// simple shell
// executes one command a time without arguments and flags
// not supports pipelines 
// not supports input/output redirection 

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

#define MAXLINE 2048
enum {FOREGROUND,BACKGROUND};
static volatile sig_atomic_t sigflag; /* set nonzero by sig handler */
static sigset_t newmask, oldmask, zeromask;

void  executeCommand(char *cmd);
void forkProcess(char **,int cnt);
void wait_child(void);
void collect_child();
void sig_handler();

int main(void)
{
	char	buf[MAXLINE];

	printf("smash:>");	/* print prompt (printf requires %% to print %) */
	while (fgets(buf, MAXLINE, stdin)!=NULL) 
	{
		buf[strlen(buf) - 1] = 0;	/* replace newline with null */
		
		executeCommand(buf);
		printf("smash:>");
		
	}
	exit(0);
}

void  executeCommand(char *cmd)
{
	char **argsList=NULL;
	int argsCnt=0;
	
	char *ptr;
	char *tmpCmd=strdup(cmd);
	
	ptr=strtok(tmpCmd," 	");
	
	while(ptr!=NULL)
	{
		argsList=(char**)realloc(argsList,sizeof(char**)*(++argsCnt)+1);
		argsList[argsCnt-1]=strdup(ptr); 
		ptr=strtok(NULL," 	");
	}
	
	argsList[argsCnt]=NULL;
	
	if(strcmp(argsList[0],"exit")==0)
	{
		if(argsCnt==1)
		{
			printf("Bye\n");
			exit(0);
		}
		else
			printf("error : exit does'nt accept arguments.\n")	;	
	}
	
	else if(strcmp(argsList[0],"cd")==0)
	{
		if(argsCnt==2)
			chdir(argsList[1]);
		else
			printf("error : invalid number of arguments for cd.\n");	
	}
	
	else 
		forkProcess(argsList,argsCnt);
}

void forkProcess(char **argsList,int cnt)
{
	pid_t	pid;
	int runStyle;
	
	
	if(strcmp(argsList[cnt-1],"&")==0)
	{
		runStyle=BACKGROUND ;
		argsList[cnt-1]=NULL;
	}
	else
		runStyle=FOREGROUND;
	
		
	if ( (pid = fork()) < 0)
		fprintf(stderr,"fork error");

	if (pid == 0) 
	{		
		if (execvp(argsList[0], argsList)< 0)
		  fprintf(stderr,"execl error");
	}
	else //parent
	{		
		if(runStyle==FOREGROUND)  
		{
			printf("waitttt\n");
			wait_child();
		}
		else
		{
			if (signal(SIGCHLD, sig_handler) == SIG_ERR)        
				printf("signal(SIGUSR1) error");    
		}
	}
}

void sig_handler()
{
	pid_t	pid;
	int	status;
	
	printf("sig handler\n");
	sigflag = 1;
	
	if ((pid=wait(&status)) < 0)	
	{
      		perror("Wait failed\n");
      		exit(3);
    	}
    	else
	{
      		if (WIFEXITED(status))
        		printf ("Pid %d terminated with status %d\n", pid, WEXITSTATUS(status));
      		else if (WIFSIGNALED(status))
        		printf ("Pid %d terminated by signal %d\n", pid, WTERMSIG(status));
    	}	
}

void wait_child(void){   

	if (signal(SIGCHLD, sig_handler) == SIG_ERR)        
		printf("signal(SIGUSR1) error");    
		
	sigemptyset(&zeromask);    
	sigemptyset(&newmask);    
	sigaddset(&newmask, SIGCHLD);    
  
	
	if (sigprocmask(SIG_BLOCK, &newmask, &oldmask) < 0)        
		printf("SIG_BLOCK error");
 
		
	while (sigflag == 0)        
		sigsuspend(&zeromask);  /* and wait for child */    
	
	sigflag = 0;    /*     * Reset signal mask to original value.     */    

	if (sigprocmask(SIG_SETMASK, &oldmask, NULL) < 0)        
		printf("SIG_SETMASK error");

}