Tighten when various SampleSource methods can be called.

This removes the need for each SampleSource implementation to
implement 3x "if(condition) {noop}" tests (ChunkSampleSource
and SingleSampleSource were missing some of these checks).
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=118036233

library/src/main/java/com/google/android/exoplayer/ExoPlayerImplInternal.java

@@ -125,11 +125,13 @@ import java.util.concurrent.atomic.AtomicInteger;
   }
 
   public long getBufferedPosition() {
+    long bufferedPositionUs = this.bufferedPositionUs;
     return bufferedPositionUs == C.UNKNOWN_TIME_US ? ExoPlayer.UNKNOWN_TIME
         : bufferedPositionUs / 1000;
   }
 
   public long getDuration() {
+    long durationUs = this.durationUs;
     return durationUs == C.UNKNOWN_TIME_US ? ExoPlayer.UNKNOWN_TIME : durationUs / 1000;
   }
 
@@ -279,7 +281,6 @@ import java.util.concurrent.atomic.AtomicInteger;
     }
 
     durationUs = source.getDurationUs();
-    bufferedPositionUs = source.getBufferedPositionUs();
     selectTracksInternal(true);
 
     boolean allRenderersEnded = true;
@@ -363,6 +364,13 @@ import java.util.concurrent.atomic.AtomicInteger;
     elapsedRealtimeUs = SystemClock.elapsedRealtime() * 1000;
   }
 
+  private void updateBufferedPositionUs() {
+    long sourceBufferedPositionUs = enabledRenderers.length > 0 ? source.getBufferedPositionUs()
+        : C.END_OF_SOURCE_US;
+    bufferedPositionUs = sourceBufferedPositionUs == C.END_OF_SOURCE_US
+        && durationUs != C.UNKNOWN_TIME_US ? durationUs : sourceBufferedPositionUs;
+  }
+
   private void doSomeWork() throws ExoPlaybackException, IOException {
     TraceUtil.beginSection("doSomeWork");
     long operationStartTimeMs = SystemClock.elapsedRealtime();
@@ -373,8 +381,10 @@ import java.util.concurrent.atomic.AtomicInteger;
     }
 
     updatePositionUs();
-    bufferedPositionUs = source.getBufferedPositionUs();
+    updateBufferedPositionUs();
+    if (enabledRenderers.length > 0) {
       source.continueBuffering(positionUs);
+    }
 
     boolean allRenderersEnded = true;
     boolean allRenderersReadyOrEnded = true;
@@ -444,14 +454,15 @@ import java.util.concurrent.atomic.AtomicInteger;
         return;
       }
 
+      if (enabledRenderers != null) {
         for (TrackRenderer renderer : enabledRenderers) {
           ensureStopped(renderer);
         }
-      setState(ExoPlayer.STATE_BUFFERING);
         source.seekToUs(positionUs);
         for (TrackRenderer renderer : enabledRenderers) {
           renderer.checkForReset();
         }
+      }
 
       handler.sendEmptyMessage(MSG_DO_SOME_WORK);
     } finally {
@@ -622,6 +633,7 @@ import java.util.concurrent.atomic.AtomicInteger;
     }
 
     source.endTrackSelection(positionUs);
+    updateBufferedPositionUs();
   }
 
   private void reselectTracksInternal() throws ExoPlaybackException {

library/src/main/java/com/google/android/exoplayer/MultiSampleSource.java

@@ -20,6 +20,7 @@ import com.google.android.exoplayer.util.Assertions;
 import android.util.Pair;
 
 import java.io.IOException;
+import java.util.Arrays;
 import java.util.IdentityHashMap;
 
