/*
 *  OpenVPN -- An application to securely tunnel IP networks
 *             over a single TCP/UDP port, with support for SSL/TLS-based
 *             session authentication and key exchange,
 *             packet encryption, packet authentication, and
 *             packet compression.
 *
 *  Copyright (C) 2002-2005 OpenVPN Solutions LLC <info@openvpn.net>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  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 (see the file COPYING included with this
 *  distribution); if not, write to the Free Software Foundation, Inc.,
 *  59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#ifdef WIN32
#include "config-win32.h"
#else
#include "config.h"
#endif

#include "syshead.h"

#if P2MP_SERVER

#include "buffer.h"
#include "misc.h"
#include "crypto.h"
#include "schedule.h"

#include "memdbg.h"

#ifdef SCHEDULE_TEST

struct status
{
  int sru;
  int ins;
  int coll;
  int lsteps;
};

static struct status z;

#endif

#ifdef ENABLE_DEBUG
static void
schedule_entry_debug_info (const char *caller, const struct schedule_entry *e)
{
  struct gc_arena gc = gc_new ();
  if (e)
    {
      dmsg (D_SCHEDULER, "SCHEDULE: %s wakeup=[%s] pri=%u",
	   caller,
	   tv_string_abs (&e->tv, &gc),
	   e->pri);
    }
  else
    {
      dmsg (D_SCHEDULER, "SCHEDULE: %s NULL",
	   caller);
    }
  gc_free (&gc);
}
#endif

static inline void
schedule_set_pri (struct schedule_entry *e)
{
  e->pri = random ();
  if (e->pri < 1)
    e->pri = 1;
}

/* This is the master key comparison routine.  A key is
 * simply a struct timeval containing the absolute time for
 * an event.  The unique treap priority (pri) is used to ensure
 * that keys do not collide.
 */
static inline int
schedule_entry_compare (const struct schedule_entry *e1,
			const struct schedule_entry *e2)
{
  if (e1->tv.tv_sec < e2->tv.tv_sec)
    return -1;
  else if (e1->tv.tv_sec > e2->tv.tv_sec)
    return 1;
  else
    {
      if (e1->tv.tv_usec < e2->tv.tv_usec)
	return -1;
      else if (e1->tv.tv_usec > e2->tv.tv_usec)
	return 1;
      else
	{
	  if (e1->pri < e2->pri)
	    return -1;
	  else if (e1->pri > e2->pri)
	    return 1;
	  else
	    return 0;
	}
    }
}

/*
 * Detach a btree node from its parent
 */
static inline void
schedule_detach_parent (struct schedule *s, struct schedule_entry *e)
{
  if (e)
    {
      if (e->parent)
	{
	  if (e->parent->lt == e)
	    e->parent->lt = NULL;
	  else if (e->parent->gt == e)
	    e->parent->gt = NULL;
	  else
	    {
	      /* parent <-> child linkage is corrupted */
	      ASSERT (0);
	    }
	  e->parent = NULL;
	}
      else
	{
	  if (s->root == e) /* last element deleted, tree is empty */
	    s->root = NULL;
	}
    }
}

/*
 *
 * Given a binary search tree, move a node toward the root
 * while still maintaining the correct ordering relationships
 * within the tree.  This function is the workhorse
 * of the tree balancer.
 *
 * This code will break on key collisions, which shouldn't
 * happen because the treap priority is considered part of the key
 * and is guaranteed to be unique.
 */
static void
schedule_rotate_up (struct schedule *s, struct schedule_entry *e)
{
  if (e && e->parent)
    {
      struct schedule_entry *lt = e->lt;
      struct schedule_entry *gt = e->gt;
      struct schedule_entry *p = e->parent;
      struct schedule_entry *gp = p->parent;

      if (gp) /* if grandparent exists, modify its child link */
	{
	  if (gp->gt == p)
	    gp->gt = e;
	  else if (gp->lt == p)
	    gp->lt = e;
	  else
	    {
	      ASSERT (0);
	    }
	}
      else /* no grandparent, now we are the root */
	{
	  s->root = e;
	}

