/**
 * inotify.c from Lsyncd - Live (Mirror) Syncing Demon
 *
 * License: GPLv2 (see COPYING) or any later version
 *
 * Authors: Axel Kittenberger <axkibe@gmail.com>
 *
 * -----------------------------------------------------------------------
 *
 * Event interface for Lsyncd to Linux´ inotify.
 */

#include "lsyncd.h"

#ifndef HAVE_SYS_INOTIFY_H
#  error Missing <sys/inotify.h>; supply kernel-headers and rerun configure.
#endif

#include <sys/stat.h>
#include <sys/times.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/inotify.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <signal.h>
#include <stdbool.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <syslog.h>
#include <math.h>
#include <time.h>
#include <unistd.h>

#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>

/*-----------------------------------------------------------------------------
 * Event types.
 */
static const char * ATTRIB = "Attrib";
static const char * MODIFY = "Modify";
static const char * CREATE = "Create";
static const char * DELETE = "Delete";
static const char * MOVE   = "Move";

/**
 * The inotify file descriptor.
 */
static int inotify_fd = -1;

/**
 * Standard inotify events to listen to.
 */
static const uint32_t standard_event_mask =
		IN_ATTRIB   | IN_CLOSE_WRITE | IN_CREATE     |
		IN_DELETE   | IN_DELETE_SELF | IN_MOVED_FROM |
		IN_MOVED_TO | IN_DONT_FOLLOW | IN_ONLYDIR;


/**
 * Adds an inotify watch
 *
 * @param dir         (Lua stack) path to directory
 * @param inotifyMode (Lua stack) path to directory
 * @return            (Lua stack) numeric watch descriptor
 */
static int
l_addwatch(lua_State *L)
{
	const char *path  = luaL_checkstring(L, 1);
	const char *imode = luaL_checkstring(L, 2);
	uint32_t mask = standard_event_mask;
	if (*imode) {
		if (!strcmp(imode, "Modify")) {
			// act on modify instead of closeWrite
			mask |= IN_MODIFY;
			mask &= ~IN_CLOSE_WRITE;
		} else if (!strcmp(imode, "CloseWrite")) {
			// default
		} else if (!strcmp(imode, "CloseWrite or Modify")) {
			// acts on modify and closeWrite
			mask |= IN_MODIFY;
		} else if (!strcmp(imode, "CloseWrite after Modify")) {
			// might be done in future
			printlogf(L, "Error", "'CloseWrite after Modify' not implemented.");
			exit(-1); // ERRNO
		} else {
			printlogf(L, "Error", "'%s' not a valid inotfiyMode.", imode);
			exit(-1); // ERRNO
		}
	}


	int wd = inotify_add_watch(inotify_fd, path, mask);
	if (wd < 0) {
		if (errno == ENOSPC) {
			printlogf(L, "Error", "Terminating since out of inotify watches.");
			printlogf(L, "Error", "Consider increasing /proc/sys/fs/inotify/max_user_watches");
			exit(-1); // ERRNO.
		}
		printlogf(L, "Inotify", "addwatch(%s)->%d; err=%d:%s", path, wd, errno, strerror(errno));
	} else {
		printlogf(L, "Inotify", "addwatch(%s)->%d", path, wd);
	}
	lua_pushinteger(L, wd);
	return 1;
}

/**
 * Removes an inotify watch
 *
 * @param dir (Lua stack) numeric watch descriptor
 * @return    nil
 */
static int
l_rmwatch(lua_State *L)
{
	int wd = luaL_checkinteger(L, 1);
	inotify_rm_watch(inotify_fd, wd);
	printlogf(L, "Inotify", "rmwatch()<-%d", wd);
	return 0;
}

/**
 * Cores inotify functions.
 */
static const luaL_Reg linotfylib[] = {
		{"addwatch",   l_addwatch   },
		{"rmwatch",    l_rmwatch    },
		{NULL, NULL}
};

/**
 * Buffer for MOVE_FROM events.
 * Lsyncd buffers MOVE_FROM events to check if
 * they are followed by MOVE_TO events with identical cookie
 * then they are condensed into one move event to be sent to the
 * runner
 */
static struct inotify_event * move_event_buf = NULL;

/**
 * Memory allocated for move_event_buf
 */
static size_t move_event_buf_size = 0;

/**
 * true if the buffer is used.
 */
static bool move_event = false;

/**
 * Handles an inotify event.
 */
static void
handle_event(lua_State *L,
             struct inotify_event *event)
{
	const char *event_type = NULL;

	// used to execute two events in case of unmatched MOVE_FROM buffer
	struct inotify_event *after_buf = NULL;
	if (event && (IN_Q_OVERFLOW & event->mask)) {
		/* and overflow happened, tells the runner */
		load_runner_func(L, "overflow");
		if (lua_pcall(L, 0, 0, -2)) {
			exit(-1); // ERRNO
		}
		lua_pop(L, 1);
		hup = 1;
		return;
	}
	// cancel on ignored or resetting
	if (event && (IN_IGNORED & event->mask)) {
		return;
	}
	if (event && event->len == 0) {
		// sometimes inotify sends such strange events,
		// (e.g. when touching a dir
		return;
	}

