"load_from_db" yaml:"load_from_db"`
	// 是否从Redis加载
	LoadFromRedis bool `mapstructure:"load_from_redis" yaml:"load_from_redis"`
	// Redis键前缀
	RedisKeyPrefix string `mapstructure:"redis_key_prefix" yaml:"redis_key_prefix"`
}

// NewSensitiveService 创建敏感词服务
func NewSensitiveService(db *gorm.DB, redisClient *redisclient.Client, config *SensitiveConfig) SensitiveService {
	s := &sensitiveServiceImpl{
		tree:       NewSensitiveWordTree(),
		db:         db,
		redis:      redisClient,
		config:     config,
		replaceStr: config.ReplaceStr,
	}

	// 如果未设置替换符，默认使用 ***
	if s.replaceStr == "" {
		s.replaceStr = "***"
	}

	// 初始化加载敏感词
	if config.LoadFromDB {
		if err := s.loadFromDB(context.Background()); err != nil {
			log.Printf("Failed to load sensitive words from database: %v", err)
		}
	}

	if config.LoadFromRedis && redisClient != nil {
		if err := s.loadFromRedis(context.Background()); err != nil {
			log.Printf("Failed to load sensitive words from redis: %v", err)
		}
	}

	return s
}

// Check 检查文本是否包含敏感词
func (s *sensitiveServiceImpl) Check(ctx context.Context, text string) (bool, []string) {
	if !s.config.Enabled {
		return false, nil
	}
	if text == "" {
		return false, nil
	}
	return s.tree.Check(text)
}

// Replace 替换敏感词
func (s *sensitiveServiceImpl) Replace(ctx context.Context, text string, repl string) string {
	if !s.config.Enabled {
		return text
	}
	if text == "" {
		return text
	}

	// 如果未指定替换符，使用默认替换符
	if repl == "" {
		repl = s.replaceStr
	}

	return s.tree.Replace(text, repl)
}

// AddWord 添加敏感词
func (s *sensitiveServiceImpl) AddWord(ctx context.Context, word string, category string, level int) error {
	if word == "" {
		return fmt.Errorf("word cannot be empty")
	}

	// 转换为敏感词级别
	wordLevel := model.SensitiveWordLevel(level)
	if wordLevel < 1 || wordLevel > 3 {
		wordLevel = model.SensitiveWordLevelLow
	}

	// 转换为敏感词分类
	wordCategory := model.SensitiveWordCategory(category)
	if wordCategory == "" {
		wordCategory = model.SensitiveWordCategoryOther
	}

	// 添加到树
	s.tree.AddWord(word, wordLevel, wordCategory)

	// 持久化到数据库
	if s.db != nil {
		sensitiveWord := model.SensitiveWord{
			Word:     word,
			Category: wordCategory,
			Level:    wordLevel,
			IsActive: true,
		}

		// 使用 upsert 逻辑
		var existing model.SensitiveWord
		result := s.db.Where("word = ?", word).First(&existing)
		if result.Error == gorm.ErrRecordNotFound {
			if err := s.db.Create(&sensitiveWord).Error; err != nil {
				log.Printf("Failed to save sensitive word to database: %v", err)
			}
		} else if result.Error == nil {
			// 更新已存在的记录
			existing.Category = wordCategory
			existing.Level = wordLevel
			existing.IsActive = true
			if err := s.db.Save(&existing).Error; err != nil {
				log.Printf("Failed to update sensitive word in database: %v", err)
			}
		}
	}

	// 同步到 Redis
	if s.redis != nil && s.config.RedisKeyPrefix != "" {
		key := fmt.Sprintf("%s:%s", s.config.RedisKeyPrefix, word)
		data := map[string]interface{}{
			"word":     word,
			"category": category,
			"level":    level,
		}
		jsonData, _ := json.Marshal(data)
		s.redis.Set(ctx, key, jsonData, 0)
	}

	return nil
}

// RemoveWord 移除敏感词
func (s *sensitiveServiceImpl) RemoveWord(ctx context.Context, word string) error {
	if word == "" {
		return fmt.Errorf("word cannot be empty")
	}

	// 从树中移除
	s.tree.RemoveWord(word)

	// 从数据库中标记为不活跃
	if s.db != nil {
		result := s.db.Model(&model.SensitiveWord{}).Where("word = ?", word).Update("is_active", false)
		if result.Error != nil {
			log.Printf("Failed to deactivate sensitive word in database: %v", result.Error)
		}
	}

