From 790f8426ac870fda1cc7889fe48fcc00f074f6c3 Mon Sep 17 00:00:00 2001
From: Alex Hart <alex@signal.org>
Date: Thu, 14 Jan 2021 06:53:18 -0400
Subject: [PATCH] Fix issue when single user leaves ParticipantCollection.

---
 .../collections/ParticipantCollection.java    |  2 +-
 .../ParticipantCollectionTest.java            | 31 +++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/app/src/main/java/org/thoughtcrime/securesms/service/webrtc/collections/ParticipantCollection.java b/app/src/main/java/org/thoughtcrime/securesms/service/webrtc/collections/ParticipantCollection.java
index fa32e7d992..6e2a65a90e 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/service/webrtc/collections/ParticipantCollection.java
+++ b/app/src/main/java/org/thoughtcrime/securesms/service/webrtc/collections/ParticipantCollection.java
@@ -62,7 +62,7 @@ public class ParticipantCollection {
                              .indexOf(oldId);
 
         if (newIndex != -1 && newIndex != i) {
-          Collections.swap(newParticipants, newIndex, i);
+          Collections.swap(newParticipants, newIndex, Math.min(i, newParticipants.size() - 1));
         }
       }
 
diff --git a/app/src/test/java/org/thoughtcrime/securesms/service/webrtc/collections/ParticipantCollectionTest.java b/app/src/test/java/org/thoughtcrime/securesms/service/webrtc/collections/ParticipantCollectionTest.java
index 46963fc98d..bd805cd357 100644
--- a/app/src/test/java/org/thoughtcrime/securesms/service/webrtc/collections/ParticipantCollectionTest.java
+++ b/app/src/test/java/org/thoughtcrime/securesms/service/webrtc/collections/ParticipantCollectionTest.java
@@ -87,6 +87,37 @@ public class ParticipantCollectionTest {
     assertThat(result.getGridParticipants(), Matchers.contains(id(1), id(2), id(3)));
   }
 
+  @Test
+  public void givenACollection_whenSomeoneLeaves_thenIDoNotExpectToSeeThemInTheNewList() {
+    // GIVEN
+    List<CallParticipant> initial           = Arrays.asList(participant(1, 1, 2), participant(2, 1, 3), participant(3, 1, 4));
+    ParticipantCollection initialCollection = testSubject.getNext(initial);
+    List<CallParticipant> next              = Arrays.asList(participant(2, 2, 3), participant(3, 1, 4));
+
+    // WHEN
+    ParticipantCollection result = initialCollection.getNext(next);
+
+    // THEN
+    assertThat(result.getGridParticipants(), Matchers.contains(id(2), id(3)));
+  }
+
+  @Test
+  public void givenACollection_whenMultipleLeave_thenIDoNotExpectToSeeThemInTheNewList() {
+    // GIVEN
+    ParticipantCollection testSubject       = new ParticipantCollection(4);
+    List<CallParticipant> initial           = Arrays.asList(participant(1, 1, 2), participant(2, 1, 3), participant(3, 1, 4), participant(4, 1, 5));
+    ParticipantCollection initialCollection = testSubject.getNext(initial);
+    List<CallParticipant> next              = Arrays.asList(participant(3, 1, 4), participant(2, 1, 3));
+
+    // WHEN
+    ParticipantCollection result = initialCollection.getNext(next);
+
+    // THEN
+    assertThat(result.getGridParticipants(), Matchers.contains(id(2), id(3)));
+  }
+
+
+
   @Test
   public void bigTest() {