package org.apache.lucene.codecs.lucene410;

/*
 * 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.Closeable; // javadocs
import java.io.IOException;
import java.util.Arrays;
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.store.RAMOutputStream;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.BytesRefBuilder;
import org.apache.lucene.util.IOUtils;
import org.apache.lucene.util.MathUtil;
import org.apache.lucene.util.PagedBytes;
import org.apache.lucene.util.PagedBytes.PagedBytesDataInput;
import org.apache.lucene.util.StringHelper;
import org.apache.lucene.util.packed.DirectWriter;
import org.apache.lucene.util.packed.MonotonicBlockPackedWriter;
import org.apache.lucene.util.packed.PackedInts;

/** writer for {@link Lucene410DocValuesFormat} */
class Lucene410DocValuesConsumer extends DocValuesConsumer implements Closeable {

  static final int BLOCK_SIZE = 16384;
  
  // address terms in blocks of 16 terms
  static final int INTERVAL_SHIFT = 4;
  static final int INTERVAL_COUNT = 1 << INTERVAL_SHIFT;
  static final int INTERVAL_MASK = INTERVAL_COUNT - 1;
  
  // build reverse index from every 1024th term
  static final int REVERSE_INTERVAL_SHIFT = 10;
  static final int REVERSE_INTERVAL_COUNT = 1 << REVERSE_INTERVAL_SHIFT;
  static final int REVERSE_INTERVAL_MASK = REVERSE_INTERVAL_COUNT - 1;
  
  // for conversion from reverse index to block
  static final int BLOCK_INTERVAL_SHIFT = REVERSE_INTERVAL_SHIFT - INTERVAL_SHIFT;
  static final int BLOCK_INTERVAL_COUNT = 1 << BLOCK_INTERVAL_SHIFT;
  static final int BLOCK_INTERVAL_MASK = BLOCK_INTERVAL_COUNT - 1;

  /** Compressed using packed blocks of ints. */
  public static final int DELTA_COMPRESSED = 0;
  /** Compressed by computing the GCD. */
  public static final int GCD_COMPRESSED = 1;
  /** Compressed by giving IDs to unique values. */
  public static final int TABLE_COMPRESSED = 2;
  /** Compressed with monotonically increasing values */
  public static final int MONOTONIC_COMPRESSED = 3;
  
  /** Uncompressed binary, written directly (fixed length). */
  public static final int BINARY_FIXED_UNCOMPRESSED = 0;
  /** Uncompressed binary, written directly (variable length). */
  public static final int BINARY_VARIABLE_UNCOMPRESSED = 1;
  /** Compressed binary with shared prefixes */
  public static final int BINARY_PREFIX_COMPRESSED = 2;

  /** Standard storage for sorted set values with 1 level of indirection:
   *  docId -> address -> ord. */
  public static final int SORTED_WITH_ADDRESSES = 0;
  /** Single-valued sorted set values, encoded as sorted values, so no level
   *  of indirection: docId -> ord. */
  public static final int SORTED_SINGLE_VALUED = 1;

  IndexOutput data, meta;
  final int maxDoc;
  
  /** expert: Creates a new writer */
  public Lucene410DocValuesConsumer(SegmentWriteState state, String dataCodec, String dataExtension, String metaCodec, String metaExtension) throws IOException {
    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, Lucene410DocValuesFormat.VERSION_CURRENT);
      String metaName = IndexFileNames.segmentFileName(state.segmentInfo.name, state.segmentSuffix, metaExtension);
      meta = state.directory.createOutput(metaName, state.context);
      CodecUtil.writeHeader(meta, metaCodec, Lucene410DocValuesFormat.VERSION_CURRENT);
      maxDoc = state.segmentInfo.getDocCount();
      success = true;
    } finally {
      if (!success) {
        IOUtils.closeWhileHandlingException(this);
      }
    }
  }
  
