CavalliumDBEngine/src/main/java/it/cavallium/dbengine/lucene/LuceneUtils.java

package it.cavallium.dbengine.lucene;

import it.cavallium.dbengine.client.MultiSort;
import it.cavallium.dbengine.lucene.analyzer.N4CharGramAnalyzer;
import it.cavallium.dbengine.lucene.analyzer.N4CharGramEdgeAnalyzer;
import it.cavallium.dbengine.lucene.analyzer.TextFieldsAnalyzer;
import it.cavallium.dbengine.lucene.analyzer.TextFieldsSimilarity;
import it.cavallium.dbengine.lucene.analyzer.WordAnalyzer;
import it.cavallium.dbengine.lucene.similarity.NGramSimilarity;
import org.apache.lucene.analysis.Analyzer;
import org.apache.lucene.analysis.LowerCaseFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.en.EnglishPossessiveFilter;
import org.apache.lucene.analysis.en.KStemFilter;
import org.apache.lucene.analysis.miscellaneous.ASCIIFoldingFilter;
import org.apache.lucene.analysis.standard.StandardAnalyzer;
import org.apache.lucene.misc.SweetSpotSimilarity;
import org.apache.lucene.search.similarities.BooleanSimilarity;
import org.apache.lucene.search.similarities.ClassicSimilarity;
import org.apache.lucene.search.similarities.Similarity;
import org.jetbrains.annotations.Nullable;
import org.novasearch.lucene.search.similarities.BM25Similarity;
import org.novasearch.lucene.search.similarities.BM25Similarity.BM25Model;
import org.novasearch.lucene.search.similarities.LdpSimilarity;
import org.novasearch.lucene.search.similarities.LtcSimilarity;
import org.novasearch.lucene.search.similarities.RobertsonSimilarity;
import reactor.core.publisher.Flux;

public class LuceneUtils {
	private static final Analyzer lucene4GramWordsAnalyzerEdgeInstance = new N4CharGramEdgeAnalyzer(true);
	private static final Analyzer lucene4GramStringAnalyzerEdgeInstance = new N4CharGramEdgeAnalyzer(false);
	private static final Analyzer lucene4GramWordsAnalyzerInstance = new N4CharGramAnalyzer(true);
	private static final Analyzer lucene4GramStringAnalyzerInstance = new N4CharGramAnalyzer(false);
	private static final Analyzer luceneStandardAnalyzerInstance = new StandardAnalyzer();
	private static final Analyzer luceneWordAnalyzerStopWordsAndStemInstance = new WordAnalyzer(true, true);
	private static final Analyzer luceneWordAnalyzerStopWordsInstance = new WordAnalyzer(true, false);
	private static final Analyzer luceneWordAnalyzerStemInstance = new WordAnalyzer(false, true);
	private static final Analyzer luceneWordAnalyzerSimpleInstance = new WordAnalyzer(false, false);
	private static final Similarity luceneBM25ClassicSimilarityInstance = new BM25Similarity(BM25Model.CLASSIC);
	private static final Similarity luceneBM25PlusSimilarityInstance = new BM25Similarity(BM25Model.PLUS);
	private static final Similarity luceneBM25LSimilarityInstance = new BM25Similarity(BM25Model.L);
	private static final Similarity luceneBM15PlusSimilarityInstance = new BM25Similarity(1.2f, 0.0f, 0.5f, BM25Model.PLUS);
	private static final Similarity luceneBM11PlusSimilarityInstance = new BM25Similarity(1.2f, 1.0f, 0.5f, BM25Model.PLUS);
	private static final Similarity luceneBM25ClassicNGramSimilarityInstance = NGramSimilarity.bm25(BM25Model.CLASSIC);
	private static final Similarity luceneBM25PlusNGramSimilarityInstance = NGramSimilarity.bm25(BM25Model.PLUS);
	private static final Similarity luceneBM25LNGramSimilarityInstance = NGramSimilarity.bm25(BM25Model.L);
	private static final Similarity luceneBM15PlusNGramSimilarityInstance = NGramSimilarity.bm15(BM25Model.PLUS);
	private static final Similarity luceneBM11PlusNGramSimilarityInstance = NGramSimilarity.bm11(BM25Model.PLUS);
	private static final Similarity luceneClassicSimilarityInstance = new ClassicSimilarity();
	private static final Similarity luceneClassicNGramSimilarityInstance = NGramSimilarity.classic();
	private static final Similarity luceneSweetSpotSimilarityInstance = new SweetSpotSimilarity();
	private static final Similarity luceneLTCSimilarityInstance = new LtcSimilarity();
	private static final Similarity luceneLDPSimilarityInstance = new LdpSimilarity();
	private static final Similarity luceneLDPNoLengthSimilarityInstance = new LdpSimilarity(0, 0.5f);
	private static final Similarity luceneBooleanSimilarityInstance = new BooleanSimilarity();
	private static final Similarity luceneRobertsonSimilarityInstance = new RobertsonSimilarity();

