ui: scroll the library tab strip and explain offline mode

The tab bar measured the selected tab's full label before the trailing
controls, so a long translation or a large font scale squeezed the
settings gear and eventually removed it, and an indicator in the bar
made that happen sooner. Put the tabs in a weighted, horizontally
scrollable strip and keep the gear outside it, then scroll the selected
tab into view when the pager settles, in either layout direction.

Move the offline indicator out of the bar into a strip above the tabs
that names the mode and offers to go online. Offline mode limits every
list, and Home already swaps to downloaded content without saying why;
an icon in the bar could not explain that and competed for the same
width.

app/src/main/kotlin/com/subtracks/ui/library/LibraryScreen.kt

@@ -6,6 +6,7 @@ import androidx.compose.foundation.BorderStroke
 import androidx.compose.foundation.Canvas
 import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
+import androidx.compose.foundation.horizontalScroll
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Box
 import androidx.compose.foundation.layout.Column
@@ -16,6 +17,7 @@ import androidx.compose.foundation.layout.WindowInsets
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.heightIn
 import androidx.compose.foundation.layout.offset
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
@@ -25,6 +27,7 @@ import androidx.compose.foundation.layout.width
 import androidx.compose.foundation.pager.HorizontalPager
 import androidx.compose.foundation.pager.PagerState
 import androidx.compose.foundation.pager.rememberPagerState
+import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.foundation.shape.RoundedCornerShape
 import androidx.compose.material.icons.Icons
@@ -47,6 +50,7 @@ import androidx.compose.material3.FilterChip
 import androidx.compose.material3.FilterChipDefaults
 import androidx.compose.material3.FloatingActionButton
 import androidx.compose.material3.FloatingActionButtonDefaults
+import androidx.compose.material3.HorizontalDivider
 import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.LocalContentColor
@@ -94,12 +98,14 @@ import androidx.compose.ui.layout.onGloballyPositioned
 import androidx.compose.ui.layout.onSizeChanged
 import androidx.compose.ui.platform.LocalDensity
 import androidx.compose.ui.platform.LocalFocusManager
+import androidx.compose.ui.platform.LocalLayoutDirection
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.semantics.clearAndSetSemantics
 import androidx.compose.ui.semantics.contentDescription
 import androidx.compose.ui.semantics.semantics
 import androidx.compose.ui.unit.Constraints
 import androidx.compose.ui.unit.Dp
+import androidx.compose.ui.unit.LayoutDirection
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.paging.PagingData
@@ -586,14 +592,15 @@ fun LibraryScreen(
                         .onSizeChanged { tabBarHeightPx = it.height.toFloat() }
                         .padding(bottom = bottomInset),
             ) {
+                if (offline) {
+                    OfflineStrip(onGoOnline = onExitOffline)
+                }
                 LibraryTabs(
                     pagerState = pagerState,
                     onTabSelected = { tab ->
                         if (tab == selectedTab) topRequest++ else onTabSelected(tab)
                     },
                     onOpenSettings = onOpenSettings,
-                    offline = offline,
-                    onExitOffline = onExitOffline,
                     artwork = artwork,
                     syncing = syncing,
                 )
@@ -856,13 +863,12 @@ internal fun LibraryTabs(
     pagerState: PagerState,
     onTabSelected: (LibraryTab) -> Unit,
     onOpenSettings: () -> Unit,
-    offline: Boolean = false,
-    onExitOffline: () -> Unit = {},
     artwork: ArtworkColors?,
     syncing: Boolean = false,
 ) {
     val indicatorStretch = 18.dp
     val density = LocalDensity.current
+    val layoutDirection = LocalLayoutDirection.current
     val bounds = remember { mutableStateMapOf<Int, Rect>() }
     val page = pagerState.currentPage
     val fraction = pagerState.currentPageOffsetFraction
@@ -894,6 +900,28 @@ internal fun LibraryTabs(
     val indicatorColor = artwork?.scheme?.primary ?: MaterialTheme.colorScheme.onBackground
     val tabContentHeightPx = with(density) { (TAB_ICON_SIZE + TAB_VERTICAL_PADDING * 2).toPx() }
 
