Add signature method for a scale. Closes #89

README.md

@@ -181,8 +181,10 @@ The chroma number is ranging from pitch class C which is 0 to 11 which is B
 #### Note#interval(interval)
  - A sugar function for calling teoria.interval(note, interval);
 
+
 Look at the documentation for `teoria.interval`
 
+
 #### Note#transpose(interval)
  - Like the `#interval` method, but changes `this` note, instead of returning a new
 
@@ -415,6 +417,9 @@ scale step. E.g. 'first', 'second', 'fourth', 'seventh'.
 
 *showOctaves* - A boolean meaning the same as `showOctaves` in `Note#solfege`
 
+#### Scale#signature()
+ - Returns the sequence of notes representing the key signature of a scale
+
 
 ## teoria.interval(from, to)
  - A sugar function for the `#from` and `#between` methods of the same namespace and

lib/scale.js

@@ -102,6 +102,33 @@ Scale.prototype = {
     this.tonic = scale.tonic;
 
     return this;
+  },
+
+  /**
+   * Get the sequence of notes representing key signature of a scale, in proper order.
+   * There are two possible signatures for any scale: flats and sharps.
+   * Sharps signature is got by traversing notes by P5 intervals to the right
+   * till all the notes of the scale are covered.
+   * Flats signature is got by traversing by P4 intervals to the left in the same manner, which is equal to reversed sharps.
+   */
+  signature: function() {
+    var sequence = this.notes().sort(function (a, b) {
+      var aCoord = a.coord[1] < 0 ? a.coord[1] + 12 : a.coord[1];
+      var bCoord = b.coord[1] < 0 ? b.coord[1] + 12 : b.coord[1];
+      return aCoord - bCoord;
+    });
+
+    var hasFlat = sequence.some(function (note) {
+      return note.accidentalValue() < 0;
+    });
+
+    if (hasFlat) {
+      sequence = sequence.reverse();
+    }
+
+    return sequence.filter(function (note) {
+      return note.accidentalValue() !== 0;
+    });
   }
 };
 

test/scales.js

@@ -57,6 +57,18 @@ vows.describe('Scales').addBatch({
       assert.deepEqual(note.scale('chromatic').simple(),
           ["ab", "bbb", "bb", "cb", "c", "db",
            "d", "eb", "fb", "f", "gb", "g"]);
+    },
+
+    'Signature': function(note) {
+      function name (note) {return note.name() + note.accidental() }
+
+      assert.equal(teoria.note('f#').scale('major').signature().map(name).toString(), 'f#,c#,g#,d#,a#,e#');
+      assert.equal(teoria.note('db').scale('major').signature().map(name).toString(), 'bb,eb,ab,db,gb');
+
+      assert.equal(teoria.note('c').scale('major').signature().map(name).toString(), '');
+      assert.equal(teoria.note('a').scale('minor').signature().map(name).toString(), '');
+      assert.equal(teoria.note('d').scale('major').signature().map(name).toString(), 'f#,c#');
+      assert.equal(teoria.note('b').scale('minor').signature().map(name).toString(), 'f#,c#');
     }
   }
 }).export(module);