Packs a short string into a Fixnum and vise-versa

short_string_packer.rb

class ShortStringPacker
  ## Packs a short string into a Fixnum
  # Arguments:
  #   str - String object
  # Returns: a Fixnum object
  def self.pack(str)
    abc = [*'a'..'z']
    arr = str.chars.map { |x| abc.find_index(x) + 1 }
    arr.reduce { |item, key| (item << 5.0) | key }
  end

  ## Unpacks a Fixnum from pack() method into a short string
  # Arguments:
  #   packed - a Fixnum object
  # Returns: a String object
  def self.unpack(packed)
    abc = [*'a'..'z']
    binary_string = packed.to_s 2
    amt_chars_in_packed = (binary_string.length / 5.0).ceil

    binary_string.rjust(amt_chars_in_packed * 5.0, '0')
    .to_s
    .chars
    .each_slice(5)
    .map(&:join)
    .map! { |x| abc[(x.to_i 2) - 1] }
    .join
  end
end