pubsub/test/event-target-websocket-client.test.ts

import { describe, it, expect, vi, beforeEach } from "vitest";
import { createWebSocketClientEventTarget } from "../src/event-target-websocket-client.js";
import type { EventEnvelope, TypedEvent } from "../src/types.js";

type TestEvent = TypedEvent<string, EventEnvelope>;

function createMockWebSocket() {
  const sent: string[] = [];
  let onmessageHandler: ((event: { data: string }) => void) | null = null;
  let oncloseHandler: ((event: { code: number; reason: string }) => void) | null = null;

  const ws = {
    send: vi.fn((data: string) => {
      sent.push(data);
    }),
    get onmessage() {
      return onmessageHandler;
    },
    set onmessage(handler: ((event: { data: string }) => void) | null) {
      onmessageHandler = handler;
    },
    get onclose() {
      return oncloseHandler;
    },
    set onclose(handler: ((event: { code: number; reason: string }) => void) | null) {
      oncloseHandler = handler;
    },
    sent,
    simulateMessage(data: string) {
      if (onmessageHandler) {
        onmessageHandler({ data });
      }
    },
    simulateClose(code = 1000, reason = "") {
      if (oncloseHandler) {
        oncloseHandler({ code, reason });
      }
      onmessageHandler = null;
    },
  };

  Object.defineProperty(ws, "onmessage", {
    get() {
      return onmessageHandler;
    },
    set(handler: ((event: { data: string }) => void) | null) {
      onmessageHandler = handler;
    },
  });

  Object.defineProperty(ws, "onclose", {
    get() {
      return oncloseHandler;
    },
    set(handler: ((event: { code: number; reason: string }) => void) | null) {
      oncloseHandler = handler;
    },
  });

  return ws;
}

describe("createWebSocketClientEventTarget", () => {
  describe("dispatchEvent (send path)", () => {
    it("serializes envelope detail and calls ws.send", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const envelope: EventEnvelope<"call.responded", { status: string }> = {
        type: "call.responded",
        id: "uuid-123",
        payload: { status: "ok" },
      };

      const event = new CustomEvent("call.responded:uuid-123", {
        detail: envelope,
      }) as TestEvent;

      eventTarget.dispatchEvent(event);

      expect(ws.send).toHaveBeenCalledTimes(1);
      expect(ws.send).toHaveBeenCalledWith(JSON.stringify(envelope));
    });

    it("returns true from dispatchEvent", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const event = new CustomEvent("test:event", {
        detail: { type: "test", id: "event", payload: null },
      }) as TestEvent;

      const result = eventTarget.dispatchEvent(event);
      expect(result).toBe(true);
    });

    it("propagates ws.send() errors to caller", () => {
      const ws = createMockWebSocket();
      ws.send.mockImplementation(() => {
        throw new Error("WebSocket is not open");
      });
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const event = new CustomEvent("test:event", {
        detail: { type: "test", id: "event", payload: null },
      }) as TestEvent;

      expect(() => eventTarget.dispatchEvent(event)).toThrow("WebSocket is not open");
    });
  });

  describe("addEventListener (subscribe path)", () => {
    it("sends __subscribe control event on first listener for a topic", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("call.responded:uuid-123", listener);

      expect(ws.send).toHaveBeenCalledTimes(1);
      expect(ws.send).toHaveBeenCalledWith(
        JSON.stringify({
          type: "__subscribe",
          id: "",
          payload: { topic: "call.responded:uuid-123" },
        }),
      );
    });

    it("sends __subscribe only once when multiple listeners are added for the same topic", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener1 = vi.fn();
      const listener2 = vi.fn();
      eventTarget.addEventListener("message.sent:msg1", listener1);
      eventTarget.addEventListener("message.sent:msg1", listener2);

      expect(ws.send).toHaveBeenCalledTimes(1);
    });

    it("does not send __subscribe when callback is null", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      eventTarget.addEventListener("topic:a", null as any);

      expect(ws.send).not.toHaveBeenCalled();
    });

    it("supports EventListenerObject with handleEvent", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const handleEvent = vi.fn();
      const listenerObject = { handleEvent };

      eventTarget.addEventListener("obj:test", listenerObject);

      expect(ws.send).toHaveBeenCalledTimes(1);
      expect(ws.send).toHaveBeenCalledWith(
        JSON.stringify({
          type: "__subscribe",
          id: "",
          payload: { topic: "obj:test" },
        }),
      );
    });
  });

