sclass LineCompSemiCached implements AutoCloseable {

  File f; // must be the raw text version

  RandomAccessFile raf;

  int[] literalOffsets;

  int[] pairs;

  Map<S, int[]> files;

  S encoding = "UTF-8";

  transient Lock lock = lock();

  *() {}

  *(File f) {

    if (isGZipFile(f)) fail("Must not be gzipped: " + f2s(f));

    init(f);

  }

  LineCompReader init(File f) {

    this.f = f;

    LineCompReader reader = new(f);

    literalOffsets = reader.literalOffsets;

    pairs = intPairsToIntArray(reader.pairs);

    files = mapValues toIntArray(reader.versions);

    ret reader;

  }

  void openFile {

    lock lock;

    if (raf == null)

      raf = randomAccessFileForReading(f);

  }

  S getLiteral(int i) {

    openFile();

    int start = literalOffsets[i];

    ret bytesToString(raf_readFilePart(raf, start, literalOffsets[i+1]-start), encoding);

  }

  public void close ctex {

    if (raf != null) raf.close();

  }

  int nLiterals() { ret literalOffsets.length-1; }

  S getFile(S name) {

    int[] encoded = files.get(name);

    if (encoded == null) null;

    new StringBuilder buf;

    for (int idx : encoded)

      decode(idx, buf);

    ret str(buf);

  }

  Set<S> files() { ret keys(files); }

  void decode(int idx, StringBuilder buf) {

    if (idx < nLiterals()) {

      if (empty(buf)) buf.append('\n');

      buf.append(getLiteral(idx));

    } else {

      int idx2 = (idx-nLiterals())*2;

      decode(pairs[idx2], buf);

      decode(pairs[idx2+1], buf);

    }

  }

}