/*
 * Copyright (c) 2016 Nicholas De Nova.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * 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.
 *
 * logname.c
 * Print login name.
 */

#include <err.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

static void compact_arguments(int* argc, char*** argv)
{
	for ( int i = 0; i < *argc; i++ )
	{
		while ( i < *argc && !(*argv)[i] )
		{
			for ( int n = i; n < *argc; n++ )
				(*argv)[n] = (*argv)[n+1];
			(*argc)--;
		}
	}
}

int main(int argc, char* argv[])
{
	for ( int i = 1; i < argc; i++ )
	{
		const char* arg = argv[i];
		if ( arg[0] != '-' || !arg[1] )
			continue;
		argv[i] = NULL;
		if ( !strcmp(arg, "--") )
			break;
		if ( arg[1] != '-' )
		{
			char c;
			while ( (c = *++arg) )
				switch ( c )
				{
				default:
					errx(1, "unknown option -- '%c'", c);
				}
		}
		else
			errx(1, "unknown option: %s", arg);
	}

	compact_arguments(&argc, &argv);

	if ( 1 < argc )
		errx(1, "unexpected extra operand");

	errno = 0;
	char* login_name = getlogin();
	if ( !login_name )
	{
		if ( errno )
			err(1, "could not get login name");
		else
			errx(1, "could not get login name");
	}

	printf("%s\n", login_name);
	if ( ferror(stdout) || fflush(stdout) == EOF )
		err(1, "stdout");

	return 0;
}
