Implement simple avatar color picking algorithm to align with iOS.

app/src/main/java/org/thoughtcrime/securesms/conversation/colors/AvatarColor.java

@@ -98,7 +98,7 @@ public enum AvatarColor {
   }
 
   /** Colors that can be assigned via {@link #random()}. */
-  private static final AvatarColor[] RANDOM_OPTIONS = new AvatarColor[] {
+  static final AvatarColor[] RANDOM_OPTIONS = new AvatarColor[] {
       A100,
       A110,
       A120,

app/src/main/java/org/thoughtcrime/securesms/conversation/colors/AvatarColorHash.kt

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2023 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.thoughtcrime.securesms.conversation.colors
+
+import org.thoughtcrime.securesms.groups.GroupId
+
+/**
+ * Stolen from iOS. Utilizes a simple hash to map different characteristics to an avatar color index.
+ */
+object AvatarColorHash {
+
+  /**
+   * Utilize Uppercase UUID of ServiceId.
+   *
+   * Uppercase is necessary here because iOS utilizes uppercase UUIDs by default.
+   */
+  fun forAddress(serviceId: String?, e164: String?): AvatarColor {
+    if (!serviceId.isNullOrEmpty()) {
+      return forSeed(serviceId.toString().uppercase())
+    }
+
+    if (!e164.isNullOrEmpty()) {
+      return forSeed(e164)
+    }
+
+    return AvatarColor.A100
+  }
+
+  fun forGroupId(group: GroupId): AvatarColor {
+    return forData(group.decodedId)
+  }
+
+  fun forSeed(seed: String): AvatarColor {
+    return forData(seed.toByteArray())
+  }
+
+  fun forCallLink(rootKey: ByteArray): AvatarColor {
+    return forIndex(rootKey.first().toInt())
+  }
+
+  private fun forData(data: ByteArray): AvatarColor {
+    var hash = 0
+    for (value in data) {
+      hash = hash.rotateLeft(3) xor value.toInt()
+    }
+
+    return forIndex(hash)
+  }
+
+  private fun forIndex(index: Int): AvatarColor {
+    return AvatarColor.RANDOM_OPTIONS[(index.toUInt() % AvatarColor.RANDOM_OPTIONS.size.toUInt()).toInt()]
+  }
+}