+    val scrollState = rememberScrollState()
+    var viewportWidth by remember { mutableIntStateOf(0) }
+    var contentWidth by remember { mutableIntStateOf(0) }
+    var revealed by remember { mutableStateOf(false) }
+    LaunchedEffect(pagerState.settledPage, viewportWidth, contentWidth, layoutDirection, bounds[pagerState.settledPage]) {
+        if (viewportWidth == 0) return@LaunchedEffect
+        val settled = bounds[pagerState.settledPage] ?: return@LaunchedEffect
+        val start = if (layoutDirection == LayoutDirection.Rtl) contentWidth - settled.right else settled.left
+        val end = if (layoutDirection == LayoutDirection.Rtl) contentWidth - settled.left else settled.right
+        val target =
+            when {
+                start < scrollState.value -> start
+                end > scrollState.value + viewportWidth -> end - viewportWidth
+                else -> null
+            }
+        if (target != null) {
+            val offset = target.roundToInt().coerceIn(0, scrollState.maxValue)
+            if (revealed) scrollState.animateScrollTo(offset) else scrollState.scrollTo(offset)
+        }
+        revealed = true
+    }
+
     Box(Modifier.fillMaxWidth()) {
         Box(
             modifier =
@@ -902,71 +930,125 @@ internal fun LibraryTabs(
                     .background(headerColor)
                     .padding(horizontal = 8.dp, vertical = 2.dp),
         ) {
-            Box(
-                modifier =
-                    Modifier.drawBehind {
-                        if (current != null && indicatorLeft != null && indicatorRight != null && indicatorRight > indicatorLeft) {
-                            val height = tabContentHeightPx.coerceAtMost(current.height)
-                            drawRoundRect(
-                                color = indicatorColor,
-                                topLeft = Offset(indicatorLeft, current.top + (current.height - height) / 2f),
-                                size = Size(indicatorRight - indicatorLeft, height),
-                                cornerRadius = CornerRadius(8.dp.toPx()),
-                            )
-                        }
-                    },
+            Row(
+                modifier = Modifier.fillMaxWidth(),
+                verticalAlignment = Alignment.CenterVertically,
+                horizontalArrangement = Arrangement.spacedBy(4.dp),
             ) {
                 Row(
-                    modifier = Modifier.fillMaxWidth(),
+                    modifier =
+                        Modifier
+                            .weight(1f)
+                            .onSizeChanged { viewportWidth = it.width }
+                            .horizontalScroll(scrollState),
                     verticalAlignment = Alignment.CenterVertically,
-                    horizontalArrangement = Arrangement.spacedBy(4.dp),
                 ) {
-                    LibraryTab.entries.forEachIndexed { index, tab ->
-                        TabButton(
-                            tab = tab,
-                            artwork = artwork,
-                            progress =
-                                when (index) {
-                                    page -> 1f - transition
-                                    page + (if (fraction >= 0f) 1 else -1) -> transition
-                                    else -> 0f
+                    Box(
+                        modifier =
+                            Modifier
+                                .onSizeChanged { contentWidth = it.width }
+                                .drawBehind {
+                                    if (current != null &&
+                                        indicatorLeft != null &&
+                                        indicatorRight != null &&
+                                        indicatorRight > indicatorLeft
+                                    ) {
+                                        val height = tabContentHeightPx.coerceAtMost(current.height)
+                                        drawRoundRect(
+                                            color = indicatorColor,
+                                            topLeft = Offset(indicatorLeft, current.top + (current.height - height) / 2f),
+                                            size = Size(indicatorRight - indicatorLeft, height),
+                                            cornerRadius = CornerRadius(8.dp.toPx()),
+                                        )
+                                    }
                                 },
-                            indicatorLeft = indicatorLeft,
-                            indicatorRight = indicatorRight,
-                            onClick = { onTabSelected(tab) },
-                            modifier =
-                                Modifier.onGloballyPositioned { coordinates ->
-                                    bounds[index] = coordinates.boundsInParent()
-                                },
-                        )
-                    }
-                    Spacer(Modifier.weight(1f))
-                    if (offline) {
