refactor: replace ListView with CustomScrollView and SliverList in chat page for improved performance

- Updated the loading messages list to use CustomScrollView and SliverList, enhancing the layout and performance during message loading.
- Refactored the actual messages display to utilize OptimizedSliverList, allowing for better lazy loading and smoother scrolling.
- Adjusted padding and cache extent settings to optimize the user experience while navigating through messages.
- Streamlined the message rendering logic to improve maintainability and responsiveness of the chat interface.

lib/features/chat/views/chat_page.dart

@@ -687,82 +687,95 @@ class _ChatPageState extends ConsumerState<ChatPage> {
   }
 
   Widget _buildLoadingMessagesList() {
-    return ListView.builder(
+    // Use slivers to align with the actual messages view.
+    // Do not attach the primary scroll controller here to avoid
+    // AnimatedSwitcher attaching the same controller twice.
+    return CustomScrollView(
       key: const ValueKey('loading_messages'),
-      // Do not reuse the primary scroll controller here to avoid
-      // attaching the same controller to multiple lists during
-      // AnimatedSwitcher transitions.
       controller: null,
-      padding: const EdgeInsets.fromLTRB(
-        Spacing.lg,
-        Spacing.md,
-        Spacing.lg,
-        Spacing.lg,
-      ),
-      physics:
-          const AlwaysScrollableScrollPhysics(), // Allow pull-to-refresh while loading
-      // Modest cache extent to avoid offscreen overwork but keep shimmer smooth
+      physics: const AlwaysScrollableScrollPhysics(),
       cacheExtent: 300,
-      itemCount: 6,
-      itemBuilder: (context, index) {
-        final isUser = index.isOdd;
-        return Align(
-          alignment: isUser ? Alignment.centerRight : Alignment.centerLeft,
-          child: Container(
-            margin: const EdgeInsets.only(bottom: Spacing.md),
-            constraints: BoxConstraints(
-              maxWidth: MediaQuery.of(context).size.width * 0.82,
-            ),
-            padding: const EdgeInsets.all(Spacing.md),
-            decoration: BoxDecoration(
-              color: isUser
-                  ? context.conduitTheme.buttonPrimary.withValues(alpha: 0.15)
-                  : context.conduitTheme.cardBackground,
-              borderRadius: BorderRadius.circular(
-                AppBorderRadius.messageBubble,
-              ),
-              border: Border.all(
-                color: context.conduitTheme.cardBorder,
-                width: BorderWidth.regular,
-              ),
-              boxShadow: ConduitShadows.messageBubble(context),
-            ),
-            child: Column(
-              crossAxisAlignment: CrossAxisAlignment.start,
-              children: [
-                Container(
-                  height: 14,
-                  width: index % 3 == 0 ? 140 : 220,
-                  decoration: BoxDecoration(
-                    color: context.conduitTheme.shimmerBase,
-                    borderRadius: BorderRadius.circular(AppBorderRadius.xs),
-                  ),
-                ).animate().shimmer(duration: AnimationDuration.slow),
-                const SizedBox(height: Spacing.xs),
-                Container(
-                  height: 14,
-                  width: double.infinity,
-                  decoration: BoxDecoration(
-                    color: context.conduitTheme.shimmerBase,
-                    borderRadius: BorderRadius.circular(AppBorderRadius.xs),
-                  ),
-                ).animate().shimmer(duration: AnimationDuration.slow),
-                if (index % 3 != 0) ...[
-                  const SizedBox(height: Spacing.xs),
-                  Container(
-                    height: 14,
-                    width: index % 2 == 0 ? 180 : 120,
-                    decoration: BoxDecoration(
-                      color: context.conduitTheme.shimmerBase,
-                      borderRadius: BorderRadius.circular(AppBorderRadius.xs),
-                    ),
-                  ).animate().shimmer(duration: AnimationDuration.slow),
-                ],
-              ],
-            ),
+      slivers: [
+        SliverPadding(
+          padding: const EdgeInsets.fromLTRB(
+            Spacing.lg,
+            Spacing.md,
+            Spacing.lg,
+            Spacing.lg,
           ),
-        );
-      },
+          sliver: SliverList(
+            delegate: SliverChildBuilderDelegate((context, index) {
+              final isUser = index.isOdd;
+              return Align(
+                alignment: isUser
+                    ? Alignment.centerRight
+                    : Alignment.centerLeft,
+                child: Container(
+                  margin: const EdgeInsets.only(bottom: Spacing.md),
+                  constraints: BoxConstraints(
+                    maxWidth: MediaQuery.of(context).size.width * 0.82,
+                  ),
+                  padding: const EdgeInsets.all(Spacing.md),
+                  decoration: BoxDecoration(
+                    color: isUser
+                        ? context.conduitTheme.buttonPrimary.withValues(
+                            alpha: 0.15,
+                          )
+                        : context.conduitTheme.cardBackground,
+                    borderRadius: BorderRadius.circular(
+                      AppBorderRadius.messageBubble,
+                    ),
+                    border: Border.all(
+                      color: context.conduitTheme.cardBorder,
+                      width: BorderWidth.regular,
+                    ),
+                    boxShadow: ConduitShadows.messageBubble(context),
+                  ),
+                  child: Column(
+                    crossAxisAlignment: CrossAxisAlignment.start,
+                    children: [
+                      Container(
+                        height: 14,
+                        width: index % 3 == 0 ? 140 : 220,
+                        decoration: BoxDecoration(
+                          color: context.conduitTheme.shimmerBase,
+                          borderRadius: BorderRadius.circular(
+                            AppBorderRadius.xs,
+                          ),
+                        ),
+                      ).animate().shimmer(duration: AnimationDuration.slow),
+                      const SizedBox(height: Spacing.xs),
+                      Container(
+                        height: 14,
+                        width: double.infinity,
+                        decoration: BoxDecoration(
+                          color: context.conduitTheme.shimmerBase,
+                          borderRadius: BorderRadius.circular(
+                            AppBorderRadius.xs,
+                          ),
+                        ),
+                      ).animate().shimmer(duration: AnimationDuration.slow),
+                      if (index % 3 != 0) ...[
+                        const SizedBox(height: Spacing.xs),
+                        Container(
+                          height: 14,
+                          width: index % 2 == 0 ? 180 : 120,
+                          decoration: BoxDecoration(
+                            color: context.conduitTheme.shimmerBase,
+                            borderRadius: BorderRadius.circular(
+                              AppBorderRadius.xs,
+                            ),
+                          ),
+                        ).animate().shimmer(duration: AnimationDuration.slow),
+                      ],
+                    ],
+                  ),
+                ),
+              );
+            }, childCount: 6),
+          ),
+        ),
+      ],
     );
   }
 
