feat(connectivity): add offline resilience with server reachability checks

app/src/main/java/hu/bbara/purefin/ui/screen/AppScreen.kt

@@ -13,11 +13,11 @@ import androidx.compose.material3.TextButton
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
 import androidx.compose.runtime.getValue
-import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.compose.runtime.remember
 import androidx.compose.ui.Modifier
 import androidx.hilt.navigation.compose.hiltViewModel
 import androidx.lifecycle.compose.LifecycleResumeEffect
+import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.navigation3.runtime.NavBackStack
 import androidx.navigation3.runtime.NavKey
 import androidx.navigation3.runtime.entryProvider
@@ -46,6 +46,7 @@ fun AppScreen(
     val nextUp by viewModel.nextUp.collectAsStateWithLifecycle()
     val isRefreshing by viewModel.isRefreshing.collectAsStateWithLifecycle()
     val isOnline by viewModel.isOnline.collectAsStateWithLifecycle()
+    val isCheckingConnection by viewModel.isCheckingConnection.collectAsStateWithLifecycle()
     val isCheckingForUpdates by updateViewModel.isCheckingForUpdates.collectAsStateWithLifecycle()
     val availableUpdate by updateViewModel.availableUpdate.collectAsStateWithLifecycle()
     val navigationManager = LocalNavigationManager.current
@@ -133,6 +134,8 @@ fun AppScreen(
             DownloadsScreen(
                 selectedTab = selectedTab,
                 isOnline = isOnline,
+                isCheckingConnection = isCheckingConnection,
+                onCheckConnection = viewModel::checkConnection,
                 onTabSelected = onTabSelected,
                 modifier = Modifier.fillMaxSize()
             )

app/src/main/java/hu/bbara/purefin/ui/screen/download/DownloadsScreen.kt

@@ -10,12 +10,15 @@ import androidx.compose.ui.Modifier
 import hu.bbara.purefin.ui.screen.AppBottomBar
 import hu.bbara.purefin.ui.screen.download.components.DownloadsContent
 import hu.bbara.purefin.ui.screen.home.components.DefaultTopBar
+import hu.bbara.purefin.ui.screen.home.components.DefaultTopBarTextButton
 
 @OptIn(ExperimentalMaterial3Api::class)
 @Composable
 fun DownloadsScreen(
     selectedTab: Int,
     isOnline: Boolean,
+    isCheckingConnection: Boolean,
+    onCheckConnection: () -> Unit,
     onTabSelected: (Int) -> Unit,
     modifier: Modifier = Modifier
 ) {
@@ -23,7 +26,19 @@ fun DownloadsScreen(
         modifier = modifier.fillMaxSize(),
         containerColor = MaterialTheme.colorScheme.background,
         contentColor = MaterialTheme.colorScheme.onBackground,
-        topBar = { DefaultTopBar() },
+        topBar = {
+            DefaultTopBar(
+                rightActions = {
+                    if (!isOnline) {
+                        DefaultTopBarTextButton(
+                            text = if (isCheckingConnection) "Checking…" else "Check connection",
+                            onClick = onCheckConnection,
+                            enabled = !isCheckingConnection
+                        )
+                    }
+                }
+            )
+        },
         bottomBar = {
             AppBottomBar(
                 selectedTab = selectedTab,

app/src/main/java/hu/bbara/purefin/ui/screen/download/components/DownloadsContent.kt

@@ -5,14 +5,17 @@ import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
 import androidx.compose.foundation.layout.PaddingValues
 import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.widthIn
 import androidx.compose.foundation.lazy.grid.GridCells
 import androidx.compose.foundation.lazy.grid.GridItemSpan
 import androidx.compose.foundation.lazy.grid.LazyVerticalGrid
 import androidx.compose.foundation.lazy.grid.items
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.outlined.Download
+import androidx.compose.material3.Card
 import androidx.compose.material3.Icon
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text

app/src/main/java/hu/bbara/purefin/ui/screen/home/components/DefaultTopBar.kt

@@ -5,18 +5,23 @@ import androidx.compose.animation.SharedTransitionScope
 import androidx.compose.animation.fadeIn
 import androidx.compose.animation.fadeOut
 import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.PaddingValues
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.RowScope
+import androidx.compose.foundation.layout.height
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.layout.size
 import androidx.compose.foundation.shape.CircleShape
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.outlined.Search
+import androidx.compose.material3.ButtonDefaults
 import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.Icon
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.IconButtonColors
 import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
 import androidx.compose.material3.TopAppBar
 import androidx.compose.material3.TopAppBarDefaults
 import androidx.compose.material3.TopAppBarScrollBehavior
@@ -114,6 +119,37 @@ fun DefaultTopBarIconButton(
     }
 }
 
+@Composable
+fun DefaultTopBarTextButton(
+    text: String,
+    onClick: () -> Unit,
+    modifier: Modifier = Modifier,
+    enabled: Boolean = true,
+) {
+    val scheme = MaterialTheme.colorScheme
+
+    TextButton(
+        onClick = onClick,
+        enabled = enabled,
+        shape = CircleShape,
+        colors = ButtonDefaults.textButtonColors(
+            containerColor = scheme.surface,
+            contentColor = scheme.onSurface,
+            disabledContainerColor = scheme.surface,
+            disabledContentColor = scheme.onSurface
+        ),
+        contentPadding = PaddingValues(horizontal = 18.dp),
+        modifier = modifier
+            .height(50.dp)
+            .clip(CircleShape),
+    ) {
+        Text(
+            text = text,
+            style = MaterialTheme.typography.labelLarge,
+        )
+    }
+}
+
 @OptIn(ExperimentalSharedTransitionApi::class)
 @Composable
 fun DefaultTopBarSearchButton(