[feat] add basic domain

usecase/user.py

@@ -0,0 +1,41 @@
+from dataclasses import dataclass
+
+from domain.error import UserNotFoundError
+from domain.user import User
+from usecase.interface import Logger, Tracer, UserRepository
+
+
+@dataclass(frozen=True, slots=True)
+class GetUserQuery:
+    user_id: str
+
+
+class GetUser:
+    def __init__(
+        self,
+        repository: UserRepository,
+        logger: Logger,
+        tracer: Tracer,
+    ) -> None:
+        self._repository = repository
+        self._logger = logger
+        self._tracer = tracer
+
+    def execute(self, query: GetUserQuery) -> User:
+        with self._tracer.start_span(
+            'usecase.get_user',
+            attrs={'user.id': query.user_id},
+        ) as span:
+            user = self._repository.get(query.user_id)
+            if user is None:
+                error = UserNotFoundError(query.user_id)
+                span.record_error(error)
+                self._logger.warning(
+                    'user_not_found',
+                    attrs={'user_id': query.user_id},
+                )
+                raise error
+
+            span.set_attribute('user.email', user.email)
+            self._logger.info('user_loaded', attrs={'user_id': user.id})
+            return user