@@ -805,102 +818,109 @@ class _ChatPageState extends ConsumerState<ChatPage> {
       });
     }
 
-    return OptimizedList<ChatMessage>(
+    return CustomScrollView(
       key: const ValueKey('actual_messages'),
-      scrollController: _scrollController,
+      controller: _scrollController,
       physics: const AlwaysScrollableScrollPhysics(),
-      items: messages,
-      padding: const EdgeInsets.fromLTRB(
-        Spacing.lg,
-        Spacing.md,
-        Spacing.lg,
-        Spacing.lg,
-      ),
-      itemBuilder: (context, message, index) {
-        final isUser = message.role == 'user';
-        final isStreaming = message.isStreaming;
+      cacheExtent: 600,
+      slivers: [
+        SliverPadding(
+          padding: const EdgeInsets.fromLTRB(
+            Spacing.lg,
+            Spacing.md,
+            Spacing.lg,
+            Spacing.lg,
+          ),
+          sliver: OptimizedSliverList<ChatMessage>(
+            items: messages,
+            itemBuilder: (context, message, index) {
+              final isUser = message.role == 'user';
+              final isStreaming = message.isStreaming;
 
-        final isSelected = _selectedMessageIds.contains(message.id);
+              final isSelected = _selectedMessageIds.contains(message.id);
 
