feat: 初始提交

backend/app/services/usage_service.py

@@ -0,0 +1,21 @@
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from ..repositories.usage_metric_repository import UsageMetricRepository
+
+
+class UsageService:
+    """通用计数服务，目前用于统计 API 请求次数等。"""
+
+    def __init__(self, session: AsyncSession):
+        self.session = session
+        self.repo = UsageMetricRepository(session)
+
+    async def increment(self, key: str) -> None:
+        counter = await self.repo.get_or_create(key)
+        counter.value += 1
+        await self.session.commit()
+
+    async def get_value(self, key: str) -> int:
+        counter = await self.repo.get_or_create(key)
+        await self.session.commit()
+        return counter.value