      /* grandparent is now our parent */
      e->parent = gp;

      /* parent is now our child */
      p->parent = e;

      /* reorient former parent's links
	 to reflect new position in the tree */
      if (p->gt == e)
	{
	  e->lt = p;
	  p->gt = lt;
	  if (lt)
	    lt->parent = p;
	}
      else if (p->lt == e)
	{
	  e->gt = p;
	  p->lt = gt;
	  if (gt)
	    gt->parent = p;
	}
      else
	{
	  /* parent <-> child linkage is corrupted */
	  ASSERT (0);
	}

#ifdef SCHEDULE_TEST
      ++z.sru;
#endif
    }
}

/*
 * This is the treap deletion algorithm:
 *
 * Rotate lesser-priority children up in the tree
 * until we are childless.  Then delete.
 */
void
schedule_remove_node (struct schedule *s, struct schedule_entry *e)
{
  while (e->lt || e->gt)
    {
      if (e->lt)
	{
	  if (e->gt)
	    {
	      if (e->lt->pri < e->gt->pri)
		schedule_rotate_up (s, e->lt);
	      else
		schedule_rotate_up (s, e->gt);
	    }
	  else
	    schedule_rotate_up (s, e->lt);
	}
      else if (e->gt)
	schedule_rotate_up (s, e->gt);
    }

  schedule_detach_parent (s, e);
  e->pri = 0;
}

/*
 * Trivially add a node to a binary search tree without
 * regard for balance.
 */
static void
schedule_insert (struct schedule *s, struct schedule_entry *e)
{
  struct schedule_entry *c = s->root;
  while (true)
    {
      const int comp = schedule_entry_compare (e, c);

#ifdef SCHEDULE_TEST
      ++z.ins;
#endif

      if (comp == -1)
	{
	  if (c->lt)
	    {
	      c = c->lt;
	      continue;
	    }
	  else
	    {
	      c->lt = e;
	      e->parent = c;
	      break;
	    }
	}
      else if (comp == 1)
	{
	  if (c->gt)
	    {
	      c = c->gt;
	      continue;
	    }
	  else
	    {
	      c->gt = e;
	      e->parent = c;
	      break;
	    }
	}
      else
	{
	  /* rare key/priority collision -- no big deal,
	     just choose another priority and retry */
#ifdef SCHEDULE_TEST
	  ++z.coll;
#endif
	  schedule_set_pri (e);
	  /* msg (M_INFO, "PRI COLLISION pri=%u", e->pri); */
	  c = s->root;
	  continue;
	}
    }
}

/*
 * Given an element, remove it from the btree if it's already
 * there and re-insert it based on its current key.
 */
void
schedule_add_modify (struct schedule *s, struct schedule_entry *e)
{
#ifdef ENABLE_DEBUG
  if (check_debug_level (D_SCHEDULER))
    schedule_entry_debug_info ("schedule_add_modify", e);
#endif

  /* already in tree, remove */
  if (IN_TREE (e))
    schedule_remove_node (s, e);

  /* set random priority */
  schedule_set_pri (e);

  if (s->root)
    schedule_insert (s, e);      /* trivial insert into tree */
  else
    s->root = e; /* tree was empty, we are the first element */

  /* This is the magic of the randomized treap algorithm which
     keeps the tree balanced.  Move the node up the tree until
     its own priority is greater than that of its parent */
  while (e->parent && e->parent->pri > e->pri)
    schedule_rotate_up (s, e);
}

/*
 * Find the earliest event to be scheduled
 */
struct schedule_entry *
schedule_find_least (struct schedule_entry *e)
{
  if (e)
    {
      while (e->lt)
	{
#ifdef SCHEDULE_TEST
	  ++z.lsteps;
#endif
	  e = e->lt;
	}
    }
  
