Generalize to #inversion method and make aliases for convenience

lib/music/chord.rb

@@ -65,20 +65,31 @@ def to_s
       @notes.to_a.sort.collect(&:to_s).join(' / ')
     end
 
-    # Give the first inversion of the chord which simply adjusts the lowest note up by one octive
+    # Give the Nth inversion of the chord which simply adjusts the lowest N notes up by one octive
     #
-    # @returns [Chord] The first inversion of chord
-    def first_inversion
+    # @returns [Chord] The specified inversion of chord
+    def inversion(amount)
+      raise ArgumentError, "Inversion amount must be greater than or equal to 1" if amount < 1
+      raise ArgumentError, "Not enough notes in chord for inversion" if amount >= @notes.size
+
       note_array = @notes.to_a.sort
-      note = note_array.shift
-      Chord.new([note.adjust_by_semitones(12)] + note_array)
+      notes = (0...amount).collect { note_array.shift.adjust_by_semitones(12) }
+      Chord.new(notes + note_array)
     end
 
-    # Give the first inversion of the chord which simply adjusts the lowest two notes up by one octive
-    #
-    # @returns [Chord] The second inversion of chord
+    # Calls inversion(1)
+    def first_inversion
+      self.inversion(1)
+    end
+
+    # Calls inversion(2)
     def second_inversion
-      self.first_inversion.first_inversion
+      self.inversion(2)
+    end
+
+    # Calls inversion(3)
+    def third_inversion
+      self.inversion(3)
     end
 
     class << self

spec/classes/chord_spec.rb

@@ -137,19 +137,46 @@
     # TODO: Fill out other chords
   end
 
+  describe '#inversion' do
+    it 'should adjust the lowest n notes up by an octive' do
+      @c_major.inversion(1).should == Chord.new(['E4', 'G4', 'C5'])
+      Chord.new(['Eb4', 'C4', 'Gb4']).inversion(1).should == Chord.new(['Eb4', 'C5', 'Gb4'])
+
+      @c_major.inversion(2).should == Chord.new(['E5', 'G4', 'C5'])
+      Chord.new(['Eb4', 'C4', 'Gb4']).inversion(2).should == Chord.new(['Eb5', 'C5', 'Gb4'])
+
+      @c_augmented_seventh.inversion(3).should == Chord.new(['E5', 'G#5', 'C5', 'Bb4'])
+    end
+
+    it 'should raise an error when the inversion amount is too great' do
+      lambda { @c_major.inversion(3) }.should raise_error(ArgumentError, 'Not enough notes in chord for inversion')
+      lambda { @c_major.inversion(4) }.should raise_error(ArgumentError, 'Not enough notes in chord for inversion')
+
+      lambda { @c_augmented_seventh.inversion(4) }.should raise_error(ArgumentError, 'Not enough notes in chord for inversion')
+      lambda { @c_augmented_seventh.inversion(5) }.should raise_error(ArgumentError, 'Not enough notes in chord for inversion')
+    end
+
+    it 'should raise an error when the inversion amount is too small' do
+      lambda { @c_major.inversion(0) }.should raise_error(ArgumentError, 'Inversion amount must be greater than or equal to 1')
+      lambda { @c_major.inversion(-1) }.should raise_error(ArgumentError, 'Inversion amount must be greater than or equal to 1')
+    end
+  end
+
   describe '#first_inversion' do
     it 'should adjust the lowest note up by an octive' do
       @c_major.first_inversion.should == Chord.new(['E4', 'G4', 'C5'])
-
-      Chord.new(['Eb4', 'C4', 'Gb4']).first_inversion.should == Chord.new(['Eb4', 'C5', 'Gb4'])
     end
   end
 
   describe '#second_inversion' do
     it 'should adjust the lowest two notes up by an octive' do
       @c_major.second_inversion.should == Chord.new(['E5', 'G4', 'C5'])
+    end
+  end
 
-      Chord.new(['Eb4', 'C4', 'Gb4']).second_inversion.should == Chord.new(['Eb5', 'C5', 'Gb4'])
+  describe '#third_inversion' do
+    it 'should adjust the lowest three notes up by an octive' do
+      @c_augmented_seventh.third_inversion.should == Chord.new(['E5', 'G#5', 'C5', 'Bb4'])
     end
   end
 end