/*******************************************************************************
 * Copyright (c) 2000, 2007 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
module dwt.dnd;


import dwt.*;
import dwt.widgets.*;
import dwt.internal.*;
import dwt.internal.carbon.*;

/**
 *
 * Class <code>DropTarget</code> defines the target object for a drag and drop transfer.
 *
 * IMPORTANT: This class is <em>not</em> intended to be subclassed.
 *
 * <p>This class identifies the <code>Control</code> over which the user must position the cursor
 * in order to drop the data being transferred.  It also specifies what data types can be dropped on 
 * this control and what operations can be performed.  You may have several DropTragets in an 
 * application but there can only be a one to one mapping between a <code>Control</code> and a <code>DropTarget</code>.
 * The DropTarget can receive data from within the same application or from other applications 
 * (such as text dragged from a text editor like Word).</p>
 *
 * <code><pre>
 *  int operations = DND.DROP_MOVE | DND.DROP_COPY | DND.DROP_LINK;
 *  Transfer[] types = new Transfer[] {TextTransfer.getInstance()};
 *  DropTarget target = new DropTarget(label, operations);
 *  target.setTransfer(types);
 * </code></pre>
 *
 * <p>The application is notified of data being dragged over this control and of when a drop occurs by 
 * implementing the interface <code>DropTargetListener</code> which uses the class 
 * <code>DropTargetEvent</code>.  The application can modify the type of drag being performed 
 * on this Control at any stage of the drag by modifying the <code>event.detail</code> field or the 
 * <code>event.currentDataType</code> field.  When the data is dropped, it is the responsibility of 
 * the application to copy this data for its own purposes.
 *
 * <code><pre>
 *  target.addDropListener (new DropTargetListener() {
 *      public void dragEnter(DropTargetEvent event) {};
 *      public void dragOver(DropTargetEvent event) {};
 *      public void dragLeave(DropTargetEvent event) {};
 *      public void dragOperationChanged(DropTargetEvent event) {};
 *      public void dropAccept(DropTargetEvent event) {}
 *      public void drop(DropTargetEvent event) {
 *          // A drop has occurred, copy over the data
 *          if (event.data is null) { // no data to copy, indicate failure in event.detail
 *              event.detail = DND.DROP_NONE;
 *              return;
 *          }
 *          label.setText (cast(String) event.data); // data copied to label text
 *      }
 *  });
 * </pre></code>
 *
 * <dl>
 *  <dt><b>Styles</b></dt> <dd>DND.DROP_NONE, DND.DROP_COPY, DND.DROP_MOVE, DND.DROP_LINK</dd>
 *  <dt><b>Events</b></dt> <dd>DND.DragEnter, DND.DragLeave, DND.DragOver, DND.DragOperationChanged, 
 *                             DND.DropAccept, DND.Drop </dd>
 * </dl>
 */
public class DropTarget : Widget {

    Control control;
    Listener controlListener;
    Transfer[] transferAgents = new Transfer[0];
    DropTargetEffect dropEffect;
    int feedback = DND.FEEDBACK_NONE;

    // Track application selections
    TransferData selectedDataType;
    int selectedOperation;
    
    // workaround - There is no event for "operation changed" so track operation based on key state
    int keyOperation = -1;
    
    // workaround - Simulate events when mouse is not moving
    long dragOverStart;
    Runnable dragOverHeartbeat;
    DNDEvent dragOverEvent;
    
    // workaround - OS events are relative to the application, not the control.
    // Track which control is the current target to determine when drag and
    // drop enters or leaves a widget.
    static DropTarget CurrentDropTarget = null;
    
    static final String DEFAULT_DROP_TARGET_EFFECT = "DEFAULT_DROP_TARGET_EFFECT"; //$NON-NLS-1$
    static final int DRAGOVER_HYSTERESIS = 50;
    
    static Callback DragTrackingHandler;
    static Callback DragReceiveHandler;
    
    static {
        DragTrackingHandler = new Callback(DropTarget.class, "DragTrackingHandler", 4); //$NON-NLS-1$
        int dragTrackingHandlerAddress = DragTrackingHandler.getAddress();
        if (dragTrackingHandlerAddress is 0) DWT.error(DWT.ERROR_NO_MORE_CALLBACKS);
        DragReceiveHandler = new Callback(DropTarget.class, "DragReceiveHandler", 3); //$NON-NLS-1$
        int dragReceiveHandlerAddress = DragReceiveHandler.getAddress();
        if (dragReceiveHandlerAddress is 0) DWT.error(DWT.ERROR_NO_MORE_CALLBACKS);
        OS.InstallTrackingHandler(dragTrackingHandlerAddress, 0, null);
        OS.InstallReceiveHandler(dragReceiveHandlerAddress, 0, null);
    }

