Move playback session manager to core library.

This allows to use the session management capabilities for other analytics
purposes.

PiperOrigin-RevId: 245710588

library/core/src/main/java/com/google/android/exoplayer2/analytics/PlaybackSessionManager.java

+/*
+ * Copyright (C) 2019 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.google.android.exoplayer2.analytics;
+
+import com.google.android.exoplayer2.Player.DiscontinuityReason;
+import com.google.android.exoplayer2.Timeline;
+import com.google.android.exoplayer2.analytics.AnalyticsListener.EventTime;
+import com.google.android.exoplayer2.source.MediaSource.MediaPeriodId;
+
+/**
+ * Manager for active playback sessions.
+ *
+ * <p>The manager keeps track of the association between window index and/or media period id to
+ * session identifier.
+ */
+public interface PlaybackSessionManager {
+
+  /** A listener for session updates. */
+  interface Listener {
+
+    /**
+     * Called when a new session is created as a result of {@link #updateSessions(EventTime)}.
+     *
+     * @param eventTime The {@link EventTime} at which the session is created.
+     * @param sessionId The identifier of the new session.
+     */
+    void onSessionCreated(EventTime eventTime, String sessionId);
+
+    /**
+     * Called when a session becomes active, i.e. playing in the foreground.
+     *
+     * @param eventTime The {@link EventTime} at which the session becomes active.
+     * @param sessionId The identifier of the session.
+     */
+    void onSessionActive(EventTime eventTime, String sessionId);
+
+    /**
+     * Called when a session is interrupted by ad playback.
+     *
+     * @param eventTime The {@link EventTime} at which the ad playback starts.
+     * @param contentSessionId The session identifier of the content session.
+     * @param adSessionId The identifier of the ad session.
+     */
+    void onAdPlaybackStarted(EventTime eventTime, String contentSessionId, String adSessionId);
+
+    /**
+     * Called when a session is permanently finished.
+     *
+     * @param eventTime The {@link EventTime} at which the session finished.
+     * @param sessionId The identifier of the finished session.
+     * @param automaticTransitionToNextPlayback Whether the session finished because of an automatic
+     *     transition to the next playback item.
+     */
+    void onSessionFinished(
+        EventTime eventTime, String sessionId, boolean automaticTransitionToNextPlayback);
+  }
+
+  /**
+   * Sets the listener to be notified of session updates. Must be called before the session manager
+   * is used.
+   *
+   * @param listener The {@link Listener} to be notified of session updates.
+   */
+  void setListener(Listener listener);
+
+  /**
+   * Returns the session identifier for the given media period id.
+   *
+   * <p>Note that this will reserve a new session identifier if it doesn't exist yet, but will not
+   * call any {@link Listener} callbacks.
+   *
+   * @param timeline The timeline, {@code mediaPeriodId} is part of.
+   * @param mediaPeriodId A {@link MediaPeriodId}.
+   */
+  String getSessionForMediaPeriodId(Timeline timeline, MediaPeriodId mediaPeriodId);
+
+  /**
+   * Returns whether an event time belong to a session.
+   *
+   * @param eventTime The {@link EventTime}.
+   * @param sessionId A session identifier.
+   * @return Whether the event belongs to the specified session.
+   */
+  boolean belongsToSession(EventTime eventTime, String sessionId);
+
+  /**
+   * Updates or creates sessions based on a player {@link EventTime}.
+   *
+   * @param eventTime The {@link EventTime}.
+   */
+  void updateSessions(EventTime eventTime);
+
+  /**
+   * Updates the session associations to a new timeline.
+   *
+   * @param eventTime The event time with the timeline change.
+   */
+  void handleTimelineUpdate(EventTime eventTime);
+
+  /**
+   * Handles a position discontinuity.
+   *
+   * @param eventTime The event time of the position discontinuity.
+   * @param reason The {@link DiscontinuityReason}.
+   */
+  void handlePositionDiscontinuity(EventTime eventTime, @DiscontinuityReason int reason);
+}