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/*
 * Copyright 2007 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.user.client.DOM;
import com.google.gwt.user.client.Element;

import java.util.Iterator;

/**
 * Abstract base class for all panels, which are widgets that can contain other
 * widgets.
 */
public abstract class Panel extends Widget implements HasWidgets {

  /**
   * Adds a child widget.
   * 
   * <p>
   * <b>How to Override this Method</b>
   * </p>
   * <p>
   * There are several important things that must take place in the correct
   * order to properly add or insert a Widget to a Panel. Not all of these steps
   * will be relevant to every Panel, but all of the steps must be considered.
   * <ol>
   * <li><b>Validate:</b> Perform any sanity checks to ensure the Panel can
   * accept a new Widget. Examples: checking for a valid index on insertion;
   * checking that the Panel is not full if there is a max capacity.</li>
   * <li><b>Adjust for Reinsertion:</b> Some Panels need to handle the case
   * where the Widget is already a child of this Panel. Example: when performing
   * a reinsert, the index might need to be adjusted to account for the Widget's
   * removal. See {@link ComplexPanel#adjustIndex(Widget, int)}.</li>
   * <li><b>Detach Child:</b> Remove the Widget from its existing parent, if
   * any. Most Panels will simply call {@link Widget#removeFromParent()} on the
   * Widget.</li>
   * <li><b>Logical Attach:</b> Any state variables of the Panel should be
   * updated to reflect the addition of the new Widget. Example: the Widget is
   * added to the Panel's {@link WidgetCollection} at the appropriate index.</li>
   * <li><b>Physical Attach:</b> The Widget's Element must be physically
   * attached to the Panel's Element, either directly or indirectly.</li>
   * <li><b>Adopt:</b> Call {@link #adopt(Widget)} to finalize the add as the
   * very last step.</li>
   * </ol>
   * </p>
   * 
   * @param child the widget to be added
   * @throws UnsupportedOperationException if this method is not supported (most
   *           often this means that a specific overload must be called)
   * @see HasWidgets#add(Widget)
   */
  public void add(Widget child) {
    throw new UnsupportedOperationException(
        "This panel does not support no-arg add()");
  }

  public void clear() {
    Iterator<Widget> it = iterator();
    while (it.hasNext()) {
      it.next();
      it.remove();
    }
  }

  /**
   * Removes a child widget.
   * 
   * <p>
   * <b>How to Override this Method</b>
   * </p>
   * <p>
   * There are several important things that must take place in the correct
   * order to properly remove a Widget from a Panel. Not all of these steps will
   * be relevant to every Panel, but all of the steps must be considered.
   * <ol>
   * <li><b>Validate:</b> Make sure this Panel is actually the parent of the
   * child Widget; return <code>false</code> if it is not.</li>
   * <li><b>Orphan:</b> Call {@link #orphan(Widget)} first while the child
   * Widget is still attached.</li>
   * <li><b>Physical Detach:</b> Adjust the DOM to account for the removal of
   * the child Widget. The Widget's Element must be physically removed from the
   * DOM.</li>
   * <li><b>Logical Detach:</b> Update the Panel's state variables to reflect
   * the removal of the child Widget. Example: the Widget is removed from the
   * Panel's {@link WidgetCollection}.</li>
   * </ol>
   * </p>
   * 
   * @param child the widget to be removed
   * @return <code>true</code> if the child was present
   */
  public abstract boolean remove(Widget child);

  /**
   * Finalize the attachment of a Widget to this Panel. This method is the
   * <b>last</b> step in adding or inserting a Widget into a Panel, and should
   * be called after physical attachment in the DOM is complete. This Panel
   * becomes the parent of the child Widget, and the child will now fire its
   * {@link Widget#onAttach()} event if this Panel is currently attached.
   * 
   * @param child the widget to be adopted
   * @see #add(Widget)
   */
  protected final void adopt(Widget child) {
    assert (child.getParent() == null);
    child.setParent(this);
  }

  /**
   * This method was formerly part of the process of adding a Widget to a Panel
   * but has been deprecated in favor of {@link #adopt(Widget)}.
   * 
   * @deprecated Use {@link #adopt(Widget)}.
   */
  @Deprecated
  protected void adopt(Widget w, Element container) {
    // Remove the widget from its current parent, if any.
    w.removeFromParent();

    // Attach it at the DOM and GWT levels.
    if (container != null) {
      DOM.appendChild(container, w.getElement());
    }
    w.setParent(this);
  }

  /**
   * This method was formerly part of the process of removing a Widget from a
   * Panel but has been deprecated in favor of {@link #orphan(Widget)}.
   * 
   * @deprecated Use {@link #orphan(Widget)}.
   */
  @Deprecated
  protected void disown(Widget w) {
    // Only disown it if it's actually contained in this panel.
    if (w.getParent() != this) {
      throw new IllegalArgumentException("w is not a child of this panel");
    }

    // setParent() must be called before removeChild() to ensure that the
    // element is still attached when onDetach()/onUnload() are called.
    Element elem = w.getElement();
    w.setParent(null);
    DOM.removeChild(DOM.getParent(elem), elem);
  }

  @Override
  protected void doAttachChildren() {
    AttachDetachException.tryCommand(this, AttachDetachException.attachCommand);
  }

  @Override
  protected void doDetachChildren() {
    AttachDetachException.tryCommand(this, AttachDetachException.detachCommand);
  }

  /**
   * A Panel's onLoad method will be called after all of its children are
   * attached.
   * 
   * @see Widget#onLoad()
   */
  @Override
  protected void onLoad() {
  }

  /**
   * A Panel's onUnload method will be called before its children become
   * detached themselves.
   * 
   * @see Widget#onLoad()
   */
  @Override
  protected void onUnload() {
  }

  /**
   * <p>
   * This method must be called as part of the remove method of any Panel. It
   * ensures that the Widget's parent is cleared. This method should be called
   * after verifying that the child Widget is an existing child of the Panel,
   * but before physically removing the child Widget from the DOM. The child
   * will now fire its {@link Widget#onDetach()} event if this Panel is
   * currently attached.
   * </p>
   * <p>
   * Calls to {@link #orphan(Widget)} should be wrapped in a try/finally block
   * to ensure that the widget is physically detached even if orphan throws an
   * exception.
   * </p>
   * 
   * @param child the widget to be disowned
   * @see #add(Widget)
   */
  protected final void orphan(Widget child) {
    assert (child.getParent() == this);
    child.setParent(null);
  }
}