  describe("removeEventListener (unsubscribe path)", () => {
    it("sends __unsubscribe when the last listener for a topic is removed", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      expect(ws.send).toHaveBeenCalledTimes(1);

      eventTarget.removeEventListener("topic:a", listener);

      expect(ws.send).toHaveBeenCalledTimes(2);
      expect(ws.send).toHaveBeenCalledWith(
        JSON.stringify({
          type: "__unsubscribe",
          id: "",
          payload: { topic: "topic:a" },
        }),
      );
    });

    it("does not send __unsubscribe while other listeners remain for the same topic", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener1 = vi.fn();
      const listener2 = vi.fn();
      eventTarget.addEventListener("event:type1", listener1);
      eventTarget.addEventListener("event:type1", listener2);

      expect(ws.send).toHaveBeenCalledTimes(1);

      eventTarget.removeEventListener("event:type1", listener1);

      expect(ws.send).toHaveBeenCalledTimes(1);

      eventTarget.removeEventListener("event:type1", listener2);

      expect(ws.send).toHaveBeenCalledTimes(2);
      expect(ws.send).toHaveBeenCalledWith(
        JSON.stringify({
          type: "__unsubscribe",
          id: "",
          payload: { topic: "event:type1" },
        }),
      );
    });

    it("does not send __unsubscribe when removing a callback that was never registered", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener1 = vi.fn();
      eventTarget.addEventListener("topic:a", listener1);

      const unregisteredListener = vi.fn();
      eventTarget.removeEventListener("topic:a", unregisteredListener);

      expect(ws.send).toHaveBeenCalledTimes(1);
    });

    it("does not send __unsubscribe when callback is null", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      eventTarget.addEventListener("topic:a", null as any);

      eventTarget.removeEventListener("topic:a", null as any);

      expect(ws.send).not.toHaveBeenCalled();
    });

    it("supports EventListenerObject with handleEvent for removal", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const handleEvent = vi.fn();
      const listenerObject = { handleEvent };

      eventTarget.addEventListener("obj:test", listenerObject);
      expect(ws.send).toHaveBeenCalledWith(
        JSON.stringify({
          type: "__subscribe",
          id: "",
          payload: { topic: "obj:test" },
        }),
      );

      eventTarget.removeEventListener("obj:test", listenerObject);
      expect(ws.send).toHaveBeenCalledWith(
        JSON.stringify({
          type: "__unsubscribe",
          id: "",
          payload: { topic: "obj:test" },
        }),
      );
    });
  });

  describe("receive path (ws.onmessage)", () => {
    it("parses envelope, creates CustomEvent with type:id topic, and dispatches to listeners", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("message.sent:msg1", listener);

      const envelope: EventEnvelope = {
        type: "message.sent",
        id: "msg1",
        payload: "hello world",
      };
      ws.simulateMessage(JSON.stringify(envelope));

      expect(listener).toHaveBeenCalledTimes(1);
      const receivedEvent = listener.mock.calls[0][0] as TestEvent;
      expect(receivedEvent.type).toBe("message.sent:msg1");
      expect(receivedEvent.detail).toEqual(envelope);
    });

    it("delivers messages to all listeners on the same topic", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener1 = vi.fn();
      const listener2 = vi.fn();
      eventTarget.addEventListener("topic:x", listener1);
      eventTarget.addEventListener("topic:x", listener2);

      const envelope: EventEnvelope = { type: "topic", id: "x", payload: "data" };
      ws.simulateMessage(JSON.stringify(envelope));

      expect(listener1).toHaveBeenCalledTimes(1);
      expect(listener2).toHaveBeenCalledTimes(1);
      expect((listener1.mock.calls[0][0] as TestEvent).detail).toEqual(envelope);
      expect((listener2.mock.calls[0][0] as TestEvent).detail).toEqual(envelope);
    });

    it("ignores messages for topics with no registered listeners", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      const envelope: EventEnvelope = { type: "other", id: "b", payload: null };
      ws.simulateMessage(JSON.stringify(envelope));

      expect(listener).not.toHaveBeenCalled();
    });
  });

  describe("malformed JSON handling", () => {
    it("silently ignores malformed JSON and logs a warning", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});

      ws.simulateMessage("not valid json{{");