	if (event == NULL) {
		// a buffered MOVE_FROM is not followed by anything,
		// thus it is unary
		event = move_event_buf;
		event_type = "Delete";
		move_event = false;
	} else if (move_event &&
	            ( !(IN_MOVED_TO & event->mask) ||
			      event->cookie != move_event_buf->cookie) ) {
		// there is a MOVE_FROM event in the buffer and this is not the match
		// continue in this function iteration to handle the buffer instead */
		logstring("Inotify", "icore, changing unary MOVE_FROM into DELETE")
		after_buf = event;
		event = move_event_buf;
		event_type = "Delete";
		move_event = false;
	} else if ( move_event &&
	            (IN_MOVED_TO & event->mask) &&
			    event->cookie == move_event_buf->cookie ) {
		// this is indeed a matched move */
		event_type = "Move";
		move_event = false;
	} else if (IN_MOVED_FROM & event->mask) {
		// just the MOVE_FROM, buffers this event, and wait if next event is
		// a matching MOVED_TO of this was an unary move out of the watched
		// tree.
		size_t el = sizeof(struct inotify_event) + event->len;
		if (move_event_buf_size < el) {
			move_event_buf_size = el;
			move_event_buf = s_realloc(move_event_buf, el);
		}
		memcpy(move_event_buf, event, el);
		move_event = true;
		return;
	} else if (IN_MOVED_TO & event->mask) {
		// must be an unary move-to
		event_type = CREATE;
	} else if (IN_ATTRIB & event->mask) {
		// just attrib change
		event_type = ATTRIB;
	} else if ((IN_CLOSE_WRITE | IN_MODIFY) & event->mask) {
		// modify, or closed after written something
		// the event type received depends settings.inotifyMode
		event_type = MODIFY;
	} else if (IN_CREATE & event->mask) {
		// a new file
		event_type = CREATE;
	} else if (IN_DELETE & event->mask) {
		// rm'ed
		event_type = DELETE;
	} else {
		logstring("Inotify", "icore, skipped some inotify event.");
		return;
	}

	// and hands over to runner
	load_runner_func(L, "inotifyEvent");
	if (!event_type) {
		logstring("Error", "Internal: unknown event in handle_event()");
		exit(-1);	// ERRNO
	}
	lua_pushstring(L, event_type);
	if (event_type != MOVE) {
		lua_pushnumber(L, event->wd);
	} else {
		lua_pushnumber(L, move_event_buf->wd);
	}
	lua_pushboolean(L, (event->mask & IN_ISDIR) != 0);
	l_now(L);
	if (event_type == MOVE) {
		lua_pushstring(L, move_event_buf->name);
		lua_pushnumber(L, event->wd);
		lua_pushstring(L, event->name);
	} else {
		lua_pushstring(L, event->name);
		lua_pushnil(L);
		lua_pushnil(L);
	}
	if (lua_pcall(L, 7, 0, -9)) {
		exit(-1); // ERRNO
	}
	lua_pop(L, 1);

	// if there is a buffered event, executes it
	if (after_buf) {
		logstring("Inotify", "icore, handling buffered event.");
		handle_event(L, after_buf);
	}
}

/**
 * buffer to read inotify events into
 */
static size_t readbuf_size = 2048;
static char * readbuf = NULL;

/**
 * Called by function pointer from when the inotify file descriptor
 * became ready. Reads it contents and forward all received events
 * to the runner.
 */
static void
inotify_ready(lua_State *L, struct observance *obs)
{
	if (obs->fd != inotify_fd) {
		logstring("Error", "Internal, inotify_fd != ob->fd");
		exit(-1); // ERRNO
	}
	while(true) {
		ptrdiff_t len;
		int err;
		do {
			len = read (inotify_fd, readbuf, readbuf_size);
			err = errno;
			if (len < 0 && err == EINVAL) {
				// kernel > 2.6.21 indicates that way that way that
				// the buffer was too small to fit a filename.
				// double its size and try again. When using a lower
				// kernel and a filename > 2KB appears lsyncd
				// will fail. (but does a 2KB filename really happen?)
				//
				readbuf_size *= 2;
				readbuf = s_realloc(readbuf, readbuf_size);
			}
		} while(len < 0 && err == EINVAL);
		if (len == 0) {
			// nothing more inotify
			break;
		}
		if (len < 0) {
			if (err == EAGAIN) {
				// nothing more inotify
				break;
			} else {
				printlogf(L, "Error", "Read fail on inotify");
				exit(-1); // ERRNO
			}
		}
		{
			int i = 0;
			while (i < len && !hup && !term) {
				struct inotify_event *event =
					(struct inotify_event *) &readbuf[i];
				handle_event(L, event);
				i += sizeof(struct inotify_event) + event->len;
			}
		}
		if (!move_event) {
			// give it a pause if not endangering splitting a move
			break;
		}
	}

	// checks if there is an unary MOVE_FROM left in the buffer
	if (move_event) {
		logstring("Inotify", "icore, handling unary move from.");
		handle_event(L, NULL);
	}
}

/**
 * registers inotify functions.
 */
extern void
register_inotify(lua_State *L)
{
	lua_pushstring(L, "inotify");
	luaL_register(L, "inotify", linotfylib);
}

/**
 * closes inotify
 */
static void
inotify_tidy(struct observance *obs)
{
	if (obs->fd != inotify_fd) {
		logstring("Error", "Internal, inotify_fd != ob->fd");
		exit(-1); // ERRNO
	}
	close(inotify_fd);
	free(readbuf);
	readbuf = NULL;
}

/**
 * opens and initalizes inotify.
 */
extern void
open_inotify(lua_State *L)
{
	if (readbuf) {
		logstring("Error",
			"internal fail, inotify readbuf!=NULL in open_inotify()")
		exit(-1); // ERRNO
	}
	readbuf = s_malloc(readbuf_size);

	inotify_fd = inotify_init();
	if (inotify_fd < 0) {
		printlogf(L, "Error",
			"Cannot access inotify monitor! (%d:%s)",
			errno, strerror(errno));
		exit(-1); // ERRNO
	}
	printlogf(L, "Inotify", "inotify fd = %d", inotify_fd);

	close_exec_fd(inotify_fd);
	non_block_fd(inotify_fd);
	observe_fd(inotify_fd, inotify_ready, NULL, inotify_tidy, NULL);
}