/**
 * Creates a new <code>DropTarget</code> to allow data to be dropped on the specified 
 * <code>Control</code>.
 * Creating an instance of a DropTarget may cause system resources to be allocated 
 * depending on the platform.  It is therefore mandatory that the DropTarget instance 
 * be disposed when no longer required.
 * 
 * @param control the <code>Control</code> over which the user positions the cursor to drop the data
 * @param style the bitwise OR'ing of allowed operations; this may be a combination of any of 
 *         DND.DROP_NONE, DND.DROP_COPY, DND.DROP_MOVE, DND.DROP_LINK
 *
 * @exception DWTException <ul>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the parent</li>
 *    <li>ERROR_INVALID_SUBCLASS - if this class is not an allowed subclass</li>
 * </ul>
 * @exception DWTError <ul>
 *    <li>ERROR_CANNOT_INIT_DROP - unable to initiate drop target; this will occur if more than one
 *        drop target is created for a control or if the operating system will not allow the creation
 *        of the drop target</li>
 * </ul>
 *
 * <p>NOTE: ERROR_CANNOT_INIT_DROP should be an DWTException, since it is a
 * recoverable error, but can not be changed due to backward compatibility.</p>
 * 
 * @see Widget#dispose
 * @see DropTarget#checkSubclass
 * @see DND#DROP_NONE
 * @see DND#DROP_COPY
 * @see DND#DROP_MOVE
 * @see DND#DROP_LINK
 */
public this(Control control, int style) {
    super(control, checkStyle(style));
    this.control = control;
    if (DragTrackingHandler is null || DragTrackingHandler is null) {
        DND.error(DND.ERROR_CANNOT_INIT_DROP);
    }
    if (control.getData(DND.DROP_TARGET_KEY) !is null) {
        DND.error(DND.ERROR_CANNOT_INIT_DROP);
    }
    control.setData(DND.DROP_TARGET_KEY, this);

    controlListener = new Listener () {
        public void handleEvent (Event event) {
            if (!DropTarget.this.isDisposed()) {
                DropTarget.this.dispose();
            }
        }
    };
    control.addListener (DWT.Dispose, controlListener);
    
    this.addListener(DWT.Dispose, new Listener() {
        public void handleEvent (Event event) {
            onDispose();
        }
    });

    Object effect = control.getData(DEFAULT_DROP_TARGET_EFFECT);
    if (effect instanceof DropTargetEffect) {
        dropEffect = cast(DropTargetEffect) effect;
    } else if (control instanceof Table) {
        dropEffect = new TableDropTargetEffect(cast(Table) control);
    } else if (control instanceof Tree) {
        dropEffect = new TreeDropTargetEffect(cast(Tree) control);
    }

    dragOverHeartbeat = new Runnable() {
        public void run() {
            Control control = DropTarget.this.control;
            if (control is null || control.isDisposed() || dragOverStart is 0) return;
            long time = System.currentTimeMillis();
            int delay = DRAGOVER_HYSTERESIS;
            if (time < dragOverStart) {
                delay = cast(int)(dragOverStart - time);
            } else {    
                int allowedOperations = dragOverEvent.operations;
                TransferData[] allowedTypes = dragOverEvent.dataTypes;
                //pass a copy of data types in to listeners in case application modifies it
                TransferData[] dataTypes = new TransferData[allowedTypes.length];
                System.arraycopy(allowedTypes, 0, dataTypes, 0, dataTypes.length);
    