  @Override
  public void addNumericField(FieldInfo field, Iterable<Number> values) throws IOException {
    addNumericField(field, values, true);
  }

  void addNumericField(FieldInfo field, Iterable<Number> values, boolean optimizeStorage) throws IOException {
    long count = 0;
    long minValue = Long.MAX_VALUE;
    long maxValue = Long.MIN_VALUE;
    long gcd = 0;
    boolean missing = false;
    // TODO: more efficient?
    HashSet<Long> uniqueValues = null;
    if (optimizeStorage) {
      uniqueValues = new HashSet<>();

      for (Number nv : values) {
        final long v;
        if (nv == null) {
          v = 0;
          missing = true;
        } else {
          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;
      }
    } else {
      for (Number nv : values) {
        long v = nv.longValue();
        minValue = Math.min(minValue, v);
        maxValue = Math.max(maxValue, v);
        ++count;
      }
    }
    
    final long delta = maxValue - minValue;
    final int deltaBitsRequired = DirectWriter.unsignedBitsRequired(delta);
    final int tableBitsRequired = uniqueValues == null
        ? Integer.MAX_VALUE
        : DirectWriter.bitsRequired(uniqueValues.size() - 1);

    final int format;
    if (uniqueValues != null && tableBitsRequired < deltaBitsRequired) {
      format = TABLE_COMPRESSED;
    } else if (gcd != 0 && gcd != 1) {
      final long gcdDelta = (maxValue - minValue) / gcd;
      final long gcdBitsRequired = DirectWriter.unsignedBitsRequired(gcdDelta);
      format = gcdBitsRequired < deltaBitsRequired ? GCD_COMPRESSED : DELTA_COMPRESSED;
    } else {
      format = DELTA_COMPRESSED;
    }
    meta.writeVInt(field.number);
    meta.writeByte(Lucene410DocValuesFormat.NUMERIC);
    meta.writeVInt(format);
    if (missing) {
      meta.writeLong(data.getFilePointer());
      writeMissingBitset(values);
    } else {
      meta.writeLong(-1L);
    }
    meta.writeLong(data.getFilePointer());
    meta.writeVLong(count);

    switch (format) {
      case GCD_COMPRESSED:
        meta.writeLong(minValue);
        meta.writeLong(gcd);
        final long maxDelta = (maxValue - minValue) / gcd;
        final int bits = DirectWriter.unsignedBitsRequired(maxDelta);
        meta.writeVInt(bits);
        final DirectWriter quotientWriter = DirectWriter.getInstance(data, count, bits);
        for (Number nv : values) {
          long value = nv == null ? 0 : nv.longValue();
          quotientWriter.add((value - minValue) / gcd);
        }
        quotientWriter.finish();
        break;
      case DELTA_COMPRESSED:
        final long minDelta = delta < 0 ? 0 : minValue;
        meta.writeLong(minDelta);
        meta.writeVInt(deltaBitsRequired);
        final DirectWriter writer = DirectWriter.getInstance(data, count, deltaBitsRequired);
        for (Number nv : values) {
          long v = nv == null ? 0 : nv.longValue();
          writer.add(v - minDelta);
        }
        writer.finish();
        break;
      case TABLE_COMPRESSED:
        final Long[] decode = uniqueValues.toArray(new Long[uniqueValues.size()]);
        Arrays.sort(decode);
        final HashMap<Long,Integer> encode = new HashMap<>();
        meta.writeVInt(decode.length);
        for (int i = 0; i < decode.length; i++) {
          meta.writeLong(decode[i]);
          encode.put(decode[i], i);
        }
        meta.writeVInt(tableBitsRequired);
        final DirectWriter ordsWriter = DirectWriter.getInstance(data, count, tableBitsRequired);
        for (Number nv : values) {
          ordsWriter.add(encode.get(nv == null ? 0 : nv.longValue()));
        }
        ordsWriter.finish();
        break;
      default:
        throw new AssertionError();
    }
    meta.writeLong(data.getFilePointer());
  }
  
