Refactor ActivityStatus to not store current activity

base/android/java/src/org/chromium/base/ApplicationStatus.java

Index: base/android/java/src/org/chromium/base/ApplicationStatus.java
diff --git a/base/android/java/src/org/chromium/base/ApplicationStatus.java b/base/android/java/src/org/chromium/base/ApplicationStatus.java
new file mode 100644
index 0000000000000000000000000000000000000000..9930682f15e9fc3ceabc7e8847caffa2b5f0d962
--- /dev/null
+++ b/base/android/java/src/org/chromium/base/ApplicationStatus.java
@@ -0,0 +1,421 @@
+// Copyright 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.base;
+
+import android.app.Activity;
+import android.app.Application;
+import android.app.Application.ActivityLifecycleCallbacks;
+import android.content.Context;
+import android.os.Bundle;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Provides information about the current activity's status, and a way
+ * to register / unregister listeners for state changes.
+ */
+@JNINamespace("base::android")
+public class ApplicationStatus {
+    private static class ActivityInfo {
+        private int mStatus = ActivityState.DESTROYED;
+        private ObserverList<ActivityStateListener> mListeners =
+                new ObserverList<ActivityStateListener>();
+
+        /**
+         * @return The current {@link ActivityState} of the activity.
+         */
+        public int getStatus() {
+            return mStatus;
+        }
+
+        /**
+         * @param status The new {@link ActivityState} of the activity.
+         */
+        public void setStatus(int status) {
+            mStatus = status;
+        }
+
+        /**
+         * @return A list of {@link ActivityStateListener}s listening to this activity.
+         */
+        public ObserverList<ActivityStateListener> getListeners() {
+            return mListeners;
+        }
+    }
+
+    private static Application sApplication;
+
+    private static Integer sCachedApplicationState;
+
+    /** Last activity that was shown (or null if none or it was destroyed). */
+    private static Activity sActivity;
+
+    /**
+     *
+     */
+    private static final Map<Activity, ActivityInfo> sActivityInfo =
+            new HashMap<Activity, ActivityInfo>();
+
+    /**
+     *
+     */
+    private static final ObserverList<ActivityStateListener> sGeneralActivityStateListeners =
+            new ObserverList<ActivityStateListener>();
+
+    /**
+     * A list of observers to be notified when the visibility state of this {@link Application}
+     * changes.  See {@link #getStateForApplication()}.
+     */
+    private static final ObserverList<ApplicationStateListener> sApplicationStateListeners =
+            new ObserverList<ApplicationStateListener>();
+
+    /**
+     * Interface to be implemented by listeners.
+     */
+    public interface ApplicationStateListener {
+        /**
+         * Called when the application's state changes.
+         * @param newState The application state.
+         */
+        public void onApplicationStateChange(int newState);
+    }
+
+    /**
+     * Interface to be implemented by listeners.
+     */
+    public interface ActivityStateListener {
+        /**
+         * Called when the activity's state changes.
+         * @param activity The activity that had a state change.
+         * @param newState New activity state.
+         */
+        public void onActivityStateChange(Activity activity, int newState);
+    }
+
+    private ApplicationStatus() {}
+
+    /**
+     * Initializes the activity status for a specified application.
+     *
+     * @param application The application whose status you wish to monitor.
+     */
+    public static void initialize(BaseChromiumApplication application) {
+        sApplication = application;
+
+        application.registerWindowFocusChangedListener(
+                new BaseChromiumApplication.WindowFocusChangedListener() {
+            @Override
+            public void onWindowFocusChanged(Activity activity, boolean hasFocus) {
+                if (!hasFocus || activity == sActivity) return;
+
+                int state = getStateForActivity(activity);
+
+                if (state != ActivityState.DESTROYED && state != ActivityState.STOPPED) {
+                    sActivity = activity;
+                }
+
+                // TODO(dtrainor): Notify of active activity change?
+            }
+        });
+
+        application.registerActivityLifecycleCallbacks(new ActivityLifecycleCallbacks() {
+            @Override
+            public void onActivityCreated(final Activity activity, Bundle savedInstanceState) {
+                onStateChange(activity, ActivityState.CREATED);
+            }
+
+            @Override
+            public void onActivityDestroyed(Activity activity) {
+                onStateChange(activity, ActivityState.DESTROYED);
+            }
+
+            @Override
+            public void onActivityPaused(Activity activity) {
+                onStateChange(activity, ActivityState.PAUSED);
+            }
+
+            @Override
+            public void onActivityResumed(Activity activity) {
+                onStateChange(activity, ActivityState.RESUMED);
+            }
+
+            @Override
+            public void onActivitySaveInstanceState(Activity activity, Bundle outState) {}
+
+            @Override
+            public void onActivityStarted(Activity activity) {
+                onStateChange(activity, ActivityState.STARTED);
+            }
+
+            @Override
+            public void onActivityStopped(Activity activity) {
+                onStateChange(activity, ActivityState.STOPPED);
+            }
+        });
+    }
+
+    /**
+     * Must be called by the main activity when it changes state.
