/*
 * Copyright 2011 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.editor.client;

import java.util.List;

import javax.validation.ConstraintViolation;

/**
 * Defines common capabilities of editor drivers.
 * <p>
 * The {@code EditorDriver} interface cannot be used with
 * {@link com.google.gwt.core.client.GWT#create(Class) GWT.create()} directly.
 * Instead, use one of the specializations of this interface.
 * 
 * @param <T> the type of data returned from {@link #flush()}
 * @see com.google.gwt.editor.client.SimpleBeanEditorDriver
 * @see com.google.gwt.requestfactory.client.RequestFactoryEditorDriver
 */
public interface EditorDriver<T> {
  /**
   * Visit the Editor hierarchy controlled by the EditorDriver.
   */
  void accept(EditorVisitor visitor);

  /**
   * Update the object being edited with the current state of the Editor.
   * 
   * @return an implementation-specific value
   */
  T flush();

  /**
   * Returns any unconsumed EditorErrors from the last call to {@link #flush()}.
   * 
   * @return a List of {@link EditorError} instances
   */
  List<EditorError> getErrors();

  /**
   * Indicates if the last call to {@link #flush()} resulted in any errors.
   * 
   * @return {@code true} if errors are present
   */
  boolean hasErrors();

  /**
   * Returns {@code true} if any of the Editors in the hierarchy have been
   * modified relative to the last value passed into {@link #edit(Object)}.
   * <p>
   * This method is not affected by {@link #flush()} to support the following
   * workflow:
   * <ol>
   * <li>{@code EditorDriver.edit()}</li>
   * <li>The user edits the on-screen values</li>
   * <li>{@code EditorDriver.flush()}</li>
   * <li>The data in the edited object is validated:
   * <ol>
   * <li>The validation fails, returning to step 2</li>
   * <li>The validation succeeds and the editing UI is dismissed</li>
   * </ol>
   * </ol>
   * The simplest implementation of a "navigate away from dirty UI warning" by
   * checking {@code isDirty()} is correct for the above workflow. If the
   * {@link #flush()} method were to clear the dirty state, it would be
   * necessary to implement an alternate flag to distinguish between a
   * newly-initialized editor entering step 2 or re-entering step 2.
   * 
   * @see EditorDelegate#setDirty(boolean)
   */
  boolean isDirty();

  /**
   * Show {@link ConstraintViolation ConstraintViolations} generated through a
   * {@link javax.validation.Validator Validator}. The violations will be
   * converted into {@link EditorError} objects whose
   * {@link EditorError#getUserData() getUserData()} method can be used to
   * access the original ConstraintViolation object.
   * 
   * @param violations an Iterable over {@link ConstraintViolation} instances
   * @return <code>true</code> if there were any unconsumed EditorErrors which
   *         can be retrieved from {@link #getErrors()}
   */
  boolean setConstraintViolations(Iterable<ConstraintViolation<?>> violations);
}