server/media/MediaSessionStack.java

/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * 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.android.server.media;

import android.media.session.PlaybackState;
import android.media.session.Session;
import android.text.TextUtils;

import java.io.PrintWriter;
import java.util.ArrayList;

/**
 * Keeps track of media sessions and their priority for notifications, media
 * button routing, etc.
 */
public class MediaSessionStack {
    /**
     * These are states that usually indicate the user took an action and should
     * bump priority regardless of the old state.
     */
    private static final int[] ALWAYS_PRIORITY_STATES = {
            PlaybackState.PLAYSTATE_FAST_FORWARDING,
            PlaybackState.PLAYSTATE_REWINDING,
            PlaybackState.PLAYSTATE_SKIPPING_BACKWARDS,
            PlaybackState.PLAYSTATE_SKIPPING_FORWARDS };
    /**
     * These are states that usually indicate the user took an action if they
     * were entered from a non-priority state.
     */
    private static final int[] TRANSITION_PRIORITY_STATES = {
            PlaybackState.PLAYSTATE_BUFFERING,
            PlaybackState.PLAYSTATE_CONNECTING,
            PlaybackState.PLAYSTATE_PLAYING };

    private final ArrayList<MediaSessionRecord> mSessions = new ArrayList<MediaSessionRecord>();

    private MediaSessionRecord mCachedButtonReceiver;
    private MediaSessionRecord mCachedDefault;
    private ArrayList<MediaSessionRecord> mCachedActiveList;
    private ArrayList<MediaSessionRecord> mCachedTransportControlList;

    /**
     * Add a record to the priority tracker.
     *
     * @param record The record to add.
     */
    public void addSession(MediaSessionRecord record) {
        mSessions.add(record);
        clearCache();
    }

    /**
     * Remove a record from the priority tracker.
     *
     * @param record The record to remove.
     */
    public void removeSession(MediaSessionRecord record) {
        mSessions.remove(record);
        clearCache();
    }

    /**
     * Notify the priority tracker that a session's state changed.
     *
     * @param record The record that changed.
     * @param oldState Its old playback state.
     * @param newState Its new playback state.
     */
    public void onPlaystateChange(MediaSessionRecord record, int oldState, int newState) {
        if (shouldUpdatePriority(oldState, newState)) {
            mSessions.remove(record);
            mSessions.add(0, record);
            clearCache();
        }
    }

    /**
     * Handle any stack changes that need to occur in response to a session
     * state change. TODO add the old and new session state as params
     *
     * @param record The record that changed.
     */
    public void onSessionStateChange(MediaSessionRecord record) {
        // For now just clear the cache. Eventually we'll selectively clear
        // depending on what changed.
        clearCache();
    }

    /**
     * Get the current priority sorted list of active sessions. The most
     * important session is at index 0 and the least important at size - 1.
     *
     * @return All the active sessions in priority order.
     */
    public ArrayList<MediaSessionRecord> getActiveSessions() {
        if (mCachedActiveList == null) {
            mCachedActiveList = getPriorityListLocked(true, 0);
        }
        return mCachedActiveList;
    }

    /**
     * Get the current priority sorted list of active sessions that use
     * transport controls. The most important session is at index 0 and the
     * least important at size -1.
     *
     * @return All the active sessions that handle transport controls in
     *         priority order.
     */
    public ArrayList<MediaSessionRecord> getTransportControlSessions() {
        if (mCachedTransportControlList == null) {
            mCachedTransportControlList = getPriorityListLocked(true,
                    Session.FLAG_HANDLES_TRANSPORT_CONTROLS);
        }
        return mCachedTransportControlList;
    }

    /**
     * Get the highest priority active session.
     *
     * @return The current highest priority session or null.
     */
    public MediaSessionRecord getDefaultSession() {
        if (mCachedDefault != null) {
            return mCachedDefault;
        }
        ArrayList<MediaSessionRecord> records = getPriorityListLocked(true, 0);
        if (records.size() > 0) {
            return records.get(0);
        }
        return null;
    }