+     *
+     * @param activity Current activity.
+     * @param newState New state value.
+     */
+    private static void onStateChange(Activity activity, int newState) {
+        if (activity == null) throw new IllegalArgumentException("null activity is not supported");
+
+        if (sActivity == null
+                || newState == ActivityState.CREATED
+                || newState == ActivityState.RESUMED
+                || newState == ActivityState.STARTED) {
+            sActivity = activity;
+        }
+
+        int oldApplicationState = getStateForApplication();
+
+        if (newState == ActivityState.CREATED) {
+            assert !sActivityInfo.containsKey(activity);
+            sActivityInfo.put(activity, new ActivityInfo());
+        }
+
+        // Invalidate the cached application state.
+        sCachedApplicationState = null;
+
+        ActivityInfo info = sActivityInfo.get(activity);
+        info.setStatus(newState);
+
+        // Notify all state observers that are specifically listening to this activity.
+        for (ActivityStateListener listener : info.getListeners()) {
+            listener.onActivityStateChange(activity, newState);
+        }
+
+        // Notify all state observers that are listening globally for all activity state
+        // changes.
+        for (ActivityStateListener listener : sGeneralActivityStateListeners) {
+            listener.onActivityStateChange(activity, newState);
+        }
+
+        int applicationState = getStateForApplication();
+        if (applicationState != oldApplicationState) {
+            for (ApplicationStateListener listener : sApplicationStateListeners) {
+                listener.onApplicationStateChange(applicationState);
+            }
+        }
+
+        if (newState == ActivityState.DESTROYED) {
+            sActivityInfo.remove(activity);
+            if (activity == sActivity) sActivity = null;
+        }
+    }
+
+    /**
+     * Testing method to update the state of the specified activity.
+     */
+    public static void onStateChangeForTesting(Activity activity, int newState) {
+        onStateChange(activity, newState);
+    }
+
+    /**
+     * @return The most recent focused {@link Activity} tracked by this class.  Being focused means
+     *         out of all the activities tracked here, it has most recently gained window focus.
+     */
+    public static Activity getLastTrackedFocusedActivity() {
+        return sActivity;
+    }
+
+    /**
+     * @return The {@link Context} for the {@link Application}.
+     */
+    public static Context getApplicationContext() {
+        return sApplication != null ? sApplication.getApplicationContext() : null;
+    }
+
+    /**
+     * Query the state for a given activity.  If the activity is not being tracked, this will
+     * return {@link ActivityState#DESTROYED}.
+     *
+     * <p>
+     * Please note that Chrome can have multiple activities running simultaneously.  Please also
+     * look at {@link #getStateForApplication()} for more details.
+     *
+     * <p>
+     * When relying on this method, be familiar with the expected life cycle state
+     * transitions:
+     * <a href="http://developer.android.com/guide/components/activities.html#Lifecycle">
+     *   Activity Lifecycle
+     * </a>
+     *
+     * <p>
+     * During activity transitions (activity B launching in front of activity A), A will completely
+     * paused before the creation of activity B begins.
+     *
+     * <p>
+     * A basic flow for activity A starting, followed by activity B being opened and then closed:
+     * <ul>
+     *   <li> -- Starting Activity A --
+     *   <li> Activity A - ActivityState.CREATED
+     *   <li> Activity A - ActivityState.STARTED
+     *   <li> Activity A - ActivityState.RESUMED
+     *   <li> -- Starting Activity B --
+     *   <li> Activity A - ActivityState.PAUSED
+     *   <li> Activity B - ActivityState.CREATED
+     *   <li> Activity B - ActivityState.STARTED
+     *   <li> Activity B - ActivityState.RESUMED
+     *   <li> Activity A - ActivityState.STOPPED
+     *   <li> -- Closing Activity B, Activity A regaining focus --
+     *   <li> Activity B - ActivityState.PAUSED
+     *   <li> Activity A - ActivityState.STARTED
+     *   <li> Activity A - ActivityState.RESUMED
+     *   <li> Activity B - ActivityState.STOPPED
+     *   <li> Activity B - ActivityState.DESTROYED
+     * </ul>
+     *
+     * @param activity The activity whose state is to be returned.
+     * @return The state of the specified activity (see {@link ActivityState}).
+     */
+    public static int getStateForActivity(Activity activity) {
+        ActivityInfo info = sActivityInfo.get(activity);
+        return info != null ? info.getStatus() : ActivityState.DESTROYED;
+    }
+
+    /**
+     * @return The state of the application (see {@link ApplicationState}).
+     */
+    public static int getStateForApplication() {
+        if (sCachedApplicationState == null) sCachedApplicationState = determineApplicationState();
+
+        return sCachedApplicationState.intValue();
+    }
+
+    /**
+     * Checks whether or not any Activity in this Application is visible to the user.  Note that
+     * this includes the PAUSED state, which can happen when the Activity is temporarily covered
+     * by another Activity's Fragment (e.g.).
