package btools.codec;

/**
 * Special integer fifo suitable for 3-pass encoding
 */
public class IntegerFifo3Pass
{
  private int[] a;
  private int size;
  private int pos;

  private int pass;

  public IntegerFifo3Pass( int capacity )
  {
    a = capacity < 4 ? new int[4] : new int[capacity];
  }

  /**
   * Starts a new encoding pass and resets the reading pointer
   * from the stats collected in pass2 and writes that to the given context
   */
  public void init()
  {
    pass++;
    pos = 0;
  }

  /**
   * writes to the fifo in pass2
   */
  public void add( int value )
  {
    if ( pass == 2 )
    {
      if ( size == a.length )
      {
        int[] aa = new int[2 * size];
        System.arraycopy( a, 0, aa, 0, size );
        a = aa;
      }
      a[size++] = value;
    }
  }

  /**
   * reads from the fifo in pass3 (in pass1/2 returns just 1)
   */
  public int getNext()
  {
    return pass == 3 ? get( pos++ ) : 1;
  }

  private int get( int idx )
  {
    if ( idx >= size )
    {
      throw new IndexOutOfBoundsException( "list size=" + size + " idx=" + idx );
    }
    return a[idx];
  }
}