package org.eclipse.swt.dnd;


import org.eclipse.swt.internal.ole.win32.COM;
import org.eclipse.swt.internal.ole.win32.FORMATETC;
import org.eclipse.swt.internal.ole.win32.IDataObject;
import org.eclipse.swt.internal.ole.win32.STGMEDIUM;
import org.eclipse.swt.internal.win32.OS;


/**
 * The class provides a platform specific mechanism for reading and writing
 * the preffered drop effect (copy or paste) from and to the clipboard.<br>
 * This class is intended to be used in addition to {@link FileTransfer}.
 * See {@link Transfer} for additional information.
 * <p>
 * An example is shown below:
 * </p>
 * <code><pre>
 * PreferredDropEffectTransfer pdet = PreferredDropEffectTransfer.getInstance();
 * FileTransfer ft = FileTransfer.getInstance();
 * String[] files = (String[]) clipboard.getContents(ft);
 * int effect = ((Integer) clipboard.getContents(pdet)).intValue();
 * // copy files
 * if ((effect & DND.DROP_MOVE) != 0)
 *     for (int i = 0; i < files.length; i++)
 *         new File(files[i]).delete();
 * </code></pre>
 * 
 * @author Thomas Braun
 */
public class PreferredDropEffectTransfer extends ByteArrayTransfer
{
	private static PreferredDropEffectTransfer _instance = 
		new PreferredDropEffectTransfer();
	private static final String CFSTR_PREFERREDDROPEFFECT = 
		"Preferred DropEffect"; //$NON-NLS-1$
	private static final int CF_ID = 
		registerType(CFSTR_PREFERREDDROPEFFECT);

	private PreferredDropEffectTransfer()
	{}

	/**
	 * Returns the singleton instance of the class.
	 * 
	 * @return the singleton instance of the class
	 */
	public static PreferredDropEffectTransfer getInstance()
	{
		return _instance;
	}

	/**
	 * Not emplemented because the transfer type "Preferred DropEffect"
	 * generated by windows seems not compatible to the one of SWT.
	 */
	@Override
	public void javaToNative(Object object, TransferData transferData)
	{
		if (!validate(object) || !isSupportedType(transferData)) {
			DND.error(DND.ERROR_INVALID_DATA);
		}
		
		// ...
	}

	/**
	 * The method returns the preferred drop operation as integer object.
	 * The default result is DND.DROP_COPY.
	 * 
	 * @see DND#DROP_COPY
	 * @see DND#DROP_LINK
	 * @see DND#DROP_MOVE
	 * @return an <code>Integer</code> containing the preferred drop operation
	 */
	@Override
	public Object nativeToJava(TransferData transferData)
	{
		if (!isSupportedType(transferData) || transferData.pIDataObject == 0)
			return DND.DROP_COPY;

		IDataObject dataObject = new IDataObject(transferData.pIDataObject);
		dataObject.AddRef();
		FORMATETC formatetc = new FORMATETC();
		formatetc.cfFormat = CF_ID;
		formatetc.ptd = 0;
		formatetc.dwAspect = COM.DVASPECT_CONTENT;
		formatetc.lindex = -1;
		formatetc.tymed = COM.TYMED_HGLOBAL;
		STGMEDIUM stgmedium = new STGMEDIUM();
		stgmedium.tymed = COM.TYMED_HGLOBAL;
		transferData.result = dataObject.GetData(formatetc, stgmedium);
		int[] i1 = new int[1];
		OS.MoveMemory(i1, stgmedium.unionField, 4);
		int[] i2 = new int[1];
		OS.MoveMemory(i2, i1[0], 4);
		dataObject.Release();
		
		if (transferData.result != COM.S_OK)
			return DND.DROP_COPY;
		else
			return osToOp(i2[0]);
	}

	@Override
	protected int[] getTypeIds()
	{
		return new int[]{
			CF_ID
		};
	}

	private int osToOp(int osOperation)
	{
		int operation = 0;
		if ((osOperation & COM.DROPEFFECT_COPY) != 0) {
			operation |= DND.DROP_COPY;
		}
		if ((osOperation & COM.DROPEFFECT_LINK) != 0) {
			operation |= DND.DROP_LINK;
		}
		if ((osOperation & COM.DROPEFFECT_MOVE) != 0) {
			operation |= DND.DROP_MOVE;
		}
		return operation;
	}

	@Override
	protected String[] getTypeNames()
	{
		return new String[]{
			CFSTR_PREFERREDDROPEFFECT
		};
	}

	@Override
	protected boolean validate(Object object)
	{
		return object instanceof Integer;
	}
}