+     * @return Whether any Activity under this Application is visible.
+     */
+    public static boolean hasVisibleActivities() {
+        int state = getStateForApplication();
+        return state == ApplicationState.HAS_RUNNING_ACTIVITIES
+                || state == ApplicationState.HAS_PAUSED_ACTIVITIES;
+    }
+
+    /**
+     * Checks to see if there are any active Activity instances being watched by ApplicationStatus.
+     * @return True if all Activities have been destroyed.
+     */
+    public static boolean isEveryActivityDestroyed() {
+        return sActivityInfo.isEmpty();
+    }
+
+    /**
+     * Registers the given listener to receive state changes for all activities.
+     * @param listener Listener to receive state changes.
+     */
+    public static void registerStateListenerForAllActivities(ActivityStateListener listener) {
+        sGeneralActivityStateListeners.addObserver(listener);
+    }
+
+    /**
+     * Registers the given listener to receive state changes for {@code activity}.  After a call to
+     * {@link ActivityStateListener#onActivityStateChange(Activity, int)} with
+     * {@link ActivityState#DESTROYED} all listeners associated with that particular
+     * {@link Activity} are removed.
+     * @param listener Listener to receive state changes.
+     * @param activity Activity to track or {@code null} to track all activities.
+     */
+    public static void registerStateListenerForActivity(ActivityStateListener listener,
+            Activity activity) {
+        assert activity != null;
+
+        ActivityInfo info = sActivityInfo.get(activity);
+        assert info != null && info.getStatus() != ActivityState.DESTROYED;
+        info.getListeners().addObserver(listener);
+    }
+
+    /**
+     * Unregisters the given listener from receiving activity state changes.
+     * @param listener Listener that doesn't want to receive state changes.
+     */
+    public static void unregisterActivityStateListener(ActivityStateListener listener) {
+        sGeneralActivityStateListeners.removeObserver(listener);
+
+        // Loop through all observer lists for all activities and remove the listener.
+        for (ActivityInfo info : sActivityInfo.values()) {
+            info.getListeners().removeObserver(listener);
+        }
+    }
+
+    /**
+     * Registers the given listener to receive state changes for the application.
+     * @param listener Listener to receive state state changes.
+     */
+    public static void registerApplicationStateListener(ApplicationStateListener listener) {
+        sApplicationStateListeners.addObserver(listener);
+    }
+
+    /**
+     * Unregisters the given listener from receiving state changes.
+     * @param listener Listener that doesn't want to receive state changes.
+     */
+    public static void unregisterApplicationStateListener(ApplicationStateListener listener) {
+        sApplicationStateListeners.removeObserver(listener);
+    }
+
+    /**
+     * Registers the single thread-safe native activity status listener.
+     * This handles the case where the caller is not on the main thread.
+     * Note that this is used by a leaky singleton object from the native
+     * side, hence lifecycle management is greatly simplified.
+     */
+    @CalledByNative
+    private static void registerThreadSafeNativeApplicationStateListener() {
+        ThreadUtils.runOnUiThread(new Runnable () {
+            @Override
+            public void run() {
+                registerApplicationStateListener(new ApplicationStateListener() {
+                    @Override
+                    public void onApplicationStateChange(int newState) {
+                        nativeOnApplicationStateChange(newState);
+                    }
+                });
+            }
+        });
+    }
+
+    /**
+     * Determines the current application state as defined by {@link ApplicationState}.  This will
+     * loop over all the activities and check their state to determine what the general application
+     * state should be.
+     * @return HAS_RUNNING_ACTIVITIES if any activity is not paused, stopped, or destroyed.
+     *         HAS_PAUSED_ACTIVITIES if none are running and one is paused.
+     *         HAS_STOPPED_ACTIVITIES if none are running/paused and one is stopped.
+     *         HAS_DESTROYED_ACTIVITIES if none are running/paused/stopped.
+     */
+    private static int determineApplicationState() {
+        boolean hasPausedActivity = false;
+        boolean hasStoppedActivity = false;
+
+        for (ActivityInfo info : sActivityInfo.values()) {
+            int state = info.getStatus();
+            if (state != ActivityState.PAUSED
+                    && state != ActivityState.STOPPED
+                    && state != ActivityState.DESTROYED) {
+                return ApplicationState.HAS_RUNNING_ACTIVITIES;
+            } else if (state == ActivityState.PAUSED) {
+                hasPausedActivity = true;
+            } else if (state == ActivityState.STOPPED) {
+                hasStoppedActivity = true;
+            }
+        }
+
+        if (hasPausedActivity) return ApplicationState.HAS_PAUSED_ACTIVITIES;
+        if (hasStoppedActivity) return ApplicationState.HAS_STOPPED_ACTIVITIES;
+        return ApplicationState.HAS_DESTROYED_ACTIVITIES;
+    }
+
+    // Called to notify the native side of state changes.
+    // IMPORTANT: This is always called on the main thread!
+    private static native void nativeOnApplicationStateChange(int newState);
+}