#include <inc/lib.h>

#define BUFSIZ 1024		/* Find the buffer overrun bug! */
int debug = 1;


// gettoken(s, 0) prepares gettoken for subsequent calls and returns 0.
// gettoken(0, token) parses a shell token from the previously set string,
// null-terminates that token, stores the token pointer in '*token',
// and returns a token ID (0, '<', '>', '|', or 'w').
// Subsequent calls to 'gettoken(0, token)' will return subsequent
// tokens from the string.
int gettoken(char *s, char **token);


// Parse a shell command from string 's' and execute it.
// Do not return until the shell command is finished.
// runcmd() is called in a forked child,
// so it's OK to manipulate file descriptor state.
#define MAXARGS 16
void
runcmd(char* s)
{
	char *argv[MAXARGS], *t, argv0buf[BUFSIZ];
	int argc, c, i, r, p[2], fd, pipe_child;

	pipe_child = 0;
	gettoken(s, 0);
	
again:
	argc = 0;
	while (1) {
		switch ((c = gettoken(0, &t))) {

		case 'w':	// Add an argument
			if (argc == MAXARGS) {
				cprintf("too many arguments\n");
				exit();
			}
			argv[argc++] = t;
			break;
			
		case '<':	// Input redirection
			// Grab the filename from the argument list
			if (gettoken(0, &t) != 'w') {
				cprintf("syntax error: < not followed by word\n");
				exit();
			}
			// Open 't' for reading as file descriptor 0
			// (which environments use as standard input).
			// We can't open a file onto a particular descriptor,
			// so open the file as 'fd',
			// then check whether 'fd' is 0.
			// If not, dup 'fd' onto file descriptor 0,
			// then close the original 'fd'.
			
			// LAB 5: Your code here.
            if ((fd = open(t, O_RDONLY)) < 0) {
                cprintf("could not open stdin: %e\n",fd);
                exit();
            }
            if (fd != 0) {
                if ((r = dup(fd, 0)) < 0) {
                    cprintf("could not change file descriptor to 0: %e\n",r);
                    exit();
                } else {
                    close(fd);
                }
            }
            break;
			
		case '>':	// Output redirection
			// Grab the filename from the argument list
			if (gettoken(0, &t) != 'w') {
				cprintf("syntax error: > not followed by word\n");
				exit();
			}
			// Open 't' for writing as file descriptor 1
			// (which environments use as standard output).
			// We can't open a file onto a particular descriptor,
			// so open the file as 'fd',
			// then check whether 'fd' is 1.
			// If not, dup 'fd' onto file descriptor 1,
			// then close the original 'fd'.
			
			// LAB 5: Your code here.
			if ((fd = open(t, O_WRONLY)) < 0) {
                cprintf("could not open stdin: %e\n",fd);
                exit();
            }
            if (fd != 1) {
                if ((r = dup(fd, 1)) < 0) {
                    cprintf("could not change file descriptor to 0: %e\n",r);
                    exit();
                } else {
                    close(fd);
                }
            }
            break;
			
		case '|':	// Pipe
			// Set up pipe redirection.
			
			// Allocate a pipe by calling 'pipe(p)'.
			// Like the Unix version of pipe() (man 2 pipe),
			// this function allocates two file descriptors;
			// data written onto 'p[1]' can be read from 'p[0]'.
			// Then fork.
			// The child runs the right side of the pipe:
			//	Use dup() to duplicate the read end of the pipe
			//	(p[0]) onto file descriptor 0 (standard input).
			//	Then close the pipe (both p[0] and p[1]).
			//	(The read end will still be open, as file
			//	descriptor 0.)
			//	Then 'goto again', to parse the rest of the
			//	command line as a new command.
			// The parent runs the left side of the pipe:
			//	Set 'pipe_child' to the child env ID.
			//	dup() the write end of the pipe onto
			//	file descriptor 1 (standard output).
			//	Then close the pipe.
			//	Then 'goto runit', to execute this piece of
			//	the pipeline.

			// LAB 5: Your code here.
			if ((r = pipe(p)) < 0) {
                cprintf("could not open a pipe: %e\n",r);
                exit();
            }
            if ((pipe_child = fork()) < 0) {
                cprintf("could not fork a child: %e\n",pipe_child);
                exit();
            }
            if (pipe_child == 0) {
                if ((r = dup(p[0], 0)) < 0) {
                    cprintf("could not move pipe to stdin: %e\n",r);
                    exit();
                }
                close(p[0]);
                close(p[1]);
                goto again;
            } else {
                if ((r = dup(p[1],1)) < 0) {
                    cprintf("could not move pipe to stdout: %e\n",r);
                    exit();
                }
                close(p[0]);
                close(p[1]);
                goto runit;
            }
			break;

		case 0:		// String is complete
			// Run the current command!
			goto runit;
			
		default:
			panic("bad return %d from gettoken", c);
			break;
			