 /**
@@ -28,14 +29,17 @@ import java.util.IdentityHashMap;
 public final class MultiSampleSource implements SampleSource {
 
   private final SampleSource[] sources;
+  private final int[] sourceEnabledTrackCounts;
   private final IdentityHashMap<TrackStream, Integer> trackStreamSourceIndices;
 
   private int state;
   private long durationUs;
   private TrackGroupArray trackGroups;
+  private SampleSource[] enabledSources;
 
   public MultiSampleSource(SampleSource... sources) {
     this.sources = sources;
+    sourceEnabledTrackCounts = new int[sources.length];
     trackStreamSourceIndices = new IdentityHashMap<>();
     state = STATE_UNPREPARED;
   }
@@ -100,7 +104,9 @@ public final class MultiSampleSource implements SampleSource {
     Pair<Integer, Integer> sourceAndGroup = getSourceAndTrackGroupIndices(selection.group);
     TrackStream trackStream = sources[sourceAndGroup.first].selectTrack(
         new TrackSelection(sourceAndGroup.second, selection.getTracks()), positionUs);
-    trackStreamSourceIndices.put(trackStream, sourceAndGroup.first);
+    int sourceIndex = sourceAndGroup.first;
+    sourceEnabledTrackCounts[sourceIndex]++;
+    trackStreamSourceIndices.put(trackStream, sourceIndex);
     return trackStream;
   }
 
@@ -109,27 +115,34 @@ public final class MultiSampleSource implements SampleSource {
     Assertions.checkState(state == STATE_SELECTING_TRACKS);
     int sourceIndex = trackStreamSourceIndices.remove(trackStream);
     sources[sourceIndex].unselectTrack(trackStream);
+    sourceEnabledTrackCounts[sourceIndex]--;
   }
 
   @Override
   public void endTrackSelection(long positionUs) {
     Assertions.checkState(state == STATE_SELECTING_TRACKS);
     state = STATE_READING;
-    for (SampleSource source : sources) {
-      source.endTrackSelection(positionUs);
+    int newEnabledSourceCount = 0;
+    SampleSource[] newEnabledSources = new SampleSource[sources.length];
+    for (int i = 0; i < sources.length; i++) {
+      sources[i].endTrackSelection(positionUs);
+      if (sourceEnabledTrackCounts[i] > 0) {
+        newEnabledSources[newEnabledSourceCount++] = sources[i];
+      }
     }
+    enabledSources = Arrays.copyOf(newEnabledSources, newEnabledSourceCount);
   }
 
   @Override
   public void continueBuffering(long positionUs) {
-    for (SampleSource source : sources) {
+    for (SampleSource source : enabledSources) {
       source.continueBuffering(positionUs);
     }
   }
 
   @Override
   public void seekToUs(long positionUs) {
-    for (SampleSource source : sources) {
+    for (SampleSource source : enabledSources) {
       source.seekToUs(positionUs);
     }
   }
@@ -142,7 +155,7 @@ public final class MultiSampleSource implements SampleSource {
   @Override
   public long getBufferedPositionUs() {
     long bufferedPositionUs = durationUs != C.UNKNOWN_TIME_US ? durationUs : Long.MAX_VALUE;
-    for (SampleSource source : sources) {
+    for (SampleSource source : enabledSources) {
       long rendererBufferedPositionUs = source.getBufferedPositionUs();
       if (rendererBufferedPositionUs == C.UNKNOWN_TIME_US) {
         return C.UNKNOWN_TIME_US;

library/src/main/java/com/google/android/exoplayer/SampleSource.java

@@ -132,7 +132,8 @@ public interface SampleSource {
   /**
    * Indicates to the source that it should continue buffering data for its enabled tracks.
    * <p>
-   * This method should only be called when the state is {@link #STATE_READING}.
+   * This method should only be called when the state is {@link #STATE_READING} and at least one
+   * track is selected.
    *
    * @param positionUs The current playback position.
    */
@@ -141,19 +142,20 @@ public interface SampleSource {
   /**
    * Returns an estimate of the position up to which data is buffered for the enabled tracks.
    * <p>
-   * This method should only be called when the state is {@link #STATE_READING}.
+   * This method should only be called when the state is {@link #STATE_READING} and at least one
+   * track is selected.
    *
    * @return An estimate of the absolute position in microseconds up to which data is buffered,
    *     or {@link C#END_OF_SOURCE_US} if the track is fully buffered, or {@link C#UNKNOWN_TIME_US}
-   *     if no estimate is available. If no tracks are enabled then {@link C#END_OF_SOURCE_US} is
-   *     returned.
+   *     if no estimate is available.
    */
   long getBufferedPositionUs();
 
