Add shimmer loading effect for email list

Introduced ShimmerEffect composables to display a skeleton loading UI while emails are loading. Refactored MaskedEmailCard to disable shared element transitions during scrolling for smoother performance. Updated MaskedEmailListScreen to use the shimmer effect instead of a generic loading indicator.

app/src/main/java/com/fastmask/domain/model/MaskedEmail.kt

@@ -15,26 +15,23 @@ data class MaskedEmail(
     val url: String?,
     val emailPrefix: String?,
     val createdAt: Instant?,
-    val lastMessageAt: Instant?
+    val lastMessageAt: Instant?,
+    val formattedCreatedAt: String? = createdAt?.let { formatInstant(it) },
+    val formattedLastMessageAt: String? = lastMessageAt?.let { formatInstant(it) }
 ) {
     val displayName: String
         get() = description?.takeIf { it.isNotBlank() }
             ?: forDomain?.takeIf { it.isNotBlank() }
             ?: email.substringBefore("@")
 
-    val formattedCreatedAt: String?
-        get() = createdAt?.let { formatInstant(it) }
-
-    val formattedLastMessageAt: String?
-        get() = lastMessageAt?.let { formatInstant(it) }
-
     val isActive: Boolean
         get() = state == EmailState.ENABLED || state == EmailState.PENDING
 
-    private fun formatInstant(instant: Instant): String {
-        val formatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM)
+    companion object {
+        private val formatter = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.MEDIUM)
             .withZone(ZoneId.systemDefault())
-        return formatter.format(instant)
+
+        fun formatInstant(instant: Instant): String = formatter.format(instant)
     }
 }
 

app/src/main/java/com/fastmask/ui/components/MaskedEmailCard.kt

@@ -46,7 +46,8 @@ fun MaskedEmailCard(
     onClick: () -> Unit,
     sharedTransitionScope: SharedTransitionScope,
     animatedContentScope: AnimatedContentScope,
-    modifier: Modifier = Modifier
+    modifier: Modifier = Modifier,
+    isScrolling: Boolean = false
 ) {
     val haptic = LocalHapticFeedback.current
 
@@ -61,9 +62,13 @@ fun MaskedEmailCard(
         Card(
             modifier = modifier
                 .fillMaxWidth()
-                .sharedBounds(
-                    sharedContentState = rememberSharedContentState(key = "card-${maskedEmail.id}"),
-                    animatedVisibilityScope = animatedContentScope
+                .then(
+                    if (!isScrolling) {
+                        Modifier.sharedBounds(
+                            sharedContentState = rememberSharedContentState(key = "card-${maskedEmail.id}"),
+                            animatedVisibilityScope = animatedContentScope
+                        )
+                    } else Modifier
                 )
                 .clickable {
                     haptic.performHapticFeedback(HapticFeedbackType.LongPress)
@@ -85,10 +90,12 @@ fun MaskedEmailCard(
             ) {
                 StatusIcon(
                     state = maskedEmail.state,
-                    modifier = Modifier.sharedElement(
-                        state = rememberSharedContentState(key = "icon-${maskedEmail.id}"),
-                        animatedVisibilityScope = animatedContentScope
-                    )
+                    modifier = if (!isScrolling) {
+                        Modifier.sharedElement(
+                            state = rememberSharedContentState(key = "icon-${maskedEmail.id}"),
+                            animatedVisibilityScope = animatedContentScope
+                        )
+                    } else Modifier
                 )
                 Spacer(modifier = Modifier.width(16.dp))
                 Column(modifier = Modifier.weight(1f)) {
@@ -97,10 +104,12 @@ fun MaskedEmailCard(
                         style = MaterialTheme.typography.titleMedium,
                         maxLines = 1,
                         overflow = TextOverflow.Ellipsis,
-                        modifier = Modifier.sharedElement(
-                            state = rememberSharedContentState(key = "title-${maskedEmail.id}"),
-                            animatedVisibilityScope = animatedContentScope
-                        )
+                        modifier = if (!isScrolling) {
+                            Modifier.sharedElement(
+                                state = rememberSharedContentState(key = "title-${maskedEmail.id}"),
+                                animatedVisibilityScope = animatedContentScope
+                            )
+                        } else Modifier
                     )
                     Text(
                         text = maskedEmail.email,
@@ -108,10 +117,12 @@ fun MaskedEmailCard(
                         color = MaterialTheme.colorScheme.onSurfaceVariant,
                         maxLines = 1,
                         overflow = TextOverflow.Ellipsis,
-                        modifier = Modifier.sharedElement(
-                            state = rememberSharedContentState(key = "email-${maskedEmail.id}"),
-                            animatedVisibilityScope = animatedContentScope
-                        )
+                        modifier = if (!isScrolling) {
+                            Modifier.sharedElement(
+                                state = rememberSharedContentState(key = "email-${maskedEmail.id}"),
+                                animatedVisibilityScope = animatedContentScope
+                            )
+                        } else Modifier
                     )
                     maskedEmail.forDomain?.let { domain ->
                         Text(

