}

    /**
     * Returns the promise.
     * @return The promise.
     */
    public Promise promise() {
        return promise;
    }

    /**
     * The promise.
     */
    public class Promise {
        /**
         * Constructs a new Promise object.
         */
        public Promise() {
            // nothing
        }

        /**

  }

  @JsFunction
  interface IThenOnRejectedCallbackFn<V extends @Nullable Object> {
    V onInvoke(Object p0);
  }
}

/** Subset of the elemental2 Promise API. */
@JsType(isNative = true, namespace = JsPackage.GLOBAL, name = "Promise")
class Promise<T extends @Nullable Object> implements IThenable<T> {

  @JsFunction
  interface PromiseExecutorCallbackFn<T extends @Nullable Object> {
    @JsFunction

        // All should be the same promise instance
        assertEquals("Promise chain should return same instance", promise1, promise2);
        assertEquals("Promise chain should return same instance", promise2, promise3);
    }

    @Test
    public void test_promiseFromDeferredThen() throws Exception {

        AtomicReference<Throwable> errorRef = new AtomicReference<>();

        Deferred<SuggestIndexResponse>.Promise promise = suggester.indexer().indexFromQueryLog(emptyReader, 10, 0);

        promise.then(response -> {
            responseRef.set(response);
            latch.countDown();
        }).error(error -> {
            errorRef.set(error);

     */
    public Request() {
        // nothing
    }

    /**
     * Executes the request.
     * @param client The OpenSearch client.
     * @return A Promise that will be resolved with the response or rejected with an error.
     */
    public Deferred<T>.Promise execute(final Client client) {
        final String error = getValidationError();
        if (!Strings.isNullOrEmpty(error)) {

     * @param docPerReq The number of documents to process per request
     * @param requestInterval The interval between requests
     * @return A Promise that will be resolved with the SuggestIndexResponse
     */
    public Deferred<SuggestIndexResponse>.Promise indexFromQueryLog(final ContentIndexingContext ctx, final QueryLogReader queryLogReader,
            final int docPerReq, final long requestInterval) {

        this.client = client;
        this.request = request;
    }

    /**
     * Executes the request.
     * @return A Promise that will be resolved with the response or rejected with an error.
     */
    public Deferred<Res>.Promise execute() {
        return request.execute(client);
    }

     * @param docPerReq The number of documents to process per request.
     * @param requestInterval The interval between requests.
     * @return A Promise that will be resolved with the SuggestIndexResponse or rejected with an error.
     */
    public Deferred<SuggestIndexResponse>.Promise indexFromQueryLog(final QueryLogReader queryLogReader, final int docPerReq,
            final long requestInterval) {
        ensureOperations();

├── concurrent/                 # Async patterns (Deferred/Promise)
└── util/                      # Utilities
```

### Key Design Patterns

- **Builder**: SuggesterBuilder, SuggestRequestBuilder
- **Facade**: Suggester (main entry point)
- **Composite**: NormalizerChain, ReadingConverterChain
- **Strategy**: Normalizer, ReadingConverter, ContentsParser
- **Deferred/Promise**: Async operations

### Index Alias Strategy

       * we're copying into a `contents` array whose type allows it to contain nulls. Still, it's
       * worth noting that we promise not to put nulls into the array in the first `size` elements.
       * We uphold that promise here because our callers promise that `elements` will not contain
       * nulls in its first `n` elements.
       */
      System.arraycopy(elements, 0, contents, size, n);
      size += n;