#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>

char *HOME;
char *HOSTNAME;
char *USER;

char PROMPT[50];

void do_exec (char *argv[])
{
	switch (fork ())
	{
	case -1:
		perror ("fork()");
		break;
	case 0:
		execvp (argv[0], argv);
		perror ("execvp()");
		exit (1);
		break;
	default:
		wait (NULL);
		break;
	}
}

int is_special_command (char *argv[])
{
	if (!strcmp (argv[0], "exit"))
	{
		exit (0);
	}

	if (!strcmp (argv[0], "cd"))
	{
		if (!argv[1])
		{
			chdir (HOME);
			return 1;
		}
		
		if (strchr (argv[1], '~'))
		{
			char aux[1024] = {};

			strcat (aux, HOME);
			strcat (aux, argv[1] + 1);
			chdir (aux);
		}
		
		chdir (argv[1]);
		
		return 1;
	}
	
	return 0;
}

void parse_command (char *command)
{
	char *argv[255];
	unsigned char idx = 1;

	argv[0] = strtok (command, " \t\n");
	while (argv[idx++] = strtok (NULL, " \t\n"))
		;
	
	if (!is_special_command (argv))
	{
		do_exec (argv);
	}
}

char *get_command ()
{
	char command[1024];
	char c;
	int idx = 0;
	
	printf ("%s ", PROMPT);
	
	while ((c = getchar ()) != '\n')
	{
		switch (c)
		{
		case '\b':
			idx--;
			break;
		default:
			command[idx++] = c;
			break;
		}
	}
	
	command[idx] = '\0';
	
	return command;
}

void setup ()
{
	HOME = getenv ("HOME");
	HOSTNAME = getenv ("HOSTNAME");
	USER = getenv ("USER");

	strcpy (PROMPT, USER);
	strcat (PROMPT, "@");
	strcat (PROMPT, HOSTNAME);
	strcat (PROMPT, "$ ");
}

int main (int argc, char *argv[])
{
	char *command;

	setup ();

	while (1)
		parse_command (get_command ());

	return 0;
}