/* Emacs style mode select   -*- C++ -*-
 *-----------------------------------------------------------------------------
 *
 *
 *  PrBoom: a Doom port merged with LxDoom and LSDLDoom
 *  based on BOOM, a modified and improved DOOM engine
 *  Copyright (C) 1999 by
 *  id Software, Chi Hoang, Lee Killough, Jim Flynn, Rand Phares, Ty Halderman
 *  Copyright (C) 1999-2000,2002 by
 *  Jess Haas, Nicolas Kalkhof, Colin Phipps, Florian Schulze
 *  Copyright 2005, 2006 by
 *  Florian Schulze, Colin Phipps, Neil Stevens, Andrey Budko
 *
 *  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., 59 Temple Place - Suite 330, Boston, MA
 *  02111-1307, USA.
 *
 * DESCRIPTION:
 *      Thinker, Ticker.
 *
 *-----------------------------------------------------------------------------*/

#include "doomstat.h"
#include "p_user.h"
#include "p_spec.h"
#include "p_tick.h"
#include "p_map.h"
#include "r_fps.h"

int leveltime;

static boolean newthinkerpresent;

//
// THINKERS
// All thinkers should be allocated by Z_Malloc
// so they can be operated on uniformly.
// The actual structures will vary in size,
// but the first element must be thinker_t.
//

// killough 8/29/98: we maintain several separate threads, each containing
// a special class of thinkers, to allow more efficient searches.
thinker_t thinkerclasscap[th_all+1];

//
// P_InitThinkers
//

void P_InitThinkers(void)
{
  int i;

  for (i=0; i<NUMTHCLASS; i++)  // killough 8/29/98: initialize threaded lists
    thinkerclasscap[i].cprev = thinkerclasscap[i].cnext = &thinkerclasscap[i];

  thinkercap.prev = thinkercap.next  = &thinkercap;
}

//
// killough 8/29/98:
//
// We maintain separate threads of friends and enemies, to permit more
// efficient searches.
//

void P_UpdateThinker(thinker_t *thinker)
{
  register thinker_t *th;
  // find the class the thinker belongs to

  int class =
    thinker->function == P_RemoveThinkerDelayed ? th_delete :
    thinker->function == P_MobjThinker &&
    ((mobj_t *) thinker)->health > 0 &&
    (((mobj_t *) thinker)->flags & MF_COUNTKILL ||
     ((mobj_t *) thinker)->type == MT_SKULL) ?
    ((mobj_t *) thinker)->flags & MF_FRIEND ?
    th_friends : th_enemies : th_misc;

  {
    /* Remove from current thread, if in one */
    if ((th = thinker->cnext)!= NULL)
      (th->cprev = thinker->cprev)->cnext = th;
  }

  // Add to appropriate thread
  th = &thinkerclasscap[class];
  th->cprev->cnext = thinker;
  thinker->cnext = th;
  thinker->cprev = th->cprev;
  th->cprev = thinker;
}

//
// P_AddThinker
// Adds a new thinker at the end of the list.
//

void P_AddThinker(thinker_t* thinker)
{
  thinkercap.prev->next = thinker;
  thinker->next = &thinkercap;
  thinker->prev = thinkercap.prev;
  thinkercap.prev = thinker;

  thinker->references = 0;    // killough 11/98: init reference counter to 0

  // killough 8/29/98: set sentinel pointers, and then add to appropriate list
  thinker->cnext = thinker->cprev = NULL;
  P_UpdateThinker(thinker);
  newthinkerpresent = true;
}

//
// killough 11/98:
//
// Make currentthinker external, so that P_RemoveThinkerDelayed
// can adjust currentthinker when thinkers self-remove.

static thinker_t *currentthinker;

