/*
 * 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.codecs.compressing;


import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.BYTE_ARR;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.DAY;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.DAY_ENCODING;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.FIELDS_EXTENSION;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.HOUR;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.HOUR_ENCODING;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.INDEX_CODEC_NAME;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.INDEX_EXTENSION;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.META_EXTENSION;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.META_VERSION_START;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.NUMERIC_DOUBLE;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.NUMERIC_FLOAT;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.NUMERIC_INT;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.NUMERIC_LONG;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.SECOND;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.SECOND_ENCODING;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.STRING;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.TYPE_BITS;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.TYPE_MASK;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.VERSION_CURRENT;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.VERSION_META;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.VERSION_OFFHEAP_INDEX;
import static org.apache.lucene.codecs.compressing.CompressingStoredFieldsWriter.VERSION_START;

import java.io.EOFException;
import java.io.IOException;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;

import org.apache.lucene.codecs.CodecUtil;
import org.apache.lucene.codecs.StoredFieldsReader;
import org.apache.lucene.document.Document;
import org.apache.lucene.index.CorruptIndexException;
import org.apache.lucene.index.FieldInfo;
import org.apache.lucene.index.FieldInfos;
import org.apache.lucene.index.IndexFileNames;
import org.apache.lucene.index.SegmentInfo;
import org.apache.lucene.index.StoredFieldVisitor;
import org.apache.lucene.store.AlreadyClosedException;
import org.apache.lucene.store.ByteArrayDataInput;
import org.apache.lucene.store.ChecksumIndexInput;
import org.apache.lucene.store.DataInput;
import org.apache.lucene.store.Directory;
import org.apache.lucene.store.IOContext;
import org.apache.lucene.store.IndexInput;
import org.apache.lucene.util.Accountable;
import org.apache.lucene.util.Accountables;
import org.apache.lucene.util.ArrayUtil;
import org.apache.lucene.util.BitUtil;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.IOUtils;
import org.apache.lucene.util.LongsRef;
import org.apache.lucene.util.packed.PackedInts;

/**
 * {@link StoredFieldsReader} impl for {@link CompressingStoredFieldsFormat}.
 * @lucene.experimental
 */
public final class CompressingStoredFieldsReader extends StoredFieldsReader {

  private final int version;
  private final FieldInfos fieldInfos;
  private final FieldsIndex indexReader;
  private final long maxPointer;
  private final IndexInput fieldsStream;
  private final int chunkSize;
  private final int packedIntsVersion;
  private final CompressionMode compressionMode;
  private final Decompressor decompressor;
  private final int numDocs;
  private final boolean merging;
  private final BlockState state;
  private final long numDirtyChunks; // number of incomplete compressed blocks written
  private final long numDirtyDocs; // cumulative number of missing docs in incomplete chunks
  private boolean closed;

  // used by clone
  private CompressingStoredFieldsReader(CompressingStoredFieldsReader reader, boolean merging) {
    this.version = reader.version;
    this.fieldInfos = reader.fieldInfos;
    this.fieldsStream = reader.fieldsStream.clone();
    this.indexReader = reader.indexReader.clone();
    this.maxPointer = reader.maxPointer;
    this.chunkSize = reader.chunkSize;
    this.packedIntsVersion = reader.packedIntsVersion;
    this.compressionMode = reader.compressionMode;
    this.decompressor = reader.decompressor.clone();
    this.numDocs = reader.numDocs;
    this.numDirtyChunks = reader.numDirtyChunks;
    this.numDirtyDocs = reader.numDirtyDocs;
    this.merging = merging;
    this.state = new BlockState();
    this.closed = false;
  }

