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

int wr = -1;
int rd = -1;

void do_write (int fd, char * buf, int len)
{
	int done = 0;
	int ret;
	while (done < len) {
		ret = write (fd, buf+done, len - done);
		if (ret < 0) {
			if ((errno != EINTR) || (errno == EAGAIN)) {
				continue;
			}
			perror ("write");
			fprintf (stderr, "Aborting\n");
			exit (1);
		}
		done += ret;
	}
}

int readline (int fd, stralloc * sa)
{
	int ret = 0;
	if (!sa)
		return 0;
	sa->len = 0;
	while (1) {
		char ch;
		int tmp;
		tmp = read (fd, &ch, 1);
		if (tmp == 0)
			break;
		if (tmp < 0)
			continue;
		if (!stralloc_readyplus (sa, 1))
			return 0;
		sa->s[sa->len] = ch;
		sa->len++;
		if (ch == '\n')
			break;
	}
	ret = (sa->len > 0);
	while (sa->len && ((sa->s[sa->len-1] == '\r')
			   || (sa->s[sa->len-1] == '\n')))
		sa->len--;
	return ret;
}

void readreply (int expect);

void terminate (stralloc * error)
{
	static int in_terminate = 0;
	if (error) {
		fwrite (error->s, sizeof (char), error->len, stderr);
		fprintf (stderr, "\n");
	}
	if (!in_terminate) {
		do_write (wr, "QUIT\r\n", 6);
		in_terminate = 1;
		readreply  (2);
	}
	exit (1);
}

void temp_error (stralloc * error)
{
	fprintf (stderr, "Temporary failure: ");
	terminate (error);
}

void fatal_error (stralloc * error)
{
	fprintf (stderr, "Fatal error: ");
	terminate (error);
}

void do_quit (stralloc * error)
{
	stralloc sa = {0};
	do_write (wr, "QUIT\r\n", 6);
	readreply (2);
	stralloc_copys (&sa, "Server sent unexpected answer: ");
	stralloc_cat (&sa, error);
	fatal_error (&sa);
}

void readreply (int expect)
{
	struct stralloc sa = {0};
	int code;
	char ch;
	if (!readline (rd, &sa)) {
		stralloc_copys (&sa, "Unexpected end of file");
		fatal_error (&sa);
	}
	if ((sscanf (sa.s, "%d%c", &code, &ch) != 2)
	    || (code < 0) || (code > 999)) {
		stralloc_copys (&sa, "Badly formed reply from server");
		fatal_error (&sa);
	}
	switch (sa.s[0]) {
	default:
		stralloc_copys (&sa, "Badly formed reply from server");
		fatal_error (&sa);
		break;
	case '1':
		do_quit (&sa);
		break;
	case '2':
		if (expect != 2)
			do_quit (&sa);
		break;
	case '3':
		if (expect != 3)
			do_quit (&sa);
		break;
	case '4':
		temp_error (&sa);
		break;
	case '5':
		fatal_error (&sa);
		break;
	}
}

const char thishost[] = "elbereth.mathematik.uni-ulm.de";
const char domain[] = "mathematik.uni-ulm.de";
const char * buddies[] = {
	"ehrhardt@mathematik.uni-ulm.de",
	"Christian.Ehrhardt@mathematik.uni-ulm.de",
	/* Hier sollten alle Tutoriumsteilnehmer stehen. */
	NULL
};

int main ()
{
	int i, pid;
	char * user = getenv ("USER");
	stralloc sa = {0};
	int p1[2], p2[2];

	if (!user) {
		fprintf (stderr, "Can't find out username\n");
		exit (1);
	}
	if (pipe (p1) < 0) {
		perror ("pipe");
		exit (1);
	}
	if (pipe (p2) < 0) {
		perror ("pipe");
		exit (1);
	}
	pid = fork ();
	if (pid < 0) {
		perror ("fork");
		exit (1);
	}
	if (pid == 0) {   /* CHILD */
		if (dup2 (p1[0], 0) < 0) {
			perror ("dup2");
			exit (1);
		}
		close (p1[0]); close (p1[1]);
		if (dup2 (p2[1], 1) < 0) {
			perror ("dup2");
			exit (1);
		}
		close (p2[0]); close (p2[1]);
		execlp ("nc", "nc", "theseus.mathematik.uni-ulm.de", "25", NULL);
		perror ("execlp");
		exit (1);
	}
	/* PARENT */
	close (p1[0]); close (p2[1]);
	wr = p1[1];
	rd = p2[0];
	/* Read greating. */
	readreply (2);
	/* Send HELO */
	if (!stralloc_copys (&sa, "HELO ") || !stralloc_cats (&sa, thishost)
	    || !stralloc_cats (&sa, "\r\n")) {
		terminate (NULL);
	}
	do_write (wr, sa.s, sa.len);
	readreply (2);
	/* Send our Email-Adresse as Sender. */
	if (!stralloc_copys (&sa, "MAIL From: ") ||
	    !stralloc_cats (&sa, user) || 
	    !stralloc_cats (&sa, "@") ||
	    !stralloc_cats (&sa, domain) ||
	    !stralloc_cats (&sa, "\r\n"))
		terminate (NULL);
	do_write (wr, sa.s, sa.len);
	readreply (2);
	for (i = 0; buddies[i]; i++) {
		if (!stralloc_copys (&sa, "RCPT To: ") ||
		    !stralloc_cats (&sa, buddies[i]) ||
		    !stralloc_cats (&sa, "\r\n"))
			terminate (NULL);
		do_write (wr, sa.s, sa.len);
		readreply (2);
	}
	do_write (wr, "DATA\r\n", 6);
	readreply (3);
	/* Header */
	if (!stralloc_copys (&sa,
	        "Subject: Wichtige Nachricht an die Tutoriumsgruppe\r\n") ||
	    !stralloc_cats (&sa, "From: ") ||
	    !stralloc_cats (&sa, user) ||
	    !stralloc_cats (&sa, "@") ||
	    !stralloc_cats (&sa, domain) ||
	    !stralloc_cats (&sa, "\r\n") ||
	    !stralloc_cats (&sa,
	    	"To: mein.tutorium@mathematik.uni-ulm.de\r\n\r\n"))
		terminate (NULL);
	do_write (wr, sa.s, sa.len);
	/* Text von der Standardeingabe */
	while (readline (0, &sa)) {
		if (sa.s[0] == '.')
			do_write (wr, ".", 1);
		do_write (wr, sa.s, sa.len);
		do_write (wr, "\r\n", 2);
	}
	do_write (wr, ".\r\n", 3);
	readreply (2);
	do_write (wr, "QUIT\r\n", 6);
	readreply (2);
	close (wr); close (rd);
	wait (NULL);
	printf ("Mail sent\n");
	return 0;
}