-                        IconButton(onClick = onExitOffline) {
-                            Icon(
-                                imageVector = Icons.Rounded.CloudOff,
-                                contentDescription = stringResource(R.string.offline_mode_status),
-                                tint = MaterialTheme.colorScheme.onBackground,
-                            )
-                        }
-                    }
-                    IconButton(onClick = onOpenSettings) {
-                        Box(contentAlignment = Alignment.Center) {
-                            Icon(
-                                imageVector = Icons.Rounded.Settings,
-                                contentDescription = stringResource(R.string.navigation_tabs_settings),
-                                tint = MaterialTheme.colorScheme.onBackground,
-                            )
-                            if (syncing) {
-                                CircularProgressIndicator(
-                                    modifier = Modifier.size(32.dp),
-                                    strokeWidth = 2.dp,
-                                    color = MaterialTheme.colorScheme.primary,
+                    ) {
+                        Row(
+                            verticalAlignment = Alignment.CenterVertically,
+                            horizontalArrangement = Arrangement.spacedBy(4.dp),
+                        ) {
+                            LibraryTab.entries.forEachIndexed { index, tab ->
+                                TabButton(
+                                    tab = tab,
+                                    artwork = artwork,
+                                    progress =
+                                        when (index) {
+                                            page -> 1f - transition
+                                            page + (if (fraction >= 0f) 1 else -1) -> transition
+                                            else -> 0f
+                                        },
+                                    indicatorLeft = indicatorLeft,
+                                    indicatorRight = indicatorRight,
+                                    onClick = { onTabSelected(tab) },
+                                    modifier =
+                                        Modifier.onGloballyPositioned { coordinates ->
+                                            bounds[index] = coordinates.boundsInParent()
+                                        },
                                 )
                             }
                         }
                     }
                 }
+                IconButton(onClick = onOpenSettings) {
+                    Box(contentAlignment = Alignment.Center) {
+                        Icon(
+                            imageVector = Icons.Rounded.Settings,
+                            contentDescription = stringResource(R.string.navigation_tabs_settings),
+                            tint = MaterialTheme.colorScheme.onBackground,
+                        )
+                        if (syncing) {
+                            CircularProgressIndicator(
+                                modifier = Modifier.size(32.dp),
+                                strokeWidth = 2.dp,
+                                color = MaterialTheme.colorScheme.primary,
+                            )
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
+
+@Composable
+private fun OfflineStrip(
+    onGoOnline: () -> Unit,
+    modifier: Modifier = Modifier,
+) {
+    Column(modifier.fillMaxWidth()) {
+        HorizontalDivider(color = MaterialTheme.colorScheme.outlineVariant)
+        Surface(
+            onClick = onGoOnline,
+            color = Color.Transparent,
+            contentColor = MaterialTheme.colorScheme.onBackground,
+            modifier = Modifier.fillMaxWidth(),
+        ) {
+            Row(
+                modifier =
+                    Modifier
+                        .fillMaxWidth()
+                        .heightIn(min = 44.dp)
+                        .padding(horizontal = 16.dp, vertical = 6.dp),
+                verticalAlignment = Alignment.CenterVertically,
+                horizontalArrangement = Arrangement.spacedBy(8.dp),
+            ) {
+                Icon(
+                    imageVector = Icons.Rounded.CloudOff,
+                    contentDescription = null,
+                    tint = MaterialTheme.colorScheme.primary,
+                    modifier = Modifier.size(18.dp),
+                )
+                Text(
+                    text = stringResource(R.string.offline_mode_banner),
+                    style = MaterialTheme.typography.bodyMedium,
+                    maxLines = 2,
+                    modifier = Modifier.weight(1f),
+                )
+                Text(
+                    text = stringResource(R.string.offline_go_online),
+                    style = MaterialTheme.typography.labelLarge,
+                    color = MaterialTheme.colorScheme.primary,
+                )
             }
         }
     }

