refactor: Type event_processor_class against the AsyncEventProcessor interface

Mirror how the sync Config types event_processor_class against the
EventProcessor interface. Add an AsyncEventProcessor ABC to interfaces
and reference it directly instead of the concrete implementation, which
also removes the aiohttp-avoiding TYPE_CHECKING import.

Author: jsonbailey

ldclient/async_config.py

@@ -8,7 +8,7 @@
     compatibility guarantees.
 """
 
-from typing import TYPE_CHECKING, Callable, List, Optional, Set
+from typing import Callable, List, Optional, Set
 
 from ldclient.config import (
     GET_LATEST_FEATURES_PATH,
@@ -28,16 +28,12 @@
 from ldclient.interfaces import (
     AsyncBigSegmentStore,
     AsyncDataSourceUpdateSink,
+    AsyncEventProcessor,
     AsyncFeatureStore,
     UpdateProcessor
 )
 from ldclient.plugin import AsyncPlugin
 
-if TYPE_CHECKING:
-    # Imported for typing only. The concrete AsyncEventProcessor pulls in aiohttp
-    # transitively, so it is kept out of the runtime import graph.
-    from ldclient.impl.events.async_event_processor import AsyncEventProcessor
-
 
 class AsyncBigSegmentsConfig:
     """Configuration options related to Big Segments for the async SDK client.
@@ -120,7 +116,7 @@ def __init__(
         use_ldd: bool = False,
         feature_store: Optional[AsyncFeatureStore] = None,
         feature_requester_class=None,
-        event_processor_class: Optional[Callable[['AsyncConfig'], 'AsyncEventProcessor']] = None,
+        event_processor_class: Optional[Callable[['AsyncConfig'], AsyncEventProcessor]] = None,
         private_attributes: Set[str] = set(),
         all_attributes_private: bool = False,
         offline: bool = False,
@@ -313,7 +309,7 @@ def feature_store(self) -> Optional[AsyncFeatureStore]:
         return self.__feature_store
 
     @property
-    def event_processor_class(self) -> Optional[Callable[['AsyncConfig'], 'AsyncEventProcessor']]:
+    def event_processor_class(self) -> Optional[Callable[['AsyncConfig'], AsyncEventProcessor]]:
         return self.__event_processor_class
 
     @property

ldclient/interfaces.py

@@ -484,6 +484,39 @@ def stop(self):
         """
 
 
+class AsyncEventProcessor(ABC):
+    """
+    Async interface for the component that buffers analytics events and sends them to LaunchDarkly,
+    for use with :class:`ldclient.async_client.AsyncLDClient`. It mirrors :class:`EventProcessor`,
+    except ``stop`` is a coroutine. The default implementation can be replaced for testing.
+
+    .. caution::
+        This feature is experimental and should NOT be considered ready for production
+        use. It may change or be removed without notice and is not subject to backwards
+        compatibility guarantees.
+    """
+
+    @abstractmethod
+    def send_event(self, event):
+        """
+        Processes an event to be sent at some point.
+        """
+
+    @abstractmethod
+    def flush(self):
+        """
+        Specifies that any buffered events should be sent as soon as possible, rather than waiting
+        for the next flush interval. This method is not awaitable; calling ``stop()`` will deliver
+        any events not yet sent prior to shutting down.
+        """
+
+    @abstractmethod
+    async def stop(self):
+        """
+        Shuts down the event processor after first delivering all pending events.
+        """
+
+
 class FeatureRequester(ABC):
     """
     Interface for the component that acquires feature flag data in polling mode. The default