package btools.util;

/**
 * Something like LinkedHashMap, but purpose build, less dynamic and memory efficient
 *
 * @author ab
 */
public final class LruMap
{
  private int hashbins;
  private int maxsize;
  private int size;
  
  private LruMapNode lru;
  private LruMapNode mru;

  private LruMapNode[] binArray;

  public LruMap( int bins, int size)
  {
    hashbins = bins;
    maxsize = size;
    binArray = new LruMapNode[hashbins];
  }
  
  public LruMapNode get( LruMapNode key )
  {
    int bin = ( key.hash & 0xfffffff ) % hashbins;
    
    LruMapNode e = binArray[bin];
    while ( e != null )
    {
      if ( key.equals( e ) )
      {
        return e;
      }
      e = e.nextInBin;
    }
    return null;
  }
  
  // put e to the mru end of the queue
  public void touch( LruMapNode e )
  {
    LruMapNode n = e.next;
    LruMapNode p = e.previous;
    
    if ( n == null )
    {
      return; // already at mru
    }
    n.previous = p;
    if ( p != null )
    {
      p.next = n;
    }
    else
    {
      lru = n;
    }
    
    mru.next = e;
    e.previous =  mru;
    e.next = null;
    mru = e;
  }
  
  public LruMapNode removeLru()
  {
    if ( size < maxsize )
    {
      return null;
    }
    size--;
    // unlink the lru from it's bin-queue
    int bin = ( lru.hashCode() & 0xfffffff ) % hashbins;
    LruMapNode e = binArray[bin];
    if ( e == lru )
    {
      binArray[bin] = lru.nextInBin;
    }
    else
    {
      while( e != null )
      {
        LruMapNode prev = e;
        e = e.nextInBin;
        if ( e == lru )
        {
          prev.nextInBin = lru.nextInBin;
          break;
        }
      }
    }
    
    LruMapNode res = lru;
    lru = lru.next;
    lru.previous = null;
    return res;
  }

  public void put( LruMapNode val )
  {
    int bin = ( val.hashCode() & 0xfffffff ) % hashbins;
    val.nextInBin = binArray[bin];
    binArray[bin] = val;
    
    val.previous =  mru;
    val.next = null;
    if ( mru == null )
    {
      lru = val;
    }
    else
    {
      mru.next = val;
    }
    mru = val;
    size++;
  }
}