public class SimpleFacetsExample {

  private final Directory indexDir = new RAMDirectory();
  private final Directory taxoDir = new RAMDirectory();
  private final FacetsConfig config = new FacetsConfig();

  /** Empty constructor */
  public SimpleFacetsExample() {
    config.setHierarchical("Publish Date", true);
  }
  
  /** Build the example index. */
  private void index() throws IOException {
    IndexWriter indexWriter = new IndexWriter(indexDir, new IndexWriterConfig(
        new WhitespaceAnalyzer()).setOpenMode(OpenMode.CREATE));

    // Writes facet ords to a separate directory from the main index
    DirectoryTaxonomyWriter taxoWriter = new DirectoryTaxonomyWriter(taxoDir);

    Document doc = new Document();
    doc.add(new FacetField("Author", "Bob"));
    doc.add(new FacetField("Publish Date", "2010", "10", "15"));
    indexWriter.addDocument(config.build(taxoWriter, doc));

    doc = new Document();
    doc.add(new FacetField("Author", "Lisa"));
    doc.add(new FacetField("Publish Date", "2010", "10", "20"));
    indexWriter.addDocument(config.build(taxoWriter, doc));

    doc = new Document();
    doc.add(new FacetField("Author", "Lisa"));
    doc.add(new FacetField("Publish Date", "2012", "1", "1"));
    indexWriter.addDocument(config.build(taxoWriter, doc));

    doc = new Document();
    doc.add(new FacetField("Author", "Susan"));
    doc.add(new FacetField("Publish Date", "2012", "1", "7"));
    indexWriter.addDocument(config.build(taxoWriter, doc));

    doc = new Document();
    doc.add(new FacetField("Author", "Frank"));
    doc.add(new FacetField("Publish Date", "1999", "5", "5"));
    indexWriter.addDocument(config.build(taxoWriter, doc));
    
    indexWriter.close();
    taxoWriter.close();
  }

  /** User runs a query and counts facets. */
  private List<FacetResult> facetsWithSearch() throws IOException {
    DirectoryReader indexReader = DirectoryReader.open(indexDir);
    IndexSearcher searcher = new IndexSearcher(indexReader);
    TaxonomyReader taxoReader = new DirectoryTaxonomyReader(taxoDir);

    FacetsCollector fc = new FacetsCollector();

    // MatchAllDocsQuery is for "browsing" (counts facets
    // for all non-deleted docs in the index); normally
    // you'd use a "normal" query:
    FacetsCollector.search(searcher, new MatchAllDocsQuery(), 10, fc);

    // Retrieve results
    List<FacetResult> results = new ArrayList<>();

    // Count both "Publish Date" and "Author" dimensions
    Facets facets = new FastTaxonomyFacetCounts(taxoReader, config, fc);
    results.add(facets.getTopChildren(10, "Author"));
    results.add(facets.getTopChildren(10, "Publish Date"));
    
    indexReader.close();
    taxoReader.close();
    
    return results;
  }
  
  /** User runs a query and counts facets only without collecting the matching documents.*/
  private List<FacetResult> facetsOnly() throws IOException {
    DirectoryReader indexReader = DirectoryReader.open(indexDir);
    IndexSearcher searcher = new IndexSearcher(indexReader);
    TaxonomyReader taxoReader = new DirectoryTaxonomyReader(taxoDir);

    FacetsCollector fc = new FacetsCollector();

    // MatchAllDocsQuery is for "browsing" (counts facets
    // for all non-deleted docs in the index); normally
    // you'd use a "normal" query:
    searcher.search(new MatchAllDocsQuery(), fc);

    // Retrieve results
    List<FacetResult> results = new ArrayList<>();

