Class: OutroRails::ChordSeedGenerator

Inherits:
Object
  • Object
show all
Defined in:
lib/outro_rails/generators/chord_seed_generator.rb

Overview

Generates seed data for OutroRails::Chord for a given root.

Constant Summary collapse

Vocabulary =

Shorthand for the theory vocabulary used to build intervals and symbols

Theory::ChordVocabulary
ALTERED_DOMINANTS =

Alterations on dominant chords to generate

{
  '7':  [
          %i[b5],
          %i[#5],
          %i[b9],
          %i[#9],
          %i[#11],
          %i[b13],
          %i[b5 b9],
          %i[b5 #9],
          %i[#5 b9],
          %i[#5 #9],
          %i[b9 b13],
          %i[#9 b13],
          %i[b9 #11]
        ],
  '9':  [
          %i[#11],
          %i[b13]
        ],
  '13': [
          %i[b9],
          %i[#9],
          %i[#11]
        ]
}.freeze
ADDED_TONE_POLICY =

Added tones to generate { quality: { extension: [added_tone] } }

{
  major:  {
            base: %i[add2 add4 add9 add11 add13]
          },
  minor:  {
            base: %i[add2 add4 add9 add11 add13],
            '7':  %i[add11]
          }
}.freeze

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(root_name:, root_pitch_class: nil) ⇒ ChordSeedGenerator

Parses the root note name, optionally verifying it against an expected pitch class. Raises ArgumentError when the two disagree.



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# File 'lib/outro_rails/generators/chord_seed_generator.rb', line 55

def initialize(root_name:, root_pitch_class: nil)
  @root = Theory::NoteName.parse(root_name)

  if root_pitch_class && Integer(root_pitch_class) != @root.pitch_class
    raise ArgumentError,
          "#{root} has pitch class #{root.pitch_class}, " \
          "specified #{root_pitch_class}"
  end
end

Instance Attribute Details

#root ⇒ Object (readonly)

The parsed Theory::NoteName every generated chord is built from



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# File 'lib/outro_rails/generators/chord_seed_generator.rb', line 51

def root
  @root
end

Instance Method Details

#chords ⇒ Object

Builds every chord row for this root: each base quality, its permitted extensions, the altered dominants, and the allowed added tones. Raises if the result contains duplicate symbols or interval sets.



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# File 'lib/outro_rails/generators/chord_seed_generator.rb', line 78

def chords
  rows = []

  Vocabulary::QUALITIES.each do |quality, base|
    rows << build(quality, nil, [], [], base)

    Vocabulary::EXTENSIONS.each do |extension, spec|
      next unless spec[:qualities].include?(quality)

      rows << build(quality,
                    extension,
                    [],
                    [],
                    Vocabulary.merge(base, spec[:add]))
    end
  end

  ALTERED_DOMINANTS.each do |extension, alteration_sets|
    base = Vocabulary.intervals(quality: :major, extension: extension)

    alteration_sets.each do |alterations|
      rows << build(:major,
                    extension,
                    alterations,
                    [],
                    Vocabulary.apply_alterations(base, alterations))
    end
  end

  ADDED_TONE_POLICY.each do |quality, by_extension|
    by_extension.each do |extension_key, tones|
      extension = extension_key == :base ? nil : extension_key
      base = Vocabulary.intervals(quality: quality, extension: extension)

      tones.each do |tone|
        interval = Vocabulary::ADDED_TONE_INTERVALS.fetch(tone)
        pitch_classes = Vocabulary.pitch_classes(base)

        next if pitch_classes.include?(
          interval % Theory::Interval::SEMITONES_PER_OCTAVE
        )

        rows << build(
          quality,
          extension,
          [],
          [ tone ],
          (base + [interval]).sort
        )
      end
    end
  end

  assert_no_duplicates!(rows)
  rows
end

#root_name ⇒ Object

The root spelled as written, e.g. "Bb"



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# File 'lib/outro_rails/generators/chord_seed_generator.rb', line 66

def root_name
  root.to_s
end

#root_pitch_class ⇒ Object

The root's pitch class, 0-11



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# File 'lib/outro_rails/generators/chord_seed_generator.rb', line 71

def root_pitch_class
  root.pitch_class
end

#to_yaml ⇒ Object

Renders all chords as a YAML fixture fragment



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# File 'lib/outro_rails/generators/chord_seed_generator.rb', line 136

def to_yaml
  chords.map { |chord| entry_yaml(chord) }.join("\n")
end