Class: HeadMusic::Notation::ABC::DurationResolver

Inherits:
Object
  • Object
show all
Defined in:
lib/head_music/notation/abc/duration_resolver.rb

Overview

Converts the tune's unit note length and a per-note multiplier string (e.g. "2", "3/2", "/", "//") into a HeadMusic::Rudiment::RhythmicValue.

Constant Summary collapse

MAX_FRACTION = 
HeadMusic::Notation::DottedDuration::MAX_FRACTION
MULTIPLIER_PATTERN = 
%r{\A(\d+)?(?:(/+)(\d+)?)?\z}

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(unit_note_length) ⇒ DurationResolver

Returns a new instance of DurationResolver.



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# File 'lib/head_music/notation/abc/duration_resolver.rb', line 12

def initialize(unit_note_length)
  @unit_note_length = Rational(unit_note_length)
end

Instance Attribute Details

#unit_note_length ⇒ Object (readonly)

Returns the value of attribute unit_note_length.



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# File 'lib/head_music/notation/abc/duration_resolver.rb', line 10

def unit_note_length
  @unit_note_length
end

Instance Method Details

#explicit_ratio(numerator, slashes, denominator, source) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/duration_resolver.rb', line 48

def explicit_ratio(numerator, slashes, denominator, source)
  # An explicit denominator pairs with exactly one slash ("3/2", not "3//2").
  raise_error("malformed note length multiplier", source) if slashes.length > 1
  raise_error("note length denominator cannot be zero", source) if denominator.to_i.zero?
  Rational(numerator, denominator.to_i)
end

#length_fraction(multiplier_string) ⇒ Object

The bare fraction a length string denotes (e.g. "2" -> 2, "/2" -> 1/2, "" -> 1), without the unit note length applied. Used to compare a chord's per-note lengths for uniformity.



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# File 'lib/head_music/notation/abc/duration_resolver.rb', line 28

def length_fraction(multiplier_string)
  multiplier(multiplier_string)
end

#multiplier(multiplier_string) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/duration_resolver.rb', line 34

def multiplier(multiplier_string)
  source = multiplier_string.to_s
  match = MULTIPLIER_PATTERN.match(source)
  raise_error("malformed note length multiplier", source) unless match

  numerator = (match[1] || 1).to_i
  slashes = match[2]
  denominator = match[3]
  return Rational(numerator) unless slashes
  return Rational(numerator, 2**slashes.length) unless denominator

  explicit_ratio(numerator, slashes, denominator, source)
end

#raise_error(message, source) ⇒ Object (private)

Raises:



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# File 'lib/head_music/notation/abc/duration_resolver.rb', line 63

def raise_error(message, source)
  raise HeadMusic::Notation::ABC::ParseError.new(message, snippet: source)
end

#rhythmic_value(multiplier_string, scale: Rational(1)) ⇒ Object

scale: an extra multiplier applied outside the note's own length string, used for broken-rhythm pairs (3/2 and 1/2).



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# File 'lib/head_music/notation/abc/duration_resolver.rb', line 18

def rhythmic_value(multiplier_string, scale: Rational(1))
  fraction = unit_note_length * multiplier(multiplier_string) * scale
  validate_fraction!(fraction, multiplier_string)
  HeadMusic::Notation::DottedDuration.rhythmic_value_for(fraction) ||
    raise_error("no rhythmic unit for a note length of #{fraction}", multiplier_string)
end

#validate_fraction!(fraction, source) ⇒ Object (private) 



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# File 'lib/head_music/notation/abc/duration_resolver.rb', line 55

def validate_fraction!(fraction, source)
  raise_error("note length must be positive", source) if fraction <= 0
  raise_error("note length exceeds #{MAX_FRACTION.to_i} whole notes", source) if fraction > MAX_FRACTION
  return if HeadMusic::Notation::DottedDuration.power_of_two?(fraction.denominator)

  raise_error("note length #{fraction} is not expressible in binary note values", source)
end