design : introduce CounterAtom and ListItemContent.Counter

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/atomic/atoms/CounterAtom.kt

@@ -0,0 +1,83 @@
+/*
+ * Copyright 2025 New Vector Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ * Please see LICENSE in the repository root for full details.
+ */
+
+package io.element.android.libraries.designsystem.atomic.atoms
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Arrangement.spacedBy
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.runtime.Composable
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.text.rememberTextMeasurer
+import androidx.compose.ui.unit.dp
+import io.element.android.compound.theme.ElementTheme
+import io.element.android.libraries.designsystem.preview.ElementPreview
+import io.element.android.libraries.designsystem.preview.PreviewsDayNight
+import io.element.android.libraries.designsystem.text.toDp
+import io.element.android.libraries.designsystem.theme.components.Text
+
+private const val MAX_COUNT = 99
+private const val MAX_COUNT_STRING = "+$MAX_COUNT"
+
+/**
+ * A counter atom that displays a number in a circle.
+ * Figma link : https://www.figma.com/design/G1xy0HDZKJf5TCRFmKb5d5/Compound-Android-Components?node-id=2805-2649&m=dev
+ *
+ * @param count The number to display. If the number is greater than [MAX_COUNT], the counter will display [MAX_COUNT_STRING].
+ * If the number is less than 1, the counter will not be displayed.
+ * @param modifier The modifier to apply to this layout.
+ */
+@Composable
+fun CounterAtom(
+    count: Int,
+    modifier: Modifier = Modifier,
+) {
+    if (count < 1) return
+    val countAsText = when (count) {
+        in 0..MAX_COUNT -> count.toString()
+        else -> MAX_COUNT_STRING
+    }
+    val textStyle = ElementTheme.typography.fontBodyMdMedium
+    val textMeasurer = rememberTextMeasurer()
+    // Measure the maximum count string size
+    val textLayoutResult = textMeasurer.measure(
+        text = MAX_COUNT_STRING,
+        style = textStyle
+    )
+    val textSize = textLayoutResult.size
+    val squareSize = maxOf(textSize.width, textSize.height)
+    Box(
+        modifier = modifier
+                .size(squareSize.toDp() + 1.dp)
+                .clip(CircleShape)
+                .background(ElementTheme.colors.iconSuccessPrimary)
+    ) {
+        Text(
+            modifier = Modifier.align(Alignment.Center),
+            text = countAsText,
+            style = textStyle,
+            color = Color.White,
+        )
+    }
+}
+
+@PreviewsDayNight
+@Composable
+internal fun CounterAtomPreview() = ElementPreview {
+    Column(verticalArrangement = spacedBy(2.dp)) {
+        CounterAtom(count = 0)
+        CounterAtom(count = 4)
+        CounterAtom(count = 99)
+        CounterAtom(count = 100)
+    }
+}

libraries/designsystem/src/main/kotlin/io/element/android/libraries/designsystem/components/list/ListItemContent.kt

@@ -17,6 +17,7 @@ import androidx.compose.ui.Modifier
 import androidx.compose.ui.text.style.TextOverflow
 import androidx.compose.ui.unit.DpSize
 import androidx.compose.ui.unit.dp
+import io.element.android.libraries.designsystem.atomic.atoms.CounterAtom
 import io.element.android.libraries.designsystem.atomic.atoms.RedIndicatorAtom
 import io.element.android.libraries.designsystem.theme.components.IconSource
 import io.element.android.libraries.designsystem.theme.components.ListItem
@@ -91,6 +92,9 @@ sealed interface ListItemContent {
     /** Displays a badge. */
     data object Badge : ListItemContent
 
+    /** Displays a counter. */
+    data class Counter(val count: Int) : ListItemContent
+
     @Composable
     fun View() {
         when (this) {
@@ -125,6 +129,9 @@ sealed interface ListItemContent {
             ) {
                 RedIndicatorAtom()
             }
+            is Counter -> {
+                CounterAtom(count = count)
+            }
             is Custom -> content()
         }
     }