package it.cavallium.dbengine.lucene.searcher;

import static it.cavallium.dbengine.client.UninterruptibleScheduler.uninterruptibleScheduler;
import static it.cavallium.dbengine.database.LLUtils.singleOrClose;
import static java.util.Objects.requireNonNull;

import it.cavallium.dbengine.database.LLKeyScore;
import it.cavallium.dbengine.database.LLUtils;
import it.cavallium.dbengine.database.disk.LLIndexSearchers;
import it.cavallium.dbengine.lucene.LuceneUtils;
import java.io.IOException;
import java.io.UncheckedIOException;
import java.util.List;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.ScoreDoc;
import org.apache.lucene.search.TopDocs;
import org.apache.lucene.search.TopDocsCollector;
import org.apache.lucene.search.TopFieldCollector;
import org.apache.lucene.search.TopFieldDocs;
import org.apache.lucene.search.TopScoreDocCollector;
import org.jetbrains.annotations.Nullable;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;
import reactor.core.scheduler.Schedulers;

public class StandardSearcher implements MultiSearcher {

	protected static final Logger LOG = LogManager.getLogger(StandardSearcher.class);

	public StandardSearcher() {
	}

	@Override
	public Mono<LuceneSearchResult> collectMulti(Mono<LLIndexSearchers> indexSearchersMono,
			LocalQueryParams queryParams,
			@Nullable String keyFieldName,
			GlobalQueryRewrite transformer) {
		return singleOrClose(indexSearchersMono, indexSearchers -> {
			Mono<LocalQueryParams> queryParamsMono;
			if (transformer == GlobalQueryRewrite.NO_REWRITE) {
				queryParamsMono = Mono.just(queryParams);
			} else {
				queryParamsMono = Mono
						.fromCallable(() -> transformer.rewrite(indexSearchers, queryParams))
						.subscribeOn(uninterruptibleScheduler(Schedulers.boundedElastic()));
			}

			return queryParamsMono.flatMap(queryParams2 -> this
					// Search results
					.search(indexSearchers.shards(), queryParams2)
					// Compute the results
					.transform(fullDocsMono -> this.computeResults(fullDocsMono, indexSearchers, keyFieldName, queryParams2))
					// Ensure that one LuceneSearchResult is always returned
					.single());
		});
	}

	/**
	 * Search effectively the raw results
	 */
	@SuppressWarnings({"unchecked", "rawtypes"})
	private Mono<TopDocs> search(Iterable<IndexSearcher> indexSearchers,
			LocalQueryParams queryParams) {
		return Mono
				.fromCallable(() -> {
					LLUtils.ensureBlocking();
					var totalHitsThreshold = queryParams.getTotalHitsThresholdInt();
					if (queryParams.isSorted() && !queryParams.isSortedByScore()) {
						return TopFieldCollector.createSharedManager(queryParams.sort(), queryParams.limitInt(), null,
								totalHitsThreshold);
					} else {
						return TopScoreDocCollector.createSharedManager(queryParams.limitInt(), null, totalHitsThreshold);
					}
				})
				.subscribeOn(uninterruptibleScheduler(Schedulers.boundedElastic()))
				.flatMap(sharedManager -> Flux
						.fromIterable(indexSearchers)
						.<TopDocsCollector<?>>handle((shard, sink) -> {
							LLUtils.ensureBlocking();
							try {
								var collector = sharedManager.newCollector();
								assert queryParams.computePreciseHitsCount() == null || (queryParams.computePreciseHitsCount()
										== collector.scoreMode().isExhaustive());

								shard.search(queryParams.query(), LuceneUtils.withTimeout(collector, queryParams.timeout()));
								sink.next(collector);
							} catch (IOException e) {
								sink.error(e);
							}
						})
						.collectList()
						.handle((collectors, sink) -> {
							LLUtils.ensureBlocking();
							try {
								if (collectors.size() <= 1) {
									sink.next(sharedManager.reduce((List) collectors));
								} else if (queryParams.isSorted() && !queryParams.isSortedByScore()) {
									final TopFieldDocs[] topDocs = new TopFieldDocs[collectors.size()];
									int i = 0;
									for (var collector : collectors) {
										var topFieldDocs = ((TopFieldCollector) collector).topDocs();
										for (ScoreDoc scoreDoc : topFieldDocs.scoreDocs) {
											scoreDoc.shardIndex = i;
										}
										topDocs[i++] = topFieldDocs;
									}
									sink.next(TopDocs.merge(requireNonNull(queryParams.sort()), 0, queryParams.limitInt(), topDocs));
								} else {
									final TopDocs[] topDocs = new TopDocs[collectors.size()];
									int i = 0;
									for (var collector : collectors) {
										var topScoreDocs = collector.topDocs();
										for (ScoreDoc scoreDoc : topScoreDocs.scoreDocs) {
											scoreDoc.shardIndex = i;
										}
										topDocs[i++] = topScoreDocs;
									}
									sink.next(TopDocs.merge(0, queryParams.limitInt(), topDocs));
								}
							} catch (IOException ex) {
								sink.error(ex);
							}
						}));
	}

	/**
	 * Compute the results, extracting useful data
	 */
	private Mono<LuceneSearchResult> computeResults(Mono<TopDocs> dataMono,
			LLIndexSearchers indexSearchers,
			String keyFieldName,
			LocalQueryParams queryParams) {
		return dataMono.map(data -> {
			var totalHitsCount = LuceneUtils.convertTotalHitsCount(data.totalHits);

			Flux<LLKeyScore> hitsFlux = LuceneUtils
					.convertHits(Flux.fromArray(data.scoreDocs),
							indexSearchers.shards(), keyFieldName, true)
					.skip(queryParams.offsetLong())
					.take(queryParams.limitLong(), true);

			return new LuceneSearchResult(totalHitsCount, hitsFlux, () -> {
				try {
					indexSearchers.close();
				} catch (UncheckedIOException e) {
					LOG.error("Can't close index searchers", e);
				}
			});
		});
	}

	@Override
	public String getName() {
		return "standard";
	}
}