Class: Coltrane::RomanChord

Inherits:
Object
  • Object
show all
Defined in:
lib/coltrane/roman_chord.rb

Overview

This class deals with chords in roman notation. Ex: IVº.

Constant Summary collapse

DIGITS = 
%w[I II III IV V VI VII].freeze
NOTATION_REGEX = 
%r{
  (?<degree>b?[ivIV]*)
  (?<quality>.*)
}x
NOTATION_SUBSTITUTIONS = 
[
%w[º dim],
%w[o dim],
%w[ø m7b5]

Instance Method Summary collapse

Constructor Details

#initialize(notation = nil, chord: nil, key: nil, scale: nil) ⇒ RomanChord

Returns a new instance of RomanChord.



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# File 'lib/coltrane/roman_chord.rb', line 18

def initialize(notation=nil, chord: nil, key: nil, scale: nil)
  if notation.nil? && chord.nil? || key.nil? && scale.nil?
    raise WrongKeywordsError,
      '[notation, [scale: || key:]] '\
      '[chord:, [scale: || key:]] '\
  end
  @scale = scale || Scale.from_key(key)
  if !notation.nil?
    @notation = notation
  elsif !chord.nil?
    @chord = chord.is_a?(String) ? Chord.new(name: chord) : chord
  end
end

Instance Method Details

#chord ⇒ Object 



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# File 'lib/coltrane/roman_chord.rb', line 49

def chord
  @chord ||= Chord.new root_note: root_note,
                       quality: quality
end

#degree ⇒ Object 



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# File 'lib/coltrane/roman_chord.rb', line 32

def degree
  return @scale.degree_of_note(root_note) unless @chord.nil?
  d      = regexed_notation['degree']
  @flats = d.count('b')
  d      = d.delete('b')
  @degree ||= DIGITS.index(d.upcase) + 1
end

#major? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/coltrane/roman_chord.rb', line 58

def major?
  quality.has_major_third?
end

#minor? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/coltrane/roman_chord.rb', line 54

def minor?
  quality.has_minor_third?
end

#notation ⇒ Object 



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# File 'lib/coltrane/roman_chord.rb', line 80

def notation
  q = case quality_name
  when 'm', 'M' then ''
  when 'm7', 'M' then '7'
  else quality_name
  end

  @notation ||= [
    roman_numeral,
    q,
  ].join
end

#quality ⇒ Object 



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# File 'lib/coltrane/roman_chord.rb', line 70

def quality
  return @chord.quality unless @chord.nil?
  ChordQuality.new(name: quality_name) if quality_name
end

#quality_name ⇒ Object 



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# File 'lib/coltrane/roman_chord.rb', line 62

def quality_name
  return @chord.quality.name unless @chord.nil?
  q     = normalize_quality_name(regexed_notation['quality'])
  minor = 'm' if !q.match?((/dim|m7b5/)) && !upcase?
  q     = [minor, q].join
  q.empty? ? 'M' : q
end

#roman_numeral ⇒ Object 



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# File 'lib/coltrane/roman_chord.rb', line 40

def roman_numeral
  r = DIGITS[degree]
  minor? ? r.downcase : r
end

#root_note ⇒ Object 



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# File 'lib/coltrane/roman_chord.rb', line 75

def root_note
  return @chord.root_note unless @chord.nil?
  @scale[degree] - @flats
end

#upcase? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/coltrane/roman_chord.rb', line 45

def upcase?
  !!(regexed_notation['degree'][0].match /[[:upper:]]/)
end