 paulfioravanti's solution

to Scale Generator in the Ruby Track

Published at May 09 2019 · 0 comments
Instructions
Test suite
Solution

Given a tonic, or starting note, and a set of intervals, generate the musical scale starting with the tonic and following the specified interval pattern.

Scales in Western music are based on the chromatic (12-note) scale. This scale can be expressed as the following group of pitches:

A, A#, B, C, C#, D, D#, E, F, F#, G, G#

A given sharp note (indicated by a #) can also be expressed as the flat of the note above it (indicated by a b) so the chromatic scale can also be written like this:

A, Bb, B, C, Db, D, Eb, E, F, Gb, G, Ab

The major and minor scale and modes are subsets of this twelve-pitch collection. They have seven pitches, and are called diatonic scales. The collection of notes in these scales is written with either sharps or flats, depending on the tonic. Here is a list of which are which:

No Sharps or Flats: C major a minor

Use Sharps: G, D, A, E, B, F# major e, b, f#, c#, g#, d# minor

Use Flats: F, Bb, Eb, Ab, Db, Gb major d, g, c, f, bb, eb minor

The diatonic scales, and all other scales that derive from the chromatic scale, are built upon intervals. An interval is the space between two pitches.

The simplest interval is between two adjacent notes, and is called a "half step", or "minor second" (sometimes written as a lower-case "m"). The interval between two notes that have an interceding note is called a "whole step" or "major second" (written as an upper-case "M"). The diatonic scales are built using only these two intervals between adjacent notes.

Non-diatonic scales can contain other intervals. An "augmented first" interval, written "A", has two interceding notes (e.g., from A to C or Db to E). There are also smaller and larger intervals, but they will not figure into this exercise.

For installation and learning resources, refer to the Ruby resources page.

For running the tests provided, you will need the Minitest gem. Open a terminal window and run the following command to install minitest:

gem install minitest

If you would like color output, you can require 'minitest/pride' in the test file, or note the alternative instruction, below, for running the test file.

Run the tests from the exercise directory using the following command:

ruby scale_generator_test.rb

To include color from the command line:

ruby -r minitest/pride scale_generator_test.rb

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

scale_generator_test.rb

require 'minitest/autorun'
require_relative 'scale_generator'

class ScaleGeneratorTest < Minitest::Test
def test_naming_scale
chromatic = Scale.new('c', :chromatic)
expected = 'C chromatic'
actual = chromatic.name
assert_equal expected, actual
end

def test_chromatic_scale
skip
chromatic = Scale.new('C', :chromatic)
expected = %w(C C# D D# E F F# G G# A A# B)
actual = chromatic.pitches
assert_equal expected, actual
end

def test_another_chromatic_scale
skip
chromatic = Scale.new('F', :chromatic)
expected = %w(F Gb G Ab A Bb B C Db D Eb E)
actual = chromatic.pitches
assert_equal expected, actual
end

def test_naming_major_scale
skip
major = Scale.new('G', :major, 'MMmMMMm')
expected = 'G major'
actual = major.name
assert_equal expected, actual
end

def test_major_scale
skip
major = Scale.new('C', :major, 'MMmMMMm')
expected = %w(C D E F G A B)
actual = major.pitches
assert_equal expected, actual
end

def test_another_major_scale
skip
major = Scale.new('G', :major, 'MMmMMMm')
expected = %w(G A B C D E F#)
actual = major.pitches
assert_equal expected, actual
end

def test_minor_scale
skip
minor = Scale.new('f#', :minor, 'MmMMmMM')
expected = %w(F# G# A B C# D E)
actual = minor.pitches
assert_equal expected, actual
end

def test_another_minor_scale
skip
minor = Scale.new('bb', :minor, 'MmMMmMM')
expected = %w(Bb C Db Eb F Gb Ab)
actual = minor.pitches
assert_equal expected, actual
end

def test_dorian_mode
skip
dorian = Scale.new('d', :dorian, 'MmMMMmM')
expected = %w(D E F G A B C)
actual = dorian.pitches
assert_equal expected, actual
end

def test_mixolydian_mode
skip
mixolydian = Scale.new('Eb', :mixolydian, 'MMmMMmM')
expected = %w(Eb F G Ab Bb C Db)
actual = mixolydian.pitches
assert_equal expected, actual
end

def test_lydian_mode
skip
lydian = Scale.new('a', :lydian, 'MMMmMMm')
expected = %w(A B C# D# E F# G#)
actual = lydian.pitches
assert_equal expected, actual
end

def test_phrygian_mode
skip
phrygian = Scale.new('e', :phrygian, 'mMMMmMM')
expected = %w(E F G A B C D)
actual = phrygian.pitches
assert_equal expected, actual
end

def test_locrian_mode
skip
locrian = Scale.new('g', :locrian, 'mMMmMMM')
expected = %w(G Ab Bb C Db Eb F)
actual = locrian.pitches
assert_equal expected, actual
end

def test_harmonic_minor
skip
harmonic_minor = Scale.new('d', :harmonic_minor, 'MmMMmAm')
expected = %w(D E F G A Bb Db)
actual = harmonic_minor.pitches
assert_equal expected, actual
end

def test_octatonic
skip
octatonic = Scale.new('C', :octatonic, 'MmMmMmMm')
expected = %w(C D D# F F# G# A B)
actual = octatonic.pitches
assert_equal expected, actual
end

def test_hexatonic
skip
hexatonic = Scale.new('Db', :hexatonic, 'MMMMMM')
expected = %w(Db Eb F G A B)
actual = hexatonic.pitches
assert_equal expected, actual
end

def test_pentatonic
skip
pentatonic = Scale.new('A', :pentatonic, 'MMAMA')
expected = %w(A B C# E F#)
actual = pentatonic.pitches
assert_equal expected, actual
end

def test_enigmatic
skip
enigmatic = Scale.new('G', :enigma, 'mAMMMmM')
expected = %w(G G# B C# D# F F#)
actual = enigmatic.pitches
assert_equal expected, actual
end
end
# frozen_string_literal: true

class Scale
FLAT_SCALE_TONICS = %w[F Bb Eb Ab Db Gb d g c f bb eb].freeze
private_constant :FLAT_SCALE_TONICS
FLAT_SCALE = %w[C Db D Eb E F Gb G Ab A Bb B].freeze
private_constant :FLAT_SCALE
INITIAL_SCALE_INDEX = 0
private_constant :INITIAL_SCALE_INDEX
INTERVALS = { "m" => 1, "M" => 2, "A" => 3 }.freeze
private_constant :INTERVALS
NAME_FORMAT = "%<tonic>s %<scale_name>s"
private_constant :NAME_FORMAT
SHARP_SCALE = %w[C C# D D# E F F# G G# A A# B].freeze
private_constant :SHARP_SCALE

def initialize(tonic, scale_name, intervals = nil)
@tonic = tonic.capitalize
@scale_name = scale_name
@intervals = intervals
@scale = FLAT_SCALE_TONICS.include?(tonic) ? FLAT_SCALE : SHARP_SCALE
end

def name
format(NAME_FORMAT, tonic: tonic, scale_name: scale_name)
end

def pitches
tonic_scale =
scale
.index(tonic)
.then { |index| scale.rotate(index) }

generate_pitches(tonic_scale)
end

private

attr_reader :tonic, :scale_name, :intervals, :scale

def generate_pitches(tonic_scale)
intervals
.chars
.each
.with_object(tonic_scale)
.last
end

def add_tonic_scale((last_index, acc), (interval, tonic_scale))
acc << tonic_scale[last_index]
last_index += INTERVALS[interval]
[last_index, acc]
end
end