feat(backend): add SIMPLE_STREAMING WebRTC control-path streaming

Backend/streaming/simple.ts

@@ -0,0 +1,80 @@
+type StreamSessionLike = {
+  id: string;
+  ownerUserId: string;
+  cameraDeviceId: string;
+  requesterDeviceId: string;
+  status: string;
+  reason: string;
+  metadata: Record<string, unknown> | null;
+  startedAt: Date | null;
+  endedAt: Date | null;
+  createdAt: Date;
+  updatedAt: Date;
+};
+
+type StreamEndedPayloadInput = {
+  streamSessionId: string;
+  cameraDeviceId: string;
+  requesterDeviceId: string;
+  endedAt: Date;
+  reason: 'completed' | 'cancelled' | 'failed';
+};
+
+export const isStreamParticipant = (session: Pick<StreamSessionLike, 'cameraDeviceId' | 'requesterDeviceId'>, deviceId: string): boolean =>
+  session.cameraDeviceId === deviceId || session.requesterDeviceId === deviceId;
+
+export const canRelayWebrtcSignal = (
+  session: Pick<StreamSessionLike, 'cameraDeviceId' | 'requesterDeviceId'>,
+  fromDeviceId: string,
+  toDeviceId: string,
+): boolean => {
+  if (fromDeviceId === toDeviceId) {
+    return false;
+  }
+
+  return isStreamParticipant(session, fromDeviceId) && isStreamParticipant(session, toDeviceId);
+};
+
+export const createStreamRequestedPayload = (
+  session: Pick<StreamSessionLike, 'id' | 'cameraDeviceId' | 'requesterDeviceId' | 'status' | 'reason'>,
+) => ({
+  streamSessionId: session.id,
+  cameraDeviceId: session.cameraDeviceId,
+  requesterDeviceId: session.requesterDeviceId,
+  status: session.status,
+  reason: session.reason,
+});
+
+export const createStreamStartedPayload = (
+  session: Pick<StreamSessionLike, 'id' | 'cameraDeviceId' | 'requesterDeviceId' | 'status' | 'startedAt'>,
+) => ({
+  streamSessionId: session.id,
+  cameraDeviceId: session.cameraDeviceId,
+  requesterDeviceId: session.requesterDeviceId,
+  status: session.status,
+  startedAt: session.startedAt,
+  transport: 'webrtc',
+});
+
+export const createStreamEndedPayload = (input: StreamEndedPayloadInput) => ({
+  streamSessionId: input.streamSessionId,
+  cameraDeviceId: input.cameraDeviceId,
+  requesterDeviceId: input.requesterDeviceId,
+  status: 'ended',
+  endedAt: input.endedAt,
+  reason: input.reason,
+});
+
+export const toSimpleStreamSessionResponse = (session: StreamSessionLike) => ({
+  id: session.id,
+  ownerUserId: session.ownerUserId,
+  cameraDeviceId: session.cameraDeviceId,
+  requesterDeviceId: session.requesterDeviceId,
+  status: session.status,
+  reason: session.reason,
+  metadata: session.metadata,
+  startedAt: session.startedAt,
+  endedAt: session.endedAt,
+  createdAt: session.createdAt,
+  updatedAt: session.updatedAt,
+});