  // TODO: in some cases representing missing with minValue-1 wouldn't take up additional space and so on,
  // but this is very simple, and algorithms only check this for values of 0 anyway (doesnt slow down normal decode)
  void writeMissingBitset(Iterable<?> values) throws IOException {
    byte bits = 0;
    int count = 0;
    for (Object v : values) {
      if (count == 8) {
        data.writeByte(bits);
        count = 0;
        bits = 0;
      }
      if (v != null) {
        bits |= 1 << (count & 7);
      }
      count++;
    }
    if (count > 0) {
      data.writeByte(bits);
    }
  }

  @Override
  public void addBinaryField(FieldInfo field, Iterable<BytesRef> values) throws IOException {
    // write the byte[] data
    meta.writeVInt(field.number);
    meta.writeByte(Lucene410DocValuesFormat.BINARY);
    int minLength = Integer.MAX_VALUE;
    int maxLength = Integer.MIN_VALUE;
    final long startFP = data.getFilePointer();
    long count = 0;
    boolean missing = false;
    for(BytesRef v : values) {
      final int length;
      if (v == null) {
        length = 0;
        missing = true;
      } else {
        length = v.length;
      }
      minLength = Math.min(minLength, length);
      maxLength = Math.max(maxLength, length);
      if (v != null) {
        data.writeBytes(v.bytes, v.offset, v.length);
      }
      count++;
    }
    meta.writeVInt(minLength == maxLength ? BINARY_FIXED_UNCOMPRESSED : BINARY_VARIABLE_UNCOMPRESSED);
    if (missing) {
      meta.writeLong(data.getFilePointer());
      writeMissingBitset(values);
    } else {
      meta.writeLong(-1L);
    }
    meta.writeVInt(minLength);
    meta.writeVInt(maxLength);
    meta.writeVLong(count);
    meta.writeLong(startFP);
    
    // if minLength == maxLength, its a fixed-length byte[], we are done (the addresses are implicit)
    // otherwise, we need to record the length fields...
    if (minLength != maxLength) {
      meta.writeLong(data.getFilePointer());
      meta.writeVInt(PackedInts.VERSION_CURRENT);
      meta.writeVInt(BLOCK_SIZE);

      final MonotonicBlockPackedWriter writer = new MonotonicBlockPackedWriter(data, BLOCK_SIZE);
      long addr = 0;
      writer.add(addr);
      for (BytesRef v : values) {
        if (v != null) {
          addr += v.length;
        }
        writer.add(addr);
      }
      writer.finish();
    }
  }
  
  /** expert: writes a value dictionary for a sorted/sortedset field */
  private void addTermsDict(FieldInfo field, final Iterable<BytesRef> values) throws IOException {
    // first check if its a "fixed-length" terms dict
    int minLength = Integer.MAX_VALUE;
    int maxLength = Integer.MIN_VALUE;
    long numValues = 0;
    for (BytesRef v : values) {
      minLength = Math.min(minLength, v.length);
      maxLength = Math.max(maxLength, v.length);
      numValues++;
    }
    if (minLength == maxLength) {
      // no index needed: direct addressing by mult
      addBinaryField(field, values);
    } else if (numValues < REVERSE_INTERVAL_COUNT) {
      // low cardinality: waste a few KB of ram, but can't really use fancy index etc
      addBinaryField(field, values);
    } else {
      assert numValues > 0; // we don't have to handle the empty case
      // header
      meta.writeVInt(field.number);
      meta.writeByte(Lucene410DocValuesFormat.BINARY);
      meta.writeVInt(BINARY_PREFIX_COMPRESSED);
      meta.writeLong(-1L);
      // now write the bytes: sharing prefixes within a block
      final long startFP = data.getFilePointer();
      // currently, we have to store the delta from expected for every 1/nth term
      // we could avoid this, but its not much and less overall RAM than the previous approach!
      RAMOutputStream addressBuffer = new RAMOutputStream();
      MonotonicBlockPackedWriter termAddresses = new MonotonicBlockPackedWriter(addressBuffer, BLOCK_SIZE);
      // buffers up 16 terms
      RAMOutputStream bytesBuffer = new RAMOutputStream();
      // buffers up block header
      RAMOutputStream headerBuffer = new RAMOutputStream();
      BytesRefBuilder lastTerm = new BytesRefBuilder();
      lastTerm.grow(maxLength);
      long count = 0;
      int suffixDeltas[] = new int[INTERVAL_COUNT];
      for (BytesRef v : values) {
        int termPosition = (int) (count & INTERVAL_MASK);
        if (termPosition == 0) {
          termAddresses.add(data.getFilePointer() - startFP);
          // abs-encode first term
          headerBuffer.writeVInt(v.length);
          headerBuffer.writeBytes(v.bytes, v.offset, v.length);
          lastTerm.copyBytes(v);
        } else {
          // prefix-code: we only share at most 255 characters, to encode the length as a single
          // byte and have random access. Larger terms just get less compression.
          int sharedPrefix = Math.min(255, StringHelper.bytesDifference(lastTerm.get(), v));
          bytesBuffer.writeByte((byte) sharedPrefix);
          bytesBuffer.writeBytes(v.bytes, v.offset + sharedPrefix, v.length - sharedPrefix);
          // we can encode one smaller, because terms are unique.
          suffixDeltas[termPosition] = v.length - sharedPrefix - 1;
        }
        
