/**
 * 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.
 *
 * Copyright 2012-2015 the original author or authors.
 */
package org.assertj.swing.core;

import java.awt.Component;
import java.awt.Container;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

import org.assertj.swing.annotation.RunsInCurrentThread;

/**
 * Finds the focus owner using the roots of a {@code Component} hierarchy.
 * 
 * @author Alex Ruiz
 */
class HierarchyBasedFocusOwnerFinder implements FocusOwnerFinderStrategy {
  private final ContainerFocusOwnerFinder delegate;
  private final HierarchyRootsSource rootsSource;

  HierarchyBasedFocusOwnerFinder() {
    this(new ContainerFocusOwnerFinder(), new HierarchyRootsSource());
  }

  HierarchyBasedFocusOwnerFinder(@Nonnull ContainerFocusOwnerFinder newDelegate,
      @Nonnull HierarchyRootsSource newRootsSource) {
    delegate = newDelegate;
    rootsSource = newRootsSource;
  }

  @Override
  @RunsInCurrentThread
  public @Nullable Component focusOwner() {
    for (Container c : rootsSource.existingHierarchyRoots()) {
      Component focus = delegate.focusOwnerOf(c);
      if (focus != null) {
        return focus;
      }
    }
    return null;
  }
}