      expect(listener).not.toHaveBeenCalled();
      expect(warnSpy).toHaveBeenCalledTimes(1);
      expect(warnSpy).toHaveBeenCalledWith(
        expect.stringContaining("Failed to parse WebSocket message"),
      );

      warnSpy.mockRestore();
    });

    it("continues delivering valid messages after a parse error", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      const warnSpy = vi.spyOn(console, "warn").mockImplementation(() => {});

      ws.simulateMessage("broken{{{");

      expect(listener).not.toHaveBeenCalled();

      const envelope: EventEnvelope = { type: "topic", id: "a", payload: "good" };
      ws.simulateMessage(JSON.stringify(envelope));

      expect(listener).toHaveBeenCalledTimes(1);
      expect((listener.mock.calls[0][0] as TestEvent).detail).toEqual(envelope);

      warnSpy.mockRestore();
    });
  });

  describe("control events from server", () => {
    it("silently ignores __subscribe control events received from server", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      ws.simulateMessage(JSON.stringify({
        type: "__subscribe",
        id: "",
        payload: { topic: "topic:a" },
      }));

      expect(listener).not.toHaveBeenCalled();
    });

    it("silently ignores __unsubscribe control events received from server", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      ws.simulateMessage(JSON.stringify({
        type: "__unsubscribe",
        id: "",
        payload: { topic: "topic:a" },
      }));

      expect(listener).not.toHaveBeenCalled();
    });

    it("ignores any event type starting with __", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("__custom:thing", listener);

      ws.simulateMessage(JSON.stringify({
        type: "__custom",
        id: "thing",
        payload: null,
      }));

      expect(listener).not.toHaveBeenCalled();
    });
  });

  describe("EventEnvelope round-trip", () => {
    it("round-trips full { type, id, payload } envelope through send and receive", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("user.joined:user-99", listener);

      const originalEnvelope: EventEnvelope<"user.joined", { name: string; role: string }> = {
        type: "user.joined",
        id: "user-99",
        payload: { name: "Bob", role: "admin" },
      };

      const event = new CustomEvent("user.joined:user-99", {
        detail: originalEnvelope,
      }) as TestEvent;

      eventTarget.dispatchEvent(event);

      const dispatchedData = ws.sent[1];
      expect(dispatchedData).toBe(JSON.stringify(originalEnvelope));

      const sentData = dispatchedData;

      ws.simulateMessage(sentData);

      expect(listener).toHaveBeenCalledTimes(1);
      const receivedDetail = (listener.mock.calls[0][0] as TestEvent).detail as EventEnvelope;
      expect(receivedDetail).toEqual(originalEnvelope);
      expect(receivedDetail.type).toBe("user.joined");
      expect(receivedDetail.id).toBe("user-99");
      expect(receivedDetail.payload).toEqual({ name: "Bob", role: "admin" });
    });

    it("round-trips envelope with null payload", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("ping:1", listener);

      const envelope: EventEnvelope = { type: "ping", id: "1", payload: null };
      ws.simulateMessage(JSON.stringify(envelope));

      expect(listener).toHaveBeenCalledTimes(1);
      const receivedDetail = (listener.mock.calls[0][0] as TestEvent).detail as EventEnvelope;
      expect(receivedDetail).toEqual(envelope);
    });
  });

  describe("topic scoping", () => {
    it("forms topic from envelope type and id fields", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("user.action:abc-123", listener);

      const envelope: EventEnvelope = {
        type: "user.action",
        id: "abc-123",
        payload: { done: true },
      };
      ws.simulateMessage(JSON.stringify(envelope));

      expect(listener).toHaveBeenCalledTimes(1);
      expect((listener.mock.calls[0][0] as TestEvent).type).toBe("user.action:abc-123");
    });

    it("does not match when type differs even if id is the same", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("user.created:id1", listener);

      ws.simulateMessage(JSON.stringify({ type: "user.deleted", id: "id1", payload: null }));

      expect(listener).not.toHaveBeenCalled();
    });

    it("does not match when id differs even if type is the same", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("event:alpha", listener);

      ws.simulateMessage(JSON.stringify({ type: "event", id: "beta", payload: null }));

      expect(listener).not.toHaveBeenCalled();
    });

    it("forms topic with undefined id as 'type:undefined' which does not match 'type:'", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("ping:", listener);

