/*
 * Copyright 2008 Google Inc.
 * 
 * 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 com.google.gwt.user.client.ui;

import com.google.gwt.dom.client.Document;
import com.google.gwt.dom.client.Element;
import com.google.gwt.dom.client.InputElement;
import com.google.gwt.event.dom.client.ChangeEvent;
import com.google.gwt.event.dom.client.ChangeHandler;
import com.google.gwt.event.dom.client.HasChangeHandlers;
import com.google.gwt.event.shared.HandlerRegistration;

/**
 * A widget that wraps the HTML <input type='file'> element. This widget
 * must be used with {@link com.google.gwt.user.client.ui.FormPanel} if it is to
 * be submitted to a server.
 * 
 * <p>
 * <h3>Example</h3>
 * {@example com.google.gwt.examples.FormPanelExample}
 * </p>
 *
 * <h3>CSS Style Rules</h3>
 * <dl>
 * <dt>.gwt-FileUpload {} </dt>
 *
 * <h3>NOTICE about styling</h3>
 * <p>
 * The developer should be aware that most browsers do not allow styling
 * many properties of the rendered input-file element because of security restrictions.<br/>
 * You can style certain properties like position, visibility, opacity, etc. But size,
 * color, backgrounds etc. will not work either using css or calling widget methods like setSize().
 * </p>
 * </dl>
 */
public class FileUpload extends FocusWidget implements HasName, HasChangeHandlers, HasEnabled {

  /**
   * Creates a FileUpload widget that wraps an existing <input
   * type='file'> element.
   * 
   * This element must already be attached to the document. If the element is
   * removed from the document, you must call
   * {@link RootPanel#detachNow(Widget)}.
   * 
   * @param element the element to be wrapped
   */
  public static FileUpload wrap(Element element) {
    // Assert that the element is attached.
    assert Document.get().getBody().isOrHasChild(element);

    FileUpload fileUpload = new FileUpload(element);

    // Mark it attached and remember it for cleanup.
    fileUpload.onAttach();
    RootPanel.detachOnWindowClose(fileUpload);

    return fileUpload;
  }

  /**
   * Constructs a new file upload widget.
   */
  public FileUpload() {
    this(Document.get().createFileInputElement());
    setStyleName("gwt-FileUpload");
  }

  /**
   * This constructor may be used by subclasses to explicitly use an existing
   * element. This element must be an <input> element whose type is
   * 'file'.
   * 
   * @param element the element to be used
   */
  protected FileUpload(Element element) {
    assert InputElement.as(element).getType().equalsIgnoreCase("file");
    setElement(element);
  }

  public HandlerRegistration addChangeHandler(ChangeHandler handler) {
    return addDomHandler(handler, ChangeEvent.getType());
  }

  /**
   * Gets the filename selected by the user. This property has no mutator, as
   * browser security restrictions preclude setting it.
   * 
   * @return the widget's filename
   */
  public String getFilename() {
    return getInputElement().getValue();
  }

  public String getName() {
    return getInputElement().getName();
  }

  /**
   * Gets whether this widget is enabled.
   * 
   * @return <code>true</code> if the widget is enabled
   */
  public boolean isEnabled() {
    return !getElement().getPropertyBoolean("disabled");
  }

  /**
   * Sets whether this widget is enabled.
   * 
   * @param enabled <code>true</code> to enable the widget, <code>false</code>
   *          to disable it
   */
  public void setEnabled(boolean enabled) {
    getElement().setPropertyBoolean("disabled", !enabled);
  }

  public void setName(String name) {
    getInputElement().setName(name);
  }

  private InputElement getInputElement() {
    return getElement().cast();
  }

  /**
   * Programmatic equivalent of the user clicking the button, opening
   * the file selection browser.
   *
   * <p>
   * NOTE: in certain browsers programmatic click is disabled if the
   * element display is none, for instance in webkit you have to move
   * the element off screen.
   * </p>
   *
   */
  public void click() {
    getInputElement().click();
  }
}