  /** Sole constructor. */
  public CompressingStoredFieldsReader(Directory d, SegmentInfo si, String segmentSuffix, FieldInfos fn,
      IOContext context, String formatName, CompressionMode compressionMode) throws IOException {
    this.compressionMode = compressionMode;
    final String segment = si.name;
    boolean success = false;
    fieldInfos = fn;
    numDocs = si.maxDoc();

    final String fieldsStreamFN = IndexFileNames.segmentFileName(segment, segmentSuffix, FIELDS_EXTENSION);
    ChecksumIndexInput metaIn = null;
    try {
      // Open the data file
      fieldsStream = d.openInput(fieldsStreamFN, context);
      version = CodecUtil.checkIndexHeader(fieldsStream, formatName, VERSION_START, VERSION_CURRENT, si.getId(), segmentSuffix);
      assert CodecUtil.indexHeaderLength(formatName, segmentSuffix) == fieldsStream.getFilePointer();

      if (version >= VERSION_OFFHEAP_INDEX) {
        final String metaStreamFN = IndexFileNames.segmentFileName(segment, segmentSuffix, META_EXTENSION);
        metaIn = d.openChecksumInput(metaStreamFN, IOContext.READONCE);
        CodecUtil.checkIndexHeader(metaIn, INDEX_CODEC_NAME + "Meta", META_VERSION_START, version, si.getId(), segmentSuffix);
      }
      if (version >= VERSION_META) {
        chunkSize = metaIn.readVInt();
        packedIntsVersion = metaIn.readVInt();
      } else {
        chunkSize = fieldsStream.readVInt();
        packedIntsVersion = fieldsStream.readVInt();
      }

      decompressor = compressionMode.newDecompressor();
      this.merging = false;
      this.state = new BlockState();

      // NOTE: data file is too costly to verify checksum against all the bytes on open,
      // but for now we at least verify proper structure of the checksum footer: which looks
      // for FOOTER_MAGIC + algorithmID. This is cheap and can detect some forms of corruption
      // such as file truncation.
      CodecUtil.retrieveChecksum(fieldsStream);

      long maxPointer = -1;
      FieldsIndex indexReader = null;

      if (version < VERSION_OFFHEAP_INDEX) {
        // Load the index into memory
        final String indexName = IndexFileNames.segmentFileName(segment, segmentSuffix, "fdx");
        try (ChecksumIndexInput indexStream = d.openChecksumInput(indexName, context)) {
          Throwable priorE = null;
          try {
            assert formatName.endsWith("Data");
            final String codecNameIdx = formatName.substring(0, formatName.length() - "Data".length()) + "Index";
            final int version2 = CodecUtil.checkIndexHeader(indexStream, codecNameIdx, VERSION_START, VERSION_CURRENT, si.getId(), segmentSuffix);
            if (version != version2) {
              throw new CorruptIndexException("Version mismatch between stored fields index and data: " + version2 + " != " + version, indexStream);
            }
            assert CodecUtil.indexHeaderLength(codecNameIdx, segmentSuffix) == indexStream.getFilePointer();
            indexReader = new LegacyFieldsIndexReader(indexStream, si);
            maxPointer = indexStream.readVLong();
          } catch (Throwable exception) {
            priorE = exception;
          } finally {
            CodecUtil.checkFooter(indexStream, priorE);
          }
        }
      } else {
        FieldsIndexReader fieldsIndexReader = new FieldsIndexReader(d, si.name, segmentSuffix, INDEX_EXTENSION, INDEX_CODEC_NAME, si.getId(), metaIn);
        indexReader = fieldsIndexReader;
        maxPointer = fieldsIndexReader.getMaxPointer();
      }

      this.maxPointer = maxPointer;
      this.indexReader = indexReader;

      if (version >= VERSION_META) {
        numDirtyChunks = metaIn.readVLong();
        numDirtyDocs = metaIn.readVLong();
      } else {
        // Old versions of this format did not record numDirtyDocs. Since bulk
        // merges are disabled on version increments anyway, we make no effort
        // to get valid values of numDirtyChunks and numDirtyDocs.
        numDirtyChunks = numDirtyDocs = -1;
      }

      if (metaIn != null) {
        CodecUtil.checkFooter(metaIn, null);
        metaIn.close();
      }

      success = true;
    } catch (Throwable t) {
      if (metaIn != null) {
        CodecUtil.checkFooter(metaIn, t);
        throw new AssertionError("unreachable");
      } else {
        throw t;
      }
    } finally {
      if (!success) {
        IOUtils.closeWhileHandlingException(this, metaIn);
      }
    }
  }

