Encode text to base64

base64.rb

# References: 
#
# https://en.wikipedia.org/wiki/Base64

require 'base64'

TABLE = ('A'..'Z').to_a + ('a'..'z').to_a + ("0".."9").to_a + ['+','/']

class String
  def bit_string
    bytes.collect do |byte|
      byte.to_s(2).rjust(8, "0")
    end.join
  end
end

def pad_len(str)
  if str.length % 24 == 0
    0
  else
    24 - (str.length % 24)
  end
end

def add_padding(bit_string)
  bit_string + "0" * pad_len(bit_string)
end

def _encode(text)
  if text == "000000"
    "="
  else
    TABLE[text.to_i(2)]
  end
end

def encode(text)
  text = add_padding(text.bit_string)

  result = ""
  while text.length != 0
    result += _encode(text.slice!(0,6))
  end
  result
end

def _decode(text)
  out_char_len = 4
  if text[-1] == "="
    out_char_len = 3
    text[-1] = "" 
  end

  if text[-1] == "="
    out_char_len = 2
    text[-1] = "" 
  end

  bit_string = text.length.times.collect do |i|
    TABLE.index(text[i]).to_s(2).rjust(6, "0")
  end.join
  out_char_len.times.collect do |i|
    if bit_string[0+(i*8)...8+(i*8)].to_i(2) > 0
      bit_string[0+(i*8)...8+(i*8)].to_i(2).chr
    end
  end.join
end

def decode(text)
  result = ""
  while text.length >= 4
    result += _decode(text.slice!(0,4))
  end
  result
end

text = "Olá"

puts encode(text) == Base64.strict_encode64(text) 
puts encode(text)

puts decode(encode(text))