app/src/main/res/values/strings.xml

@@ -175,7 +175,8 @@
     <string name="filters">Filters</string>
     <string name="filter_downloaded">Downloaded</string>
     <string name="close_search">Close search</string>
-    <string name="offline_mode_status">Offline mode; tap to go online</string>
+    <string name="offline_mode_banner">Offline mode — downloads only</string>
+    <string name="offline_go_online">Go online</string>
     <string name="shuffle_artist">Shuffle artist</string>
 
     <string name="status_playing">Playing</string>

app/src/test/kotlin/com/subtracks/ui/LibraryScreenTest.kt

@@ -2,8 +2,10 @@ package com.subtracks.ui
 
 import androidx.activity.ComponentActivity
 import androidx.compose.foundation.pager.PagerState
+import androidx.compose.material3.MaterialTheme
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
+import androidx.compose.ui.test.assertWidthIsEqualTo
 import androidx.compose.ui.test.junit4.v2.createAndroidComposeRule
 import androidx.compose.ui.test.onAllNodesWithContentDescription
 import androidx.compose.ui.test.onAllNodesWithTag
@@ -16,6 +18,9 @@ import androidx.compose.ui.test.performTouchInput
 import androidx.compose.ui.test.swipeDown
 import androidx.compose.ui.test.swipeLeft
 import androidx.compose.ui.test.swipeRight
+import androidx.compose.ui.text.AnnotatedString
+import androidx.compose.ui.text.rememberTextMeasurer
+import androidx.compose.ui.unit.dp
 import androidx.paging.LoadState
 import androidx.paging.LoadStates
 import androidx.paging.PagingData
@@ -342,6 +347,170 @@ class LibraryScreenTest {
         assertTrue("the tab row should reflow in one direction, but the icons moved $samples", monotonic)
     }
 