        count++;
        // flush block
        if ((count & INTERVAL_MASK) == 0) {
          flushTermsDictBlock(headerBuffer, bytesBuffer, suffixDeltas);
        }
      }
      // flush trailing crap
      int leftover = (int) (count & INTERVAL_MASK);
      if (leftover > 0) {
        Arrays.fill(suffixDeltas, leftover, suffixDeltas.length, 0);
        flushTermsDictBlock(headerBuffer, bytesBuffer, suffixDeltas);
      }
      final long indexStartFP = data.getFilePointer();
      // write addresses of indexed terms
      termAddresses.finish();
      addressBuffer.writeTo(data);
      addressBuffer = null;
      termAddresses = null;
      meta.writeVInt(minLength);
      meta.writeVInt(maxLength);
      meta.writeVLong(count);
      meta.writeLong(startFP);
      meta.writeLong(indexStartFP);
      meta.writeVInt(PackedInts.VERSION_CURRENT);
      meta.writeVInt(BLOCK_SIZE);
      addReverseTermIndex(field, values, maxLength);
    }
  }
  
  // writes term dictionary "block"
  // first term is absolute encoded as vint length + bytes.
  // lengths of subsequent N terms are encoded as either N bytes or N shorts.
  // in the double-byte case, the first byte is indicated with -1.
  // subsequent terms are encoded as byte suffixLength + bytes.
  private void flushTermsDictBlock(RAMOutputStream headerBuffer, RAMOutputStream bytesBuffer, int suffixDeltas[]) throws IOException {
    boolean twoByte = false;
    for (int i = 1; i < suffixDeltas.length; i++) {
      if (suffixDeltas[i] > 254) {
        twoByte = true;
      }
    }
    if (twoByte) {
      headerBuffer.writeByte((byte)255);
      for (int i = 1; i < suffixDeltas.length; i++) {
        headerBuffer.writeShort((short) suffixDeltas[i]);
      }
    } else {
      for (int i = 1; i < suffixDeltas.length; i++) {
        headerBuffer.writeByte((byte) suffixDeltas[i]);
      }
    }
    headerBuffer.writeTo(data);
    headerBuffer.reset();
    bytesBuffer.writeTo(data);
    bytesBuffer.reset();
  }
  
  // writes reverse term index: used for binary searching a term into a range of 64 blocks
  // for every 64 blocks (1024 terms) we store a term, trimming any suffix unnecessary for comparison
  // terms are written as a contiguous byte[], but never spanning 2^15 byte boundaries.
  private void addReverseTermIndex(FieldInfo field, final Iterable<BytesRef> values, int maxLength) throws IOException {
    long count = 0;
    BytesRefBuilder priorTerm = new BytesRefBuilder();
    priorTerm.grow(maxLength);
    BytesRef indexTerm = new BytesRef();
    long startFP = data.getFilePointer();
    PagedBytes pagedBytes = new PagedBytes(15);
    MonotonicBlockPackedWriter addresses = new MonotonicBlockPackedWriter(data, BLOCK_SIZE);
    