  /**
   * @throws AlreadyClosedException if this FieldsReader is closed
   */
  private void ensureOpen() throws AlreadyClosedException {
    if (closed) {
      throw new AlreadyClosedException("this FieldsReader is closed");
    }
  }

  /** 
   * Close the underlying {@link IndexInput}s.
   */
  @Override
  public void close() throws IOException {
    if (!closed) {
      IOUtils.close(indexReader, fieldsStream);
      closed = true;
    }
  }

  private static void readField(DataInput in, StoredFieldVisitor visitor, FieldInfo info, int bits) throws IOException {
    switch (bits & TYPE_MASK) {
      case BYTE_ARR:
        int length = in.readVInt();
        byte[] data = new byte[length];
        in.readBytes(data, 0, length);
        visitor.binaryField(info, data);
        break;
      case STRING:
        length = in.readVInt();
        data = new byte[length];
        in.readBytes(data, 0, length);
        visitor.stringField(info, data);
        break;
      case NUMERIC_INT:
        visitor.intField(info, in.readZInt());
        break;
      case NUMERIC_FLOAT:
        visitor.floatField(info, readZFloat(in));
        break;
      case NUMERIC_LONG:
        visitor.longField(info, readTLong(in));
        break;
      case NUMERIC_DOUBLE:
        visitor.doubleField(info, readZDouble(in));
        break;
      default:
        throw new AssertionError("Unknown type flag: " + Integer.toHexString(bits));
    }
  }

  private static void skipField(DataInput in, int bits) throws IOException {
    switch (bits & TYPE_MASK) {
      case BYTE_ARR:
      case STRING:
        final int length = in.readVInt();
        in.skipBytes(length);
        break;
      case NUMERIC_INT:
        in.readZInt();
        break;
      case NUMERIC_FLOAT:
        readZFloat(in);
        break;
      case NUMERIC_LONG:
        readTLong(in);
        break;
      case NUMERIC_DOUBLE:
        readZDouble(in);
        break;
      default:
        throw new AssertionError("Unknown type flag: " + Integer.toHexString(bits));
    }
  }

  /**
   * Reads a float in a variable-length format.  Reads between one and
   * five bytes. Small integral values typically take fewer bytes.
   */
  static float readZFloat(DataInput in) throws IOException {
    int b = in.readByte() & 0xFF;
    if (b == 0xFF) {
      // negative value
      return Float.intBitsToFloat(in.readInt());
    } else if ((b & 0x80) != 0) {
      // small integer [-1..125]
      return (b & 0x7f) - 1;
    } else {
      // positive float
      int bits = b << 24 | ((in.readShort() & 0xFFFF) << 8) | (in.readByte() & 0xFF);
      return Float.intBitsToFloat(bits);
    }
  }

  /**
   * Reads a double in a variable-length format.  Reads between one and
   * nine bytes. Small integral values typically take fewer bytes.
   */
  static double readZDouble(DataInput in) throws IOException {
    int b = in.readByte() & 0xFF;
    if (b == 0xFF) {
      // negative value
      return Double.longBitsToDouble(in.readLong());
    } else if (b == 0xFE) {
      // float
      return Float.intBitsToFloat(in.readInt());
    } else if ((b & 0x80) != 0) {
      // small integer [-1..124]
      return (b & 0x7f) - 1;
    } else {
      // positive double
      long bits = ((long) b) << 56 | ((in.readInt() & 0xFFFFFFFFL) << 24) | ((in.readShort() & 0xFFFFL) << 8) | (in.readByte() & 0xFFL);
      return Double.longBitsToDouble(bits);
    }
  }

