Fix splitting ad playback state for partial ad group when joining

This change addresses the case when the user joins the live stream
on an ad period but the metadata for the ad period is not emitted.
This results in inserting a partial ad group.

In this case the ad group duration is longer than the partial ad
group. If now the partial ad group ends at the period before the
last period of the window (unknown duration), the splitting algorithm
didn't recognize that the ad group already ended and made the last
period wrongly an ad period.

This change handles this edge case by counting the mapped ads in
the partial ad group to detect this situation and stops splitting.

#minor-release

PiperOrigin-RevId: 539102785

libraries/exoplayer_ima/src/main/java/androidx/media3/exoplayer/ima/ImaUtil.java

@@ -421,6 +421,7 @@ public static ImmutableMap<Object, AdPlaybackState> splitAdPlaybackStateForPerio
     Map<Object, AdPlaybackState> adPlaybackStates = new HashMap<>();
     for (int i = adPlaybackState.removedAdGroupCount; i < adPlaybackState.adGroupCount; i++) {
       AdGroup adGroup = adPlaybackState.getAdGroup(/* adGroupIndex= */ i);
+      int mappedAdCount = 0;
       if (adGroup.timeUs == C.TIME_END_OF_SOURCE) {
         checkState(i == adPlaybackState.adGroupCount - 1);
         // The last ad group is a placeholder for a potential post roll. We can just stop here.
@@ -454,8 +455,10 @@ public static ImmutableMap<Object, AdPlaybackState> splitAdPlaybackStateForPerio
                     adsId, adGroup, periodStartUs, periodDurationUs, window.isLive()));
             // Current period added as an ad period. Advance and look at the next period.
             periodIndex++;
+            mappedAdCount++;
             elapsedAdGroupAdDurationUs += periodDurationUs;
-            if (periodStartUs + periodDurationUs == adGroup.timeUs + adGroupDurationUs) {
+            if ((adGroup.originalCount > adGroup.count && adGroup.count == mappedAdCount)
+                || periodStartUs + periodDurationUs == adGroup.timeUs + adGroupDurationUs) {
               // Periods have consumed the ad group. We're at the end of the ad group.
               if (window.isLive()) {
                 // Add elapsed ad duration to elapsed content duration for live streams to account

libraries/exoplayer_ima/src/test/java/androidx/media3/exoplayer/ima/ImaUtilTest.java

@@ -853,6 +853,46 @@ public void splitAdPlaybackStateForPeriods_earlyMidrollAdGroupStartTimeUs_adGrou
     assertThat(adPlaybackStates.get("uid-14[a]").adGroupCount).isEqualTo(2);
   }
 
+  @Test
+  public void
+      splitAdPlaybackStateForPeriods_partialAdGroupEndingAtPeriodBeforeLast_adPeriodsCorrectlyDetected() {
+    AdPlaybackState adPlaybackState =
+        new AdPlaybackState(/* adsId= */ "adsId", C.TIME_END_OF_SOURCE)
+            .withIsServerSideInserted(/* adGroupIndex= */ 0, true);
+    FakeMultiPeriodLiveTimeline liveTimeline =
+        new FakeMultiPeriodLiveTimeline(
+            /* availabilityStartTimeMs= */ 0,
+            /* liveWindowDurationUs= */ 60_000_000,
+            /* nowUs= */ 70_000_000,
+            /* adSequencePattern= */ new boolean[] {false, true, true, true},
+            /* periodDurationMsPattern= */ new long[] {30_000, 10_000, 10_000, 10_000},
+            /* isContentTimeline= */ true,
+            /* populateAds= */ false,
+            /* playedAds= */ false);
+    // Ad event received from SDK around 30s.
+    adPlaybackState =
+        addLiveAdBreak(
+            /* currentContentPeriodPositionUs= */ 40_000_000,
+            /* adDurationUs= */ 10_000_000,
+            /* adPositionInAdPod= */ 2,
+            /* totalAdDurationUs= */ 30_000_000,
+            /* totalAdsInAdPod= */ 3,
+            adPlaybackState);
+
+    ImmutableMap<Object, AdPlaybackState> splitAdPlaybackStates =
+        ImaUtil.splitAdPlaybackStateForPeriods(adPlaybackState, liveTimeline);
+
+    assertThat(liveTimeline.getPeriodCount()).isEqualTo(5);
+    assertThat(splitAdPlaybackStates).hasSize(5);
+    assertThat(liveTimeline.getWindow(0, new Window()).windowStartTimeMs).isEqualTo(10_000L);
+    assertThat(liveTimeline.getPeriod(0, new Period()).positionInWindowUs).isEqualTo(-10_000_000L);
+    assertThat(splitAdPlaybackStates.get("uid-0[c]").adGroupCount).isEqualTo(1);
+    assertThat(splitAdPlaybackStates.get("uid-1[a]").adGroupCount).isEqualTo(1);
+    assertThat(splitAdPlaybackStates.get("uid-2[a]").adGroupCount).isEqualTo(2);
+    assertThat(splitAdPlaybackStates.get("uid-3[a]").adGroupCount).isEqualTo(2);
+    assertThat(splitAdPlaybackStates.get("uid-4[c]").adGroupCount).isEqualTo(1);
+  }
+
   @Test
   public void
       splitAdPlaybackStateForPeriods_fullAdGroupAtBeginOfWindow_adPeriodsCorrectlyDetected() {