Function useBadgeController

export function useBadgeController(): void {
  useEffect(() => {
    // Badge state is external; keep it in the closure, not React state.
    let state = initialBadgeState;
    // Skip re-emitting an identical output (e.g. repeated mid-search 0 → animate).
    let lastOutput: BadgeOutput | null = null;
    // Serialize applies so their async getBadgeText reads don't interleave.
    let applyChain: Promise<void> = Promise.resolve();

    const handle = (event: BadgeEvent) => {
      const result = reduceBadge(state, event);
      state = result.state;
      if (isSameBadgeOutput(lastOutput, result.output)) return;
      lastOutput = result.output;
      const output = result.output;
      applyChain = applyChain.then(() => applyBadgeOutput(output));
    };

    const unsubscribers = [
      onSearchEvent(SearchEvent.STARTED, () => handle({ type: SearchEvent.STARTED })),
      onSearchEvent(SearchEvent.RESULTS_COUNT, ({ count }) =>
        handle({ type: SearchEvent.RESULTS_COUNT, count }),
      ),
      onSearchEvent(SearchEvent.COMPLETED, ({ count }) =>
        handle({ type: SearchEvent.COMPLETED, count }),
      ),
      onSearchEvent(SearchEvent.ABORTED, () => handle({ type: SearchEvent.ABORTED })),
      onSearchEvent(SearchEvent.FAILED, () => handle({ type: SearchEvent.FAILED })),
    ];

    const onResultsCleared = () => handle({ type: IDB_SEARCH_RESULTS_CLEARED });
    window.addEventListener(IDB_SEARCH_RESULTS_CLEARED, onResultsCleared);

    return () => {
      for (const unsubscribe of unsubscribers) unsubscribe();
      window.removeEventListener(IDB_SEARCH_RESULTS_CLEARED, onResultsCleared);
    };
  }, []);
}
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