      ws.simulateMessage(JSON.stringify({ type: "ping", payload: "hello" }));

      expect(listener).not.toHaveBeenCalled();
    });
  });

  describe("envelope validation on receive", () => {
    it("ignores messages where type is not a string", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      ws.simulateMessage(JSON.stringify({ type: 123, id: "a", payload: null }));

      expect(listener).not.toHaveBeenCalled();
    });

    it("ignores messages where type is undefined", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      ws.simulateMessage(JSON.stringify({ id: "a", payload: null }));

      expect(listener).not.toHaveBeenCalled();
    });

    it("ignores messages where type is null", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      ws.simulateMessage(JSON.stringify({ type: null, id: "a", payload: null }));

      expect(listener).not.toHaveBeenCalled();
    });
  });

  describe("reconnection", () => {
    it("restores subscriptions on a new event target with a new WebSocket", () => {
      const ws1 = createMockWebSocket();
      const eventTarget1 = createWebSocketClientEventTarget<TestEvent>(ws1 as any);

      const listener1 = vi.fn();
      eventTarget1.addEventListener("order.created:ord-1", listener1);
      expect(ws1.send).toHaveBeenCalledTimes(1);

      ws1.simulateClose();

      const ws2 = createMockWebSocket();
      const eventTarget2 = createWebSocketClientEventTarget<TestEvent>(ws2 as any);

      const listener2 = vi.fn();
      eventTarget2.addEventListener("order.created:ord-1", listener2);
      expect(ws2.send).toHaveBeenCalledTimes(1);
      expect(ws2.send).toHaveBeenCalledWith(
        JSON.stringify({ type: "__subscribe", id: "", payload: { topic: "order.created:ord-1" } }),
      );

      const envelope: EventEnvelope = { type: "order.created", id: "ord-1", payload: { item: "book" } };
      ws2.simulateMessage(JSON.stringify(envelope));

      expect(listener2).toHaveBeenCalledTimes(1);
      expect((listener2.mock.calls[0][0] as TestEvent).detail).toEqual(envelope);
    });

    it("does not receive messages on old connection after reconnect", () => {
      const ws1 = createMockWebSocket();
      const eventTarget1 = createWebSocketClientEventTarget<TestEvent>(ws1 as any);

      const listener1 = vi.fn();
      eventTarget1.addEventListener("chat.msg:1", listener1);

      ws1.simulateClose();

      const ws2 = createMockWebSocket();
      const eventTarget2 = createWebSocketClientEventTarget<TestEvent>(ws2 as any);

      const listener2 = vi.fn();
      eventTarget2.addEventListener("chat.msg:1", listener2);

      ws1.simulateMessage(JSON.stringify({ type: "chat.msg", id: "1", payload: "stale" }));

      expect(listener1).not.toHaveBeenCalled();
      expect(listener2).not.toHaveBeenCalled();
    });
  });

  describe("connection close", () => {
    it("does not send __unsubscribe on close since lifecycle is caller-managed", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      expect(ws.send).toHaveBeenCalledTimes(1);

      ws.simulateClose();

      expect(ws.send).toHaveBeenCalledTimes(1);
    });
  });

  describe("close()", () => {
    it("sends __unsubscribe for all active subscriptions", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener1 = vi.fn();
      const listener2 = vi.fn();
      eventTarget.addEventListener("topic:a", listener1);
      eventTarget.addEventListener("topic:b", listener2);

      (ws.send as ReturnType<typeof vi.fn>).mockClear();

      eventTarget.close();

      const sent = ws.sent.map((s: string) => JSON.parse(s));
      const unsubscribes = sent.filter((e: any) => e.type === "__unsubscribe");
      expect(unsubscribes).toHaveLength(2);
      const topics = unsubscribes.map((e: any) => e.payload.topic);
      expect(topics).toContain("topic:a");
      expect(topics).toContain("topic:b");
    });

    it("restores original onmessage handler", () => {
      const ws = createMockWebSocket();
      const originalOnmessage = vi.fn();
      ws.onmessage = originalOnmessage;

      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);
      expect(ws.onmessage).not.toBe(originalOnmessage);

      eventTarget.close();

      expect(ws.onmessage).toBe(originalOnmessage);
    });

    it("does not deliver messages after close", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      eventTarget.close();

      const envelope: EventEnvelope = { type: "topic", id: "a", payload: "hello" };
      ws.simulateMessage(JSON.stringify(envelope));

      expect(listener).not.toHaveBeenCalled();
    });

    it("does not send __subscribe after close", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);
      eventTarget.close();