-        // Resolve a friendly model display name for message headers
-        String? displayModelName;
-        Model? matchedModel;
-        final rawModel = message.model;
-        if (rawModel != null && rawModel.isNotEmpty) {
-          final modelsAsync = ref.watch(modelsProvider);
-          if (modelsAsync.hasValue) {
-            final models = modelsAsync.value!;
-            try {
-              // Prefer exact ID match; fall back to exact name match
-              final match = models.firstWhere(
-                (m) => m.id == rawModel || m.name == rawModel,
+              // Resolve a friendly model display name for message headers
+              String? displayModelName;
+              Model? matchedModel;
+              final rawModel = message.model;
+              if (rawModel != null && rawModel.isNotEmpty) {
+                final modelsAsync = ref.watch(modelsProvider);
+                if (modelsAsync.hasValue) {
+                  final models = modelsAsync.value!;
+                  try {
+                    // Prefer exact ID match; fall back to exact name match
+                    final match = models.firstWhere(
+                      (m) => m.id == rawModel || m.name == rawModel,
+                    );
+                    matchedModel = match;
+                    displayModelName = _formatModelDisplayName(match.name);
+                  } catch (_) {
+                    // As a fallback, format the raw value to be more readable
+                    displayModelName = _formatModelDisplayName(rawModel);
+                  }
+                } else {
+                  // Models not loaded yet; format raw value for readability
+                  displayModelName = _formatModelDisplayName(rawModel);
+                }
+              }
+
+              final modelIconUrl = resolveModelIconUrlForModel(
+                apiService,
+                matchedModel,
               );
-              matchedModel = match;
-              displayModelName = _formatModelDisplayName(match.name);
-            } catch (_) {
-              // As a fallback, format the raw value to be more readable
-              displayModelName = _formatModelDisplayName(rawModel);
-            }
-          } else {
-            // Models not loaded yet; format raw value for readability
-            displayModelName = _formatModelDisplayName(rawModel);
-          }
-        }
 
-        final modelIconUrl = resolveModelIconUrlForModel(
-          apiService,
-          matchedModel,
-        );
+              // Wrap message in selection container if in selection mode
+              Widget messageWidget;
 
-        // Wrap message in selection container if in selection mode
-        Widget messageWidget;
+              // Use documentation style for assistant messages, bubble for user messages
+              if (isUser) {
+                messageWidget = UserMessageBubble(
+                  key: ValueKey('user-${message.id}'),
+                  message: message,
+                  isUser: isUser,
+                  isStreaming: isStreaming,
+                  modelName: displayModelName,
+                  onCopy: () => _copyMessage(message.content),
+                  onRegenerate: () => _regenerateMessage(message),
+                );
+              } else {
+                messageWidget = assistant.AssistantMessageWidget(
+                  key: ValueKey('assistant-${message.id}'),
+                  message: message,
+                  isStreaming: isStreaming,
+                  modelName: displayModelName,
+                  modelIconUrl: modelIconUrl,
+                  onCopy: () => _copyMessage(message.content),
+                  onRegenerate: () => _regenerateMessage(message),
+                );
+              }
 
-        // Use documentation style for assistant messages, bubble for user messages
-        if (isUser) {
-          messageWidget = UserMessageBubble(
-            key: ValueKey('user-${message.id}'),
-            message: message,
-            isUser: isUser,
-            isStreaming: isStreaming,
-            modelName: displayModelName,
-            onCopy: () => _copyMessage(message.content),
-            onRegenerate: () => _regenerateMessage(message),
-          );
-        } else {
-          messageWidget = assistant.AssistantMessageWidget(
-            key: ValueKey('assistant-${message.id}'),
-            message: message,
-            isStreaming: isStreaming,
-            modelName: displayModelName,
-            modelIconUrl: modelIconUrl,
-            onCopy: () => _copyMessage(message.content),
-            onRegenerate: () => _regenerateMessage(message),
-          );
-        }
-
-        // Add selection functionality if in selection mode
-        if (_isSelectionMode) {
-          return _SelectableMessageWrapper(
-            isSelected: isSelected,
-            onTap: () => _toggleMessageSelection(message.id),
-            onLongPress: () {
-              if (!_isSelectionMode) {
-                _toggleSelectionMode();
-                _toggleMessageSelection(message.id);
+              // Add selection functionality if in selection mode
+              if (_isSelectionMode) {
+                return _SelectableMessageWrapper(
+                  isSelected: isSelected,
+                  onTap: () => _toggleMessageSelection(message.id),
+                  onLongPress: () {
+                    if (!_isSelectionMode) {
+                      _toggleSelectionMode();
+                      _toggleMessageSelection(message.id);
+                    }
+                  },
+                  child: messageWidget,
+                );
+              } else {
+                return GestureDetector(
+                  onLongPress: () {
+                    _toggleSelectionMode();
+                    _toggleMessageSelection(message.id);
+                  },
+                  child: messageWidget,
+                );
               }
             },
-            child: messageWidget,
-          );
-        } else {
-          return GestureDetector(
-            onLongPress: () {
-              _toggleSelectionMode();
-              _toggleMessageSelection(message.id);
-            },
-            child: messageWidget,
-          );
-        }
-      },
+          ),
+        ),
+      ],
     );
   }
 

