normalize data

packages/z-timeline/lib/main.dart

@@ -45,8 +45,8 @@ class _MainAppState extends State<MainApp> {
   }
 
   void _applyState(TimelineState state) {
-    final groups = _convertGroups(state.timeline.groups);
-    final entries = _convertEntries(state.timeline.groups);
+    final groups = _convertGroups(state);
+    final entries = _convertEntries(state);
     final domain = _computeDomain(entries);
 
     setState(() {
@@ -63,32 +63,35 @@ class _MainAppState extends State<MainApp> {
     _emitContentHeight();
   }
 
-  List<TimelineGroup> _convertGroups(List<TimelineGroupData> groups) {
-    return [for (final g in groups) TimelineGroup(id: g.id, title: g.title)];
+  /// Build an ordered list of [TimelineGroup] using [groupOrder].
+  List<TimelineGroup> _convertGroups(TimelineState state) {
+    return [
+      for (final id in state.groupOrder)
+        if (state.groups[id] case final g?)
+          TimelineGroup(id: g.id, title: g.title),
+    ];
   }
 
-  List<TimelineEntry> _convertEntries(List<TimelineGroupData> groups) {
-    final entries = <TimelineEntry>[];
-    for (final group in groups) {
-      for (final item in group.items) {
-        final start = DateTime.parse(item.start);
-        final end = item.end != null
-            ? DateTime.parse(item.end!)
-            : start.add(const Duration(days: 1));
+  /// Build a flat list of [TimelineEntry] from the normalized items map.
+  List<TimelineEntry> _convertEntries(TimelineState state) {
+    return [
+      for (final item in state.items.values)
+        () {
+          final start = DateTime.parse(item.start);
+          final end = item.end != null
+              ? DateTime.parse(item.end!)
+              : start.add(const Duration(days: 1));
 
-        entries.add(
-          TimelineEntry(
+          return TimelineEntry(
             id: item.id,
-            groupId: group.id,
+            groupId: item.groupId,
             start: start,
             end: end,
             lane: item.lane,
             hasEnd: item.end != null,
-          ),
-        );
-      }
-    }
-    return entries;
+          );
+        }(),
+    ];
   }
 
   ({DateTime start, DateTime end}) _computeDomain(List<TimelineEntry> entries) {
@@ -156,16 +159,9 @@ class _MainAppState extends State<MainApp> {
     emitEvent('content_height', {'height': totalHeight});
   }
 
+  /// O(1) label lookup from the normalized items map.
   String _labelForEntry(TimelineEntry entry) {
-    final state = _state;
-    if (state == null) return entry.id;
-
-    for (final group in state.timeline.groups) {
-      for (final item in group.items) {
-        if (item.id == entry.id) return item.title;
-      }
-    }
-    return entry.id;
+    return _state?.items[entry.id]?.title ?? entry.id;
   }
 
   static const _groupColors = [