                DNDEvent event = new DNDEvent();
                event.widget = dragOverEvent.widget;
                event.x = dragOverEvent.x;
                event.y = dragOverEvent.y;
                event.time = cast(int)time;
                event.feedback = DND.FEEDBACK_SELECT;
                event.dataTypes = dataTypes;
                event.dataType = selectedDataType;
                event.operations = dragOverEvent.operations;
                event.detail  = selectedOperation;
                if (dropEffect !is null) {
                    event.item = dropEffect.getItem(event.x, event.y);
                }
                selectedDataType = null;
                selectedOperation = DND.DROP_NONE;              
                notifyListeners(DND.DragOver, event);
                if (event.dataType !is null) {
                    for (int i = 0; i < allowedTypes.length; i++) {
                        if (allowedTypes[i].type is event.dataType.type) {
                            selectedDataType = event.dataType;
                            break;
                        }
                    }
                }
                if (selectedDataType !is null && (event.detail & allowedOperations) !is 0) {
                    selectedOperation = event.detail;
                }
            }
            control = DropTarget.this.control;
            if (control is null || control.isDisposed()) return;
            control.getDisplay().timerExec(delay, dragOverHeartbeat);
        }
    };
}

static int checkStyle (int style) {
    if (style is DWT.NONE) return DND.DROP_MOVE;
    return style;
}

static int DragReceiveHandler(int theWindow, int handlerRefCon, int theDrag) {
    DropTarget target = FindDropTarget(theWindow, theDrag);
    if (target is null) return OS.noErr;
    return target.dragReceiveHandler(theWindow, handlerRefCon, theDrag);   
}

static int DragTrackingHandler(int message, int theWindow, int handlerRefCon, int theDrag) {
    if (message is OS.kDragTrackingLeaveHandler || message is OS.kDragTrackingEnterHandler) {
        CurrentDropTarget = null;
        return OS.noErr;
    }
    DropTarget target = FindDropTarget(theWindow, theDrag);
    if (CurrentDropTarget !is null) {
        if (target is null || CurrentDropTarget.control.handle !is target.control.handle) {
            CurrentDropTarget.dragTrackingHandler(OS.kDragTrackingLeaveWindow, theWindow, handlerRefCon, theDrag);
            CurrentDropTarget = target;
            message = OS.kDragTrackingEnterWindow;
        }
    } else {
        CurrentDropTarget = target;
        message = OS.kDragTrackingEnterWindow;
    }
    if (target is null) return OS.noErr;
    return target.dragTrackingHandler(message, theWindow, handlerRefCon, theDrag);   
}

static DropTarget FindDropTarget(int theWindow, int theDrag) {
    Display display = Display.findDisplay(Thread.currentThread());
    if (display is null || display.isDisposed()) return null;
    Point mouse = new Point();
    OS.GetDragMouse(theDrag, mouse, null);
    int[] theRoot = new int[1];
    OS.GetRootControl(theWindow, theRoot);
    int[] theControl = new int[1];
    Rect rect = new Rect();
    OS.GetWindowBounds (theWindow, cast(short) OS.kWindowContentRgn, rect);
    CGPoint inPoint = new CGPoint();
    inPoint.x = mouse.h - rect.left;
    inPoint.y = mouse.v - rect.top;
    OS.HIViewGetSubviewHit(theRoot[0], inPoint, true, theControl);
    if (!OS.IsControlEnabled(theControl[0])) return null;               
    Widget widget = display.findWidget(theControl[0]);
    if (widget is null) return null;
    return cast(DropTarget)widget.getData(DND.DROP_TARGET_KEY);
}
/**
 * Adds the listener to the collection of listeners who will
 * be notified when a drag and drop operation is in progress, by sending
 * it one of the messages defined in the <code>DropTargetListener</code>
 * interface.
 * 
 * <p><ul>
 * <li><code>dragEnter</code> is called when the cursor has entered the drop target boundaries
 * <li><code>dragLeave</code> is called when the cursor has left the drop target boundaries and just before
 * the drop occurs or is cancelled.
 * <li><code>dragOperationChanged</code> is called when the operation being performed has changed 
 * (usually due to the user changing the selected modifier key(s) while dragging)
 * <li><code>dragOver</code> is called when the cursor is moving over the drop target
 * <li><code>dropAccept</code> is called just before the drop is performed.  The drop target is given 
 * the chance to change the nature of the drop or veto the drop by setting the <code>event.detail</code> field
 * <li><code>drop</code> is called when the data is being dropped
 * </ul></p>
 *
 * @param listener the listener which should be notified
 *
 * @exception IllegalArgumentException <ul>
 *    <li>ERROR_NULL_ARGUMENT - if the listener is null</li>
 * </ul>
 * @exception DWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 *
 * @see DropTargetListener
 * @see #removeDropListener
 * @see DropTargetEvent
 */
public void addDropListener(DropTargetListener listener) {
    if (listener is null) DND.error (DWT.ERROR_NULL_ARGUMENT);
    DNDListener typedListener = new DNDListener (listener);
    typedListener.dndWidget = this;
    addListener (DND.DragEnter, typedListener);
    addListener (DND.DragLeave, typedListener);
    addListener (DND.DragOver, typedListener);
    addListener (DND.DragOperationChanged, typedListener);
    addListener (DND.Drop, typedListener);
    addListener (DND.DropAccept, typedListener);
}

