package org.apache.lucene.codecs.lucene42;

/*
 * 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.
 */

import java.io.IOException;
import java.util.HashMap;
import java.util.HashSet;

import org.apache.lucene.codecs.CodecUtil;
import org.apache.lucene.codecs.DocValuesConsumer;
import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.index.IndexFileNames;
import org.apache.lucene.index.SegmentWriteState;
import org.apache.lucene.store.IndexOutput;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.IOUtils;
import org.apache.lucene.util.MathUtil;
import org.apache.lucene.util.packed.BlockPackedWriter;
import org.apache.lucene.util.packed.PackedInts.FormatAndBits;
import org.apache.lucene.util.packed.PackedInts;

import static org.apache.lucene.codecs.lucene42.Lucene42DocValuesProducer.VERSION_CURRENT;

/**
 * Writer for {@link Lucene42NormsFormat}
 */
class Lucene42NormsConsumer extends DocValuesConsumer { 
  static final byte NUMBER = 0;

  static final int BLOCK_SIZE = 4096;
  
  static final byte DELTA_COMPRESSED = 0;
  static final byte TABLE_COMPRESSED = 1;
  static final byte UNCOMPRESSED = 2;
  static final byte GCD_COMPRESSED = 3;

  IndexOutput data, meta;
  final int maxDoc;
  final float acceptableOverheadRatio;
  
  Lucene42NormsConsumer(SegmentWriteState state, String dataCodec, String dataExtension, String metaCodec, String metaExtension, float acceptableOverheadRatio) throws IOException {
    this.acceptableOverheadRatio = acceptableOverheadRatio;
    maxDoc = state.segmentInfo.getDocCount();
    boolean success = false;
    try {
      String dataName = IndexFileNames.segmentFileName(state.segmentInfo.name, state.segmentSuffix, dataExtension);
      data = state.directory.createOutput(dataName, state.context);
      CodecUtil.writeHeader(data, dataCodec, VERSION_CURRENT);
      String metaName = IndexFileNames.segmentFileName(state.segmentInfo.name, state.segmentSuffix, metaExtension);
      meta = state.directory.createOutput(metaName, state.context);
      CodecUtil.writeHeader(meta, metaCodec, VERSION_CURRENT);
      success = true;
    } finally {
      if (!success) {
        IOUtils.closeWhileHandlingException(this);
      }
    }
  }

  @Override
  public void addNumericField(FieldInfo field, Iterable<Number> values) throws IOException {
    meta.writeVInt(field.number);
    meta.writeByte(NUMBER);
    meta.writeLong(data.getFilePointer());
    long minValue = Long.MAX_VALUE;
    long maxValue = Long.MIN_VALUE;
    long gcd = 0;
    // TODO: more efficient?
    HashSet<Long> uniqueValues = null;
    if (true) {
      uniqueValues = new HashSet<>();

      long count = 0;
      for (Number nv : values) {
        assert nv != null;
        final long v = nv.longValue();

        if (gcd != 1) {
          if (v < Long.MIN_VALUE / 2 || v > Long.MAX_VALUE / 2) {
            // in that case v - minValue might overflow and make the GCD computation return
            // wrong results. Since these extreme values are unlikely, we just discard
            // GCD computation for them
            gcd = 1;
          } else if (count != 0) { // minValue needs to be set first
            gcd = MathUtil.gcd(gcd, v - minValue);
          }
        }

        minValue = Math.min(minValue, v);
        maxValue = Math.max(maxValue, v);

        if (uniqueValues != null) {
          if (uniqueValues.add(v)) {
            if (uniqueValues.size() > 256) {
              uniqueValues = null;
            }
          }
        }

        ++count;
      }
      assert count == maxDoc;
    }

    if (uniqueValues != null) {
      // small number of unique values
      final int bitsPerValue = PackedInts.bitsRequired(uniqueValues.size()-1);
      FormatAndBits formatAndBits = PackedInts.fastestFormatAndBits(maxDoc, bitsPerValue, acceptableOverheadRatio);
      if (formatAndBits.bitsPerValue == 8 && minValue >= Byte.MIN_VALUE && maxValue <= Byte.MAX_VALUE) {
        meta.writeByte(UNCOMPRESSED); // uncompressed
        for (Number nv : values) {
          data.writeByte(nv == null ? 0 : (byte) nv.longValue());
        }
      } else {
        meta.writeByte(TABLE_COMPRESSED); // table-compressed
        Long[] decode = uniqueValues.toArray(new Long[uniqueValues.size()]);
        final HashMap<Long,Integer> encode = new HashMap<>();
        data.writeVInt(decode.length);
        for (int i = 0; i < decode.length; i++) {
          data.writeLong(decode[i]);
          encode.put(decode[i], i);
        }

        meta.writeVInt(PackedInts.VERSION_CURRENT);
        data.writeVInt(formatAndBits.format.getId());
        data.writeVInt(formatAndBits.bitsPerValue);

        final PackedInts.Writer writer = PackedInts.getWriterNoHeader(data, formatAndBits.format, maxDoc, formatAndBits.bitsPerValue, PackedInts.DEFAULT_BUFFER_SIZE);
        for(Number nv : values) {
          writer.add(encode.get(nv == null ? 0 : nv.longValue()));
        }
        writer.finish();
      }
    } else if (gcd != 0 && gcd != 1) {
      meta.writeByte(GCD_COMPRESSED);
      meta.writeVInt(PackedInts.VERSION_CURRENT);
      data.writeLong(minValue);
      data.writeLong(gcd);
      data.writeVInt(BLOCK_SIZE);

      final BlockPackedWriter writer = new BlockPackedWriter(data, BLOCK_SIZE);
      for (Number nv : values) {
        long value = nv == null ? 0 : nv.longValue();
        writer.add((value - minValue) / gcd);
      }
      writer.finish();
    } else {
      meta.writeByte(DELTA_COMPRESSED); // delta-compressed

      meta.writeVInt(PackedInts.VERSION_CURRENT);
      data.writeVInt(BLOCK_SIZE);

      final BlockPackedWriter writer = new BlockPackedWriter(data, BLOCK_SIZE);
      for (Number nv : values) {
        writer.add(nv == null ? 0 : nv.longValue());
      }
      writer.finish();
    }
  }
  
  @Override
  public void close() throws IOException {
    boolean success = false;
    try {
      if (meta != null) {
        meta.writeVInt(-1); // write EOF marker
        CodecUtil.writeFooter(meta); // write checksum
      }
      if (data != null) {
        CodecUtil.writeFooter(data); // write checksum
      }
      success = true;
    } finally {
      if (success) {
        IOUtils.close(data, meta);
      } else {
        IOUtils.closeWhileHandlingException(data, meta);
      }
      meta = data = null;
    }
  }

  @Override
  public void addBinaryField(FieldInfo field, final Iterable<BytesRef> values) throws IOException {
    throw new UnsupportedOperationException();
  }
  
  @Override
  public void addSortedField(FieldInfo field, Iterable<BytesRef> values, Iterable<Number> docToOrd) throws IOException {
    throw new UnsupportedOperationException();
  }

  @Override
  public void addSortedSetField(FieldInfo field, Iterable<BytesRef> values, final Iterable<Number> docToOrdCount, final Iterable<Number> ords) throws IOException {
    throw new UnsupportedOperationException();
  }
}
