class HeadMusic::FunctionalInterval
  NUMBER_NAMES = %w[unison second third fourth fifth sixth seventh octave ninth tenth eleventh twelfth thirteenth fourteenth fifteenth sixteenth seventeenth]
  NAME_SUFFIXES = Hash.new('th').merge({ 1 => 'st', 2 => 'nd', 3 => 'rd' })

  QUALITY = {
    unison: {perfect: 0},
    second: {major: 2},
    third: {major: 4},
    fourth: {perfect: 5},
    fifth: {perfect: 7},
    sixth: {major: 9},
    seventh: {major: 11},
  }

  attr_reader :lower_pitch, :higher_pitch

  def initialize(pitch1, pitch2)
    @lower_pitch, @higher_pitch = [HeadMusic::Pitch.get(pitch1), HeadMusic::Pitch.get(pitch2)].sort
  end

  def number
    simple_number + octaves * 7
  end

  def simple_number
    @simple_number ||= @lower_pitch.letter.steps_to(@higher_pitch.letter) + 1
  end

  def simple_semitones
    semitones % 12
  end

  def semitones
    (@higher_pitch - @lower_pitch).to_i
  end

  def octaves
    (higher_pitch.number - lower_pitch.number) / 12
  end

  def compound?
    !simple?
  end

  def simple?
    octaves == 0
  end

  def simple_name
    [quality_name, simple_number_name].join(' ')
  end

  def name
    if number < NUMBER_NAMES.length
      [quality_name, number_name].join(' ')
    elsif simple_name == 'perfect unison'
      string = "#{octaves.humanize} octaves"
    else
      "#{octaves.humanize} octaves and #{quality.article} #{simple_name}"
    end
  end

  def shorthand
    [quality.shorthand, number].join
  end

  def quality
    HeadMusic::Quality.get(quality_name)
  end

  def quality_name
    starting_quality = QUALITY[simple_number_name.to_sym].keys.first
    delta = simple_semitones - QUALITY[simple_number_name.to_sym][starting_quality]
    if starting_quality == :perfect
      HeadMusic::Quality::PERFECT_INTERVAL_MODIFICATION[delta]
    elsif starting_quality == :major
      HeadMusic::Quality::MAJOR_INTERVAL_MODIFICATION[delta]
    end
  end

  def simple_number_name
    NUMBER_NAMES[simple_number - 1]
  end

  def number_name
    NUMBER_NAMES[number - 1] || begin
      number.to_s + NAME_SUFFIXES[number % 10]
    end
  end
end