/*
 * Copyright (C) 1993 Serge Vakulenko, <vak@zebub.msk.su>
 * Tables by Andrew Chernov, <ache@astral.msk.su>
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>

void (*process) ();

unsigned char koi8_alt[] = {
	0xc4, 0xb3, 0xda, 0xbf, 0xc0, 0xd9, 0xc3, 0xb4,
	0xc2, 0xc1, 0xc5, 0xdf, 0xdc, 0xdb, 0xdd, 0xde,
	0xb0, 0xb1, 0xb2, 0xf4, 0xfe, 0xf9, 0xfb, 0xf7,
	0xf3, 0xf2, 0xff, 0xf5, 0xf8, 0xfd, 0xfa, 0xf6,
	0xcd, 0xba, 0xd5, 0xf1, 0xd6, 0xc9, 0xb8, 0xb7,
	0xbb, 0xd4, 0xd3, 0xc8, 0xbe, 0xbd, 0xbc, 0xc6,
	0xc7, 0xcc, 0xb5, 0xf0, 0xb6, 0xb9, 0xd1, 0xd2,
	0xcb, 0xcf, 0xd0, 0xca, 0xd8, 0xd7, 0xce, 0xfc,
	0xee, 0xa0, 0xa1, 0xe6, 0xa4, 0xa5, 0xe4, 0xa3,
	0xe5, 0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae,
	0xaf, 0xef, 0xe0, 0xe1, 0xe2, 0xe3, 0xa6, 0xa2,
	0xec, 0xeb, 0xa7, 0xe8, 0xed, 0xe9, 0xe7, 0xea,
	0x9e, 0x80, 0x81, 0x96, 0x84, 0x85, 0x94, 0x83,
	0x95, 0x88, 0x89, 0x8a, 0x8b, 0x8c, 0x8d, 0x8e,
	0x8f, 0x9f, 0x90, 0x91, 0x92, 0x93, 0x86, 0x82,
	0x9c, 0x9b, 0x87, 0x98, 0x9d, 0x99, 0x97, 0x9a,
};

unsigned char alt_koi8[] = {
	0xe1, 0xe2, 0xf7, 0xe7, 0xe4, 0xe5, 0xf6, 0xfa,
	0xe9, 0xea, 0xeb, 0xec, 0xed, 0xee, 0xef, 0xf0,
	0xf2, 0xf3, 0xf4, 0xf5, 0xe6, 0xe8, 0xe3, 0xfe,
	0xfb, 0xfd, 0xff, 0xf9, 0xf8, 0xfc, 0xe0, 0xf1,
	0xc1, 0xc2, 0xd7, 0xc7, 0xc4, 0xc5, 0xd6, 0xda,
	0xc9, 0xca, 0xcb, 0xcc, 0xcd, 0xce, 0xcf, 0xd0,
	0x90, 0x91, 0x92, 0x81, 0x87, 0xb2, 0xb4, 0xa7,
	0xa6, 0xb5, 0xa1, 0xa8, 0xae, 0xad, 0xac, 0x83,
	0x84, 0x89, 0x88, 0x86, 0x80, 0x8a, 0xaf, 0xb0,
	0xab, 0xa5, 0xbb, 0xb8, 0xb1, 0xa0, 0xbe, 0xb9,
	0xba, 0xb6, 0xb7, 0xaa, 0xa9, 0xa2, 0xa4, 0xbd,
	0xbc, 0x85, 0x82, 0x8d, 0x8c, 0x8e, 0x8f, 0x8b,
	0xd2, 0xd3, 0xd4, 0xd5, 0xc6, 0xc8, 0xc3, 0xde,
	0xdb, 0xdd, 0xdf, 0xd9, 0xd8, 0xdc, 0xc0, 0xd1,
	0xb3, 0xa3, 0x99, 0x98, 0x93, 0x9b, 0x9f, 0x97,
	0x9c, 0x95, 0x9e, 0x96, 0xbf, 0x9d, 0x94, 0x9a,
};

void todos ()
{
	register c;

	while ((c = getchar ()) != EOF) {
		if (c == '\n')
			putchar ('\r');
		else if (c & 0200)
			c = koi8_alt [c-0200];
		putchar (c);
	}
}

void fromdos ()
{
	register c;

	while ((c = getchar ()) != EOF && c != ('z'&037)) {
		if (c == '\r') {
			c = getchar ();
			if (c != '\n')
				putchar ('\r');
		} else if (c & 0200)
			c = alt_koi8 [c-0200];
		putchar (c);
	}
}

void usage ()
{
	printf ("Koi8-r <-> ALT converter, Copyright (C) 1993 Serge Vakulenko\n");
	printf ("Usage:\n\ttd filename...\t\tKoi8-r -> Alt\n");
	printf ("or:\n\tfd filename...\t\tAlt -> Koi8-r \n");
	exit (0);
}

int main (int argc, char **argv)
{
	register i;

	if (strcmp (*argv + strlen (*argv) - 2, "td") == 0)
		process = todos;
	else
		process = fromdos;

	if (argc <= 1) {
		if (isatty (0))
			usage ();
		(*process) ();
		return (0);
	}

	if (argv[1][0] == '-')
		usage ();

	for (i=1; i<argc; ++i) {
		char bak [512];
		struct stat s;

		if (stat(argv[i], &s) < 0)  {
			perror(argv[i]);
			continue;
		}
		if (!S_ISREG(s.st_mode)) {
			fprintf(stderr, "File %s must be regular file.\n", argv[i]);
			continue;
		}
		strcpy (bak, argv[i]);
		strcat (bak, "~");
		if (link (argv[i], bak) < 0 || unlink (argv[i]) < 0) {
			perror (argv[i]);
			continue;
		}
		if (! freopen (bak, "r", stdin)) {
			perror (bak);
			continue;
		}
		if (! freopen (argv[i], "w", stdout)) {
			perror (argv[i]);
			continue;
		}
		(*process) ();
		if (! ferror (stdout))
			unlink (bak);
	}
	return (0);
}