app/src/main/java/com/fastmask/ui/components/ShimmerEffect.kt

@@ -0,0 +1,131 @@
+package com.fastmask.ui.components
+
+import androidx.compose.animation.core.LinearEasing
+import androidx.compose.animation.core.RepeatMode
+import androidx.compose.animation.core.animateFloat
+import androidx.compose.animation.core.infiniteRepeatable
+import androidx.compose.animation.core.rememberInfiniteTransition
+import androidx.compose.animation.core.tween
+import androidx.compose.foundation.background
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.PaddingValues
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.Spacer
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.height
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.layout.width
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.foundation.shape.RoundedCornerShape
+import androidx.compose.material3.Card
+import androidx.compose.material3.CardDefaults
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.geometry.Offset
+import androidx.compose.ui.graphics.Brush
+import androidx.compose.ui.unit.dp
+
+@Composable
+fun ShimmerEmailCard(
+    modifier: Modifier = Modifier
+) {
+    val shimmerColors = listOf(
+        MaterialTheme.colorScheme.surfaceContainerHigh.copy(alpha = 0.6f),
+        MaterialTheme.colorScheme.surfaceContainerHighest.copy(alpha = 0.2f),
+        MaterialTheme.colorScheme.surfaceContainerHigh.copy(alpha = 0.6f)
+    )
+
+    val transition = rememberInfiniteTransition(label = "shimmer")
+    val translateAnim by transition.animateFloat(
+        initialValue = 0f,
+        targetValue = 1000f,
+        animationSpec = infiniteRepeatable(
+            animation = tween(durationMillis = 1000, easing = LinearEasing),
+            repeatMode = RepeatMode.Restart
+        ),
+        label = "shimmer_translate"
+    )
+
+    val brush = Brush.linearGradient(
+        colors = shimmerColors,
+        start = Offset(translateAnim - 500f, translateAnim - 500f),
+        end = Offset(translateAnim, translateAnim)
+    )
+
+    Card(
+        modifier = modifier.fillMaxWidth(),
+        elevation = CardDefaults.cardElevation(defaultElevation = 1.dp),
+        colors = CardDefaults.cardColors(
+            containerColor = MaterialTheme.colorScheme.surfaceContainerLow
+        )
+    ) {
+        Row(
+            modifier = Modifier
+                .fillMaxWidth()
+                .padding(16.dp),
+            verticalAlignment = Alignment.CenterVertically
+        ) {
+            // Status icon placeholder
+            Box(
+                modifier = Modifier
+                    .size(40.dp)
+                    .clip(CircleShape)
+                    .background(brush)
+            )
+            Spacer(modifier = Modifier.width(16.dp))
+            Column(modifier = Modifier.weight(1f)) {
+                // Title placeholder
+                Box(
+                    modifier = Modifier
+                        .fillMaxWidth(0.6f)
+                        .height(20.dp)
+                        .clip(RoundedCornerShape(4.dp))
+                        .background(brush)
+                )
+                Spacer(modifier = Modifier.height(8.dp))
+                // Email placeholder
+                Box(
+                    modifier = Modifier
+                        .fillMaxWidth(0.8f)
+                        .height(16.dp)
+                        .clip(RoundedCornerShape(4.dp))
+                        .background(brush)
+                )
+                Spacer(modifier = Modifier.height(6.dp))
+                // Domain placeholder
+                Box(
+                    modifier = Modifier
+                        .fillMaxWidth(0.4f)
+                        .height(14.dp)
+                        .clip(RoundedCornerShape(4.dp))
+                        .background(brush)
+                )
+            }
+        }
+    }
+}
+
+@Composable
+fun ShimmerEmailList(
+    modifier: Modifier = Modifier,
+    itemCount: Int = 8
+) {
+    LazyColumn(
+        modifier = modifier.fillMaxSize(),
+        contentPadding = PaddingValues(16.dp),
+        verticalArrangement = Arrangement.spacedBy(8.dp)
+    ) {
+        items(itemCount) {
+            ShimmerEmailCard()
+        }
+    }
+}

