Compute avatar color of users and apply foreground color to the sender displayname.

features/messages/impl/src/main/kotlin/io/element/android/features/messages/impl/timeline/components/TimelineItemEventRow.kt

@@ -75,7 +75,7 @@ import io.element.android.features.messages.impl.timeline.model.event.TimelineIt
 import io.element.android.features.messages.impl.timeline.model.event.aTimelineItemImageContent
 import io.element.android.features.messages.impl.timeline.model.event.aTimelineItemPollContent
 import io.element.android.features.messages.impl.timeline.model.event.aTimelineItemTextContent
-import io.element.android.libraries.designsystem.colors.AvatarColor
+import io.element.android.libraries.designsystem.colors.AvatarColors
 import io.element.android.libraries.designsystem.components.EqualWidthColumn
 import io.element.android.libraries.designsystem.components.avatar.Avatar
 import io.element.android.libraries.designsystem.components.avatar.AvatarData
@@ -328,7 +328,7 @@ private fun MessageSenderInformation(
 ) {
     val avatarStrokeColor = MaterialTheme.colorScheme.background
     val avatarSize = senderAvatar.size.dp
-    val avatarColor = AvatarColor(senderAvatar.id)
+    val avatarColors = AvatarColors(senderAvatar.id)
     Box(
         modifier = modifier
     ) {
@@ -352,7 +352,7 @@ private fun MessageSenderInformation(
                 text = sender,
                 maxLines = 1,
                 overflow = TextOverflow.Ellipsis,
-                color = avatarColor.foreground,
+                color = avatarColors.foreground,
                 style = ElementTheme.typography.fontBodyMdMedium,
             )
         }

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/colors/AvatarColors.kt

@@ -22,26 +22,26 @@ import io.element.android.libraries.theme.ElementTheme
 import io.element.android.libraries.theme.colors.avatarColorsDark
 import io.element.android.libraries.theme.colors.avatarColorsLight
 
-data class AvatarColor(
+data class AvatarColors(
     val background: Color,
     val foreground: Color,
 )
 
 @Composable
-fun AvatarColor(userId: String): AvatarColor {
+fun AvatarColors(userId: String): AvatarColors {
     val hash = userId.toHash()
     val colors = if (ElementTheme.isLightTheme) {
-        avatarColorsLight[hash % avatarColorsLight.size]
+        avatarColorsLight[hash]
     } else {
-        avatarColorsDark[hash % avatarColorsDark.size]
+        avatarColorsDark[hash]
     }
-    return AvatarColor(
+    return AvatarColors(
         background = colors.first,
         foreground = colors.second,
     )
 }
 
-private fun String.toHash(): Int {
+internal fun String.toHash(): Int {
-    return toList().sumOf { it.code } % 8 + 1
+    return toList().sumOf { it.code } % 8
 }
 

libraries/designsystem/src/test/kotlin/io/element/android/libraries/designsystem/colors/AvatarColorsTest.kt

@@ -0,0 +1,40 @@
+/*
+ * Copyright (c) 2023 New Vector Ltd
+ *
+ * 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 io.element.android.libraries.designsystem.colors
+
+import com.google.common.truth.Truth.assertThat
+import io.element.android.libraries.theme.colors.avatarColorsDark
+import io.element.android.libraries.theme.colors.avatarColorsLight
+import org.junit.Test
+
+class AvatarColorsTest {
+
+    @Test
+    fun `ensure list size`() {
+        // avatarColorsDark and avatarColorsLight size must not be modified.
+        // 8 is used as a hard-coded modulo in `String.toHash()` extension.
+        assertThat(avatarColorsDark.size).isEqualTo(8)
+        assertThat(avatarColorsLight.size).isEqualTo(8)
+    }
+
+    @Test
+    fun `compute string hash`() {
+        assertThat("@alice:domain.org".toHash()).isEqualTo(6)
+        assertThat("@bob:domain.org".toHash()).isEqualTo(3)
+        assertThat("@charlie:domain.org".toHash()).isEqualTo(0)
+    }
+}