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+# SB-3 (API Refactor)
+
+**Status**: Under Review
+
+This proposal aims to simplify the API and make it possible to build more
+scalable implementations.
+
+## Context
+
+The initial design of seabird works well for an MVP, but there are a number of
+design decisions which should be re-examined.
+
+Bidirectional streaming complicates implementations and is error prone.
+Additionally, there are a number of endpoints which are complex to maintain
+but are seldom (if at all) used.
+
+## Goals
+
+- Change bidirectional streaming to server only
+- Add callback endpoints rather than streamed messages
+- Remove currently unused endpoints
+- Allow for implementation of simple chat backends without a command stream
+
+## Details
+
+### SeabirdService
+
+The current API:
+
+```protobuf
+service Seabird {
+  rpc StreamEvents(StreamEventsRequest) returns (stream Event);
+
+  // Chat actions
+  rpc PerformAction(PerformActionRequest) returns (PerformActionResponse);
+  rpc PerformPrivateAction(PerformPrivateActionRequest) returns (PerformPrivateActionResponse);
+  rpc SendMessage(SendMessageRequest) returns (SendMessageResponse);
+  rpc SendPrivateMessage(SendPrivateMessageRequest) returns (SendPrivateMessageResponse);
+  rpc JoinChannel(JoinChannelRequest) returns (JoinChannelResponse);
+  rpc LeaveChannel(LeaveChannelRequest) returns (LeaveChannelResponse);
+  rpc UpdateChannelInfo(UpdateChannelInfoRequest) returns (UpdateChannelInfoResponse);
+
+  // Chat backend introspection
+  rpc ListBackends(ListBackendsRequest) returns (ListBackendsResponse);
+  rpc GetBackendInfo(BackendInfoRequest) returns (BackendInfoResponse);
+
+  // Chat connection introspection
+  rpc ListChannels(ListChannelsRequest) returns (ListChannelsResponse);
+  rpc GetChannelInfo(ChannelInfoRequest) returns (ChannelInfoResponse);
+
+  // Seabird introspection
+  rpc GetCoreInfo(CoreInfoRequest) returns (CoreInfoResponse);
+}
+```
+
+#### Remove Unused Endpoints
+
+While they are useful, the backend and channel introspection methods are not
+currently used by any known plugins and are complicating the implementation of
+SB-1 without an additional data store.
+
+```protobuf
+  // Chat backend introspection
+  rpc ListBackends(ListBackendsRequest) returns (ListBackendsResponse);
+  rpc GetBackendInfo(BackendInfoRequest) returns (BackendInfoResponse);
+
+  // Chat connection introspection
+  rpc ListChannels(ListChannelsRequest) returns (ListChannelsResponse);
+  rpc GetChannelInfo(ChannelInfoRequest) returns (ChannelInfoResponse);
+```
+
+Note that even though this proposal recommends dropping these methods, ideally
+they would be added back in the future when a permanent data store is added to
+seabird-core.
+
+### ChatBackendService
+
+The current API:
+
+```protobuf
+message ChatEvent {
+  string id = 1;
+
+  oneof inner {
+    // Seabird-internal event types
+    HelloChatEvent hello = 2;
+    SuccessChatEvent success = 3;
+    FailedChatEvent failed = 4;
+
+    // Messages from the service
+    common.MessageEvent message = 5;
+    common.PrivateMessageEvent private_message = 6;
+    common.MentionEvent mention = 7;
+    common.CommandEvent command = 8;
+    common.ActionEvent action = 12;
+    common.PrivateActionEvent private_action = 13;
+
+    // Channel changes
+    JoinChannelChatEvent join_channel = 9;
+    LeaveChannelChatEvent leave_channel = 10;
+    ChangeChannelChatEvent change_channel = 11;
+  }
+}
+
+message ChatRequest {
+  string id = 1;
+
+  oneof inner {
+    SendMessageChatRequest send_message = 2;
+    SendPrivateMessageChatRequest send_private_message = 3;
+    JoinChannelChatRequest join_channel = 4;
+    LeaveChannelChatRequest leave_channel = 5;
+    UpdateChannelInfoChatRequest update_channel_info = 6;
+    PerformActionChatRequest perform_action = 7;
+    PerformPrivateActionChatRequest perform_private_action = 8;
+  }
+}
+
+service ChatIngest {
+  rpc IngestEvents(stream ChatEvent) returns (stream ChatRequest);
+}
+```
+
+### Add Callback Endpoints for ChatIngest
+
+Currently, all backend chat events are shared in a bidirectional stream.
+Backend chat events are sent to the server and the server emits command
+events.
+
+Moving callbacks to separate endpoints rather than in an event stream allows
+us to scale out handling of events if necessary. Multiple seabird-core hosts
+could be handling event ingestion rather than it being limited to one.
+
+#### Separate Endpoints
+
+This portion of the proposal would add additional endpoints to ChatIngest as
+follows, to act as a replacement for incoming `ChatEvents`:
+
+```protobuf
+rpc SuccessCallback(SuccessEvent)
+rpc FailureCallback(FailureEvent)
+
+rpc MessageCallback(common.MessageEvent)
+rpc PrivateMessageCallback(common.PrivateMessageEvent)
+rpc MentionCallback(common.MentionEvent)
+rpc CommandCallback(common.CommandEvent)
+rpc ActionCallback(common.ActionEvent)
+rpc PrivateActionCallback(common.PrivateActionEvent)
+
+rpc JoinChannelCallback(JoinChannelEvent)
+rpc LeaveChannelCallback(LeaveChannelEvent)
+rpc ChangeChannelCallback(ChangeChannelEvent)
+```
+
+At this point the `ChatEvent` type would no longer be necessary, other than
+`HelloChatEvent`, which is replaced by modifying the stream endpoint in the
+next section.
+
+
+#### Single Endpoint
+
+Alternatively, we could keep `ChatEvent`, remove `HelloChatEvent` from the
+`oneof`, and add the following endpoint:
+
+```
+rpc EventCallback(repeated ChatEvent)
+```
+
+This would additionally allow for submitting multiple events at once.
+
+### Simplify Streaming to Only Server-Side
+
+The `IngestEvents` endpoint would be replaced with `CommandStream`, as below.
+`StartCommandStreamRequest` would replace `HelloChatEvent`.
+
+```protobuf
+rpc CommandStream(StartCommandStreamRequest) returns (stream ChatRequest);
+```