protected void checkSubclass () {
    String name = getClass().getName ();
    String validName = DropTarget.class.getName();
    if (!validName.opEquals(name)) {
        DND.error (DWT.ERROR_INVALID_SUBCLASS);
    }
}

int dragReceiveHandler(int theWindow, int handlerRefCon, int theDrag) {
    updateDragOverHover(0, null);
    if (keyOperation is -1) return OS.dragNotAcceptedErr;

    DNDEvent event = new DNDEvent();
    event.widget = this;
    event.time = cast(int)System.currentTimeMillis();
    event.detail = DND.DROP_NONE;
    notifyListeners(DND.DragLeave, event);
    
    event = new DNDEvent();
    if (!setEventData(theDrag, event)) {
        return OS.dragNotAcceptedErr;
    }
    
    keyOperation = -1;
    int allowedOperations = event.operations;
    TransferData[] allowedDataTypes = new TransferData[event.dataTypes.length];
    System.arraycopy(event.dataTypes, 0, allowedDataTypes, 0, event.dataTypes.length);
    event.dataType = selectedDataType;
    event.detail = selectedOperation;
    selectedDataType = null;
    selectedOperation = DND.DROP_NONE;
    notifyListeners(DND.DropAccept, event);
    
    if (event.dataType !is null) {
        for (int i = 0; i < allowedDataTypes.length; i++) {
            if (allowedDataTypes[i].type is event.dataType.type) {
                selectedDataType = allowedDataTypes[i];
                break;
            }
        }
    }
    if (selectedDataType !is null && (event.detail & allowedOperations) !is 0) {
        selectedOperation = event.detail;
    }   
    if (selectedOperation is DND.DROP_NONE) {
        // this was not a successful drop
        return OS.dragNotAcceptedErr;
    }
    // ask drag source for dropped data
    byte[][] data  = new byte[0][];
    // locate all the items with data of the desired type 
    short[] numItems = new short[1];
    OS.CountDragItems(theDrag, numItems);
    for (short i = 0; i < numItems[0]; i++) {
        int[] theItemRef = new int[1];
        OS.GetDragItemReferenceNumber(theDrag, cast(short) (i+1), theItemRef);
        int[] size = new int[1];
        OS.GetFlavorDataSize(theDrag, theItemRef[0], selectedDataType.type, size);
        if (size[0] > 0) {
            byte[] buffer = new byte[size[0]];
            OS.GetFlavorData(theDrag, theItemRef[0], selectedDataType.type, buffer, size, 0);
            byte[][] newData = new byte[data.length + 1][];
            System.arraycopy(data, 0, newData, 0, data.length);
            newData[data.length] = buffer;
            data = newData;
        }
    }
    // Get Data in a Java format
    Object object = null;
    for (int i = 0; i < transferAgents.length; i++) {
        Transfer transfer = transferAgents[i];
        if (transfer !is null && transfer.isSupportedType(selectedDataType)) {
            selectedDataType.data = data;
            object = transfer.nativeToJava(selectedDataType);
            break;
        }
    }
    
    if (object is null) {
        selectedOperation = DND.DROP_NONE;
    }
        
    event.dataType = selectedDataType;
    event.detail = selectedOperation;
    event.data = object;
    notifyListeners(DND.Drop, event);
    selectedOperation = DND.DROP_NONE;
    if ((allowedOperations & event.detail) is event.detail) {
        selectedOperation = event.detail;
    }
    //notify source of action taken
    int action = opToOsOp(selectedOperation);
    OS.SetDragDropAction(theDrag, action);
    return (selectedOperation is DND.DROP_NONE) ? OS.dragNotAcceptedErr : OS.noErr;
}

int dragTrackingHandler(int message, int theWindow, int handlerRefCon, int theDrag) {
    
    if (message is OS.kDragTrackingLeaveWindow) {
        updateDragOverHover(0, null);
        OS.SetThemeCursor(OS.kThemeArrowCursor);
        if (keyOperation is -1) return OS.dragNotAcceptedErr;
        keyOperation = -1;
        