		}
	}

runit:
	// Return immediately if command line was empty.
	if(argc == 0) {
		if (debug)
			cprintf("EMPTY COMMAND\n");
		return;
	}

	// Clean up command line.
	// Read all commands from the filesystem: add an initial '/' to
	// the command name.
	// This essentially acts like 'PATH=/'.
	if (argv[0][0] != '/') {
		argv0buf[0] = '/';
		strcpy(argv0buf + 1, argv[0]);
		argv[0] = argv0buf;
	}
	argv[argc] = 0;
	
	// Print the command.
	if (debug) {
		cprintf("[%08x] SPAWN:", env->env_id);
		for (i = 0; argv[i]; i++)
			cprintf(" %s", argv[i]);
		cprintf("\n");
	}

	// Spawn the command!
	if ((r = spawn(argv[0], (const char**) argv)) < 0)
		cprintf("spawn %s: %e\n", argv[0], r);

	// In the parent, close all file descriptors and wait for the
	// spawned command to exit.
	close_all();
	if (r >= 0) {
		if (debug)
			cprintf("[%08x] WAIT %s %08x\n", env->env_id, argv[0], r);
		wait(r);
		if (debug)
			cprintf("[%08x] wait finished\n", env->env_id);
	}

	// If we were the left-hand part of a pipe,
	// wait for the right-hand part to finish.
	if (pipe_child) {
		if (debug)
			cprintf("[%08x] WAIT pipe_child %08x\n", env->env_id, pipe_child);
		wait(pipe_child);
		if (debug)
			cprintf("[%08x] wait finished\n", env->env_id);
	}

	// Done!
	exit();
}


// Get the next token from string s.
// Set *p1 to the beginning of the token and *p2 just past the token.
// Returns
//	0 for end-of-string;
//	< for <;
//	> for >;
//	| for |;
//	w for a word.
//
// Eventually (once we parse the space where the \0 will go),
// words get nul-terminated.
#define WHITESPACE " \t\r\n"
#define SYMBOLS "<|>&;()"

int
_gettoken(char *s, char **p1, char **p2)
{
	int t;

	if (s == 0) {
		if (debug > 1)
			cprintf("GETTOKEN NULL\n");
		return 0;
	}

	if (debug > 1)
		cprintf("GETTOKEN: %s\n", s);

	*p1 = 0;
	*p2 = 0;

	while (strchr(WHITESPACE, *s))
		*s++ = 0;
	if (*s == 0) {
		if (debug > 1)
			cprintf("EOL\n");
		return 0;
	}
	if (strchr(SYMBOLS, *s)) {
		t = *s;
		*p1 = s;
		*s++ = 0;
		*p2 = s;
		if (debug > 1)
			cprintf("TOK %c\n", t);
		return t;
	}
	*p1 = s;
	while (*s && !strchr(WHITESPACE SYMBOLS, *s))
		s++;
	*p2 = s;
	if (debug > 1) {
		t = **p2;
		**p2 = 0;
		cprintf("WORD: %s\n", *p1);
		**p2 = t;
	}
	return 'w';
}

int
gettoken(char *s, char **p1)
{
	static int c, nc;
	static char* np1, *np2;

	if (s) {
		nc = _gettoken(s, &np1, &np2);
		return 0;
	}
	c = nc;
	*p1 = np1;
	nc = _gettoken(np2, &np1, &np2);
	return c;
}


void
usage(void)
{
	cprintf("usage: sh [-dix] [command-file]\n");
	exit();
}

void
umain(int argc, char **argv)
{
	int r, interactive, echocmds;

	interactive = '?';
	echocmds = 0;
	ARGBEGIN{
	case 'd':
		debug++;
		break;
	case 'i':
		interactive = 1;
		break;
	case 'x':
		echocmds = 1;
		break;
	default:
		usage();
	}ARGEND

	if (argc > 1)
		usage();
	if (argc == 1) {
		close(0);
		if ((r = open(argv[0], O_RDONLY)) < 0)
			panic("open %s: %e", argv[0], r);
		assert(r == 0);
	}
	if (interactive == '?')
		interactive = iscons(0);
	
	while (1) {
		char *buf;

		buf = readline(interactive ? "$ " : NULL);
		if (buf == NULL) {
			if (debug)
				cprintf("EXITING\n");
			exit();	// end of file
		}
		if (debug)
			cprintf("LINE: %s\n", buf);
		if (buf[0] == '#')
			continue;
		if (echocmds)
			fprintf(1, "# %s\n", buf);
		if (debug)
			cprintf("BEFORE FORK\n");
		if ((r = fork()) < 0)
			panic("fork: %e", r);
		if (debug)
			cprintf("FORK: %d\n", r);
		if (r == 0) {
			runcmd(buf);
			exit();
		} else
			wait(r);
	}
}