// nagless - mail delivery agent (MDA) that forwards but suppresses
// messages for some amount of time, to cut down on monitoring spam

#include <sys/stat.h>
#include <sys/time.h>
#include <sys/wait.h>

#include <ctype.h>
#include <err.h>
#include <getopt.h>
#include <limits.h>
#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sysexits.h>
#include <syslog.h>
#include <time.h>
#include <unistd.h>

// PORTABILITY some OS put this at /usr/lib/sendmail or you may instead
// need to use something like msmtp to send the mail off elsewhere
#ifndef SENDMAIL_PATH
#define SENDMAIL_PATH "/usr/sbin/sendmail"
#endif

// NOTE syslog any other things have limits if you want to increase the
// maximum Subject length sent
#define MAX_BLATHER 70

#define NAGFAIL EX_TEMPFAIL

enum { PIPE_R, PIPE_W };

char *Checkpoint_File;
char *Contact_Address;
int Nagless_Sec;

int Flag_Syslog; // -s

static void emit_help(void);
static void handle_subject(char *subj, ssize_t subjlen);
static void maybe_notify(char *subj, ssize_t subjlen);

int
main(int argc, char *argv[])
{
	int ch;
	const char *errstr;

	char *line      = NULL;
	size_t linesize = 0;
	ssize_t linelen;

	if (!setlocale(LC_ALL, "C")) err(1, "setlocale");

	while ((ch = getopt(argc, argv, "s")) != -1) {
		switch (ch) {
		case 's':
			Flag_Syslog = 1;
			break;
		default:
			emit_help();
		}
	}
	argc -= optind;
	argv += optind;

	if (argc != 3 || !argv[0] || !argv[0][0] || !argv[1] || !argv[1][0] ||
	    !argv[2] || !argv[2][0])
		emit_help();
	Checkpoint_File = argv[0];
	// PORTABILITY use libbsd or strtoul(3) or hopefully not atoi(3)
	Nagless_Sec = (int) strtonum(argv[1], 0, INT_MAX, &errstr);
	if (errstr) err(NAGFAIL, "strtonum '%s': %s", argv[1], errstr);
	Contact_Address = argv[2];

	if (Flag_Syslog) openlog("nagless", LOG_NDELAY, LOG_USER);

#ifdef __OpenBSD__
	if (pledge("exec fattr proc rpath stdio unveil", NULL) == -1)
		err(1, "pledge");
	if (unveil(SENDMAIL_PATH, "x") == -1) err(1, "unveil");
	if (unveil(Checkpoint_File, "rw") == -1) err(1, "unveil");
	if (unveil(NULL, NULL) == -1) err(1, "unveil");
#endif

	while ((linelen = getline(&line, &linesize, stdin)) != -1) {
		// TODO but what if we get a \r\n line??
		if (linelen == 1) goto DONE; // blank line, end of headers
		if (!strncmp(line, "Subject: ", 9)) {
			handle_subject(line + 9, linelen - 10);
			goto DONE;
		}
	}
	//free(line);
	//if (ferror(stdin)) err(NAGFAIL, "getline");
DONE:
	exit(EXIT_SUCCESS);
}

static void
emit_help(void)
{
	fputs(
	  "Usage: nagless [-s] checkpoint-file window-seconds notify-address\n",
	  stderr);
	exit(NAGFAIL);
}

inline static void
handle_subject(char *subj, ssize_t subjlen)
{
	char *cp;
	if (subjlen <= 0) return;
	if (subjlen > MAX_BLATHER) subjlen = MAX_BLATHER;
	cp = subj;
	for (size_t i = 0; i < (size_t) subjlen; ++i, ++cp)
		if (!isprint(*cp)) *cp = '.';
	if (Flag_Syslog) syslog(LOG_NOTICE, "%.*s", (int) subjlen, subj);
	maybe_notify(subj, subjlen);
}

inline static void
maybe_notify(char *subj, ssize_t subjlen)
{
	char *failure = "unknown";
	int ret, status, tochild[2];
	pid_t child, pid;
	struct stat sb;
	time_t now;
	if (time(&now) == (time_t) -1) err(NAGFAIL, "time");
	if (stat(Checkpoint_File, &sb) == -1)
		err(NAGFAIL, "stat '%s'", Checkpoint_File);
	if (llabs(now - sb.st_mtim.tv_sec) < Nagless_Sec) return;
	utimes(Checkpoint_File, NULL);

	if (pipe(tochild) == -1) {
		failure = "pipe";
		goto NOTIFY_FAIL;
	}

	pid = fork();
	if (pid < 0) {
		failure = "fork";
		goto NOTIFY_FAIL;
	} else if (pid == 0) { // child
		close(tochild[PIPE_W]);
		if (dup2(tochild[PIPE_R], STDIN_FILENO) != STDIN_FILENO)
			err(1, "dup2");
		close(tochild[PIPE_R]);
		execl(SENDMAIL_PATH, "sendmail", "-t", (char *) 0);
		err(1, "execl");
	}

	close(tochild[PIPE_R]);
	ret = dprintf(tochild[PIPE_W], "To: %s\nSubject: %.*s\n\nfyi",
	              Contact_Address, (int) subjlen, subj);
	if (ret < 0)
		warn("dprintf");
	else if (ret == 0)
		warn("dprintf zero write??");
	if (close(tochild[PIPE_W]) == -1) warn("close");
	// TODO may need timeout here, in the event the mail program gets stuck
	child = wait(&status);
	if (child == -1) warn("wait");
	if (status) warnx("non-zero exit (%d)", status);
	return;

NOTIFY_FAIL:
	if (Flag_Syslog) syslog(LOG_ERR, "notification failure: %s", failure);
	warn("notification failure: %s", failure);
}