+    @Test
+    @Config(qualifiers = "de-rDE-w320dp-h640dp-xhdpi")
+    fun aLongTabKeepsTheGearFullSizeAndScrollsIntoView() {
+        var labelWidth = 0f
+        composeRule.setContent {
+            SubtracksTheme {
+                labelWidth =
+                    rememberTextMeasurer()
+                        .measure(
+                            AnnotatedString(composeRule.activity.getString(LibraryTab.Playlists.label)),
+                            style = MaterialTheme.typography.titleSmall,
+                            maxLines = 1,
+                            softWrap = false,
+                        ).size.width
+                        .toFloat()
+                LibraryTabs(
+                    pagerState =
+                        remember {
+                            PagerState(
+                                currentPage = LibraryTab.Playlists.ordinal,
+                                pageCount = { LibraryTab.entries.size },
+                            )
+                        },
+                    onTabSelected = {},
+                    onOpenSettings = {},
+                    artwork = null,
+                )
+            }
+        }
+        composeRule.waitForIdle()
+
+        composeRule
+            .onNodeWithContentDescription(composeRule.activity.getString(R.string.navigation_tabs_settings))
+            .assertWidthIsEqualTo(40.dp)
+        assertTabFullyVisible(LibraryTab.Playlists, labelWidth)
+    }
+
+    @Test
+    @Config(qualifiers = "ar-rEG-w320dp-h640dp-xhdpi")
+    fun aLongTabScrollsIntoViewInRtl() {
+        var labelWidth = 0f
+        composeRule.setContent {
+            SubtracksTheme {
+                labelWidth =
+                    rememberTextMeasurer()
+                        .measure(
+                            AnnotatedString(composeRule.activity.getString(LibraryTab.Playlists.label)),
+                            style = MaterialTheme.typography.titleSmall,
+                            maxLines = 1,
+                            softWrap = false,
+                        ).size.width
+                        .toFloat()
+                LibraryTabs(
+                    pagerState =
+                        remember {
+                            PagerState(
+                                currentPage = LibraryTab.Playlists.ordinal,
+                                pageCount = { LibraryTab.entries.size },
+                            )
+                        },
+                    onTabSelected = {},
+                    onOpenSettings = {},
+                    artwork = null,
+                )
+            }
+        }
+        composeRule.waitForIdle()
+
+        composeRule
+            .onNodeWithContentDescription(composeRule.activity.getString(R.string.navigation_tabs_settings))
+            .assertWidthIsEqualTo(40.dp)
+        assertTabFullyVisible(LibraryTab.Playlists, labelWidth)
+    }
+
+    @Test
+    @Config(qualifiers = "de-rDE-w320dp-h640dp-xhdpi")
+    fun movingToALongTabScrollsItIntoView() {
+        val selectedTab = mutableStateOf(LibraryTab.Home)
+        var labelWidth = 0f
+        composeRule.setContent {
+            SubtracksTheme {
+                labelWidth =
+                    rememberTextMeasurer()
+                        .measure(
+                            AnnotatedString(composeRule.activity.getString(LibraryTab.Playlists.label)),
+                            style = MaterialTheme.typography.titleSmall,
+                            maxLines = 1,
+                            softWrap = false,
+                        ).size.width
+                        .toFloat()
+                LibraryScreen(
+                    selectedTab = selectedTab.value,
+                    onTabSelected = { selectedTab.value = it },
+                    albums = remember { flowOf(PagingData.empty<Album>()) },
+                    artists = remember { flowOf(PagingData.empty<Artist>()) },
+                    playlists = remember { flowOf(PagingData.empty<Playlist>()) },
+                    coverArt = { _, _ -> null },
+                    onAlbumClick = {},
+                    onArtistClick = {},
+                    onPlaylistClick = {},
+                    onSync = {},
+                    onOpenSettings = {},
+                )
+            }
+        }
+        composeRule.waitForIdle()
+
+        composeRule.runOnIdle { selectedTab.value = LibraryTab.Playlists }
+        val expected = with(composeRule.density) { TAB_LABEL_CHROME.toPx() } + labelWidth
+        composeRule.waitUntil(5_000) { tabBounds(LibraryTab.Playlists).width >= expected - 1f }
+
+        composeRule
+            .onNodeWithContentDescription(composeRule.activity.getString(R.string.navigation_tabs_settings))
+            .assertWidthIsEqualTo(40.dp)
+        assertTabFullyVisible(LibraryTab.Playlists, labelWidth)
+    }
+
+    private fun assertTabFullyVisible(
+        tab: LibraryTab,
+        labelWidth: Float,
+    ) {
+        val bounds = tabBounds(tab)
+        val expected = with(composeRule.density) { TAB_LABEL_CHROME.toPx() } + labelWidth
+        assertEquals("the selected tab should be shown in full, but was $bounds", expected, bounds.width, 1f)
+    }
+
+    @Test
+    @Config(qualifiers = "de-rDE-w320dp-h640dp-xhdpi")
+    fun theOfflineStripExplainsTheModeAndGoesOnline() {
+        var exited = false
+        composeRule.setContent {
+            SubtracksTheme {
+                LibraryScreen(
+                    selectedTab = LibraryTab.Playlists,
+                    onTabSelected = {},
+                    albums = remember { flowOf(PagingData.empty<Album>()) },
+                    artists = remember { flowOf(PagingData.empty<Artist>()) },
+                    playlists = remember { flowOf(PagingData.empty<Playlist>()) },
+                    coverArt = { _, _ -> null },
+                    onAlbumClick = {},
+                    onArtistClick = {},
+                    onPlaylistClick = {},
+                    onSync = {},
+                    onOpenSettings = {},
+                    offline = true,
+                    onExitOffline = { exited = true },
+                )
+            }
+        }
+        composeRule.waitForIdle()
+
+        composeRule.onNodeWithText(composeRule.activity.getString(R.string.offline_mode_banner)).performClick()
+        assertTrue("the offline strip should leave offline mode", exited)
+        composeRule
+            .onNodeWithContentDescription(composeRule.activity.getString(R.string.navigation_tabs_settings))
+            .assertWidthIsEqualTo(40.dp)
+    }
+
+    private fun tabBounds(tab: LibraryTab) =
+        composeRule
+            .onNodeWithContentDescription(composeRule.activity.getString(tab.label))
+            .fetchSemanticsNode()
+            .boundsInRoot
+
     private val settledLoadStates =
         LoadStates(
             refresh = LoadState.NotLoading(endOfPaginationReached = true),
@@ -378,3 +547,5 @@ class LibraryScreenTest {
             )
         }
 }
+
+private val TAB_LABEL_CHROME = 56.dp