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      expect(ws.send).not.toHaveBeenCalledWith(
        expect.stringContaining("__subscribe"),
      );
    });

    it("dispatchEvent returns true but does not send after close", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);
      eventTarget.close();

      (ws.send as ReturnType<typeof vi.fn>).mockClear();

      const event = new CustomEvent("test:event", {
        detail: { type: "test", id: "event", payload: null },
      }) as TestEvent;

      const result = eventTarget.dispatchEvent(event);
      expect(result).toBe(true);
      expect(ws.send).not.toHaveBeenCalled();
    });

    it("is idempotent", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener = vi.fn();
      eventTarget.addEventListener("topic:a", listener);

      eventTarget.close();
      eventTarget.close();

      const sentCalls = ws.sent.filter((s: string) => JSON.parse(s).type === "__unsubscribe");
      expect(sentCalls).toHaveLength(1);
    });
  });

  describe("dispatchEvent (send path) edge cases", () => {
    it("sends envelope with null payload", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const event = new CustomEvent("notify:1", {
        detail: { type: "notify", id: "1", payload: null },
      }) as TestEvent;

      eventTarget.dispatchEvent(event);

      expect(ws.send).toHaveBeenCalledTimes(1);
      const sent = JSON.parse(ws.sent[0]);
      expect(sent.type).toBe("notify");
      expect(sent.id).toBe("1");
      expect(sent.payload).toBeNull();
    });

    it("sends multiple events in order", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const event1 = new CustomEvent("a:1", {
        detail: { type: "a", id: "1", payload: "first" },
      }) as TestEvent;
      const event2 = new CustomEvent("b:2", {
        detail: { type: "b", id: "2", payload: "second" },
      }) as TestEvent;

      eventTarget.dispatchEvent(event1);
      eventTarget.dispatchEvent(event2);

      expect(ws.sent).toHaveLength(2);
      expect(JSON.parse(ws.sent[0])).toEqual({ type: "a", id: "1", payload: "first" });
      expect(JSON.parse(ws.sent[1])).toEqual({ type: "b", id: "2", payload: "second" });
    });
  });

  describe("subscription reference counting", () => {
    it("re-sends __subscribe after all listeners removed and a new one added", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listener1 = vi.fn();
      eventTarget.addEventListener("topic:a", listener1);
      expect(ws.send).toHaveBeenCalledTimes(1);

      eventTarget.removeEventListener("topic:a", listener1);
      expect(ws.send).toHaveBeenCalledTimes(2);

      const listener2 = vi.fn();
      eventTarget.addEventListener("topic:a", listener2);
      expect(ws.send).toHaveBeenCalledTimes(3);

      expect(ws.send).toHaveBeenNthCalledWith(1,
        JSON.stringify({ type: "__subscribe", id: "", payload: { topic: "topic:a" } }),
      );
      expect(ws.send).toHaveBeenNthCalledWith(2,
        JSON.stringify({ type: "__unsubscribe", id: "", payload: { topic: "topic:a" } }),
      );
      expect(ws.send).toHaveBeenNthCalledWith(3,
        JSON.stringify({ type: "__subscribe", id: "", payload: { topic: "topic:a" } }),
      );
    });

    it("tracks separate topics independently", () => {
      const ws = createMockWebSocket();
      const eventTarget = createWebSocketClientEventTarget<TestEvent>(ws as any);

      const listenerA = vi.fn();
      const listenerB = vi.fn();
      eventTarget.addEventListener("topic:a", listenerA);
      eventTarget.addEventListener("topic:b", listenerB);

      expect(ws.send).toHaveBeenCalledTimes(2);

      eventTarget.removeEventListener("topic:a", listenerA);
      expect(ws.send).toHaveBeenCalledTimes(3);

      expect(ws.send).toHaveBeenNthCalledWith(3,
        JSON.stringify({ type: "__unsubscribe", id: "", payload: { topic: "topic:a" } }),
      );

      const listenerB2 = vi.fn();
      eventTarget.addEventListener("topic:b", listenerB2);
      expect(ws.send).toHaveBeenCalledTimes(3);
    });
  });
});