	public static Analyzer getAnalyzer(TextFieldsAnalyzer analyzer) {
		switch (analyzer) {
			case PartialWords:
				return lucene4GramWordsAnalyzerInstance;
			case PartialString:
				return lucene4GramStringAnalyzerInstance;
			case PartialWordsEdge:
				return lucene4GramWordsAnalyzerEdgeInstance;
			case PartialStringEdge:
				return lucene4GramStringAnalyzerEdgeInstance;
			case Standard:
				return luceneStandardAnalyzerInstance;
			case FullText:
				return luceneWordAnalyzerStopWordsAndStemInstance;
			case WordWithStopwordsStripping:
				return luceneWordAnalyzerStopWordsInstance;
			case WordWithStemming:
				return luceneWordAnalyzerStemInstance;
			case WordSimple:
				return luceneWordAnalyzerSimpleInstance;
			default:
				throw new UnsupportedOperationException("Unknown analyzer: " + analyzer);
		}
	}

	public static Similarity getSimilarity(TextFieldsSimilarity similarity) {
		switch (similarity) {
			case BM25Classic:
				return luceneBM25ClassicSimilarityInstance;
			case NGramBM25Classic:
				return luceneBM25ClassicNGramSimilarityInstance;
			case BM25L:
				return luceneBM25LSimilarityInstance;
			case NGramBM25L:
				return luceneBM25LNGramSimilarityInstance;
			case Classic:
				return luceneClassicSimilarityInstance;
			case NGramClassic:
				return luceneClassicNGramSimilarityInstance;
			case BM25Plus:
				return luceneBM25PlusSimilarityInstance;
			case NGramBM25Plus:
				return luceneBM25PlusNGramSimilarityInstance;
			case BM15Plus:
				return luceneBM15PlusSimilarityInstance;
			case NGramBM15Plus:
				return luceneBM15PlusNGramSimilarityInstance;
			case BM11Plus:
				return luceneBM11PlusSimilarityInstance;
			case NGramBM11Plus:
				return luceneBM11PlusNGramSimilarityInstance;
			case SweetSpot:
				return luceneSweetSpotSimilarityInstance;
			case LTC:
				return luceneLTCSimilarityInstance;
			case LDP:
				return luceneLDPSimilarityInstance;
			case LDPNoLength:
				return luceneLDPNoLengthSimilarityInstance;
			case Robertson:
				return luceneRobertsonSimilarityInstance;
			case Boolean:
				return luceneBooleanSimilarityInstance;
			default:
				throw new IllegalStateException("Unknown similarity: " + similarity);
		}
	}

	/**
	 *
	 * @param stem Enable stem filters on words.
	 *              Pass false if it will be used with a n-gram filter
	 */
	public static TokenStream newCommonFilter(TokenStream tokenStream, boolean stem) {
		tokenStream = newCommonNormalizer(tokenStream);
		if (stem) {
			tokenStream = new KStemFilter(tokenStream);
			tokenStream = new EnglishPossessiveFilter(tokenStream);
		}
		return tokenStream;
	}

	public static TokenStream newCommonNormalizer(TokenStream tokenStream) {
		tokenStream = new ASCIIFoldingFilter(tokenStream);
		tokenStream = new LowerCaseFilter(tokenStream);
		return tokenStream;
	}

	/**
	 * Merge streams together maintaining absolute order
	 */
	public static <T> Flux<T> mergeStream(Flux<Flux<T>> mappedMultiResults,
			@Nullable MultiSort<T> sort,
			@Nullable Integer limit) {
		if (limit != null && limit == 0) {
			return mappedMultiResults.flatMap(f -> f).ignoreElements().flux();
		}
		return mappedMultiResults.collectList().flatMapMany(mappedMultiResultsList -> {
			Flux<T> mergedFlux;
			if (sort == null) {
				mergedFlux = Flux.merge(mappedMultiResultsList);
			} else {
				//noinspection unchecked
				mergedFlux = Flux.mergeOrdered(32, sort.getResultSort(), mappedMultiResultsList.toArray(Flux[]::new));
			}
			if (limit == null) {
				return mergedFlux;
			} else {
				return mergedFlux.take(limit);
			}
		});
	}
}