refactor: split discord gateway helpers

src/discord/monitor.gateway.ts

@@ -0,0 +1,63 @@
+import type { EventEmitter } from "node:events";
+
+export type DiscordGatewayHandle = {
+  emitter?: Pick<EventEmitter, "on" | "removeListener">;
+  disconnect?: () => void;
+};
+
+export function getDiscordGatewayEmitter(
+  gateway?: unknown,
+): EventEmitter | undefined {
+  return (gateway as { emitter?: EventEmitter } | undefined)?.emitter;
+}
+
+export async function waitForDiscordGatewayStop(params: {
+  gateway?: DiscordGatewayHandle;
+  abortSignal?: AbortSignal;
+  onGatewayError?: (err: unknown) => void;
+}): Promise<void> {
+  const { gateway, abortSignal, onGatewayError } = params;
+  const emitter = gateway?.emitter;
+  return await new Promise<void>((resolve, reject) => {
+    let settled = false;
+    const cleanup = () => {
+      abortSignal?.removeEventListener("abort", onAbort);
+      emitter?.removeListener("error", onGatewayErrorEvent);
+    };
+    const finishResolve = () => {
+      if (settled) return;
+      settled = true;
+      cleanup();
+      try {
+        gateway?.disconnect?.();
+      } finally {
+        resolve();
+      }
+    };
+    const finishReject = (err: unknown) => {
+      if (settled) return;
+      settled = true;
+      cleanup();
+      try {
+        gateway?.disconnect?.();
+      } finally {
+        reject(err);
+      }
+    };
+    const onAbort = () => {
+      finishResolve();
+    };
+    const onGatewayErrorEvent = (err: unknown) => {
+      onGatewayError?.(err);
+      finishReject(err);
+    };
+
+    if (abortSignal?.aborted) {
+      onAbort();
+      return;
+    }
+
+    abortSignal?.addEventListener("abort", onAbort, { once: true });
+    emitter?.on("error", onGatewayErrorEvent);
+  });
+}