# Represents a key signature.
# In French, sharps and flats in the key signature are called "altérations".
class HeadMusic::KeySignature
  attr_reader :tonic_spelling, :scale_type, :scale

  ORDERED_LETTER_NAMES_OF_SHARPS = %w[F C G D A E B].freeze
  ORDERED_LETTER_NAMES_OF_FLATS = ORDERED_LETTER_NAMES_OF_SHARPS.reverse.freeze

  def self.default
    @default ||= new("C", :major)
  end

  def self.get(identifier)
    return identifier if identifier.is_a?(HeadMusic::KeySignature)

    @key_signatures ||= {}
    tonic_spelling, scale_type_name = identifier.strip.split(/\s/)
    hash_key = HeadMusic::Utilities::HashKey.for(identifier.gsub(/#|♯/, " sharp").gsub(/(\w)[b♭]/, '\\1 flat'))
    @key_signatures[hash_key] ||= new(tonic_spelling, scale_type_name)
  end

  delegate :pitch_class, to: :tonic_spelling, prefix: :tonic
  delegate :to_s, to: :name
  delegate :pitches, to: :scale

  def initialize(tonic_spelling, scale_type = nil)
    @tonic_spelling = HeadMusic::Spelling.get(tonic_spelling)
    @scale_type = HeadMusic::ScaleType.get(scale_type) if scale_type
    @scale_type ||= HeadMusic::ScaleType.default
    @scale_type = @scale_type.parent || @scale_type
    @scale = HeadMusic::Scale.get(@tonic_spelling, @scale_type)
  end

  def spellings
    pitches.map(&:spelling).uniq
  end

  def sharps
    spellings.select(&:sharp?).sort_by do |spelling|
      ORDERED_LETTER_NAMES_OF_SHARPS.index(spelling.letter_name.to_s)
    end
  end

  def double_sharps
    spellings.select(&:double_sharp?).sort_by do |spelling|
      ORDERED_LETTER_NAMES_OF_SHARPS.index(spelling.letter_name.to_s)
    end
  end

  def flats
    spellings.select(&:flat?).sort_by do |spelling|
      ORDERED_LETTER_NAMES_OF_FLATS.index(spelling.letter_name.to_s)
    end
  end

  def double_flats
    spellings.select(&:double_flat?).sort_by do |spelling|
      ORDERED_LETTER_NAMES_OF_FLATS.index(spelling.letter_name.to_s)
    end
  end

  def num_sharps
    sharps.length + double_sharps.length * 2
  end

  def num_flats
    flats.length + double_flats.length * 2
  end

  def signs
    flats.any? ? flats : sharps
  end

  alias_method :sharps_and_flats, :signs
  alias_method :accidentals, :signs

  def name
    [tonic_spelling, scale_type].join(" ")
  end

  def ==(other)
    signs == self.class.get(other).signs
  end

  def to_s
    if sharps.any?
      (sharps.length == 1) ? "1 sharp" : "#{sharps.length} sharps"
    elsif flats.any?
      (flats.length == 1) ? "1 flat" : "#{flats.length} flats"
    else
      "no sharps or flats"
    end
  end

  def enharmonic_equivalent?(other)
    other = KeySignature.get(other)
    enharmonic_equivalence.equivalent?(other)
  end

  private

  def enharmonic_equivalence
    @enharmonic_equivalence ||= EnharmonicEquivalence.get(self)
  end

  # Key signatures are enharmonic when all pitch classes in one are respellings of the pitch classes in the other.
  class EnharmonicEquivalence
    def self.get(key_signature)
      key_signature = HeadMusic::KeySignature.get(key_signature)
      @enharmonic_equivalences ||= {}
      @enharmonic_equivalences[key_signature.to_s] ||= new(key_signature)
    end

    attr_reader :key_signature

    def initialize(key_signature)
      @key_signature = HeadMusic::KeySignature.get(key_signature)
    end

    def enharmonic_equivalent?(other)
      other = HeadMusic::KeySignature.get(other)
      (key_signature.signs | other.signs).map(&:to_s).uniq.length == 12
    end

    alias_method :enharmonic?, :enharmonic_equivalent?
    alias_method :equivalent?, :enharmonic_equivalent?

    private_class_method :new
  end
end