app/src/main/java/com/fastmask/ui/list/MaskedEmailListScreen.kt

@@ -57,8 +57,8 @@ import androidx.compose.ui.platform.LocalHapticFeedback
 import androidx.hilt.navigation.compose.hiltViewModel
 import com.fastmask.domain.model.MaskedEmail
 import com.fastmask.ui.components.ErrorMessage
-import com.fastmask.ui.components.LoadingIndicator
 import com.fastmask.ui.components.MaskedEmailCard
+import com.fastmask.ui.components.ShimmerEmailList
 import kotlinx.coroutines.flow.collectLatest
 
 @OptIn(ExperimentalMaterial3Api::class, ExperimentalSharedTransitionApi::class)
@@ -77,6 +77,10 @@ fun MaskedEmailListScreen(
     val listState = rememberLazyListState()
     val haptic = LocalHapticFeedback.current
 
+    val isScrolling by remember {
+        derivedStateOf { listState.isScrollInProgress }
+    }
+
     val expandedFab by remember {
         derivedStateOf {
             listState.firstVisibleItemIndex == 0 && listState.firstVisibleItemScrollOffset == 0
@@ -196,7 +200,7 @@ fun MaskedEmailListScreen(
 
             when {
                 uiState.isLoading && uiState.emails.isEmpty() -> {
-                    LoadingIndicator()
+                    ShimmerEmailList()
                 }
 
                 uiState.error != null && uiState.emails.isEmpty() -> {
@@ -214,7 +218,8 @@ fun MaskedEmailListScreen(
                         onEmailClick = { email -> onNavigateToDetail(email.id) },
                         listState = listState,
                         sharedTransitionScope = sharedTransitionScope,
-                        animatedContentScope = animatedContentScope
+                        animatedContentScope = animatedContentScope,
+                        isScrolling = isScrolling
                     )
                 }
             }
@@ -310,7 +315,8 @@ private fun EmailList(
     onEmailClick: (MaskedEmail) -> Unit,
     listState: LazyListState,
     sharedTransitionScope: SharedTransitionScope,
-    animatedContentScope: AnimatedContentScope
+    animatedContentScope: AnimatedContentScope,
+    isScrolling: Boolean
 ) {
     PullToRefreshBox(
         isRefreshing = isRefreshing,
@@ -343,7 +349,8 @@ private fun EmailList(
                         onClick = { onEmailClick(email) },
                         sharedTransitionScope = sharedTransitionScope,
                         animatedContentScope = animatedContentScope,
-                        modifier = Modifier.animateItem()
+                        modifier = Modifier.animateItem(),
+                        isScrolling = isScrolling
                     )
                 }
             }