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server/build/lib/app/services/sensitive_service.py

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+"""敏感词服务：DFA 算法，词库 Redis 缓存 60s（后台维护后即时生效，对齐《02-技术文档》6.7）"""
+import json
+import time
+
+import redis.asyncio as aioredis
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.common import SensitiveWord
+
+CACHE_KEY = "words:sensitive"
+CACHE_TTL = 60
+
+
+class DFAMatcher:
+    """确定性有穷自动机敏感词匹配器"""
+
+    def __init__(self) -> None:
+        self.root: dict = {}
+
+    def add(self, word: str) -> None:
+        node = self.root
+        for ch in word.strip().lower():
+            if not ch:
+                continue
+            node = node.setdefault(ch, {})
+        node["\x00"] = True  # 词结束标记
+
+    def find(self, text: str) -> str | None:
+        """返回命中的第一个敏感词，未命中返回 None"""
+        text = text.lower()
+        n = len(text)
+        for i in range(n):
+            node = self.root
+            j = i
+            while j < n and text[j] in node:
+                node = node[text[j]]
+                j += 1
+                if "\x00" in node:
+                    return text[i:j]
+        return None
+
+
+# 进程内缓存（matcher, 构建时间戳）
+_local_cache: tuple[DFAMatcher, float] | None = None
+
+
+async def get_matcher(db: AsyncSession, redis: aioredis.Redis) -> DFAMatcher:
+    """获取 DFA 匹配器：进程缓存 → Redis → DB，60s 重建"""
+    global _local_cache
+    now = time.time()
+    if _local_cache and now - _local_cache[1] < CACHE_TTL:
+        return _local_cache[0]
+
+    words: list[str] = []
+    cached = await redis.get(CACHE_KEY)
+    if cached:
+        words = json.loads(cached)
+    else:
+        rows = (await db.execute(select(SensitiveWord.word))).scalars().all()
+        words = [w for w in rows if w]
+        await redis.set(CACHE_KEY, json.dumps(words, ensure_ascii=False), ex=CACHE_TTL)
+
+    matcher = DFAMatcher()
+    for w in words:
+        matcher.add(w)
+    _local_cache = (matcher, now)
+    return matcher
+
+
+async def find_sensitive(db: AsyncSession, redis: aioredis.Redis, text: str) -> str | None:
+    """检查文本，返回命中的敏感词或 None"""
+    if not text:
+        return None
+    matcher = await get_matcher(db, redis)
+    return matcher.find(text)
+
+
+async def invalidate_cache(redis: aioredis.Redis) -> None:
+    """后台增删词库后调用：清 Redis 缓存，进程缓存等 60s 内自然过期"""
+    global _local_cache
+    _local_cache = None
+    await redis.delete(CACHE_KEY)