class RC4

def encrypt(text)
  process text.dup
end 

def encrypt!(text)
  process text
end  

def initialize(str)
  begin
    raise SyntaxError, "RC4: Key supplied is blank"  if str.eql?('')
    @q1, @q2 = 0, 0
    @key = []
    str.each_byte {|elem| @key << elem} while @key.size < 256
    @key.slice!(256..@key.size-1) if @key.size >= 256
    @s = (0..255).to_a
    j = 0 
    0.upto(255) do |i| 
      j = (j + @s[i] + @key[i] )%256
      @s[i], @s[j] = @s[j], @s[i]
    end    
  end
end

def process(text)
  text.unpack("C*").map { |c| c ^ round }.pack("C*")
end

def round
  @q1 = (@q1 + 1)%256
  @q2 = (@q2 + @s[@q1])%256
  @s[@q1], @s[@q2] = @s[@q2], @s[@q1]
  @s[(@s[@q1]+@s[@q2])%256]  
end