Main operations: `suggest()`, `popularWords()`, `indexer()`, `createIndexIfNothing()`, `createNextIndex()`, `switchIndex()`, `removeDisableIndices()`

### SuggestIndexer (Indexing Engine)
Location: `src/main/java/org/codelibs/fess/suggest/index/SuggestIndexer.java`

Handles all indexing operations, content parsing, and word management (bad words, elevate words).

### SuggestSettings (Configuration)

import org.codelibs.fess.suggest.settings.SuggestSettings;
import org.opensearch.OpenSearchStatusException;
import org.opensearch.transport.client.Client;

/**
 * Internal operations class for content-based indexing functionality.
 * Handles indexing from query logs, documents, and search words.
 *
 * <p>This class is package-private and intended for internal use by SuggestIndexer.
 */
public class ContentIndexingOperations {

import org.codelibs.fess.suggest.settings.SuggestSettings;
import org.opensearch.transport.client.Client;

/**
 * Internal operations class for core indexing functionality.
 * Handles indexing of SuggestItem objects with bad word filtering.
 *
 * <p>This class is package-private and intended for internal use by SuggestIndexer.
 */
public class IndexingOperations {

import org.lastaflute.web.validation.Required;

/**
 * Form for uploading stopwords files to the Fess search engine.
 * Stopwords are common words that should be ignored during search indexing and querying.
 * This form is used in the admin interface to upload custom stopwords dictionary files.
 */
public class UploadForm {

    /**

     * and performs bulk indexing operations with proper error handling.
     *
     * @param searchEngineClient the search engine client to use for indexing
     * @param docList the list of documents to be indexed
     * @throws SearchEngineClientException if the bulk indexing operation fails
     */
    public void sendDocuments(final SearchEngineClient searchEngineClient, final DocList docList) {
        if (docList.isEmpty()) {

 *
 * <p>This exception can be thrown with a message, a cause, or both.</p>
 *
 * <pre>
 * Example usage:
 * throw new SuggestIndexException("Indexing error occurred");
 * throw new SuggestIndexException(new IOException("IO error"));
 * throw new SuggestIndexException("Indexing error", new IOException("IO error"));
 * </pre>
 *
 * @see SuggesterException
 */
public class SuggestIndexException extends SuggesterException {

 * <li>Transforms document data using appropriate transformers</li>
 * <li>Applies document boosting rules and click/favorite count enhancements</li>
 * <li>Sends processed documents to the search engine for indexing</li>
 * <li>Manages cleanup of processed crawler session data</li>
 * </ul>
 *
 * <p>The updater runs continuously until crawling is finished and all documents are processed.

        // Add first document - should trigger indexing because cache size is 1
        Map<String, Object> dataMap1 = new HashMap<>();
        dataMap1.put("url", "http://example.com/test1");
        indexUpdateCallback.store(paramMap, dataMap1);
        assertEquals(1, indexingHelper.sendDocumentsCalled);

        // Add second document - should trigger indexing again
        Map<String, Object> dataMap2 = new HashMap<>();

│   │   ├── suggest/                # Suggestion requests
│   │   └── popularwords/           # Popular words requests
│   ├── index/                      # Indexing functionality
│   │   ├── SuggestIndexer.java     # Main indexing API
│   │   ├── contents/               # Content parsers and readers
│   │   └── writer/                 # Index writing strategies

 */
package org.codelibs.fess.exception;

/**
 * Exception thrown when requested content cannot be found.
 * Typically used when a document or resource is not available during crawling or indexing.
 */
public class ContentNotFoundException extends FessSystemException {

    private static final long serialVersionUID = 1L;

    /**