  /**
   * Reads a long in a variable-length format.  Reads between one andCorePropLo
   * nine bytes. Small values typically take fewer bytes.
   */
  static long readTLong(DataInput in) throws IOException {
    int header = in.readByte() & 0xFF;

    long bits = header & 0x1F;
    if ((header & 0x20) != 0) {
      // continuation bit
      bits |= in.readVLong() << 5;
    }

    long l = BitUtil.zigZagDecode(bits);

    switch (header & DAY_ENCODING) {
      case SECOND_ENCODING:
        l *= SECOND;
        break;
      case HOUR_ENCODING:
        l *= HOUR;
        break;
      case DAY_ENCODING:
        l *= DAY;
        break;
      case 0:
        // uncompressed
        break;
      default:
        throw new AssertionError();
    }

    return l;
  }

  /**
   * A serialized document, you need to decode its input in order to get an actual
   * {@link Document}.
   */
  static class SerializedDocument {

    // the serialized data
    final DataInput in;

    // the number of bytes on which the document is encoded
    final int length;

    // the number of stored fields
    final int numStoredFields;

    private SerializedDocument(DataInput in, int length, int numStoredFields) {
      this.in = in;
      this.length = length;
      this.numStoredFields = numStoredFields;
    }

  }

  /**
   * Keeps state about the current block of documents.
   */
  private class BlockState {

    private int docBase, chunkDocs;

    // whether the block has been sliced, this happens for large documents
    private boolean sliced;

    private long[] offsets = LongsRef.EMPTY_LONGS;
    private long[] numStoredFields = LongsRef.EMPTY_LONGS;

    // the start pointer at which you can read the compressed documents
    private long startPointer;

    private final BytesRef spare;
    private final BytesRef bytes;

    BlockState() {
      if (merging) {
        spare = new BytesRef();
        bytes = new BytesRef();
      } else {
        spare = bytes = null;
      }
    }

    boolean contains(int docID) {
      return docID >= docBase && docID < docBase + chunkDocs;
    }

    /**
     * Reset this block so that it stores state for the block
     * that contains the given doc id.
     */
    void reset(int docID) throws IOException {
      boolean success = false;
      try {
        doReset(docID);
        success = true;
      } finally {
        if (success == false) {
          // if the read failed, set chunkDocs to 0 so that it does not
          // contain any docs anymore and is not reused. This should help
          // get consistent exceptions when trying to get several
          // documents which are in the same corrupted block since it will
          // force the header to be decoded again
          chunkDocs = 0;
        }
      }
    }

    private void doReset(int docID) throws IOException {
      docBase = fieldsStream.readVInt();
      final int token = fieldsStream.readVInt();
      chunkDocs = token >>> 1;
      if (contains(docID) == false
          || docBase + chunkDocs > numDocs) {
        throw new CorruptIndexException("Corrupted: docID=" + docID
            + ", docBase=" + docBase + ", chunkDocs=" + chunkDocs
            + ", numDocs=" + numDocs, fieldsStream);
      }

      sliced = (token & 1) != 0;

      offsets = ArrayUtil.grow(offsets, chunkDocs + 1);
      numStoredFields = ArrayUtil.grow(numStoredFields, chunkDocs);

      if (chunkDocs == 1) {
        numStoredFields[0] = fieldsStream.readVInt();
        offsets[1] = fieldsStream.readVInt();
      } else {
        // Number of stored fields per document
        final int bitsPerStoredFields = fieldsStream.readVInt();
        if (bitsPerStoredFields == 0) {
          Arrays.fill(numStoredFields, 0, chunkDocs, fieldsStream.readVInt());
        } else if (bitsPerStoredFields > 31) {
          throw new CorruptIndexException("bitsPerStoredFields=" + bitsPerStoredFields, fieldsStream);
        } else {
          final PackedInts.ReaderIterator it = PackedInts.getReaderIteratorNoHeader(fieldsStream, PackedInts.Format.PACKED, packedIntsVersion, chunkDocs, bitsPerStoredFields, 1024);
          for (int i = 0; i < chunkDocs; ) {
            final LongsRef next = it.next(Integer.MAX_VALUE);
            System.arraycopy(next.longs, next.offset, numStoredFields, i, next.length);
            i += next.length;
          }
        }