lib/shared/widgets/optimized_list.dart

@@ -4,249 +4,7 @@ import 'skeleton_loader.dart';
 import 'package:conduit/l10n/app_localizations.dart';
 import 'improved_loading_states.dart';
 
-/// Optimized list widget with virtualization and performance enhancements
-class OptimizedList<T> extends ConsumerStatefulWidget {
-  final List<T> items;
-  final Widget Function(BuildContext context, T item, int index) itemBuilder;
-  final Widget? separatorBuilder;
-  final Widget? loadingWidget;
-  final Widget? emptyWidget;
-  final String? emptyMessage;
-  final Future<void> Function()? onRefresh;
-  final VoidCallback? onLoadMore;
-  final bool hasMore;
-  final bool isLoading;
-  final EdgeInsetsGeometry? padding;
-  final ScrollController? scrollController;
-  final ScrollPhysics? physics;
-  final bool shrinkWrap;
-  final Axis scrollDirection;
-  final bool reverse;
-  final double? cacheExtent;
-  final int? itemExtent;
-  final bool addAutomaticKeepAlives;
-  final bool addRepaintBoundaries;
-  final bool enablePagination;
-  final double paginationThreshold;
-  final ScrollViewKeyboardDismissBehavior keyboardDismissBehavior;
-
-  const OptimizedList({
-    super.key,
-    required this.items,
-    required this.itemBuilder,
-    this.separatorBuilder,
-    this.loadingWidget,
-    this.emptyWidget,
-    this.emptyMessage,
-    this.onRefresh,
-    this.onLoadMore,
-    this.hasMore = false,
-    this.isLoading = false,
-    this.padding,
-    this.scrollController,
-    this.physics,
-    this.shrinkWrap = false,
-    this.scrollDirection = Axis.vertical,
-    this.reverse = false,
-    this.cacheExtent,
-    this.itemExtent,
-    this.addAutomaticKeepAlives = true,
-    this.addRepaintBoundaries = true,
-    this.enablePagination = false,
-    this.paginationThreshold = 0.8,
-    this.keyboardDismissBehavior = ScrollViewKeyboardDismissBehavior.onDrag,
-  });
-
-  @override
-  ConsumerState<OptimizedList<T>> createState() => _OptimizedListState<T>();
-}
-
-class _OptimizedListState<T> extends ConsumerState<OptimizedList<T>> {
-  late ScrollController _scrollController;
-  bool _isLoadingMore = false;
-
-  @override
-  void initState() {
-    super.initState();
-    _scrollController = widget.scrollController ?? ScrollController();
-
-    if (widget.enablePagination) {
-      _scrollController.addListener(_onScroll);
-    }
-  }
-
-  @override
-  void dispose() {
-    if (widget.scrollController == null) {
-      _scrollController.dispose();
-    }
-    super.dispose();
-  }
-
-  void _onScroll() {
-    if (!widget.enablePagination ||
-        _isLoadingMore ||
-        !widget.hasMore ||
-        widget.onLoadMore == null) {
-      return;
-    }
-
-    final maxScroll = _scrollController.position.maxScrollExtent;
-    final currentScroll = _scrollController.position.pixels;
-    final threshold = maxScroll * widget.paginationThreshold;
-
-    if (currentScroll >= threshold) {
-      _loadMore();
-    }
-  }
-
-  Future<void> _loadMore() async {
-    if (_isLoadingMore) return;
-
-    setState(() {
-      _isLoadingMore = true;
-    });
-
-    try {
-      widget.onLoadMore?.call();
-    } finally {
-      if (mounted) {
-        setState(() {
-          _isLoadingMore = false;
-        });
-      }
-    }
-  }
-
-  @override
-  Widget build(BuildContext context) {
-    // Show loading state
-    if (widget.isLoading && widget.items.isEmpty) {
-      return widget.loadingWidget ?? _buildDefaultLoadingWidget();
-    }
-
-    // Show empty state
-    if (widget.items.isEmpty) {
-      return widget.emptyWidget ??
-          ImprovedEmptyState(
-            title: AppLocalizations.of(context)!.noItems,
-            subtitle:
-                widget.emptyMessage ??
-                AppLocalizations.of(context)!.noItemsToDisplay,
-            icon: Icons.inbox_outlined,
-          );
-    }
-
-    // Build the list
-    Widget listWidget;
-
-    final ScrollPhysics effectivePhysics =
-        widget.physics ??
-        (widget.onRefresh != null
