/**
 * DataOutputStream for fast-compact encoding of number sequences
 *
 * @author ab
 */
package btools.util;

import java.io.DataOutputStream;
import java.io.IOException;
import java.io.OutputStream;


public final class MixCoderDataOutputStream extends DataOutputStream {
  private int lastValue;
  private int lastLastValue;
  private int repCount;
  private int diffshift;

  private int bm = 1; // byte mask (write mode)
  private int b = 0;

  public static int[] diffs = new int[100];
  public static int[] counts = new int[100];

  public MixCoderDataOutputStream(OutputStream os) {
    super(os);
  }

  public void writeMixed(int v) throws IOException {
    if (v != lastValue && repCount > 0) {
      int d = lastValue - lastLastValue;
      lastLastValue = lastValue;

      encodeBit(d < 0);
      if (d < 0) {
        d = -d;
      }
      encodeVarBits(d - diffshift);
      encodeVarBits(repCount - 1);

      if (d < 100) diffs[d]++;
      if (repCount < 100) counts[repCount]++;

      diffshift = 1;
      repCount = 0;
    }
    lastValue = v;
    repCount++;
  }

  @Override
  public void flush() throws IOException {
    int v = lastValue;
    writeMixed(v + 1);
    lastValue = v;
    repCount = 0;
    if (bm > 1) {
      writeByte((byte) b); // flush bit-coding
    }
  }

  public final void encodeBit(boolean value) throws IOException {
    if (bm == 0x100) {
      writeByte((byte) b);
      bm = 1;
      b = 0;
    }
    if (value) {
      b |= bm;
    }
    bm <<= 1;
  }

  public final void encodeVarBits(int value) throws IOException {
    int range = 0;
    while (value > range) {
      encodeBit(false);
      value -= range + 1;
      range = 2 * range + 1;
    }
    encodeBit(true);
    encodeBounded(range, value);
  }

  public final void encodeBounded(int max, int value) throws IOException {
    int im = 1; // integer mask
    while (im <= max) {
      if (bm == 0x100) {
        writeByte((byte) b);
        bm = 1;
        b = 0;
      }
      if ((value & im) != 0) {
        b |= bm;
        max -= im;
      }
      bm <<= 1;
      im <<= 1;
    }
  }

  public static void stats() {
    for (int i = 1; i < 100; i++) System.out.println("diff[" + i + "] = " + diffs[i]);
    for (int i = 1; i < 100; i++) System.out.println("counts[" + i + "] = " + counts[i]);
  }
}