        // The stream encodes the length of each document and we decode
        // it into a list of monotonically increasing offsets
        final int bitsPerLength = fieldsStream.readVInt();
        if (bitsPerLength == 0) {
          final int length = fieldsStream.readVInt();
          for (int i = 0; i < chunkDocs; ++i) {
            offsets[1 + i] = (1 + i) * length;
          }
        } else if (bitsPerStoredFields > 31) {
          throw new CorruptIndexException("bitsPerLength=" + bitsPerLength, fieldsStream);
        } else {
          final PackedInts.ReaderIterator it = PackedInts.getReaderIteratorNoHeader(fieldsStream, PackedInts.Format.PACKED, packedIntsVersion, chunkDocs, bitsPerLength, 1024);
          for (int i = 0; i < chunkDocs; ) {
            final LongsRef next = it.next(Integer.MAX_VALUE);
            System.arraycopy(next.longs, next.offset, offsets, i + 1, next.length);
            i += next.length;
          }
          for (int i = 0; i < chunkDocs; ++i) {
            offsets[i + 1] += offsets[i];
          }
        }

        // Additional validation: only the empty document has a serialized length of 0
        for (int i = 0; i < chunkDocs; ++i) {
          final long len = offsets[i + 1] - offsets[i];
          final long storedFields = numStoredFields[i];
          if ((len == 0) != (storedFields == 0)) {
            throw new CorruptIndexException("length=" + len + ", numStoredFields=" + storedFields, fieldsStream);
          }
        }

      }

      startPointer = fieldsStream.getFilePointer();

      if (merging) {
        final int totalLength = Math.toIntExact(offsets[chunkDocs]);
        // decompress eagerly
        if (sliced) {
          bytes.offset = bytes.length = 0;
          for (int decompressed = 0; decompressed < totalLength; ) {
            final int toDecompress = Math.min(totalLength - decompressed, chunkSize);
            decompressor.decompress(fieldsStream, toDecompress, 0, toDecompress, spare);
            bytes.bytes = ArrayUtil.grow(bytes.bytes, bytes.length + spare.length);
            System.arraycopy(spare.bytes, spare.offset, bytes.bytes, bytes.length, spare.length);
            bytes.length += spare.length;
            decompressed += toDecompress;
          }
        } else {
          decompressor.decompress(fieldsStream, totalLength, 0, totalLength, bytes);
        }
        if (bytes.length != totalLength) {
          throw new CorruptIndexException("Corrupted: expected chunk size = " + totalLength + ", got " + bytes.length, fieldsStream);
        }
      }
    }

    /**
     * Get the serialized representation of the given docID. This docID has
     * to be contained in the current block.
     */
    SerializedDocument document(int docID) throws IOException {
      if (contains(docID) == false) {
        throw new IllegalArgumentException();
      }

      final int index = docID - docBase;
      final int offset = Math.toIntExact(offsets[index]);
      final int length = Math.toIntExact(offsets[index+1]) - offset;
      final int totalLength = Math.toIntExact(offsets[chunkDocs]);
      final int numStoredFields = Math.toIntExact(this.numStoredFields[index]);

      final BytesRef bytes;
      if (merging) {
        bytes = this.bytes;
      } else {
        bytes = new BytesRef();
      }

      final DataInput documentInput;
      if (length == 0) {
        // empty
        documentInput = new ByteArrayDataInput();
      } else if (merging) {
        // already decompressed
        documentInput = new ByteArrayDataInput(bytes.bytes, bytes.offset + offset, length);
      } else if (sliced) {
        fieldsStream.seek(startPointer);
        decompressor.decompress(fieldsStream, chunkSize, offset, Math.min(length, chunkSize - offset), bytes);
        documentInput = new DataInput() {

          int decompressed = bytes.length;

          void fillBuffer() throws IOException {
            assert decompressed <= length;
            if (decompressed == length) {
              throw new EOFException();
            }
            final int toDecompress = Math.min(length - decompressed, chunkSize);
            decompressor.decompress(fieldsStream, toDecompress, 0, toDecompress, bytes);
            decompressed += toDecompress;
          }

          @Override
          public byte readByte() throws IOException {
            if (bytes.length == 0) {
              fillBuffer();
            }
            --bytes.length;
            return bytes.bytes[bytes.offset++];
          }

