feat: display beats as arrows with correct time offset

lib/level.dart

@@ -13,6 +13,24 @@ class Level extends StatefulWidget {
   State<Level> createState() => _LevelState();
 }
 
+enum ArrowDirection {
+  left(Icons.arrow_back),
+  down(Icons.arrow_downward),
+  up(Icons.arrow_upward),
+  right(Icons.arrow_forward);
+
+  const ArrowDirection(this.icon);
+
+  final IconData icon;
+}
+
+class Note {
+  final double time;
+  final ArrowDirection direction;
+
+  const Note({required this.time, required this.direction});
+}
+
 class _LevelState extends State<Level> {
   final player = AudioPlayer();
   Simfile? simfile;
@@ -23,6 +41,8 @@ class _LevelState extends State<Level> {
   StreamSubscription? _durationSubscription;
   StreamSubscription? _positionSubscription;
 
+  List<Note> notes = [];
+
   @override
   void setState(VoidCallback fn) {
     // Subscriptions only can be closed asynchronously,
@@ -79,6 +99,25 @@ class _LevelState extends State<Level> {
     simfile = Simfile(simfilePath);
     simfile!.load();
 
+    double bpm = simfile!.bpms.entries.first.value;
+
+    for (final (measureIndex, measure)
+        in simfile!.chartSimplest!.measures!.indexed) {
+      for (final (noteIndex, noteData) in measure.indexed) {
+        int arrowIndex = noteData.indexOf('1');
+        if (arrowIndex < 0 || arrowIndex > 3) {
+          continue;
+        }
+        notes.add(Note(
+            time: (measureIndex * 4.0 +
+                        (noteIndex.toDouble() / measure.length) * 4.0) *
+                    1.0 /
+                    bpm +
+                simfile!.offset / 60.0,
+            direction: ArrowDirection.values[arrowIndex]));
+      }
+    }
+
     print(audioPath);
 
     player.play(DeviceFileSource(audioPath));
@@ -86,7 +125,6 @@ class _LevelState extends State<Level> {
 
   @override
   Widget build(BuildContext context) {
-
     return Scaffold(
         appBar: AppBar(
           leading: IconButton(
@@ -123,18 +161,16 @@ class _LevelState extends State<Level> {
               )),
         ),
         body: Stack(children: [
-          Arrow(
+          ...notes.map((note) {
-            position: -100.0,
+            return Arrow(
-          ),
+              position: _position != null
-          Arrow(
+                  ? (note.time - _position!.inMilliseconds / 60000.0) *
-            position: 00.0,
+                      20 *
-          ),
+                      MediaQuery.of(context).size.height
-          Arrow(
+                  : 0.0,
-            position: 100.0,
+              direction: note.direction,
-          ),
+            );
-          Arrow(
+          }),
-            position: 200.0,
-          ),
           Positioned(
             top: 50,
             width: MediaQuery.of(context).size.width,
@@ -171,15 +207,16 @@ class _LevelState extends State<Level> {
 
 class Arrow extends StatelessWidget {
   final double position;
+  final ArrowDirection direction;
 
-  const Arrow({super.key, required this.position});
+  const Arrow({super.key, required this.position, required this.direction});
 
   @override
   Widget build(BuildContext context) {
     return Positioned(
-      left: MediaQuery.of(context).size.width / 2 - 25, // Center the arrow
+      left: MediaQuery.of(context).size.width / 2 - 50, // Center the arrow
-      top: position,
+      bottom: position + 50,
-      child: Icon(size: 100, Icons.arrow_forward),
+      child: Icon(size: 100, color: Colors.redAccent.shade400, direction.icon),
     );
   }
 }

lib/simfile.dart

@@ -1,3 +1,4 @@
+import 'dart:ffi';
 import 'dart:io';
 
 enum Difficulty { Beginner, Easy, Medium, Hard, Challenge, Edit }
@@ -42,6 +43,9 @@ class Simfile {
 
   Chart? chartSimplest;
 
+  Map<double, double> bpms = {};
+  double offset = 0;
+
   Simfile(this.path);
 
   void load() {
@@ -55,6 +59,22 @@ class Simfile {
       List<String> keys =
           fieldData[1]!.split(':').map((key) => key.trim()).toList();
       String value = fieldData[2]!;
+      if (keys[0] == "BPMS") {
+        for (final pairRaw in value.split(',')) {
+          List<String> pair = pairRaw.split('=');
+          if (pair.length != 2) {
+            continue;
+          }
+          double time = double.parse(pair[0]);
+          double bpm = double.parse(pair[1]);
+          bpms[time] = bpm;
+        }
+      }
+
+      if (keys[0] == "OFFSET") {
+        offset = double.parse(value);
+      }
+
       if (keys[0] != "NOTES") {
         tags[keys[0]] = value;
         continue;