/*
 * Copyright 2007 Mat Gessel <mat.gessel@gmail.com>
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package org.litesoft.GWT.client.widgets.nonpublic.external;

/**
 * A DragGesture wrapper which prevents the wrapped gesture's step action
 * from occuring until a specified distance is exceeded. This can be used to
 * prevent accidental manipulation or to pervent the wrapped gesture's start
 * action from being executed until the mouse is moved.
 */
public class DragThresholdFilter extends DragGestureWrapper
{
    private final int m_threshold;

    private MouseEvent m_start;
    private boolean m_started = false;

    /**
     * Creates a new DragGesture with the specified threshold.
     *
     * @param distance the distance in screen pixels to move before taking an
     *                 action, or <code>0</code>
     */
    public DragThresholdFilter( int distance, DragGesture delegate )
    {
        super( delegate );

        if ( distance < 0 )
        {
            throw new IllegalArgumentException( String.valueOf( distance ) );
        }

        m_threshold = distance;
    }

    protected boolean equalsThreshold( int deltaX, int deltaY )
    {
        return Math.abs( deltaX ) >= m_threshold || Math.abs( deltaY ) >= m_threshold;
    }

    public void start( MouseEvent e )
    {
        if ( m_threshold == 0 )
        {
            m_started = true;
            super.start( e );
        }
        else
        {
            m_start = e;
        }
    }

    public void step( DragEvent e )
    {
        if ( !m_started && equalsThreshold( e.getDeltaX(), e.getDeltaY() ) )
        {
            m_started = true;
            super.start( m_start );
        }
        if ( m_started )
        {
            super.step( e );
        }
    }

    public void finish()
    {
        super.finish();
        m_started = false;
        m_start = null;
    }
}