/**
 * 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.monitor;

import static org.assertj.core.util.Preconditions.checkNotNull;
import static org.assertj.swing.edt.GuiActionRunner.execute;

import java.awt.Component;
import java.awt.EventQueue;
import java.awt.Frame;
import java.awt.Toolkit;
import java.awt.Window;
import java.util.Collection;

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

import org.assertj.core.util.VisibleForTesting;
import org.assertj.swing.annotation.RunsInCurrentThread;
import org.assertj.swing.annotation.RunsInEDT;
import org.assertj.swing.edt.GuiQuery;
import org.assertj.swing.util.ToolkitProvider;

/**
 * Monitor that keeps track of all known root AWT or Swing {@code Window}s (showing, hidden, closed).
 *
 * @author Alex Ruiz
 */
public class WindowMonitor {
  private final Context context;
  private final ContextMonitor contextMonitor;
  private final Windows windows;
  private final WindowStatus windowStatus;
  private final WindowAvailabilityMonitor windowAvailabilityMonitor;

  /**
   * <p>
   * Create an instance of WindowTracker which will track all windows coming and going on the current and subsequent
   * {@code AppContext}s.
   * </p>
   *
   * <p>
   * <strong>WARNING:</strong> if an applet loads this class, it will only ever see stuff in its own {@code AppContext}.
   * </p>
   *
   * @param toolkit the {@code Toolkit} to use.
   */
  @RunsInCurrentThread
  WindowMonitor(@Nonnull Toolkit toolkit) {
    this(toolkit, new Context(toolkit), new WindowStatus(new Windows()));
  }

  @VisibleForTesting
  @RunsInCurrentThread
  WindowMonitor(@Nonnull Toolkit toolkit, @Nonnull Context context, @Nonnull WindowStatus windowStatus) {
    this.context = context;
    this.windowStatus = windowStatus;
    windows = windowStatus.windows();
    contextMonitor = new ContextMonitor(context, windows);
    contextMonitor.attachTo(toolkit);
    windowAvailabilityMonitor = new WindowAvailabilityMonitor(windows);
    windowAvailabilityMonitor.attachTo(toolkit);
    populateExistingWindows();
  }

  private void populateExistingWindows() {
    for (Frame f : Frame.getFrames()) {
      examine(checkNotNull(f));
    }
  }

  @RunsInCurrentThread
  private void examine(@Nonnull Window w) {
    windows.attachNewWindowVisibilityMonitor(w);
    for (Window owned : w.getOwnedWindows()) {
      examine(checkNotNull(owned));
    }
    windows.markExisting(w);
    context.addContextFor(w);
  }

  /**
   * Returns whether the AWT or Swing {@code Window} is ready to receive OS-level event input. A {@code Window}'s
   * "isShowing" flag may be set {@code true} before the {@code WINDOW_OPENED} event is generated, and even after the
   * {@code WINDOW_OPENED} event is sent, the {@code Window} peer is not guaranteed to be ready.
   *
   * @param w the given {@code Window}.
   * @return whether the {@code Window} is ready to receive OS-level event input.
   */
  public boolean isWindowReady(@Nonnull Window w) {
    if (windows.isReady(w)) {
      return true;
    }
    windowStatus.checkIfReady(w);
    return false;
  }

  /**
   * Returns the event queue corresponding to the given AWT or Swing {@code Compoenent}. In most cases, this is the same
   * as {@code Component.getToolkit().getSystemEventQueue()}, but in the case of applets will bypass the
   * {@code AppContext} and provide the real event queue.
   *
   * @param c the given {@code Component}.
   * @return the event queue corresponding to the given component.
   */
  public @Nullable EventQueue eventQueueFor(@Nonnull Component c) {
    return context.eventQueueFor(c);
  }

  /**
   * @return all known event queues.
   */
  public @Nonnull Collection<EventQueue> allEventQueues() {
    return context.allEventQueues();
  }

  /**
   * Return all available root {@code Window}s. A root {@code Window} is one that has a {@code null} parent. Nominally
   * this means a list similar to that returned by {@code Frame.getFrames()}, but in the case of an {@code Applet} may
   * return a few dialogs as well.
   *
   * @return all available root {@code Window}s.
   */
  public @Nonnull Collection<Window> rootWindows() {
    return context.rootWindows();
  }

  /**
   * @return the singleton instance of this class.
   */
  @RunsInEDT
  public static @Nonnull WindowMonitor instance() {
    return SingletonLazyLoader.INSTANCE;
  }

  @RunsInEDT
  private static class SingletonLazyLoader {
    static final WindowMonitor INSTANCE = execute(new GuiQuery<WindowMonitor>() {
      @Override
      protected WindowMonitor executeInEDT() {
        return new WindowMonitor(ToolkitProvider.instance().defaultToolkit());
      };
    });
  }
}