/* diraction.c

diraction is done by Anthony de Boer <adb@leftmind.net>

adopted from Documentation/dnotify.txt in the Linux kernel distribution,
which was writen by Stephen Rothwell <sfr@canb.auug.org.au>

Copyright: GPL, since this is a derived work of the kernel source tree,
which is GPL'ed.

General theme: SCRIPTDIR has executables triggered for each file change
in WATCHDIR.  We're only interested in files that have scripts.

SCRIPTDIR is argv[1] and WATCHDIR is cwd.

#  Copyright (C) 2004 Anthony de Boer
#
#  This program is free software; you can redistribute it and/or modify
#  it under the terms of version 2 of the GNU General Public License as
#  published by the Free Software Foundation.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program; if not, write to the Free Software
#  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

*/


#define _GNU_SOURCE	/* needed to get the defines */
#include <fcntl.h>	/* in glibc 2.2 this has the needed
				   values defined */
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
#include <dirent.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <string.h>
#include <sys/wait.h>

/* kludge so we can compile on older Linux */
#ifdef F_NOTIFY
#if F_NOTIFY != 1026
#warning F_NOTIFY value has changed
#endif
#if DN_MODIFY != 0x00000002
#warning DN_MODIFY value has changed
#endif
#if DN_CREATE != 0x00000004
#warning DN_CREATE value has changed
#endif
#if DN_RENAME != 0x00000010
#warning DN_RENAME value has changed
#endif
#if DN_MULTISHOT != 0x80000000
#warning DN_MULTISHOT value has changed
#endif
#else
#define F_NOTIFY 1026
#define DN_ACCESS	0x00000001	/* File accessed */
#define DN_MODIFY	0x00000002	/* File modified */
#define DN_CREATE	0x00000004	/* File created */
#define DN_DELETE	0x00000008	/* File removed */
#define DN_RENAME	0x00000010	/* File renamed */
#define DN_ATTRIB	0x00000020	/* File changed attibutes */
#define DN_MULTISHOT	0x80000000	/* Don't remove notifier */
#endif

#define barf(x) { botch = x; goto punt; }

#define CFREQ 60
#define EFREQ 10

static volatile int sigged;

/* void (*sa_handler)(int) handler; */

struct filent {
	char *name;
	struct filent *next;
	ino_t inode;
	pid_t runscript;
	time_t lastmod;
	time_t lastrun;
	int need;
	};

void handler(int it)
{
	sigged = it ? it : 1;
}

int main(int argc, char *argv[])
{
	struct sigaction act;
	int fd;
	struct filent *head = NULL;
	struct filent *pf;
	char *botch;
	char *curobj;
	DIR *dirhandle;
	struct dirent *thisdir;
	int maxname = 0;
	
	act.sa_handler = handler;
	sigemptyset(&act.sa_mask);
	act.sa_flags = 0;
	if (sigaction(SIGRTMIN, &act, NULL) == -1) barf("Cannot install SIGRTMIN handler\n");
	if (sigaction(SIGALRM, &act, NULL) == -1) barf("Cannot install SIGALRM handler\n");
	act.sa_flags = SA_NOCLDSTOP;
	if (sigaction(SIGCHLD, &act, NULL) == -1) barf("Cannot install SIGCHLD handler\n");

	if (argc != 2) barf("Usage: diraction /SCRIPTDIR\n");
	
	curobj = argv[1];
	if ((dirhandle = opendir(curobj)) == NULL) goto syserr;
	while (thisdir = readdir(dirhandle)) {
		int mylen;
		curobj = thisdir->d_name;
		if (*curobj == '.') continue;
		pf = (struct filent *) malloc(sizeof(struct filent));
		curobj = strdup(curobj);
		if (pf == NULL || curobj == NULL) barf("malloc\n");
		pf->name = curobj;
		pf->next = head;
		pf->inode = 0;
		pf->runscript = 0;
		pf->lastrun = pf->lastmod = 0;
		pf->need = 0;
		head = pf;
		mylen = strlen(curobj);
		if (mylen > maxname)
			maxname = mylen;
		}
	closedir(dirhandle);

	curobj = ".";
	if ((fd = open(".", O_RDONLY)) == -1) goto syserr;
	if (fcntl(fd, F_SETSIG, SIGRTMIN) == -1) goto syserr;
	fprintf(stderr, "dnotify %s\n", fcntl(fd, F_NOTIFY, DN_MODIFY|DN_CREATE|DN_RENAME|DN_MULTISHOT) == -1 ? "unavailable" : "okay");

	/* from this point curobj is a buffer for scriptdir paths */
	curobj = (char *) malloc(strlen(argv[1] + maxname + 3));
	if (curobj == NULL) barf("malloc\n");
	strcpy(curobj, argv[1]);
	strcat(curobj, "/");

	sigged = 0;

	while (1) {
		pid_t pid;
		int status;
		time_t now = time(NULL);
		int atime = CFREQ;

		/* fprintf(stderr, "kick on signal %d\n", sigged); */
		sigged = 0;
		while (pid = waitpid(-1, &status, WNOHANG)) {
			if (pid <= 0)
				break;
			pf = head;
			while(pf) {
				if (pf->runscript == pid) {
					pf->runscript = 0;
					fprintf(stderr, "script done for %s, %s\n", pf->name, WIFSIGNALED(status) ? "killed" : (WIFEXITED(status) && WEXITSTATUS(status) == 0) ? "okay" : "failed");
					break;
					}
				pf = pf->next;
				}
			}
		pf = head;
		while(pf) {
			struct stat stbuf;
			if (stat(pf->name, &stbuf) == -1) {
				pf->need = 0;
				}
			else {
				if (stbuf.st_ino != pf->inode) {
					pf->inode = stbuf.st_ino;
					pf->need = 1;
					}
				if (stbuf.st_mtime != pf->lastmod) {
					pf->lastmod = stbuf.st_mtime;
					pf->need = 1;
					}
				}
			if (pf->need) {
				if (pf->runscript == 0 && pf->lastrun < now-EFREQ) {
					fprintf(stderr, "event on %s, running script\n", pf->name);
					pf->need = 0;
					pf->lastrun = now;
					switch(pid = fork()) {
						case 0:
							strcat(curobj, pf->name);
							alarm(0);
							execl(curobj, curobj, pf->name, NULL);
							goto syserr;
						case -1:
							barf("fork()\n");
						default:
							pf->runscript = pid;
						}
					}
				else {
					fprintf(stderr, "deferred event on %s\n", pf->name);
					atime = EFREQ;
					}
				}
			pf = pf->next;
			}
		alarm(atime);
		if (sigged == 0)
			pause();
	}

syserr:
	perror(curobj);
	exit(1);

punt:
	write(2, botch, strlen(botch));
	exit(1);

}