package btools.codec;

/**
 * Simple container for a list of lists of integers
 */
public class LinkedListContainer
{
  private int[] ia; // prev, data, prev, data, ...
  private int size;
  private int[] startpointer; // 0=void, odd=head-data-cell
  private int listpointer;

  /**
   * Construct a container for the given number of lists
   *
   * If no default-buffer is given, an int[nlists*4] is constructed,
   * able to hold 2 entries per list on average
   *
   * @param nlists the number of lists
   * @param defaultbuffer an optional data array for re-use (gets replaced if too small)
   */
  public LinkedListContainer( int nlists, int[] defaultbuffer )
  {
    ia = defaultbuffer == null ? new int[nlists*4] : defaultbuffer;
    startpointer = new int[nlists]; 
  }
  
  /**
   * Add a data element to the given list
   *
   * @param listNr the list to add the data to
   * @param data the data value
   */
  public void addDataElement( int listNr, int data )
  {
    if ( size + 2 > ia.length )
    {
      resize();
    }
    ia[size++] = startpointer[ listNr ];
    startpointer[ listNr ] = size;
    ia[size++] = data;
  }
  
  /**
   * Initialize a list for reading
   *
   * @param listNr the list to initialize
   * @return the number of entries in that list
   */
  public int initList( int listNr )
  {
    int cnt = 0;
    int lp = listpointer = startpointer[ listNr ];
    while( lp != 0 )
    {
      lp = ia[ lp-1 ];
      cnt++;
    }
    return cnt;
  }

  /**
   * Get a data element from the list previously initialized.
   * Data elements are return in reverse order (lifo)
   *
   * @return the data element
   * @throws IllegalArgumentException if no more element
   */
  public int getDataElement()
  {
    if ( listpointer == 0 )
    {
      throw new IllegalArgumentException( "no more element!" );
    }
    int data = ia[ listpointer ];
    listpointer = ia[ listpointer-1 ];
    return data;
  }
  
  private void resize()
  {
    int[] ia2 = new int[2*ia.length];
    System.arraycopy( ia, 0, ia2, 0, ia.length );
    ia = ia2;
  }
}