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package edu.isi.nlp.io;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.base.Optional;
import com.google.common.io.ByteSource;
import com.google.common.io.CharSource;
import edu.isi.nlp.files.KeyValueSource;
import edu.isi.nlp.strings.offsets.ByteOffset;
import edu.isi.nlp.strings.offsets.OffsetRange;
import edu.isi.nlp.symbols.Symbol;
import java.io.IOException;
import java.nio.charset.Charset;
import java.util.Set;

/**
 * A file which contains multiple indexed blocks of character data.
 *
 * This should get merged/replaced with the never {@link KeyValueSource} code.
 */
public final class IndexedByteSource implements CharacterChannelSet {

  private final ByteSource source;
  private final OffsetIndex offsetIndex;

  private IndexedByteSource(final ByteSource source, final OffsetIndex offsetIndex) {
    this.source = checkNotNull(source);
    this.offsetIndex = checkNotNull(offsetIndex);
  }

  public static IndexedByteSource from(final ByteSource source, final OffsetIndex offsetIndex) {
    return new IndexedByteSource(source, offsetIndex);
  }

  @Override
  public Set channelSet() {
    return offsetIndex.keySet();
  }

  public Optional channelAsByteSource(final Symbol key) throws IOException {
    final Optional> range = offsetIndex.byteOffsetsOf(checkNotNull(key));
    if (range.isPresent()) {
      final ByteOffset startInclusive = range.get().startInclusive();
      final ByteOffset endInclusive = range.get().endInclusive();

      return Optional.of(
          source.slice(startInclusive.asInt(), endInclusive.asInt() - startInclusive.asInt() + 1));
    } else {
      return Optional.absent();
    }
  }

  @Override
  public Optional channelAsCharSource(final Symbol key, Charset charset)
      throws IOException {
    final Optional channelSource = channelAsByteSource(key);
    if (channelSource.isPresent()) {
      return Optional.of(channelSource.get().asCharSource(charset));
    } else {
      return Optional.absent();
    }
  }

  public ByteSource source() {
    return source;
  }
}