/*
 * 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.lucene.sandbox.codecs.idversion;

import java.io.IOException;
import org.apache.lucene.codecs.FieldsConsumer;
import org.apache.lucene.codecs.FieldsProducer;
import org.apache.lucene.codecs.PostingsFormat;
import org.apache.lucene.codecs.PostingsReaderBase;
import org.apache.lucene.codecs.PostingsWriterBase;
import org.apache.lucene.codecs.lucene103.blocktree.Lucene103BlockTreeTermsWriter;
import org.apache.lucene.index.SegmentReadState;
import org.apache.lucene.index.SegmentWriteState;
import org.apache.lucene.search.LiveFieldValues;
import org.apache.lucene.util.BitUtil;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.IOUtils;

/**
 * A PostingsFormat optimized for primary-key (ID) fields that also record a version (long) for each
 * ID, delivered as a payload created by {@link #longToBytes} during indexing. At search time, the
 * TermsEnum implementation {@link IDVersionSegmentTermsEnum} enables fast (using only the terms
 * index when possible) lookup for whether a given ID was previously indexed with version &gt; N
 * (see {@link IDVersionSegmentTermsEnum#seekExact(BytesRef,long)}.
 *
 * <p>This is most effective if the app assigns monotonically increasing global version to each
 * indexed doc. Then, during indexing, use {@link
 * IDVersionSegmentTermsEnum#seekExact(BytesRef,long)} (along with {@link LiveFieldValues}) to
 * decide whether the document you are about to index was already indexed with a higher version, and
 * skip it if so.
 *
 * <p>The field is effectively indexed as DOCS_ONLY and the docID is pulsed into the terms
 * dictionary, but the user must feed in the version as a payload on the first token.
 *
 * <p>NOTE: term vectors cannot be indexed with this field (not that you should really ever want to
 * do this).
 *
 * @lucene.experimental
 */
public class IDVersionPostingsFormat extends PostingsFormat {

  /** version must be &gt;= this. */
  public static final long MIN_VERSION = 0;

  // TODO: we could delta encode instead, and keep the last bit:

  /** version must be &lt;= this, because we encode with ZigZag. */
  public static final long MAX_VERSION = 0x3fffffffffffffffL;

  private final int minTermsInBlock;
  private final int maxTermsInBlock;

  public IDVersionPostingsFormat() {
    this(
        Lucene103BlockTreeTermsWriter.DEFAULT_MIN_BLOCK_SIZE,
        Lucene103BlockTreeTermsWriter.DEFAULT_MAX_BLOCK_SIZE);
  }

  public IDVersionPostingsFormat(int minTermsInBlock, int maxTermsInBlock) {
    super("IDVersion");
    this.minTermsInBlock = minTermsInBlock;
    this.maxTermsInBlock = maxTermsInBlock;
    Lucene103BlockTreeTermsWriter.validateSettings(minTermsInBlock, maxTermsInBlock);
  }

  @Override
  public FieldsConsumer fieldsConsumer(SegmentWriteState state) throws IOException {
    PostingsWriterBase postingsWriter = new IDVersionPostingsWriter(state.liveDocs);
    boolean success = false;
    try {
      FieldsConsumer ret =
          new VersionBlockTreeTermsWriter(state, postingsWriter, minTermsInBlock, maxTermsInBlock);
      success = true;
      return ret;
    } finally {
      if (!success) {
        IOUtils.closeWhileHandlingException(postingsWriter);
      }
    }
  }

  @Override
  public FieldsProducer fieldsProducer(SegmentReadState state) throws IOException {
    PostingsReaderBase postingsReader = new IDVersionPostingsReader();
    boolean success = false;
    try {
      FieldsProducer ret = new VersionBlockTreeTermsReader(postingsReader, state);
      success = true;
      return ret;
    } finally {
      if (!success) {
        IOUtils.closeWhileHandlingException(postingsReader);
      }
    }
  }

  public static long bytesToLong(BytesRef bytes) {
    return (long) BitUtil.VH_BE_LONG.get(bytes.bytes, bytes.offset);
  }

  public static void longToBytes(long v, BytesRef bytes) {
    if (v > MAX_VERSION || v < MIN_VERSION) {
      throw new IllegalArgumentException(
          "version must be >= MIN_VERSION="
              + MIN_VERSION
              + " and <= MAX_VERSION="
              + MAX_VERSION
              + " (got: "
              + v
              + ")");
    }
    bytes.offset = 0;
    bytes.length = 8;
    BitUtil.VH_BE_LONG.set(bytes.bytes, 0, v);
    assert bytesToLong(bytes) == v : bytesToLong(bytes) + " vs " + v + " bytes=" + bytes;
  }
}