    // Count both "Publish Date" and "Author" dimensions
    Facets facets = new FastTaxonomyFacetCounts(taxoReader, config, fc);
   
    results.add(facets.getTopChildren(10, "Author"));
    results.add(facets.getTopChildren(10, "Publish Date"));
    
    indexReader.close();
    taxoReader.close();
    
    return results;
  }
  
  /** User drills down on 'Publish Date/2010', and we
   *  return facets for 'Author' */
  private FacetResult drillDown() throws IOException {
    DirectoryReader indexReader = DirectoryReader.open(indexDir);
    IndexSearcher searcher = new IndexSearcher(indexReader);
    TaxonomyReader taxoReader = new DirectoryTaxonomyReader(taxoDir);

    // Passing no baseQuery means we drill down on all
    // documents ("browse only"):
    DrillDownQuery q = new DrillDownQuery(config);

    // Now user drills down on Publish Date/2010:
    q.add("Publish Date", "2010");
    FacetsCollector fc = new FacetsCollector();
    FacetsCollector.search(searcher, q, 10, fc);

    // Retrieve results
    Facets facets = new FastTaxonomyFacetCounts(taxoReader, config, fc);
    FacetResult result = facets.getTopChildren(10, "Author");

    indexReader.close();
    taxoReader.close();
    
    return result;
  }

  /** User drills down on 'Publish Date/2010', and we
   *  return facets for both 'Publish Date' and 'Author',
   *  using DrillSideways. */
  private List<FacetResult> drillSideways() throws IOException {
    DirectoryReader indexReader = DirectoryReader.open(indexDir);
    IndexSearcher searcher = new IndexSearcher(indexReader);
    TaxonomyReader taxoReader = new DirectoryTaxonomyReader(taxoDir);

    // Passing no baseQuery means we drill down on all
    // documents ("browse only"):
    DrillDownQuery q = new DrillDownQuery(config);

    // Now user drills down on Publish Date/2010:
    q.add("Publish Date", "2010");

    DrillSideways ds = new DrillSideways(searcher, config, taxoReader);
    DrillSidewaysResult result = ds.search(q, 10);

    // Retrieve results
    List<FacetResult> facets = result.facets.getAllDims(10);

    indexReader.close();
    taxoReader.close();
    
    return facets;
  }

  /** Runs the search example. */
  public List<FacetResult> runFacetOnly() throws IOException {
    index();
    return facetsOnly();
  }
  
  /** Runs the search example. */
  public List<FacetResult> runSearch() throws IOException {
    index();
    return facetsWithSearch();
  }
  
  /** Runs the drill-down example. */
  public FacetResult runDrillDown() throws IOException {
    index();
    return drillDown();
  }

  /** Runs the drill-sideways example. */
  public List<FacetResult> runDrillSideways() throws IOException {
    index();
    return drillSideways();
  }

  /** Runs the search and drill-down examples and prints the results. */
  public static void main(String[] args) throws Exception {
    System.out.println("Facet counting example:");
    System.out.println("-----------------------");
    SimpleFacetsExample example = new SimpleFacetsExample();
    List<FacetResult> results1 = example.runFacetOnly();
    System.out.println("Author: " + results1.get(0));
    System.out.println("Publish Date: " + results1.get(1));
    
    System.out.println("Facet counting example (combined facets and search):");
    System.out.println("-----------------------");
    List<FacetResult> results = example.runSearch();
    System.out.println("Author: " + results.get(0));
    System.out.println("Publish Date: " + results.get(1));
    
    System.out.println("Facet drill-down example (Publish Date/2010):");
    System.out.println("---------------------------------------------");
    System.out.println("Author: " + example.runDrillDown());

    System.out.println("Facet drill-sideways example (Publish Date/2010):");
    System.out.println("---------------------------------------------");
    for(FacetResult result : example.runDrillSideways()) {
      System.out.println(result);
    }
  }
  
}

  /** Lower-level search API.
   *
   * <p>{@link LeafCollector#collect(int)} is called for every matching document.
   *
   * @throws BooleanQuery.TooManyClauses If a query would exceed 
   *         {@link BooleanQuery#getMaxClauseCount()} clauses.
   */
  public void search(Query query, Collector results)
    throws IOException {
    query = rewrite(query);
    search(leafContexts, createWeight(query, results.needsScores(), 1), results);
  }