#ifdef ENABLE_DEBUG
  if (check_debug_level (D_SCHEDULER))
    schedule_entry_debug_info ("schedule_find_least", e);
#endif

  return e;
}

/*
 *  Public functions below this point
 */

struct schedule *
schedule_init (void)
{
  struct schedule *s;

  ALLOC_OBJ_CLEAR (s, struct schedule);
  mutex_init (&s->mutex);
  return s;
}

void
schedule_free (struct schedule *s)
{
  mutex_destroy (&s->mutex);
  free (s);
}

void
schedule_remove_entry (struct schedule *s, struct schedule_entry *e)
{
  mutex_lock (&s->mutex);
  s->earliest_wakeup = NULL; /* invalidate cache */
  schedule_remove_node (s, e);
  mutex_unlock (&s->mutex);
}

/*
 *  Debug functions below this point
 */

#ifdef SCHEDULE_TEST

static inline struct schedule_entry *
schedule_find_earliest_wakeup (struct schedule *s)
{
  return schedule_find_least (s->root);
}

/*
 * Recursively check that the treap (btree) is
 * internally consistent.
 */
int
schedule_debug_entry (const struct schedule_entry* e,
		      int depth,
		      int *count,
		      struct timeval *least,
		      const struct timeval *min,
		      const struct timeval *max)
{
  struct gc_arena gc = gc_new ();
  int maxdepth = depth;
  if (e)
    {
      int d;

      ASSERT (e != e->lt);
      ASSERT (e != e->gt);
      ASSERT (e != e->parent);
      ASSERT (!e->parent || e->parent != e->lt);
      ASSERT (!e->parent || e->parent != e->gt);
      ASSERT (!e->lt || e->lt != e->gt);

      if (e->lt)
	{
	  ASSERT (e->lt->parent == e);
	  ASSERT (schedule_entry_compare (e->lt, e) == -1);
	  ASSERT (e->lt->pri >= e->pri);
	}

      if (e->gt)
	{
	  ASSERT (e->gt->parent == e);
	  ASSERT (schedule_entry_compare (e->gt, e));
	  ASSERT (e->gt->pri >= e->pri);
	}

      ASSERT (tv_le (min, &e->tv));
      ASSERT (tv_le (&e->tv, max));

      if (count)
	++(*count);

      if (least && tv_lt (&e->tv, least))
	*least = e->tv;

      d = schedule_debug_entry (e->lt, depth+1, count, least, min, &e->tv);
      if (d > maxdepth)
	maxdepth = d;

      d = schedule_debug_entry (e->gt, depth+1, count, least, &e->tv, max);
      if (d > maxdepth)
	maxdepth = d;
    }
  gc_free (&gc);
  return maxdepth;
}

int
schedule_debug (struct schedule *s, int *count, struct timeval *least)
{
  struct timeval min;
  struct timeval max;

  min.tv_sec = 0;
  min.tv_usec = 0;
  max.tv_sec = 0x7FFFFFFF;
  max.tv_usec = 0x7FFFFFFF;

  if (s->root)
    {
      ASSERT (s->root->parent == NULL);
    }
  return schedule_debug_entry (s->root, 0, count, least, &min, &max);
}

#if 1

void
tv_randomize (struct timeval *tv)
{
  tv->tv_sec += random() % 100;
  tv->tv_usec = random () % 100;
}

#else

void
tv_randomize (struct timeval *tv)
{
  struct gc_arena gc = gc_new ();
  long int choice = get_random ();
  if ((choice & 0xFF) == 0)
    tv->tv_usec += ((choice >> 8) & 0xFF);
  else
    prng_bytes ((uint8_t *)tv, sizeof (struct timeval));
  gc_free (&gc);
}

