introduce ClefSignature

Author: soumas

lib/music_xml.dart

@@ -2,6 +2,7 @@ export 'src/basic_attributes.dart';
 export 'src/barline.dart';
 export 'src/chord_symbol.dart';
 export 'src/key_signature.dart';
+export 'src/clef_signature.dart';
 export 'src/kind.dart';
 export 'src/lyric.dart';
 export 'src/measure.dart';

lib/src/clef_signature.dart

@@ -0,0 +1,48 @@
+import 'package:xml/xml.dart';
+
+import 'music_xml_parser_state.dart';
+
+/// Internal representation of a MusicXML clef signature.
+class ClefSignature {
+  // The <sign> element represents the clef symbol
+  late String sign;
+  // Line numbers are counted from the bottom of the staff. They are only needed with the G, F, and C signs in order to position a pitch correctly on the staff. Standard values are 2 for the G sign (treble clef), 4 for the F sign (bass clef), and 3 for the C sign (alto clef). Line values can be used to specify positions outside the staff, such as a C clef positioned in the middle of a grand staff.
+  late int? line;
+  // The <clef-octave-change> element is used for transposing clefs. A treble clef for tenors would have a value of -1.
+  late int? clefOctaveChange;
+
+  ClefSignature();
+
+  factory ClefSignature.parse(MusicXMLParserState state, [XmlElement? xmlKey]) {
+    final instance = ClefSignature()..sign = '';
+
+    if (xmlKey != null) instance._parse(xmlKey, state);
+    return instance;
+  }
+
+  /// Parse the MusicXML <clef> element.
+  ///
+  /// Raises:
+  ///       KeyParseError: If the sign element is missing.
+  void _parse(XmlElement xmlKey, MusicXMLParserState state) {
+    // parse sign
+    final signElem = xmlKey.getElement('sign');
+    if (signElem == null) {
+      throw XmlParserException(
+          'Could not find sign element in clef signature.');
+    }
+    sign = signElem.innerText;
+
+    // parse line
+    final lineElem = xmlKey.getElement('line');
+    if (lineElem != null && lineElem.innerText.isNotEmpty) {
+      line = int.parse(lineElem.innerText);
+    }
+
+    // parse clefOctaveChange
+    final cocElem = xmlKey.getElement('clef-octave-change');
+    if (cocElem != null && cocElem.innerText.isNotEmpty) {
+      clefOctaveChange = int.parse(cocElem.innerText);
+    }
+  }
+}

lib/src/measure.dart

@@ -1,4 +1,5 @@
 import 'package:music_xml/src/barline.dart';
+import 'package:music_xml/src/clef_signature.dart';
 import 'package:music_xml/src/print.dart';
 import 'package:xml/xml.dart';
 
@@ -16,6 +17,7 @@ class Measure {
   final chordSymbols = <ChordSymbol>[];
   final tempos = <Tempo>[];
   final prints = <Print>[];
+  ClefSignature? clefSignature;
   TimeSignature? timeSignature;
   KeySignature? keySignature;
   int duration = 0;
@@ -91,6 +93,9 @@ class Measure {
         case 'divisions':
           state.divisions = int.parse(child.innerText);
           break;
+        case 'clef':
+          clefSignature = ClefSignature.parse(state, child);
+          break;
         case 'key':
           keySignature = KeySignature.parse(state, child);
           break;