	// 从 Redis 中删除
	if s.redis != nil && s.config.RedisKeyPrefix != "" {
		key := fmt.Sprintf("%s:%s", s.config.RedisKeyPrefix, word)
		s.redis.Del(ctx, key)
	}

	return nil
}

// Reload 重新加载敏感词库
func (s *sensitiveServiceImpl) Reload(ctx context.Context) error {
	// 清空现有树
	s.tree = NewSensitiveWordTree()

	// 从数据库加载
	if s.config.LoadFromDB {
		if err := s.loadFromDB(ctx); err != nil {
			return fmt.Errorf("failed to load from database: %w", err)
		}
	}

	// 从 Redis 加载
	if s.config.LoadFromRedis && s.redis != nil {
		if err := s.loadFromRedis(ctx); err != nil {
			return fmt.Errorf("failed to load from redis: %w", err)
		}
	}

	return nil
}

// GetWordCount 获取敏感词数量
func (s *sensitiveServiceImpl) GetWordCount(ctx context.Context) int {
	return s.tree.WordCount()
}

// loadFromDB 从数据库加载敏感词
func (s *sensitiveServiceImpl) loadFromDB(ctx context.Context) error {
	if s.db == nil {
		return nil
	}

	var words []model.SensitiveWord
	if err := s.db.Where("is_active = ?", true).Find(&words).Error; err != nil {
		return err
	}

	for _, word := range words {
		s.tree.AddWord(word.Word, word.Level, word.Category)
	}

	log.Printf("Loaded %d sensitive words from database", len(words))
	return nil
}

// loadFromRedis 从 Redis 加载敏感词
func (s *sensitiveServiceImpl) loadFromRedis(ctx context.Context) error {
	if s.redis == nil || s.config.RedisKeyPrefix == "" {
		return nil
	}

	// 使用 SCAN 命令代替 KEYS，避免阻塞
	pattern := fmt.Sprintf("%s:*", s.config.RedisKeyPrefix)
	var cursor uint64
	for {
		keys, nextCursor, err := s.redis.GetClient().Scan(ctx, cursor, pattern, 100).Result()
		if err != nil {
			return err
		}

		for _, key := range keys {
			data, err := s.redis.Get(ctx, key)
			if err != nil {
				continue
			}

			var wordData map[string]interface{}
			if err := json.Unmarshal([]byte(data), &wordData); err != nil {
				continue
			}

			word, _ := wordData["word"].(string)
			category, _ := wordData["category"].(string)
			level, _ := wordData["level"].(float64)

			if word != "" {
				s.tree.AddWord(word, model.SensitiveWordLevel(int(level)), model.SensitiveWordCategory(category))
			}
		}

		cursor = nextCursor
		if cursor == 0 {
			break
		}
	}

	return nil
}

// ==================== 辅助函数 ====================

// ContainsSensitiveWord 快速检查文本是否包含敏感词
func ContainsSensitiveWord(text string, tree *SensitiveWordTree) bool {
	if tree == nil || text == "" {
		return false
	}
	hasSensitive, _ := tree.Check(text)
	return hasSensitive
}

// FilterSensitiveWords 过滤敏感词并返回替换后的文本
func FilterSensitiveWords(text string, tree *SensitiveWordTree, repl string) string {
	if tree == nil || text == "" {
		return text
	}
	if repl == "" {
		repl = "***"
	}
	return tree.Replace(text, repl)
}

// ValidateTextLength 验证文本长度是否合法
func ValidateTextLength(text string, minLen, maxLen int) bool {
	length := utf8.RuneCountInString(text)
	return length >= minLen && length <= maxLen
}

// SanitizeText 清理文本，移除多余空白字符
func SanitizeText(text string) string {
	// 替换多个连续空白字符为单个空格
	spaceReg := regexp.MustCompile(`\s+`)
	text = spaceReg.ReplaceAllString(text, " ")
	// 去除首尾空白
	return strings.TrimSpace(text)
}

// ==================== 默认敏感词列表 ====================

// DefaultSensitiveWords 返回默认敏感词列表（示例）
func DefaultSensitiveWords() map[string]struct{} {
	return map[string]struct{}{
		// 示例敏感词，实际需要从数据库或配置加载
		"测试敏感词1": {},
		"测试敏感词2": {},
		"测试敏感词3": {},
	}
}