export type BrowserPreviewCursor = {
  x: number;
  y: number;
  label: string;
};

type Listener = (activities: ReadonlyMap<string, BrowserPreviewCursor>) => void;

/**
 * In-memory cursors for the desktop browser-preview panel.
 * The shell publishes working bots here; the panel subscribes.
 */
class BrowserPreviewActivity {
  private readonly activities = new Map<string, BrowserPreviewCursor>();
  private readonly listeners = new Set<Listener>();

  subscribe(listener: Listener): () => void {
    this.listeners.add(listener);
    listener(this.snapshot());
    return () => {
      this.listeners.delete(listener);
    };
  }

  snapshot(): ReadonlyMap<string, BrowserPreviewCursor> {
    return new Map(this.activities);
  }

  set(id: string, x: number, y: number, label: string) {
    const current = this.activities.get(id);
    if (current && current.x === x && current.y === y && current.label === label) return;
    this.activities.set(id, { x, y, label });
    this.emit();
  }

  clear(id: string) {
    if (!this.activities.delete(id)) return;
    this.emit();
  }

  private emit() {
    const snapshot = this.snapshot();
    for (const listener of this.listeners) listener(snapshot);
  }
}

export const browserPreviewActivity = new BrowserPreviewActivity();