/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.cassandra.index.sai.disk.v1.segment;

import java.io.Closeable;
import java.io.IOException;
import java.util.concurrent.TimeUnit;

import com.google.common.annotations.VisibleForTesting;

import org.apache.lucene.store.IndexInput;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.cassandra.exceptions.QueryCancelledException;
import org.apache.cassandra.index.sai.QueryContext;
import org.apache.cassandra.index.sai.disk.io.IndexFileUtils;
import org.apache.cassandra.index.sai.disk.v1.postings.PostingsReader;
import org.apache.cassandra.index.sai.disk.v1.trie.TrieTermsDictionaryReader;
import org.apache.cassandra.index.sai.metrics.QueryEventListener;
import org.apache.cassandra.index.sai.postings.PostingList;
import org.apache.cassandra.index.sai.utils.IndexIdentifier;
import org.apache.cassandra.io.util.FileHandle;
import org.apache.cassandra.io.util.FileUtils;
import org.apache.cassandra.utils.Clock;
import org.apache.cassandra.utils.Throwables;
import org.apache.cassandra.utils.bytecomparable.ByteComparable;

import static org.apache.cassandra.index.sai.disk.v1.SAICodecUtils.validate;

/**
 * Synchronous reader of terms dictionary and postings lists to produce a {@link PostingList} with matching row ids.
 *
 * {@link #exactMatch(ByteComparable, QueryEventListener.TrieIndexEventListener, QueryContext)} does:
 * <ul>
 * <li>{@link TermQuery#lookupPostingsOffset(ByteComparable)}: does term dictionary lookup to find the posting list file
 * position</li>
 * <li>{@link TermQuery#getPostingsReader(long)}: reads posting list block summary and initializes posting read which
 * reads the first block of the posting list into memory</li>
 * </ul>
 */
public class LiteralIndexSegmentTermsReader implements Closeable
{
    private static final Logger logger = LoggerFactory.getLogger(LiteralIndexSegmentTermsReader.class);

    private final IndexIdentifier indexIdentifier;
    private final FileHandle termDictionaryFile;
    private final FileHandle postingsFile;
    private final long termDictionaryRoot;

    public LiteralIndexSegmentTermsReader(IndexIdentifier indexIdentifier,
                                          FileHandle termsData,
                                          FileHandle postingLists,
                                          long root,
                                          long termsFooterPointer) throws IOException
    {
        this.indexIdentifier = indexIdentifier;
        termDictionaryFile = termsData;
        postingsFile = postingLists;
        termDictionaryRoot = root;

        try (final IndexInput indexInput = IndexFileUtils.instance.openInput(termDictionaryFile))
        {
            validate(indexInput, termsFooterPointer);
        }

        try (final IndexInput indexInput = IndexFileUtils.instance.openInput(postingsFile))
        {
            validate(indexInput);
        }
    }

    @Override
    public void close()
    {
        FileUtils.closeQuietly(termDictionaryFile);
        FileUtils.closeQuietly(postingsFile);
    }

    public PostingList exactMatch(ByteComparable term, QueryEventListener.TrieIndexEventListener perQueryEventListener, QueryContext context)
    {
        perQueryEventListener.onSegmentHit();
        return new TermQuery(term, perQueryEventListener, context).execute();
    }

    @VisibleForTesting
    public class TermQuery
    {
        private final IndexInput postingsInput;
        private final IndexInput postingsSummaryInput;
        private final QueryEventListener.TrieIndexEventListener listener;
        private final long lookupStartTime;
        private final QueryContext context;
        private final ByteComparable term;

        TermQuery(ByteComparable term, QueryEventListener.TrieIndexEventListener listener, QueryContext context)
        {
            this.listener = listener;
            postingsInput = IndexFileUtils.instance.openInput(postingsFile);
            postingsSummaryInput = IndexFileUtils.instance.openInput(postingsFile);
            this.term = term;
            lookupStartTime = Clock.Global.nanoTime();
            this.context = context;
        }

        public PostingList execute()
        {
            try
            {
                long postingOffset = lookupPostingsOffset(term);
                if (postingOffset == PostingList.OFFSET_NOT_FOUND)
                {
                    FileUtils.closeQuietly(postingsInput);
                    FileUtils.closeQuietly(postingsSummaryInput);
                    return null;
                }

                context.checkpoint();

                // when posting is found, resources will be closed when posting reader is closed.
                return getPostingsReader(postingOffset);
            }
            catch (Throwable e)
            {
                if (!(e instanceof QueryCancelledException))
                    logger.error(indexIdentifier.logMessage("Failed to execute term query"), e);

                closeOnException();
                throw Throwables.cleaned(e);
            }
        }

        private void closeOnException()
        {
            FileUtils.closeQuietly(postingsInput);
            FileUtils.closeQuietly(postingsSummaryInput);
        }

        public long lookupPostingsOffset(ByteComparable term)
        {
            try (TrieTermsDictionaryReader reader = new TrieTermsDictionaryReader(termDictionaryFile.instantiateRebufferer(null), termDictionaryRoot))
            {
                final long offset = reader.exactMatch(term);

                listener.onTraversalComplete(Clock.Global.nanoTime() - lookupStartTime, TimeUnit.NANOSECONDS);

                if (offset == TrieTermsDictionaryReader.NOT_FOUND)
                    return PostingList.OFFSET_NOT_FOUND;

                return offset;
            }
        }

        public PostingsReader getPostingsReader(long offset) throws IOException
        {
            PostingsReader.BlocksSummary header = new PostingsReader.BlocksSummary(postingsSummaryInput, offset);

            return new PostingsReader(postingsInput, header, listener.postingListEventListener());
        }
    }
}
