feat: add Track.absoluteTimeAt and Track.abolusteTimeDiff

Author: alextekartik

lib/src/midi/track.dart

@@ -1,8 +1,34 @@
 import 'package:collection/collection.dart';
 import 'package:tekartik_midi/midi.dart';
 
+/// A track event contains a list of events
 class MidiTrack {
-  List<TrackEvent> events = [];
+  /// List of events, do not modify directly
+  List<TrackEvent> get events => _events;
+  final _events = <TrackEvent>[];
+
+  /// Get the time of an event at a given index
+  /// It unfortunately requires to go through all events
+  int absoluteTimeAt(int index) {
+    var time = 0;
+    for (var i = 0; i <= index; i++) {
+      time += events[i].deltaTime;
+    }
+    return time;
+  }
+
+  /// Get the time difference between two events
+  /// if (index1 <= index2) similarly to compare the result will be negative
+  int absoluteTimeDiff(int index1, int index2) {
+    if (index1 <= index2) {
+      var time = 0;
+      for (var i = index1 + 1; i <= index2; i++) {
+        time -= events[i].deltaTime;
+      }
+      return time;
+    }
+    return -absoluteTimeDiff(index2, index1);
+  }
 
   @override
   int get hashCode {
@@ -17,8 +43,10 @@ class MidiTrack {
     return false;
   }
 
+  /// Debug dump events
   void dump() {
     for (var e in events) {
+      // ignore: avoid_print
       print(e);
     }
   }
@@ -33,21 +61,25 @@ class MidiTrack {
     return out.toString();
   }
 
+  /// Add an event
   void addEvent(int deltaTime, MidiEvent midiEvent) {
     events.add(TrackEvent(deltaTime, midiEvent));
   }
 
-  void addAbsolutionEvent(int absoluteTime, MidiEvent midiEvent) {
+  /// Add an event at an absolute time
+  /// return its index
+  int addAbsolutionEvent(int absoluteTime, MidiEvent midiEvent) {
     var time = 0;
     for (var i = 0; i < events.length; i++) {
       var event = events[i];
       final newTime = time + event.deltaTime;
       if (absoluteTime < newTime) {
         events.insert(i, TrackEvent(absoluteTime - time, midiEvent));
-        return;
+        return i;
       }
       time = newTime;
     }
     events.add(TrackEvent(absoluteTime - time, midiEvent));
+    return events.length - 1;
   }
 }

test/track_test.dart

@@ -48,5 +48,18 @@ void main() {
       expect((track.events[1].midiEvent as TempoEvent).tempo, 2);
       expect(track.events.length, 2);
     });
+
+    test('absoluteTime', () {
+      final track = MidiTrack();
+      track.addEvent(10, TempoEvent(1));
+      track.addEvent(25, TempoEvent(2));
+      track.addEvent(30, TempoEvent(3));
+      expect(track.absoluteTimeAt(0), 10);
+      expect(track.absoluteTimeAt(2), 65);
+      expect(track.absoluteTimeDiff(0, 1), -25);
+      expect(track.absoluteTimeDiff(0, 2), -55);
+      expect(track.absoluteTimeDiff(1, 2), -30);
+      expect(track.absoluteTimeDiff(2, 1), 30);
+    });
   });
 }