#endif

void
schedule_verify (struct schedule *s)
{
  struct gc_arena gc = gc_new ();
  struct timeval least;
  int count;
  int maxlev;
  struct schedule_entry* e;
  const struct status zz = z;

  least.tv_sec = least.tv_usec = 0x7FFFFFFF;

  count = 0;

  maxlev = schedule_debug (s, &count, &least);

  e = schedule_find_earliest_wakeup (s);

  if (e)
    {
      printf ("Verification Phase  count=%d maxlev=%d sru=%d ins=%d coll=%d ls=%d l=%s",
	      count,
	      maxlev,
	      zz.sru,
	      zz.ins,
	      zz.coll,
	      zz.lsteps,
	      tv_string (&e->tv, &gc));
      
      if (!tv_eq (&least, &e->tv))
	printf (" [COMPUTED DIFFERENT MIN VALUES!]");

      printf ("\n");
    }
  
  CLEAR (z);
  gc_free (&gc);
}

void
schedule_randomize_array (struct schedule_entry **array, int size)
{
  int i;
  for (i = 0; i < size; ++i)
    {
      const int src = get_random () % size;
      struct schedule_entry *tmp = array [i];
      if (i != src)
	{
	  array [i] = array [src];
	  array [src] = tmp;
	}
    }
}

void
schedule_print_work (struct schedule_entry *e, int indent)
{
  struct gc_arena gc = gc_new ();
  int i;
  for (i = 0; i < indent; ++i)
    printf (" ");
  if (e)
    {
      printf ("%s [%u] e=" ptr_format ", p=" ptr_format " lt=" ptr_format " gt=" ptr_format "\n",
	      tv_string (&e->tv, &gc),
	      e->pri,
	      (ptr_type)e,
	      (ptr_type)e->parent,
	      (ptr_type)e->lt,
	      (ptr_type)e->gt);
      schedule_print_work (e->lt, indent+1);
      schedule_print_work (e->gt, indent+1);
    }
  else
    printf ("NULL\n");
  gc_free (&gc);
}

void
schedule_print (struct schedule *s)
{
  printf ("*************************\n");
  schedule_print_work (s->root, 0);
}

void
schedule_test (void)
{
  struct gc_arena gc = gc_new ();
  int n = 1000;
  int n_mod = 25;

  int i, j;
  struct schedule_entry **array;
  struct schedule *s = schedule_init ();
  struct schedule_entry* e;

  CLEAR (z);
  ALLOC_ARRAY (array, struct schedule_entry *, n);

  printf ("Creation/Insertion Phase\n");

  for (i = 0; i < n; ++i)
    {
      ALLOC_OBJ_CLEAR (array[i], struct schedule_entry);
      tv_randomize (&array[i]->tv);
      /*schedule_print (s);*/
      /*schedule_verify (s);*/
      schedule_add_modify (s, array[i]);
    }

  schedule_randomize_array (array, n);

  /*schedule_print (s);*/
  schedule_verify (s);

  for (j = 1; j <= n_mod; ++j)
    {
      printf ("Modification Phase Pass %d\n", j);

      for (i = 0; i < n; ++i)
	{
	  e = schedule_find_earliest_wakeup (s);
	  /*printf ("BEFORE %s\n", tv_string (&e->tv, &gc));*/
	  tv_randomize (&e->tv);
	  /*printf ("AFTER %s\n", tv_string (&e->tv, &gc));*/
	  schedule_add_modify (s, e);
	  /*schedule_verify (s);*/
	  /*schedule_print (s);*/
	}
      schedule_verify (s);
      /*schedule_print (s);*/
    }

  /*printf ("INS=%d\n", z.ins);*/

  while ((e = schedule_find_earliest_wakeup (s)))
    {
      schedule_remove_node (s, e);
      /*schedule_verify (s);*/
    }
  schedule_verify (s);

  printf ("S->ROOT is %s\n", s->root ? "NOT NULL" : "NULL");

  for (i = 0; i < n; ++i)
    {
      free (array[i]);
    }
  free (array);
  free (s);
  gc_free (&gc);
}

#endif
#endif
