import <Utilities/Sequence.sl>;
import <Utilities/Conversion.sl>;

lowerAlphabet := "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
upperAlphabet := "abcdefghijklmnopqrstuvwxyz";

caesarEncrypt(ch, key) :=
	let
		correctAlphabet :=
				lowerAlphabet when some(ch = lowerAlphabet)
			else
				upperAlphabet;
		
		index := Sequence::firstIndexOf(correctAlphabet, ch);
		
		newIndex := (index + key - 1) mod 26 + 1;
	in
		ch when not(some(ch = lowerAlphabet) or some(ch = upperAlphabet))
	else
		correctAlphabet[newIndex];
		
caesarDecrypt(ch, key) := caesarEncrypt(ch, 26 - key);

main(args(2)) :=
	let
		key := Conversion::stringToInt(args[2]);
		encrypted := caesarEncrypt(args[1], key);
		decrypted := caesarDecrypt(encrypted, key);
	in
		"Input: \t" ++ args[1] ++ "\n" ++
		"Encrypted:\t" ++ encrypted ++ "\n" ++
		"Decrypted:\t" ++ decrypted;