-            ? const AlwaysScrollableScrollPhysics()
-            : const ClampingScrollPhysics());
-
-    final reverse = widget.reverse;
-
-    if (widget.separatorBuilder != null) {
-      listWidget = ListView.separated(
-        controller: _scrollController,
-        padding: widget.padding,
-        physics: effectivePhysics,
-        keyboardDismissBehavior: widget.keyboardDismissBehavior,
-        shrinkWrap: widget.shrinkWrap,
-        scrollDirection: widget.scrollDirection,
-        reverse: reverse,
-        cacheExtent: widget.cacheExtent ?? 250.0,
-        addAutomaticKeepAlives: widget.addAutomaticKeepAlives,
-        addRepaintBoundaries: widget.addRepaintBoundaries,
-        itemCount: widget.items.length + (widget.hasMore ? 1 : 0),
-        separatorBuilder: (context, index) => widget.separatorBuilder!,
-        itemBuilder: (context, index) {
-          if (index >= widget.items.length) {
-            return _buildLoadMoreIndicator();
-          }
-
-          return _buildOptimizedItem(context, index, reverse: reverse);
-        },
-      );
-    } else {
-      listWidget = ListView.builder(
-        controller: _scrollController,
-        padding: widget.padding,
-        physics: effectivePhysics,
-        keyboardDismissBehavior: widget.keyboardDismissBehavior,
-        shrinkWrap: widget.shrinkWrap,
-        scrollDirection: widget.scrollDirection,
-        reverse: reverse,
-        cacheExtent: widget.cacheExtent ?? 250.0,
-        addAutomaticKeepAlives: widget.addAutomaticKeepAlives,
-        addRepaintBoundaries: widget.addRepaintBoundaries,
-        itemCount: widget.items.length + (widget.hasMore ? 1 : 0),
-        itemExtent: widget.itemExtent?.toDouble(),
-        itemBuilder: (context, index) {
-          if (index >= widget.items.length) {
-            return _buildLoadMoreIndicator();
-          }
-
-          return _buildOptimizedItem(context, index, reverse: reverse);
-        },
-      );
-    }
-
-    // Add refresh indicator if enabled
-    if (widget.onRefresh != null) {
-      return RefreshIndicator(onRefresh: widget.onRefresh!, child: listWidget);
-    }
-
-    return listWidget;
-  }
-
-  Widget _buildOptimizedItem(
-    BuildContext context,
-    int index, {
-    required bool reverse,
-  }) {
-    final effectiveIndex = reverse ? widget.items.length - index - 1 : index;
-    final item = widget.items[effectiveIndex];
-
-    if (widget.addRepaintBoundaries) {
-      return RepaintBoundary(
-        child: widget.itemBuilder(context, item, effectiveIndex),
-      );
-    }
-
-    return widget.itemBuilder(context, item, effectiveIndex);
-  }
-
-  Widget _buildLoadMoreIndicator() {
-    return Container(
-      padding: const EdgeInsets.all(16.0),
-      alignment: Alignment.center,
-      child: _isLoadingMore
-          ? const CircularProgressIndicator()
-          : TextButton(
-              onPressed: _loadMore,
-              child: Text(AppLocalizations.of(context)!.loadMore),
-            ),
-    );
-  }
-
-  Widget _buildDefaultLoadingWidget() {
-    return ListView.builder(
-      padding: widget.padding,
-      physics: const NeverScrollableScrollPhysics(),
-      shrinkWrap: true,
-      itemCount: 5,
-      itemBuilder: (context, index) => const Padding(
-        padding: EdgeInsets.symmetric(horizontal: 16, vertical: 8),
-        child: SkeletonLoader(height: 80),
-      ),
-    );
-  }
-}
-
-/// Sliver version of OptimizedList for use in CustomScrollView
+/// Sliver version of an optimized list for use in CustomScrollView.
 class OptimizedSliverList<T> extends ConsumerWidget {
   final List<T> items;
   final Widget Function(BuildContext context, T item, int index) itemBuilder;
@@ -275,14 +33,14 @@ class OptimizedSliverList<T> extends ConsumerWidget {
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
-    // Show loading state
+    // Loading state
     if (isLoading && items.isEmpty) {
       return SliverToBoxAdapter(
         child: loadingWidget ?? _buildDefaultLoadingWidget(),
       );
     }
 
