Base64 implementation in Ruby

之前一直以为 Base64 很简单，真到自己去实现才发现没那么好写☹️。

require 'base64'

class String
    def my_base64_encode(alphabeta = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/")
        # 把 str 拆成字符组成的数组
        str = self
        ary = str.split('')

        # 变成 2 进制
        bin = ary.map { |e| "%08d" % e.ord.to_s(2) }
                 .reduce("") { |memo, e| memo += e }
        # 分组:
        bin.split('').each_slice(6).to_a
        len = bin.split('').size
        # puts "length: #{len} = #{len / 6} * 6 + #{len % 6}"
        # puts "append: #{(6 - len % 6) % 6} bits zero. "

        # 填充:
        bin += ( '0' * ((6 - len % 6) % 6) )

        bin.split('').each_slice(6).to_a
        bs = bin.split('').each_slice(6).map { |e| alphabeta[e.join().to_i(2)] }

        result = bs.reduce("") { |memo, e| memo += e }

        # 填充 = :
        result += ( '=' * ((6 - len % 6) % 6 / 2) )
    end
    
    def my_base64_decode(alphabeta = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/")
        # 把 str 拆成字符组成的数组
        str = self.chomp
        dictionary = {}
        alphabeta.split('').each_with_index { |e, i| dictionary[e] = i }
        
        tail = str.scan(/=+$/).first || ""
        count = tail.size
        
        ary = str.gsub(/=+$/, '').split('')
        # pp ary.map { |e| dictionary[e] }
        bin = ary.map { |e| "%06d" % dictionary[e].to_s(2) }
        s = bin.join
        result = s[0...(s.size - count * 2)]
                    .split('')
                    .each_slice(8)
                    .to_a
                    .map { |e| e.join.to_i(2).chr }
                    .join
    end
end

str = "sky"
puts str.my_base64_encode   #=> c2t5
puts Base64.encode64(str)   #=> c2t5
puts Base64.encode64(str).my_base64_decode   #=> sky

str = "ABCD"
puts str.my_base64_encode   #=> QUJDRA==
puts Base64.encode64(str)   #=> QUJDRA==
puts Base64.encode64(str).my_base64_decode   #=> ABCD

str = "command?"
puts str.my_base64_encode("aABCDEFGHIJKLMNOPQRSTUVWXYZbcdefghijklmnopqrstuvwxyz0123456789+/")   #=> X29tbVEuYC8=
puts Base64.encode64(str)   #=> Y29tbWFuZD8=
puts str.my_base64_encode("aABCDEFGHIJKLMNOPQRSTUVWXYZbcdefghijklmnopqrstuvwxyz0123456789+/")
        .my_base64_decode("aABCDEFGHIJKLMNOPQRSTUVWXYZbcdefghijklmnopqrstuvwxyz0123456789+/")   #=> command?