// We use big-endian as DataOutputStream does
sclass ByteHead /*is DataOutput*/ {
  settable bool readMode;
  settable bool writeMode;
  settable InputStream inputStream;
  settable OutputStream outputStream;
  
  *() {}
  *(InputStream *inputStream) { readMode(true); }
  *(OutputStream *outputStream) { writeMode(true); }
  
  void writeLong(long l) {
    writeInt((int) (l >> 32));
    writeInt((int) l);
  }
  
  void writeInt(int i) {
    write(i >> 24);
    write(i >> 16);
    write(i >> 8);
    write(i);
  }
  
  void writeShort(int i) {
    write(i >> 8);
    write(i);
  }
  
  void writeByte aka write(int i) ctex {
    ensureWriteMode();
    outputStream?.write(i);
  }
  
  long readLong() {
    long i = readInt() << 32;
    ret i | (readInt() & 0xFFFFFFFFL);
  }
  
  int readInt() {
    int i = read() << 24;
    i |= read() << 16;
    i |= read() << 8;
    ret (short) (i | read());
  }
  
  short readShort() {
    int i = read() << 8;
    ret (short) (i | read());
  }
  
  // -1 for EOF
  int readByte aka read() ctex {
    ensureReadMode();
    ret inputStream.read();
  }
  
  void ensureReadMode {
    if (!readMode) fail("Not in read mode");
  }
  
  void ensureWriteMode {
    if (!writeMode) fail("Not in write mode");
  }
  
  // exchange = read or write depending on mode
  
  void exchangeShort(IF0<Short> getter, IVF1<Short> setter) {
    if (writeMode())
      writeShort(getter!);
    
    if (readMode())
      setter.get(readShort());
  }
  
  void exchangeLong(IVar<Long> var) {
    exchangeLong(var.getter(), var.setter());
  }
  
  void exchangeLong(IF0<Long> getter, IVF1<Long> setter) {
    if (writeMode())
      writeLong(getter!);

    if (readMode())
      setter.get(readLong());
  }
  
  void exchangeInt(int i) {
    exchangeInt(-> i, j -> assertEquals(i, j));
  }
  
  void exchangeInt(IF0<Int> getter, IVF1<Int> setter) {
    if (writeMode())
      writeInt(getter!);

    if (readMode())
      setter.get(readInt());
  }
  
  void exchange(ByteIO writable) {
    if (writable != null) writable.readWrite(this);
  }
  
  void exchangeAll(Iterable<? extends ByteIO> writables) {  
    if (writables != null)
      for (writable : writables)
        exchange(writable);
  }
}