/*
 * A simple shell with some basic features.
 *
 * Sami Samhuri 0327342
 * January 31, 2006
 * CSC 360, Assignment 1
 *
 * exec.c -- fork and execute a program
 * $Id: exec.c 184 2006-01-29 08:53:30Z sjs $
 */

/*#define _GNU_SOURCE*/
 
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>	/* waitpid */
#include <sys/wait.h>	/* waitpid */
#include <unistd.h>

#include "exec.h"
#include "utils.h"
#include "main.h"

char *is_executable ( char *file )
{
	if ( strchr (file, '/') )
	{	/* process absolute and relative paths directly */
		if ( access (file, X_OK) == 0 )
			return strdup (file);
		else
			return NULL;
	}

	char *path = strdup ( getenv ("PATH") );
	int file_len = strlen (file);
	char *dir = strtok (path, ":");
	char *filename = NULL;
	while ( dir )
	{
		filename = (char *)myxmalloc (strlen (dir) + file_len + 2);
		sprintf (filename, "%s/%s", dir, file);
		if ( access (filename, X_OK) == 0 )
			break;
		free (filename);
		filename = NULL;
		dir = strtok (NULL, ":");
	}
	xfree (path);
	return filename;
}

pid_t exec_command ( char **argv, int background )
{
	int status;
	pid_t pid;
	char *filename;

	if ( !(filename = is_executable (argv[0])) )
	{	/* error, not executable */
		char *msg = (char *)myxmalloc (MSGLEN);
		sprintf (msg, RED "%s: %s" CLEAR, argv[0], strerror (errno));
		queue_message (msg);
		free (msg);
		return -1;
	}
	
	if ( (pid = fork()) > 0 )
	{ /* parent */
		if ( background )
			waitpid (pid, &status, WNOHANG);
		else
			waitpid (pid, &status, 0);
	}
	else if ( pid == 0 )
	{ /* child */
		/* kludge, briefly wait for the job to be created so that if the
		 * command exits quickly, the job is found and removed. otherwise there
		 * are zombie jobs erroneously lying around. note, this isn't guaranteed
		 * to work, it just seems to be enough time in tests here.
		 */
		usleep (100);
		execv (filename, argv);

		/* if we get here there was an error, display it */
		printf (RED "\nCannot execute '%s' (%s)\n" CLEAR, argv[0],
				strerror(errno));
		free (filename);
		_exit (EXIT_FAILURE);
	}
	else
	{ /* error, pid < 0 */
		queue_message (RED "Unable to fork(), uh oh..." CLEAR);
	}
	free (filename);
	return pid;
}