#
# = base64.rb: methods for base64-encoding and -decoding stings
#

# The Base64 module provides for the encoding (#encode64, #strict_encode64,
# #urlsafe_encode64) and decoding (#decode64, #strict_decode64,
# #urlsafe_decode64) of binary data using a Base64 representation.
#
# == Example
#
# A simple encoding and decoding. 
# 
#     require "base64"
#
#     enc   = Base64.encode64('Send reinforcements')
#                         # -> "U2VuZCByZWluZm9yY2VtZW50cw==\n" 
#     plain = Base64.decode64(enc)
#                         # -> "Send reinforcements"
#
# The purpose of using base64 to encode data is that it translates any
# binary data into purely printable characters.

module Base64
  module_function

  # Returns the Base64-encoded version of +bin+.
  # This method complies with RFC 2045.
  # Line feeds are added to every 60 encoded charactors.
  #
  #    require 'base64'
  #    Base64.encode64("Now is the time for all good coders\nto learn Ruby")
  #
  # <i>Generates:</i>
  #
  #    Tm93IGlzIHRoZSB0aW1lIGZvciBhbGwgZ29vZCBjb2RlcnMKdG8gbGVhcm4g
  #    UnVieQ==
  def encode64(bin)
    [bin].pack("m")
  end

  # Returns the Base64-decoded version of +str+.
  # This method complies with RFC 2045.
  # Characters outside the base alphabet are ignored.
  #
  #   require 'base64'
  #   str = 'VGhpcyBpcyBsaW5lIG9uZQpUaGlzIG' +
  #         'lzIGxpbmUgdHdvClRoaXMgaXMgbGlu' +
  #         'ZSB0aHJlZQpBbmQgc28gb24uLi4K'
  #   puts Base64.decode64(str)
  #
  # <i>Generates:</i>
  #
  #    This is line one
  #    This is line two
  #    This is line three
  #    And so on...
  def decode64(str)
    str.unpack("m").first
  end

  # Returns the Base64-encoded version of +bin+.
  # This method complies with RFC 4648.
  # No line feeds are added.
  def strict_encode64(bin)
    [bin].pack("m0")
  end

  # Returns the Base64-decoded version of +str+.
  # This method complies with RFC 4648.
  # ArgumentError is raised if +str+ is incorrectly padded or contains
  # non-alphabet characters.  Note that CR or LF are also rejected.
  def strict_decode64(str)
    str.unpack("m0").first
  end

  # Returns the Base64-encoded version of +bin+.
  # This method complies with ``Base 64 Encoding with URL and Filename Safe
  # Alphabet'' in RFC 4648.
  # The alphabet uses '-' instead of '+' and '_' instead of '/'.
  def urlsafe_encode64(bin)
    strict_encode64(bin).tr("+/", "-_")
  end

  # Returns the Base64-decoded version of +str+.
  # This method complies with ``Base 64 Encoding with URL and Filename Safe
  # Alphabet'' in RFC 4648.
  # The alphabet uses '-' instead of '+' and '_' instead of '/'.
  def urlsafe_decode64(str)
    strict_decode64(str.tr("-_", "+/"))
  end
end
