/*

 * Copyright (c) 2005, 2008, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package javax.swing.plaf.basic;

import java.awt.Toolkit;

import java.awt.event.*;

import java.awt.dnd.DragSource;

import javax.swing.*;

import sun.awt.dnd.SunDragSourceContextPeer;

import sun.awt.AppContext;

/**

 * Drag gesture recognition support for classes that have a

 * <code>TransferHandler</code>. The gesture for a drag in this class is a mouse

 * press followed by movement by <code>DragSource.getDragThreshold()</code>

 * pixels. An instance of this class is maintained per AppContext, and the

 * public static methods call into the appropriate instance.

 *

 * @author Shannon Hickey

 */

class DragRecognitionSupport {

    private int motionThreshold;

    private MouseEvent dndArmedEvent;

    private JComponent component;

    /**

     * This interface allows us to pass in a handler to mouseDragged,

     * so that we can be notified immediately before a drag begins.

     */

    public static interface BeforeDrag {

        public void dragStarting(MouseEvent me);

    }

    /**

     * Returns the DragRecognitionSupport for the caller's AppContext.

     */

    private static DragRecognitionSupport getDragRecognitionSupport() {

        DragRecognitionSupport support =

            (DragRecognitionSupport)AppContext.getAppContext().

                get(DragRecognitionSupport.class);

        if (support == null) {

            support = new DragRecognitionSupport();

            AppContext.getAppContext().put(DragRecognitionSupport.class, support);

        }

        return support;

    }

    /**

     * Returns whether or not the event is potentially part of a drag sequence.

     */

    public static boolean mousePressed(MouseEvent me) {

        return getDragRecognitionSupport().mousePressedImpl(me);

    }

    /**

     * If a dnd recognition has been going on, return the MouseEvent

     * that started the recognition. Otherwise, return null.

     */

    public static MouseEvent mouseReleased(MouseEvent me) {

        return getDragRecognitionSupport().mouseReleasedImpl(me);

    }

    /**

     * Returns whether or not a drag gesture recognition is ongoing.

     */

    public static boolean mouseDragged(MouseEvent me, BeforeDrag bd) {

        return getDragRecognitionSupport().mouseDraggedImpl(me, bd);

    }

    private void clearState() {

        dndArmedEvent = null;

        component = null;

    }

    private int mapDragOperationFromModifiers(MouseEvent me,

                                              TransferHandler th) {

        if (th == null || !SwingUtilities.isLeftMouseButton(me)) {

            return TransferHandler.NONE;

        }

        return SunDragSourceContextPeer.

            convertModifiersToDropAction(me.getModifiersEx(),

                                         th.getSourceActions(component));

    }

    /**

     * Returns whether or not the event is potentially part of a drag sequence.

     */

    private boolean mousePressedImpl(MouseEvent me) {

        component = (JComponent)me.getSource();

        if (mapDragOperationFromModifiers(me, component.getTransferHandler())

                != TransferHandler.NONE) {

            motionThreshold = DragSource.getDragThreshold();

            dndArmedEvent = me;

            return true;

        }

        clearState();

        return false;

    }

    /**

     * If a dnd recognition has been going on, return the MouseEvent

     * that started the recognition. Otherwise, return null.

     */

    private MouseEvent mouseReleasedImpl(MouseEvent me) {

        /* no recognition has been going on */

        if (dndArmedEvent == null) {

            return null;

        }

        MouseEvent retEvent = null;

        if (me.getSource() == component) {

            retEvent = dndArmedEvent;

        } // else component has changed unexpectedly, so return null

        clearState();

        return retEvent;

    }

    /**

     * Returns whether or not a drag gesture recognition is ongoing.

     */

    private boolean mouseDraggedImpl(MouseEvent me, BeforeDrag bd) {

        /* no recognition is in progress */

        if (dndArmedEvent == null) {

            return false;

        }

        /* component has changed unexpectedly, so bail */

        if (me.getSource() != component) {

            clearState();

            return false;

        }

        int dx = Math.abs(me.getX() - dndArmedEvent.getX());

        int dy = Math.abs(me.getY() - dndArmedEvent.getY());

        if ((dx > motionThreshold) || (dy > motionThreshold)) {

            TransferHandler th = component.getTransferHandler();

            int action = mapDragOperationFromModifiers(me, th);

            if (action != TransferHandler.NONE) {

                /* notify the BeforeDrag instance */

                if (bd != null) {

                    bd.dragStarting(dndArmedEvent);

                }

                th.exportAsDrag(component, dndArmedEvent, action);

                clearState();

            }

        }

        return true;

    }

}