// author OBLiQUE
// copyleft 2009
// simple unix shell skeleton
// p0wnbox.com
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <unistd.h>
#include <signal.h>
#include <errno.h>
#include <sys/utsname.h>
#include <sys/wait.h>

#define MAX_STRING 0xfff
#define MAX_ARGS 30

const char *shell_commands[] = {"cd","exit","\0"};

void print_prompt();
int chk_sh_cmds(char *str, char **tok);
void sig_int(const int sig_num);

int main(int argc, char *arg[])
{
	char *tok, buf[MAX_STRING], *args[MAX_ARGS+1];
	int readlen, sh_cmd_num, arg_num, status;
	pid_t pid;

	// register SIGINT signal handler to disable ctrl+c
	if (signal(SIGINT,sig_int)==SIG_ERR)
		fprintf(stderr,"signal(): cannot register signal handler\n");

	print_prompt();

	while (readlen=read(STDIN_FILENO,buf,MAX_STRING)) { // read the line and return the length
		buf[readlen-1]='\0'; // remove \n from the end
		if (sh_cmd_num=chk_sh_cmds(buf,&tok)) { // check if its a shell command
			switch (sh_cmd_num) {
				case 1: // cd
					if (chdir(tok)<0) // change directory
						fprintf(stderr,"chdir(): %s\n",strerror(errno)); 
					break;
				case 2: // exit
					printf("exit\n");
					exit(EXIT_SUCCESS);
			}
		} else { // if it's not a shell command
			tok=strtok(buf," "); // replace the first space with '\0' and take the tokken
			arg_num=0; // initiliaze the arg_num
			while (tok!=NULL && arg_num<MAX_ARGS) { // repeat until the end of string or until the MAX_ARGS
				args[arg_num]=tok; // put the tokken to the array
				arg_num++; // increase the arg_num
				tok=strtok(NULL," "); // replace the next space with '\0' and take the tokken
			}
			args[arg_num]=NULL; // fill with NULL the last empty argument
			
			if (args[0]!=NULL) { // i there is a command to execute
				if ((pid=fork())<0) { // fork a child and check if it's forked
					fprintf(stderr,"fork(): %s\n",strerror(errno)); 
				} else if (pid==0) { // if i'm the child
					execvp(args[0],args); // execute the command
					// the exec replace its memory with command that executes
					// so if i get this error means that exec failed
					fprintf(stderr,"execvp(): %s\n",strerror(errno));
					exit(EXIT_FAILURE); // child exit
				}
				// i'm the parent
				if ((pid=waitpid(pid,&status,0)<0)) // wait the child to exit
					fprintf(stderr,"waitpid(): %s\n",strerror(errno));
			}
		}
		print_prompt();
	} // end of while
}

void sig_int(const int sig_num)
{
	printf("\n");
	print_prompt();
}

void print_prompt()
{
	struct utsname s_uname; // uname structure
	char path[PATH_MAX], symbol, *login_name, *dir_name;

	if (getuid()) symbol='$'; // if uid!=0 the symbol is $
	else symbol='#'; // otherwise is #
	uname(&s_uname); // retrieve system information
	login_name=getlogin(); // retrieve login username
	getcwd(path,PATH_MAX); // retrieve path
	dir_name=strrchr(path,'/'); // find the directory name
	printf("%s@%s %s/ %c ",login_name,s_uname.nodename,++dir_name,symbol);
	fflush(stdout); // force to write the buffered data to stdout
}

// this function returns 0 if the command is not a shell command
// otherwise returns the index of the shell command
int chk_sh_cmds(char *str, char **tok)
{
	if (str[0]=='\0') return 0; // if the string is null return 0
	strtok_r(str," ",tok); // find the first space and replace it with '\0'
	int i;
	for (i=0; shell_commands[i][0]!='\0'; i++) // loop until the end of array
		if (!strcmp(str,shell_commands[i])) return i+1; // i is a shell command return i+1
	if (*((*tok)-1)=='\0') *((*tok)-1)=' '; // restore the space
	return 0;
}