/*******************************************************************************
 * Copyright (c) 2000, 2008 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
 *******************************************************************************/
package org.eclipse.swt.dnd;

import org.eclipse.rwt.SessionSingletonBase;

/**
 * The class <code>HTMLTransfer</code> provides a platform specific mechanism
 * for converting text in HTML format represented as a java <code>String</code>
 * to a platform specific representation of the data and vice versa.
 * <p>
 * An example of a java <code>String</code> containing HTML text is shown below:
 * </p>
 * <code><pre>
 *     String htmlData = "<p>This is a paragraph of text.</p>";
 * </code></pre>
 * 
 * @see Transfer
 */
public class HTMLTransfer extends ByteArrayTransfer {

  static HTMLTransfer _instance = new HTMLTransfer();
  static final String TYPE_NAME = "html";
  static final int TYPE_ID = registerType( TYPE_NAME );

  private HTMLTransfer() {
  }

  /**
   * Returns the singleton instance of the HTMLTransfer class.
   * 
   * @return the singleton instance of the HTMLTransfer class
   */
  public static HTMLTransfer getInstance() {
    Object instance = SessionSingletonBase.getInstance( HTMLTransfer.class );
    return ( HTMLTransfer )instance;
  }

  /**
   * This implementation of <code>javaToNative</code> converts HTML-formatted
   * text represented by a java <code>String</code> to a platform specific
   * representation.
   * 
   * @param object a java <code>String</code> containing HTML text
   * @param transferData an empty <code>TransferData</code> object that will be
   *          filled in on return with the platform specific format of the data
   * @see Transfer#nativeToJava
   */
  public void javaToNative( Object object, TransferData transferData ) {
    if( !checkHTML( object ) || !isSupportedType( transferData ) ) {
      DND.error( DND.ERROR_INVALID_DATA );
    }
    transferData.data = object;
    transferData.result = 1;
  }

  /**
   * This implementation of <code>nativeToJava</code> converts a platform
   * specific representation of HTML text to a java <code>String</code>.
   * 
   * @param transferData the platform specific representation of the data to be
   *          converted
   * @return a java <code>String</code> containing HTML text if the conversion
   *         was successful; otherwise null
   * @see Transfer#javaToNative
   */
  public Object nativeToJava( TransferData transferData ) {
    if( !isSupportedType( transferData ) || transferData.data == null )
      return null;
    if( transferData.result != 1 ) 
      return null;
    return transferData.data;
  }

  protected int[] getTypeIds() {
    return new int[]{ TYPE_ID };
  }

  protected String[] getTypeNames() {
    return new String[]{ TYPE_NAME };
  }

  boolean checkHTML( Object object ) {
    return ( object != null && object instanceof String && ( ( String )object ).length() > 0 );
  }

  protected boolean validate( Object object ) {
    return checkHTML( object );
  }
}