        DNDEvent event = new DNDEvent();
        event.widget = this;
        event.time = cast(int)System.currentTimeMillis();
        event.detail = DND.DROP_NONE;
        notifyListeners(DND.DragLeave, event);
        return OS.noErr;
    }
    
    int oldKeyOperation = keyOperation;
    
    if (message is OS.kDragTrackingEnterWindow) {
        selectedDataType = null;
        selectedOperation = 0;
    }
    
    DNDEvent event = new DNDEvent();
    if (!setEventData(theDrag, event)) {
        keyOperation = -1;
        OS.SetThemeCursor(OS.kThemeNotAllowedCursor);
        return OS.dragNotAcceptedErr;
    }
    
    int allowedOperations = event.operations;
    TransferData[] allowedDataTypes = new TransferData[event.dataTypes.length];
    System.arraycopy(event.dataTypes, 0, allowedDataTypes, 0, allowedDataTypes.length);
    
    switch (message) {
        case OS.kDragTrackingEnterWindow:
            event.type = DND.DragEnter;
            break;
        case OS.kDragTrackingInWindow:
            if (keyOperation is oldKeyOperation) {
                event.type = DND.DragOver;
                event.dataType = selectedDataType;
                event.detail = selectedOperation;
            }else {
                event.type = DND.DragOperationChanged;
                event.dataType = selectedDataType;
            }
            break;
    }
    
    updateDragOverHover(DRAGOVER_HYSTERESIS, event);
    selectedDataType = null;
    selectedOperation = DND.DROP_NONE;
    notifyListeners(event.type, event);

    if (event.detail is DND.DROP_DEFAULT) {
        event.detail = (allowedOperations & DND.DROP_MOVE) !is 0 ? DND.DROP_MOVE : DND.DROP_NONE;
    }
    
    if (event.dataType !is null) {
        for (int i = 0; i < allowedDataTypes.length; i++) {
            if (allowedDataTypes[i].type is event.dataType.type) {
                selectedDataType = allowedDataTypes[i];
                break;
            }
        }
    }

    if (selectedDataType !is null && (allowedOperations & event.detail) !is 0) {
        selectedOperation = event.detail;
    }
    
    OS.SetDragDropAction(theDrag, opToOsOp(selectedOperation));

    switch (selectedOperation) {
        case DND.DROP_COPY:
            OS.SetThemeCursor(OS.kThemeCopyArrowCursor);
            break;
        case DND.DROP_LINK:
            OS.SetThemeCursor(OS.kThemeAliasArrowCursor);
            break;
        case DND.DROP_MOVE:
            OS.SetThemeCursor(OS.kThemeArrowCursor);
            break;
        default:
            OS.SetThemeCursor(OS.kThemeNotAllowedCursor);
    }
    
    if (message is OS.kDragTrackingEnterWindow) {
        dragOverHeartbeat.run();        
    }
    return OS.noErr;
}

/**
 * Returns the Control which is registered for this DropTarget.  This is the control over which the 
 * user positions the cursor to drop the data.
 *
 * @return the Control which is registered for this DropTarget
 */
public Control getControl () {
    return control;
}

/**
 * Returns an array of listeners who will be notified when a drag and drop 
 * operation is in progress, by sending it one of the messages defined in 
 * the <code>DropTargetListener</code> interface.
 *
 * @exception DWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 *
 * @see DropTargetListener
 * @see #addDropListener
 * @see #removeDropListener
 * @see DropTargetEvent
 * 
 * @since 3.4
 */
public DropTargetListener[] getDropListeners() {
    Listener[] listeners = getListeners(DND.DragEnter);
    int length = listeners.length;
    DropTargetListener[] dropListeners = new DropTargetListener[length];
    int count = 0;
    for (int i = 0; i < length; i++) {
        Listener listener = listeners[i];
        if (listener instanceof DNDListener) {
            dropListeners[count] = cast(DropTargetListener) (cast(DNDListener) listener).getEventListener();
            count++;
        }
    }
    if (count is length) return dropListeners;
    DropTargetListener[] result = new DropTargetListener[count];
    System.arraycopy(dropListeners, 0, result, 0, count);
    return result;
}

