# ROT13
# Joseph Ensminger

# encodes string
def encode value, offset
	cypher = ""
	value.each_char do |c|
		if c.ord <= 90 && c.ord >= 65
			cypher << ((((c.ord - 65) + offset) % 26) + 65)
		elsif c.ord <= 122 && c.ord >= 91
			cypher << ((((c.ord - 97) + offset) % 26) + 97)
		else
			cypher << c
		end
	end
	cypher
end

# decodes string
def decode value, offset
	decypher = ""
	value.each_char do |c|
		if c.ord <= 90 && c.ord >= 65
			decypher << ((((c.ord - 65) - offset) % 26) + 65)
		elsif c.ord <= 122 && c.ord >= 91
			decypher << ((((c.ord - 97) - offset) % 26) + 97)
		else
			decypher << c
		end
	end
	decypher
end

# determines which line in file to decode and encode. returns an output file.
def caesarCipher (file, offset = 13)
	input = File.open(file, "r")
	output = File.open("output","w")
	input.each_line do |line|
		if line[0] == "e"
			line = line[2..-1]
			output.write(encode(line, offset))
		elsif line[0] == "d"
			line = line[2..-1]
			output.write(decode(line, offset))
		else
			puts "No command in file"
	    end
	end
	input.close
	output.close
end

# Testing on file
caesarCipher("cipher",13)