/* 
   Unix SMB/CIFS implementation.
   main select loop and event handling
   Copyright (C) Andrew Tridgell	2003-2005
   Copyright (C) Stefan Metzmacher	2005
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   
   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., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

/*
  This is SAMBA's default event loop code

*/

#include "includes.h"
#include "system/filesys.h"
#include "system/select.h"
#include "lib/util/dlinklist.h"
#include "lib/events/events.h"
#include "lib/events/events_internal.h"

struct select_event_context {
	/* a pointer back to the generic event_context */
	struct event_context *ev;

	/* list of filedescriptor events */
	struct fd_event *fd_events;

	/* list of timed events */
	struct timed_event *timed_events;

	/* the maximum file descriptor number in fd_events */
	int maxfd;

	/* information for exiting from the event loop */
	int exit_code;

	/* this is changed by the destructors for the fd event
	   type. It is used to detect event destruction by event
	   handlers, which means the code that is calling the event
	   handler needs to assume that the linked list is no longer
	   valid
	*/
	uint32_t destruction_count;
};

/*
  create a select_event_context structure.
*/
static int select_event_context_init(struct event_context *ev)
{
	struct select_event_context *select_ev;

	select_ev = talloc_zero(ev, struct select_event_context);
	if (!select_ev) return -1;
	select_ev->ev = ev;

	ev->additional_data = select_ev;
	return 0;
}

/*
  recalculate the maxfd
*/
static void calc_maxfd(struct select_event_context *select_ev)
{
	struct fd_event *fde;

	select_ev->maxfd = 0;
	for (fde = select_ev->fd_events; fde; fde = fde->next) {
		if (fde->fd > select_ev->maxfd) {
			select_ev->maxfd = fde->fd;
		}
	}
}


/* to mark the ev->maxfd invalid
 * this means we need to recalculate it
 */
#define EVENT_INVALID_MAXFD (-1)

/*
  destroy an fd_event
*/
static int select_event_fd_destructor(struct fd_event *fde)
{
	struct event_context *ev = fde->event_ctx;
	struct select_event_context *select_ev = talloc_get_type(ev->additional_data,
							   struct select_event_context);

	if (select_ev->maxfd == fde->fd) {
		select_ev->maxfd = EVENT_INVALID_MAXFD;
	}

	DLIST_REMOVE(select_ev->fd_events, fde);
	select_ev->destruction_count++;

	return 0;
}

/*
  add a fd based event
  return NULL on failure (memory allocation error)
*/
static struct fd_event *select_event_add_fd(struct event_context *ev, TALLOC_CTX *mem_ctx,
					 int fd, uint16_t flags,
					 event_fd_handler_t handler,
					 void *private_data)
{
	struct select_event_context *select_ev = talloc_get_type(ev->additional_data,
							   struct select_event_context);
	struct fd_event *fde;

	fde = talloc(mem_ctx?mem_ctx:ev, struct fd_event);
	if (!fde) return NULL;

	fde->event_ctx		= ev;
	fde->fd			= fd;
	fde->flags		= flags;
	fde->handler		= handler;
	fde->private_data	= private_data;
	fde->additional_flags	= 0;
	fde->additional_data	= NULL;

	DLIST_ADD(select_ev->fd_events, fde);
	if (fde->fd > select_ev->maxfd) {
		select_ev->maxfd = fde->fd;
	}
	talloc_set_destructor(fde, select_event_fd_destructor);

	return fde;
}


/*
  return the fd event flags
*/
static uint16_t select_event_get_fd_flags(struct fd_event *fde)
{
	return fde->flags;
}

/*
  set the fd event flags
*/
static void select_event_set_fd_flags(struct fd_event *fde, uint16_t flags)
{
	struct event_context *ev;
	struct select_event_context *select_ev;

	if (fde->flags == flags) return;

	ev = fde->event_ctx;
	select_ev = talloc_get_type(ev->additional_data, struct select_event_context);

	fde->flags = flags;
}

/*
  event loop handling using select()
*/
static int select_event_loop_select(struct select_event_context *select_ev, struct timeval *tvalp)
{
	fd_set r_fds, w_fds;
	struct fd_event *fde;
	int selrtn;
	uint32_t destruction_count = select_ev->destruction_count;

	/* we maybe need to recalculate the maxfd */
	if (select_ev->maxfd == EVENT_INVALID_MAXFD) {
		calc_maxfd(select_ev);
	}

	FD_ZERO(&r_fds);
	FD_ZERO(&w_fds);

	/* setup any fd events */
	for (fde = select_ev->fd_events; fde; fde = fde->next) {
		if (fde->flags & EVENT_FD_READ) {
			FD_SET(fde->fd, &r_fds);
		}
		if (fde->flags & EVENT_FD_WRITE) {
			FD_SET(fde->fd, &w_fds);
		}
	}

	selrtn = select(select_ev->maxfd+1, &r_fds, &w_fds, NULL, tvalp);

	if (selrtn == -1 && errno == EBADF) {
		/* the socket is dead! this should never
		   happen as the socket should have first been
		   made readable and that should have removed
		   the event, so this must be a bug. This is a
		   fatal error. */
		DEBUG(0,("ERROR: EBADF on select_event_loop_once\n"));
		select_ev->exit_code = EBADF;
		return -1;
	}

	if (selrtn == 0 && tvalp) {
		common_event_loop_timer(select_ev->ev);
		return 0;
	}

	if (selrtn > 0) {
		/* at least one file descriptor is ready - check
		   which ones and call the handler, being careful to allow
		   the handler to remove itself when called */
		for (fde = select_ev->fd_events; fde; fde = fde->next) {
			uint16_t flags = 0;

			if (FD_ISSET(fde->fd, &r_fds)) flags |= EVENT_FD_READ;
			if (FD_ISSET(fde->fd, &w_fds)) flags |= EVENT_FD_WRITE;
			if (flags) {
				fde->handler(select_ev->ev, fde, flags, fde->private_data);
				if (destruction_count != select_ev->destruction_count) {
					break;
				}
			}
		}
	}

	return 0;
}		

/*
  do a single event loop using the events defined in ev 
*/
static int select_event_loop_once(struct event_context *ev)
{
	struct select_event_context *select_ev = talloc_get_type(ev->additional_data,
		 					   struct select_event_context);
	struct timeval tval;

	tval = common_event_loop_delay(ev);

	if (timeval_is_zero(&tval)) {
		common_event_loop_timer(ev);
		return 0;
	}

	return select_event_loop_select(select_ev, &tval);
}

/*
  return on failure or (with 0) if all fd events are removed
*/
static int select_event_loop_wait(struct event_context *ev)
{
	struct select_event_context *select_ev = talloc_get_type(ev->additional_data,
							   struct select_event_context);
	select_ev->exit_code = 0;

	while (select_ev->fd_events && select_ev->exit_code == 0) {
		if (select_event_loop_once(ev) != 0) {
			break;
		}
	}

	return select_ev->exit_code;
}

static const struct event_ops select_event_ops = {
	.context_init	= select_event_context_init,
	.add_fd		= select_event_add_fd,
	.get_fd_flags	= select_event_get_fd_flags,
	.set_fd_flags	= select_event_set_fd_flags,
	.add_timed	= common_event_add_timed,
	.loop_once	= select_event_loop_once,
	.loop_wait	= select_event_loop_wait,
};

NTSTATUS events_select_init(void)
{
	return event_register_backend("select", &select_event_ops);
}