/**
 * Returns the drop effect for this DropTarget.  This drop effect will be 
 * used during a drag and drop to display the drag under effect on the 
 * target widget.
 *
 * @return the drop effect that is registered for this DropTarget
 * 
 * @since 3.3
 */
public DropTargetEffect getDropTargetEffect() {
    return dropEffect;
}

int getOperationFromKeyState(int theDrag) {
    short[] modifiers = new short[1];
    OS.GetDragModifiers(theDrag, modifiers, null, null);
    bool option = (modifiers[0] & OS.optionKey) is OS.optionKey;
    bool command = (modifiers[0] & OS.cmdKey) is OS.cmdKey;
    if (option && command) return DND.DROP_LINK;
    if (option) return DND.DROP_COPY;
    if (command) return DND.DROP_MOVE;
    return DND.DROP_DEFAULT; 
}

/**
 * Returns a list of the data types that can be transferred to this DropTarget.
 *
 * @return a list of the data types that can be transferred to this DropTarget
 */
public Transfer[] getTransfer() {
    return transferAgents;
}

void onDispose () { 
    if (control is null)
        return;
    if (controlListener !is null)
        control.removeListener(DWT.Dispose, controlListener);
    controlListener = null;
    control.setData(DND.DROP_TARGET_KEY, null);
    transferAgents = null;
    control = null;
}

int opToOsOp(int operation) {
    int osOperation = 0;
    if ((operation & DND.DROP_COPY) !is 0){
        osOperation |= OS.kDragActionCopy;
    }
    if ((operation & DND.DROP_LINK) !is 0) {
        osOperation |= OS.kDragActionAlias;
    }
    if ((operation & DND.DROP_MOVE) !is 0) {
        osOperation |= OS.kDragActionMove;
    }
    return osOperation;
}

int osOpToOp(int osOperation){
    int operation = 0;
    if ((osOperation & OS.kDragActionCopy) !is 0){
        operation |= DND.DROP_COPY;
    }
    if ((osOperation & OS.kDragActionAlias) !is 0) {
        operation |= DND.DROP_LINK;
    }
    if ((osOperation & OS.kDragActionMove) !is 0) {
        operation |= DND.DROP_MOVE;
    }
    if (osOperation is OS.kDragActionAll) {
        operation = DND.DROP_COPY | DND.DROP_MOVE | DND.DROP_LINK;
    }
    return operation;
}

/**
 * Removes the listener from the collection of listeners who will
 * be notified when a drag and drop operation is in progress.
 *
 * @param listener the listener which should be notified
 *
 * @exception IllegalArgumentException <ul>
 *    <li>ERROR_NULL_ARGUMENT - if the listener is null</li>
 * </ul>
 * @exception DWTException <ul>
 *    <li>ERROR_WIDGET_DISPOSED - if the receiver has been disposed</li>
 *    <li>ERROR_THREAD_INVALID_ACCESS - if not called from the thread that created the receiver</li>
 * </ul>
 *
 * @see DropTargetListener
 * @see #addDropListener
 */
public void removeDropListener(DropTargetListener listener) {   
    if (listener is null) DND.error (DWT.ERROR_NULL_ARGUMENT);
    removeListener (DND.DragEnter, listener);
    removeListener (DND.DragLeave, listener);
    removeListener (DND.DragOver, listener);
    removeListener (DND.DragOperationChanged, listener);
    removeListener (DND.Drop, listener);
    removeListener (DND.DropAccept, listener);
}

/**
 * Specifies the drop effect for this DropTarget.  This drop effect will be 
 * used during a drag and drop to display the drag under effect on the 
 * target widget.
 *
 * @param effect the drop effect that is registered for this DropTarget
 * 
 * @since 3.3
 */
public void setDropTargetEffect(DropTargetEffect effect) {
    dropEffect = effect;
}

bool setEventData(int theDrag, DNDEvent event) {
    if (theDrag is 0) return false;
    
    // get allowed operations
    int style = getStyle();
    int[] outActions = new int[1];
    OS.GetDragAllowableActions(theDrag, outActions);
    int operations = osOpToOp(outActions[0]) & style;
    if (operations is DND.DROP_NONE) return false;
    
