Iterable Example -- Exercism "Protein Translation" solution

protein_translation.cr

require "string_scanner"

module ProteinTranslation
  class Polypeptide
    alias Codon = String
    include Iterator(Codon)

    CODONS = {
      /AUG/             => "Methionine",
      /UUU|UUC/         => "Phenylalanine",
      /UUA|UUG/         => "Leucine",
      /UCU|UCC|UCA|UCG/ => "Serine",
      /UAU|UAC/         => "Tyrosine",
      /UGU|UGC/         => "Cysteine",
      /UGG/             => "Tryptophan",
    }

    STOP_CODONS = "UAG|UAA|UGA"

    BASES = "UAGC"

    POLYPEPTIDE = /[#{BASES}]+(?=#{STOP_CODONS})?/

    def initialize(rna)
      @scanner = StringScanner.new(rna.sub(/(#{STOP_CODONS}).*/, ""))
    end

    def next
      @scanner.scan(/[#{BASES}]{3}/).try(&->find_codon(String)) || stop
    end

    private def find_codon(c)
      CODONS.find { |k, _| k =~ c }.try &.last
    end
  end

  def self.proteins(rna)
    Polypeptide.new(rna).to_a
  end
end