          @Override
          public void readBytes(byte[] b, int offset, int len) throws IOException {
            while (len > bytes.length) {
              System.arraycopy(bytes.bytes, bytes.offset, b, offset, bytes.length);
              len -= bytes.length;
              offset += bytes.length;
              fillBuffer();
            }
            System.arraycopy(bytes.bytes, bytes.offset, b, offset, len);
            bytes.offset += len;
            bytes.length -= len;
          }

        };
      } else {
        fieldsStream.seek(startPointer);
        decompressor.decompress(fieldsStream, totalLength, offset, length, bytes);
        assert bytes.length == length;
        documentInput = new ByteArrayDataInput(bytes.bytes, bytes.offset, bytes.length);
      }

      return new SerializedDocument(documentInput, length, numStoredFields);
    }

  }

  SerializedDocument document(int docID) throws IOException {
    if (state.contains(docID) == false) {
      fieldsStream.seek(indexReader.getStartPointer(docID));
      state.reset(docID);
    }
    assert state.contains(docID);
    return state.document(docID);
  }

  @Override
  public void visitDocument(int docID, StoredFieldVisitor visitor)
      throws IOException {

    final SerializedDocument doc = document(docID);

    for (int fieldIDX = 0; fieldIDX < doc.numStoredFields; fieldIDX++) {
      final long infoAndBits = doc.in.readVLong();
      final int fieldNumber = (int) (infoAndBits >>> TYPE_BITS);
      final FieldInfo fieldInfo = fieldInfos.fieldInfo(fieldNumber);

      final int bits = (int) (infoAndBits & TYPE_MASK);
      assert bits <= NUMERIC_DOUBLE: "bits=" + Integer.toHexString(bits);

      switch(visitor.needsField(fieldInfo)) {
        case YES:
          readField(doc.in, visitor, fieldInfo, bits);
          break;
        case NO:
          if (fieldIDX == doc.numStoredFields - 1) {// don't skipField on last field value; treat like STOP
            return;
          }
          skipField(doc.in, bits);
          break;
        case STOP:
          return;
      }
    }
  }

  @Override
  public StoredFieldsReader clone() {
    ensureOpen();
    return new CompressingStoredFieldsReader(this, false);
  }

  @Override
  public StoredFieldsReader getMergeInstance() {
    ensureOpen();
    return new CompressingStoredFieldsReader(this, true);
  }

  int getVersion() {
    return version;
  }

  CompressionMode getCompressionMode() {
    return compressionMode;
  }
  
  FieldsIndex getIndexReader() {
    return indexReader;
  }
  
  long getMaxPointer() {
    return maxPointer;
  }
  
  IndexInput getFieldsStream() {
    return fieldsStream;
  }

  int getChunkSize() {
    return chunkSize;
  }
  
  long getNumDirtyDocs() {
    if (version != VERSION_CURRENT) {
      throw new IllegalStateException("getNumDirtyDocs should only ever get called when the reader is on the current version");
    }
    assert numDirtyDocs >= 0;
    return numDirtyDocs;
  }
  
  long getNumDirtyChunks() {
    if (version != VERSION_CURRENT) {
      throw new IllegalStateException("getNumDirtyChunks should only ever get called when the reader is on the current version");
    }
    assert numDirtyChunks >= 0;
    return numDirtyChunks;
  }

  int getNumDocs() {
    return numDocs;
  }

  int getPackedIntsVersion() {
    return packedIntsVersion;
  }

  @Override
  public long ramBytesUsed() {
    return indexReader.ramBytesUsed();
  }
  
  @Override
  public Collection<Accountable> getChildResources() {
    return Collections.singleton(Accountables.namedAccountable("stored field index", indexReader));
  }

  @Override
  public void checkIntegrity() throws IOException {
    indexReader.checkIntegrity();
    CodecUtil.checksumEntireFile(fieldsStream);
  }

  @Override
  public String toString() {
    return getClass().getSimpleName() + "(mode=" + compressionMode + ",chunksize=" + chunkSize + ")";
  }
}