//
// P_RemoveThinkerDelayed()
//
// Called automatically as part of the thinker loop in P_RunThinkers(),
// on nodes which are pending deletion.
//
// If this thinker has no more pointers referencing it indirectly,
// remove it, and set currentthinker to one node preceeding it, so
// that the next step in P_RunThinkers() will get its successor.
//

void P_RemoveThinkerDelayed(thinker_t *thinker)
{
  if (!thinker->references)
    {
      { /* Remove from main thinker list */
        thinker_t *next = thinker->next;
        /* Note that currentthinker is guaranteed to point to us,
         * and since we're freeing our memory, we had better change that. So
         * point it to thinker->prev, so the iterator will correctly move on to
         * thinker->prev->next = thinker->next */
        (next->prev = currentthinker = thinker->prev)->next = next;
      }
      {
        /* Remove from current thinker class list */
        thinker_t *th = thinker->cnext;
        (th->cprev = thinker->cprev)->cnext = th;
      }
      Z_Free(thinker);
    }
}

//
// P_RemoveThinker
//
// Deallocation is lazy -- it will not actually be freed
// until its thinking turn comes up.
//
// killough 4/25/98:
//
// Instead of marking the function with -1 value cast to a function pointer,
// set the function to P_RemoveThinkerDelayed(), so that later, it will be
// removed automatically as part of the thinker process.
//

void P_RemoveThinker(thinker_t *thinker)
{
  R_StopInterpolationIfNeeded(thinker);
  thinker->function = P_RemoveThinkerDelayed;

  P_UpdateThinker(thinker);
}

/* cph 2002/01/13 - iterator for thinker list
 * WARNING: Do not modify thinkers between calls to this functin
 */
thinker_t* P_NextThinker(thinker_t* th, th_class cl)
{
  thinker_t* top = &thinkerclasscap[cl];
  if (!th) th = top;
  th = cl == th_all ? th->next : th->cnext;
  return th == top ? NULL : th;
}

/*
 * P_SetTarget
 *
 * This function is used to keep track of pointer references to mobj thinkers.
 * In Doom, objects such as lost souls could sometimes be removed despite
 * their still being referenced. In Boom, 'target' mobj fields were tested
 * during each gametic, and any objects pointed to by them would be prevented
 * from being removed. But this was incomplete, and was slow (every mobj was
 * checked during every gametic). Now, we keep a count of the number of
 * references, and delay removal until the count is 0.
 */

void P_SetTarget(mobj_t **mop, mobj_t *targ)
{
  if (*mop)             // If there was a target already, decrease its refcount
    (*mop)->thinker.references--;
  if ((*mop = targ))    // Set new target and if non-NULL, increase its counter
    targ->thinker.references++;
}

//
// P_RunThinkers
//
// killough 4/25/98:
//
// Fix deallocator to stop using "next" pointer after node has been freed
// (a Doom bug).
//
// Process each thinker. For thinkers which are marked deleted, we must
// load the "next" pointer prior to freeing the node. In Doom, the "next"
// pointer was loaded AFTER the thinker was freed, which could have caused
// crashes.
//
// But if we are not deleting the thinker, we should reload the "next"
// pointer after calling the function, in case additional thinkers are
// added at the end of the list.
//
// killough 11/98:
//
// Rewritten to delete nodes implicitly, by making currentthinker
// external and using P_RemoveThinkerDelayed() implicitly.
//

static void P_RunThinkers (void)
{
  for (currentthinker = thinkercap.next;
       currentthinker != &thinkercap;
       currentthinker = currentthinker->next)
  {
    if (newthinkerpresent)
      R_ActivateThinkerInterpolations(currentthinker);
    if (currentthinker->function)
      currentthinker->function(currentthinker);
  }
  newthinkerpresent = false;
}

//
// P_Ticker
//

void P_Ticker ()
{
  int i;

  /* pause if in menu and at least one tic has been run
   *
   * killough 9/29/98: note that this ties in with basetic,
   * since G_Ticker does the pausing during recording or
   * playback, and compenates by incrementing basetic.
   *
   * All of this complicated mess is used to preserve demo sync.
   */

  if (paused || (menuactive && !demoplayback && !netgame &&
     players[consoleplayer].viewz != 1))
    return;

  R_UpdateInterpolations ();

  P_MapStart();
               // not if this is an intermission screen
  if(gamestate==GS_LEVEL)
  for (i=0; i<MAXPLAYERS; i++)
    if (playeringame[i])
      P_PlayerThink(&players[i]);

  P_RunThinkers();
  P_UpdateSpecials();
  P_RespawnSpecials();
  P_MapEnd();
  leveltime++;                       // for par times
}