    /**
     * Get the highest priority session that can handle media buttons.
     *
     * @return The default media button session or null.
     */
    public MediaSessionRecord getDefaultMediaButtonSession() {
        if (mCachedButtonReceiver != null) {
            return mCachedButtonReceiver;
        }
        ArrayList<MediaSessionRecord> records = getPriorityListLocked(true,
                Session.FLAG_HANDLES_MEDIA_BUTTONS);
        if (records.size() > 0) {
            mCachedButtonReceiver = records.get(0);
        }
        return mCachedButtonReceiver;
    }

    public void dumpLocked(PrintWriter pw, String prefix) {
        ArrayList<MediaSessionRecord> sortedSessions = getPriorityListLocked(false, 0);
        int count = sortedSessions.size();
        pw.println(prefix + "Sessions Stack - have " + count + " sessions:");
        String indent = prefix + "  ";
        for (int i = 0; i < count; i++) {
            MediaSessionRecord record = sortedSessions.get(i);
            record.dump(pw, indent);
            pw.println();
        }
    }

    /**
     * Get a priority sorted list of sessions. Can filter to only return active
     * sessions or sessions with specific flags.
     *
     * @param activeOnly True to only return active sessions, false to return
     *            all sessions.
     * @param withFlags Only return sessions with all the specified flags set. 0
     *            returns all sessions.
     * @return The priority sorted list of sessions.
     */
    private ArrayList<MediaSessionRecord> getPriorityListLocked(boolean activeOnly, int withFlags) {
        ArrayList<MediaSessionRecord> result = new ArrayList<MediaSessionRecord>();
        int lastLocalIndex = 0;
        int lastActiveIndex = 0;
        int lastPublishedIndex = 0;

        int size = mSessions.size();
        for (int i = 0; i < size; i++) {
            final MediaSessionRecord session = mSessions.get(i);

            if ((session.getFlags() & withFlags) != withFlags) {
                continue;
            }
            if (!session.isActive()) {
                if (!activeOnly) {
                    // If we're getting unpublished as well always put them at
                    // the end
                    result.add(session);
                }
                continue;
            }

            if (session.isSystemPriority()) {
                // System priority sessions are special and always go at the
                // front. We expect there to only be one of these at a time.
                result.add(0, session);
                lastLocalIndex++;
                lastActiveIndex++;
                lastPublishedIndex++;
            } else if (session.isPlaybackActive()) {
                // TODO replace getRoute() == null with real local route check
                if(session.getRoute() == null) {
                    // Active local sessions get top priority
                    result.add(lastLocalIndex, session);
                    lastLocalIndex++;
                    lastActiveIndex++;
                    lastPublishedIndex++;
                } else {
                    // Then active remote sessions
                    result.add(lastActiveIndex, session);
                    lastActiveIndex++;
                    lastPublishedIndex++;
                }
            } else {
                // inactive sessions go at the end in order of whoever last did
                // something.
                result.add(lastPublishedIndex, session);
                lastPublishedIndex++;
            }
        }

        return result;
    }

    private boolean shouldUpdatePriority(int oldState, int newState) {
        if (containsState(newState, ALWAYS_PRIORITY_STATES)) {
            return true;
        }
        if (!containsState(oldState, TRANSITION_PRIORITY_STATES)
                && containsState(newState, TRANSITION_PRIORITY_STATES)) {
            return true;
        }
        return false;
    }

    private boolean containsState(int state, int[] states) {
        for (int i = 0; i < states.length; i++) {
            if (states[i] == state) {
                return true;
            }
        }
        return false;
    }

    private void clearCache() {
        mCachedDefault = null;
        mCachedButtonReceiver = null;
        mCachedActiveList = null;
        mCachedTransportControlList = null;
    }
}