a0_additions_rut.rb

class String # :nodoc:
  def valid_rut?(out: {})
    splitted = strip.split('-')
    rut = splitted.first.delete('.').to_i
    dv = rut.dv
    valid = dv == splitted.last.upcase

    if valid
      out[:rut] = rut
      out[:dv] = dv
      out[:formatted] = rut.to_formatted_rut
    end

    valid
  rescue StandardError
    false
  end
end

class Numeric # :nodoc:
  def dv
    reversed_digits = to_s.reverse.chars.map(&:to_i)
    factors = (2..7).to_a.cycle
    sum = reversed_digits.zip(factors).inject(0) { |s, (d, f)| s + d * f }
    (-sum) % 11 == 10 ? 'K' : ((-sum) % 11).to_s
  end

  def to_rut
    [to_s, dv].join('-')
  end

  def to_formatted_rut
    [to_s.reverse.gsub(/...(?=.)/, '\&.').reverse, dv].join('-')
  end
end

# Ejemplo de uso:
#
# 12345678.to_formatted_rut
# => "12.345.678-5" 
#
# out = {}; "12.345.678-5".valid_rut?(out: out)
# => true 
#
# out
# => {:rut=>12345678, :dv=>"5", :formatted=>"12.345.678-5"}