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

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

@@ -0,0 +1,47 @@
+/*
+ * 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 androidx.compose.runtime.Composable
+import androidx.compose.ui.graphics.Color
+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(
+    val background: Color,
+    val foreground: Color,
+)
+
+@Composable
+fun AvatarColor(userId: String): AvatarColor {
+    val hash = userId.toHash()
+    val colors = if (ElementTheme.isLightTheme) {
+        avatarColorsLight[hash % avatarColorsLight.size]
+    } else {
+        avatarColorsDark[hash % avatarColorsDark.size]
+    }
+    return AvatarColor(
+        background = colors.first,
+        foreground = colors.second,
+    )
+}
+
+private fun String.toHash(): Int {
+    return toList().sumOf { it.code } % 8 + 1
+}
+