feat: Add optional parameter to unwire event when terminated (#12)

[remdalm]

No description provided.

[velocitysystems]

Rather than refactoring DownloadEventManager we can simplify this by relocating the wrapping logic from DownloadEventManager.addListener to the listen(..) method:

async listen(
   listener: (download: DownloadWithAnyStatus) => void,
   options?: ListenOptions,
): Promise<UnlistenFn> {
   if (!options?.autoUnlisten) {
      return DownloadEventManager.shared.addListener(this.path, listener);
   }

   let unlisten: UnlistenFn;

   const wrappedListener = (download: DownloadWithAnyStatus): void => {
      try {
         listener(download);
      } finally {
         const isTerminal = download.status === DownloadStatus.Completed
            || download.status === DownloadStatus.Canceled;

         if (isTerminal) {
            unlisten();
         }
      }
   };

   unlisten = await DownloadEventManager.shared.addListener(this.path, wrappedListener);
   return unlisten;
},

However this still leaves the issue of "how do we test?" without exposing public methods/utilities for resetting state. We can solve this by extracting into a small, pure, exported function:

// actions.ts
export function wrapListenerWithAutoUnlisten(
   listener: (download: DownloadWithAnyStatus) => void,
   unlisten: () => void,
): (download: DownloadWithAnyStatus) => void {
   return (download: DownloadWithAnyStatus): void => {
      try {
         listener(download);
      } finally {
         const isTerminal = download.status === DownloadStatus.Completed
            || download.status === DownloadStatus.Canceled;

         if (isTerminal) {
            unlisten();
         }
      }
   };
}

Then in actions.listen:

async listen(
   listener: (download: DownloadWithAnyStatus) => void,
   options?: ListenOptions,
): Promise<UnlistenFn> {
   if (!options?.autoUnlisten) {
      return DownloadEventManager.shared.addListener(this.path, listener);
   }

   let unlisten: UnlistenFn;
   const wrapped = wrapListenerWithAutoUnlisten(listener, () => unlisten());

   unlisten = await DownloadEventManager.shared.addListener(this.path, wrapped);
   return unlisten;
},

Tests then become trivial — just call the wrapper directly:

it('calls unlisten on Completed', () => {
   const listener = vi.fn();
   const unlisten = vi.fn();
   const wrapped = wrapListenerWithAutoUnlisten(listener, unlisten);

   wrapped(attachDownload({ ...IDLE_STATE, status: DownloadStatus.Completed }));

   expect(listener).toHaveBeenCalledTimes(1);
   expect(unlisten).toHaveBeenCalledTimes(1);
});