    for (BytesRef b : values) {
      int termPosition = (int) (count & REVERSE_INTERVAL_MASK);
      if (termPosition == 0) {
        int len = StringHelper.sortKeyLength(priorTerm.get(), b);
        indexTerm.bytes = b.bytes;
        indexTerm.offset = b.offset;
        indexTerm.length = len;
        addresses.add(pagedBytes.copyUsingLengthPrefix(indexTerm));
      } else if (termPosition == REVERSE_INTERVAL_MASK) {
        priorTerm.copyBytes(b);
      }
      count++;
    }
    addresses.finish();
    long numBytes = pagedBytes.getPointer();
    pagedBytes.freeze(true);
    PagedBytesDataInput in = pagedBytes.getDataInput();
    meta.writeLong(startFP);
    data.writeVLong(numBytes);
    data.copyBytes(in, numBytes);
  }

  @Override
  public void addSortedField(FieldInfo field, Iterable<BytesRef> values, Iterable<Number> docToOrd) throws IOException {
    meta.writeVInt(field.number);
    meta.writeByte(Lucene410DocValuesFormat.SORTED);
    addTermsDict(field, values);
    addNumericField(field, docToOrd, false);
  }

  @Override
  public void addSortedNumericField(FieldInfo field, final Iterable<Number> docToValueCount, final Iterable<Number> values) throws IOException {
    meta.writeVInt(field.number);
    meta.writeByte(Lucene410DocValuesFormat.SORTED_NUMERIC);
    if (isSingleValued(docToValueCount)) {
      meta.writeVInt(SORTED_SINGLE_VALUED);
      // The field is single-valued, we can encode it as NUMERIC
      addNumericField(field, singletonView(docToValueCount, values, null));
    } else {
      meta.writeVInt(SORTED_WITH_ADDRESSES);
      // write the stream of values as a numeric field
      addNumericField(field, values, true);
      // write the doc -> ord count as a absolute index to the stream
      addAddresses(field, docToValueCount);
    }
  }

  @Override
  public void addSortedSetField(FieldInfo field, Iterable<BytesRef> values, final Iterable<Number> docToOrdCount, final Iterable<Number> ords) throws IOException {
    meta.writeVInt(field.number);
    meta.writeByte(Lucene410DocValuesFormat.SORTED_SET);

    if (isSingleValued(docToOrdCount)) {
      meta.writeVInt(SORTED_SINGLE_VALUED);
      // The field is single-valued, we can encode it as SORTED
      addSortedField(field, values, singletonView(docToOrdCount, ords, -1L));
    } else {
      meta.writeVInt(SORTED_WITH_ADDRESSES);

      // write the ord -> byte[] as a binary field
      addTermsDict(field, values);

      // write the stream of ords as a numeric field
      // NOTE: we could return an iterator that delta-encodes these within a doc
      addNumericField(field, ords, false);

      // write the doc -> ord count as a absolute index to the stream
      addAddresses(field, docToOrdCount);
    }
  }
  
  // writes addressing information as MONOTONIC_COMPRESSED integer
  private void addAddresses(FieldInfo field, Iterable<Number> values) throws IOException {
    meta.writeVInt(field.number);
    meta.writeByte(Lucene410DocValuesFormat.NUMERIC);
    meta.writeVInt(MONOTONIC_COMPRESSED);
    meta.writeLong(-1L);
    meta.writeLong(data.getFilePointer());
    meta.writeVLong(maxDoc);
    meta.writeVInt(PackedInts.VERSION_CURRENT);
    meta.writeVInt(BLOCK_SIZE);

    final MonotonicBlockPackedWriter writer = new MonotonicBlockPackedWriter(data, BLOCK_SIZE);
    long addr = 0;
    writer.add(addr);
    for (Number v : values) {
      addr += v.longValue();
      writer.add(addr);
    }
    writer.finish();
    meta.writeLong(data.getFilePointer());
  }

  @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;
    }
  }
}