   /**
    * Seeks to the specified time in microseconds.
    * <p>
-   * This method should only be called when the state is {@link #STATE_READING}.
+   * This method should only be called when the state is {@link #STATE_READING} and at least one
+   * track is selected.
    *
    * @param positionUs The seek position in microseconds.
    */

library/src/main/java/com/google/android/exoplayer/SingleSampleSource.java

@@ -220,7 +220,7 @@ public final class SingleSampleSource implements SampleSource, TrackStream, Load
 
   @Override
   public long getBufferedPositionUs() {
-    return streamState == STREAM_STATE_END_OF_STREAM || loadingFinished ? C.END_OF_SOURCE_US : 0;
+    return loadingFinished ? C.END_OF_SOURCE_US : 0;
   }
 
   @Override

library/src/main/java/com/google/android/exoplayer/chunk/ChunkSampleSource.java

@@ -326,7 +326,7 @@ public class ChunkSampleSource implements SampleSource, TrackStream, Loader.Call
 
   @Override
   public long getBufferedPositionUs() {
-    if (!trackEnabled || loadingFinished) {
+    if (loadingFinished) {
       return C.END_OF_SOURCE_US;
     } else if (isPendingReset()) {
       return pendingResetPositionUs;

library/src/main/java/com/google/android/exoplayer/extractor/ExtractorSampleSource.java

@@ -423,9 +423,6 @@ public final class ExtractorSampleSource implements SampleSource, ExtractorOutpu
 
   @Override
   public void continueBuffering(long playbackPositionUs) {
-    if (enabledTrackCount == 0) {
-      return;
-    }
     downstreamPositionUs = playbackPositionUs;
     discardSamplesForDisabledTracks(downstreamPositionUs);
     if (loadingFinished) {
@@ -504,9 +501,6 @@ public final class ExtractorSampleSource implements SampleSource, ExtractorOutpu
 
   @Override
   public void seekToUs(long positionUs) {
-    if (enabledTrackCount == 0) {
-      return;
-    }
     seekToInternal(positionUs);
   }
 
@@ -529,7 +523,7 @@ public final class ExtractorSampleSource implements SampleSource, ExtractorOutpu
 
   @Override
   public long getBufferedPositionUs() {
-    if (enabledTrackCount == 0 || loadingFinished) {
+    if (loadingFinished) {
       return C.END_OF_SOURCE_US;
     } else if (isPendingReset()) {
       return pendingResetPositionUs;

library/src/main/java/com/google/android/exoplayer/hls/HlsSampleSource.java

@@ -258,9 +258,6 @@ public final class HlsSampleSource implements SampleSource, Loader.Callback {
 
   @Override
   public void continueBuffering(long playbackPositionUs) {
-    if (enabledTrackCount == 0) {
-      return;
-    }
     downstreamPositionUs = playbackPositionUs;
     if (!extractors.isEmpty()) {
       discardSamplesForDisabledTracks(getCurrentExtractor(), downstreamPositionUs);
@@ -360,17 +357,12 @@ public final class HlsSampleSource implements SampleSource, Loader.Callback {
 
   @Override
   public void seekToUs(long positionUs) {
-    if (enabledTrackCount == 0) {
-      return;
-    }
     seekToInternal(positionUs);
   }
 
   @Override
   public long getBufferedPositionUs() {
-    if (enabledTrackCount == 0) {
-      return C.END_OF_SOURCE_US;
-    } else if (isPendingReset()) {
+    if (isPendingReset()) {
       return pendingResetPositionUs;
     } else if (loadingFinished) {
       return C.END_OF_SOURCE_US;