    //get current operation
    int operation =  getOperationFromKeyState(theDrag);
    keyOperation = operation;
    if (operation is DND.DROP_DEFAULT) {
         if ((style & DND.DROP_DEFAULT) is 0) {
            operation = (operations & DND.DROP_MOVE) !is 0 ? DND.DROP_MOVE : DND.DROP_NONE;
         }
    } else {
        if ((operation & operations) is 0) operation = DND.DROP_NONE;
    }
    
    // get allowed transfer types
    short[] numItems = new short[1];
    OS.CountDragItems(theDrag, numItems);
    int[] flavors = new int[10];
    int index = -1;
    //Get a unique list of flavors
    for (short i = 0; i < numItems[0]; i++) {
        int[] theItemRef = new int[1];
        OS.GetDragItemReferenceNumber(theDrag, cast(short) (i+1), theItemRef);
        short[] numFlavors = new short[1];
        OS.CountDragItemFlavors(theDrag, theItemRef[0], numFlavors);
        int[] theType = new int[1];
        for (int j = 0; j < numFlavors[0]; j++) {
            theType[0] = 0;
            if (OS.GetFlavorType(theDrag, theItemRef[0], cast(short) (j+1), theType) is OS.noErr) {
                bool unique = true;
                for (int k = 0; k < flavors.length; k++) {
                    if (flavors[k] is theType[0]) {
                        unique = false;
                        break;
                    }
                }
                if (unique) {
                    if (index is flavors.length - 1) {
                        int[] temp = new int[flavors.length + 10];
                        System.arraycopy(flavors, 0, temp, 0, flavors.length);
                        flavors = temp;
                    }
                    flavors[++index] = theType[0];
                }
            }
        }
    }
    if (index is -1) return false;
    
    TransferData[] dataTypes = new TransferData[index+1];
    index = -1;
    for (int i = 0; i < dataTypes.length; i++) {
        if (flavors[i] !is 0) {
            TransferData data = new TransferData();
            data.type = flavors[i];
            for (int j = 0; j < transferAgents.length; j++) {
                Transfer transfer = transferAgents[j];
                if (transfer !is null && transfer.isSupportedType(data)) {
                    dataTypes[++index] = data;
                    break;
                }
            }
        }
    }
    if (index is -1) return false;
    
    if (index < dataTypes.length - 1) {
        TransferData[] temp = new TransferData[index + 1];
        System.arraycopy(dataTypes, 0, temp, 0, index + 1);
        dataTypes = temp;
    }

    Point mouse = new Point();
    OS.GetDragMouse(theDrag, mouse, null);
    
    event.widget = this;
    event.x = mouse.h;
    event.y = mouse.v;
    event.time = cast(int)System.currentTimeMillis();
    event.feedback = DND.FEEDBACK_SELECT;
    event.dataTypes = dataTypes;
    event.dataType = dataTypes[0];
    event.operations = operations;
    event.detail = operation;
    if (dropEffect !is null) {
        event.item = dropEffect.getItem(event.x, event.y);
    }
    
    return true;
}

/**
 * Specifies the data types that can be transferred to this DropTarget.  If data is 
 * being dragged that does not match one of these types, the drop target will be notified of 
 * the drag and drop operation but the currentDataType will be null and the operation 
 * will be DND.NONE.
 *
 * @param transferAgents a list of Transfer objects which define the types of data that can be
 *                       dropped on this target
 * 
 * @exception IllegalArgumentException <ul>
 *    <li>ERROR_NULL_ARGUMENT - if transferAgents is null</li>
 * </ul>
 */
public void setTransfer(Transfer[] transferAgents){
    if (transferAgents is null) DND.error(DWT.ERROR_NULL_ARGUMENT);
    this.transferAgents = transferAgents;
}

void updateDragOverHover(long delay, DNDEvent event) {
    if (delay is 0) {
        dragOverStart = 0;
        dragOverEvent = null;
        return;
    }
    dragOverStart = System.currentTimeMillis() + delay;
    if (dragOverEvent is null) dragOverEvent = new DNDEvent();
    dragOverEvent.x = event.x;
    dragOverEvent.y = event.y;
    dragOverEvent.dataTypes  = event.dataTypes;
    dragOverEvent.operations = event.operations;
    dragOverEvent.dataType  = event.dataType;
    dragOverEvent.detail  = event.detail;
}

}