-    // Show empty state
+    // Empty state
     if (items.isEmpty) {
       return SliverToBoxAdapter(
         child:
@@ -300,17 +58,16 @@ class OptimizedSliverList<T> extends ConsumerWidget {
       );
     }
 
-    // Build the list
+    // List content
     return SliverList(
       delegate: SliverChildBuilderDelegate(
         (context, index) {
           if (index >= items.length) {
             if (hasMore) {
-              // Trigger load more
+              // Trigger pagination once this placeholder is built
               WidgetsBinding.instance.addPostFrameCallback((_) {
                 onLoadMore?.call();
               });
-
               return Container(
                 padding: const EdgeInsets.all(16.0),
                 alignment: Alignment.center,
@@ -323,11 +80,10 @@ class OptimizedSliverList<T> extends ConsumerWidget {
           final item = items[index];
           final widget = itemBuilder(context, item, index);
 
-          // Wrap in repaint boundary for performance
+          // Wrap in repaint boundary for perf
           if (addRepaintBoundaries) {
             return RepaintBoundary(child: widget);
           }
-
           return widget;
         },
         childCount: items.length + (hasMore ? 1 : 0),
@@ -350,7 +106,7 @@ class OptimizedSliverList<T> extends ConsumerWidget {
   }
 }
 
-/// Animated list with optimizations
+/// Animated list with lightweight add/remove animations.
 class OptimizedAnimatedList<T> extends ConsumerStatefulWidget {
   final List<T> items;
   final Widget Function(
@@ -397,7 +153,7 @@ class _OptimizedAnimatedListState<T>
   void didUpdateWidget(OptimizedAnimatedList<T> oldWidget) {
     super.didUpdateWidget(oldWidget);
 
-    // Handle item additions
+    // Additions
     for (int i = 0; i < widget.items.length; i++) {
       if (i >= _items.length || widget.items[i] != _items[i]) {
         _items.insert(i, widget.items[i]);
@@ -408,7 +164,7 @@ class _OptimizedAnimatedListState<T>
       }
     }
 
-    // Handle item removals
+    // Removals
     for (int i = _items.length - 1; i >= widget.items.length; i--) {
       final removedItem = _items[i];
       _items.removeAt(i);
@@ -431,7 +187,6 @@ class _OptimizedAnimatedListState<T>
       initialItemCount: _items.length,
       itemBuilder: (context, index, animation) {
         if (index >= _items.length) return const SizedBox.shrink();
-
         return widget.itemBuilder(context, _items[index], index, animation);
       },
     );