/*
 * ASCII caesar cipher - rotate every letter in a phrase and print the result.
 * Numbers 65-90 are capital letters A-Z. 97-122 lowercase a-z.
 * If the first argument is an integer, it is used for the number of rotations.
 * Otherwise, the first argument is treated as text.
 * 
 * Install as a command:
 * #!/bin/sh
 * gcc -s -o ~/.local/bin/caesar caesar.c
 *
 * Copyright (C) 2025 by lucke <lucke@waifu.club>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
 * WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE
 * FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY
 * DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN
 * AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT
 * OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <stdio.h>
#include <stdlib.h>

#define USAGE "%s [+/-][ROTATIONS] Your Message\n"

char caesar(int r, char c);

/*
 * rot: Number of rotations
 * one: first argument to read as text
 * cur: current character to manipulate
 */
int
main(int argc, char *argv[])
{
	int rot;
	int one;
	char cur;

	if (argc < 2) {
		putchar(7); /* bell */
		fprintf(stderr, "Usage: " USAGE, argv[0]);
		return 1;
	}

	rot = atoi(argv[1]);
	one = 2;

	/* ROT13 by default */
	if (rot == 0) {
		rot = 13;
		one = 1;
	}

	/* negatives wrap around, good for deciphering */
	if (rot < 0)
		rot = 26 - (-1 * (rot % 26));

	for (int i = one; i < argc; i++) {
		for (int j = 0; argv[i][j] != '\0'; j++) {
			cur = caesar(rot, argv[i][j]);
			putchar(cur);
		}
		/* seamlessly separate args  */
		if (i < argc - 1)
			putchar(' ');
	}

	putchar('\n');
	
	return 0;
}

char
caesar(int r, char c)
{
	/* assume lowercase first */
	if ((c > 122) || (c < 97))
		goto notlower;

	c -= 97;
	c = (c + r) % 26;
	c += 97;

	return c;

notlower:
	if ((c > 90) || (c < 65))
		return c;

	c -= 65;
	c = (c + r) % 26;
	c += 65;

	return c;
}