//
// Copyright(C) 1993-1996 Id Software, Inc.
// Copyright(C) 2005-2014 Simon Howard
// Copyright(C) 2005, 2006 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.
//
// DESCRIPTION:
//	Movement/collision utility functions,
//	as used by function in p_map.c.
//	BLOCKMAP Iterator functions,
//	and some PIT_* functions to use for iteration.
//

#include <limits.h>
#include <stdint.h>
#include <stdlib.h>

#include "doomstat.h"
#include "doomtype.h"
#include "m_bbox.h"
#include "m_fixed.h"
#include "p_local.h"
#include "p_mobj.h"
#include "r_defs.h"
#include "r_main.h"
// State.
#include "r_state.h"

//
// P_AproxDistance
// Gives an estimation of distance (not exact)
//

fixed_t P_AproxDistance(fixed_t dx, fixed_t dy) {
  dx = abs(dx);
  dy = abs(dy);
  if (dx < dy)
    return dx + dy - (dx >> 1);
  return dx + dy - (dy >> 1);
}

//
// P_PointOnLineSide
// Returns 0 or 1
//
int P_PointOnLineSide(fixed_t x, fixed_t y, line_t *line) {
  fixed_t dx;
  fixed_t dy;
  fixed_t left;
  fixed_t right;

  if (!line->dx) {
    if (x <= line->v1->x)
      return line->dy > 0;

    return line->dy < 0;
  }
  if (!line->dy) {
    if (y <= line->v1->y)
      return line->dx < 0;

    return line->dx > 0;
  }

  dx = (x - line->v1->x);
  dy = (y - line->v1->y);

  left = FixedMul(line->dy >> FRACBITS, dx);
  right = FixedMul(dy, line->dx >> FRACBITS);

  if (right < left)
    return 0; // front side
  return 1;   // back side
}

//
// P_BoxOnLineSide
// Considers the line to be infinite
// Returns side 0 or 1, -1 if box crosses the line.
//
int P_BoxOnLineSide(fixed_t *tmbox, line_t *ld) {
  int p1 = 0;
  int p2 = 0;

  switch (ld->slopetype) {
  case ST_HORIZONTAL:
    p1 = tmbox[BOXTOP] > ld->v1->y;
    p2 = tmbox[BOXBOTTOM] > ld->v1->y;
    if (ld->dx < 0) {
      p1 ^= 1;
      p2 ^= 1;
    }
    break;

  case ST_VERTICAL:
    p1 = tmbox[BOXRIGHT] < ld->v1->x;
    p2 = tmbox[BOXLEFT] < ld->v1->x;
    if (ld->dy < 0) {
      p1 ^= 1;
      p2 ^= 1;
    }
    break;

  case ST_POSITIVE:
    p1 = P_PointOnLineSide(tmbox[BOXLEFT], tmbox[BOXTOP], ld);
    p2 = P_PointOnLineSide(tmbox[BOXRIGHT], tmbox[BOXBOTTOM], ld);
    break;

  case ST_NEGATIVE:
    p1 = P_PointOnLineSide(tmbox[BOXRIGHT], tmbox[BOXTOP], ld);
    p2 = P_PointOnLineSide(tmbox[BOXLEFT], tmbox[BOXBOTTOM], ld);
    break;
  }

  if (p1 == p2)
    return p1;
  return -1;
}

//
// P_PointOnDivlineSide
// Returns 0 or 1.
//
int P_PointOnDivlineSide(fixed_t x, fixed_t y, divline_t *line) {
  fixed_t dx;
  fixed_t dy;
  fixed_t left;
  fixed_t right;

  if (!line->dx) {
    if (x <= line->x)
      return line->dy > 0;

    return line->dy < 0;
  }
  if (!line->dy) {
    if (y <= line->y)
      return line->dx < 0;

    return line->dx > 0;
  }

  dx = (x - line->x);
  dy = (y - line->y);

  // try to quickly decide by looking at sign bits
  if ((line->dy ^ line->dx ^ dx ^ dy) & 0x80000000) {
    if ((line->dy ^ dx) & 0x80000000)
      return 1; // (left is negative)
    return 0;
  }

  left = FixedMul(line->dy >> 8, dx >> 8);
  right = FixedMul(dy >> 8, line->dx >> 8);

  if (right < left)
    return 0; // front side
  return 1;   // back side
}

//
// P_MakeDivline
//
void P_MakeDivline(line_t *li, divline_t *dl) {
  dl->x = li->v1->x;
  dl->y = li->v1->y;
  dl->dx = li->dx;
  dl->dy = li->dy;
}

//
// P_InterceptVector
// Returns the fractional intercept point
// along the first divline.
// This is only called by the addthings
// and addlines traversers.
//
fixed_t P_InterceptVector(divline_t *v2, divline_t *v1) {
#if 1
  fixed_t frac;
  fixed_t num;
  fixed_t den;

  den = FixedMul(v1->dy >> 8, v2->dx) - FixedMul(v1->dx >> 8, v2->dy);

  if (den == 0)
    return 0;
  //	I_Error ("P_InterceptVector: parallel");

  num = FixedMul((v1->x - v2->x) >> 8, v1->dy) +
        FixedMul((v2->y - v1->y) >> 8, v1->dx);

  frac = FixedDiv(num, den);

  return frac;
#else // UNUSED, float debug.
  float frac;
  float num;
  float den;
  float v1x;
  float v1y;
  float v1dx;
  float v1dy;
  float v2x;
  float v2y;
  float v2dx;
  float v2dy;

  v1x = (float)v1->x / FRACUNIT;
  v1y = (float)v1->y / FRACUNIT;
  v1dx = (float)v1->dx / FRACUNIT;
  v1dy = (float)v1->dy / FRACUNIT;
  v2x = (float)v2->x / FRACUNIT;
  v2y = (float)v2->y / FRACUNIT;
  v2dx = (float)v2->dx / FRACUNIT;
  v2dy = (float)v2->dy / FRACUNIT;

  den = v1dy * v2dx - v1dx * v2dy;

  if (den == 0)
    return 0; // parallel

  num = (v1x - v2x) * v1dy + (v2y - v1y) * v1dx;
  frac = num / den;

  return frac * FRACUNIT;
#endif
}

//
// P_LineOpening
// Sets opentop and openbottom to the window
// through a two sided line.
// OPTIMIZE: keep this precalculated
//
fixed_t opentop;
fixed_t openbottom;
fixed_t openrange;
fixed_t lowfloor;

void P_LineOpening(line_t *linedef) {
  sector_t *front;
  sector_t *back;

  if (linedef->sidenum[1] == -1) {
    // single sided line
    openrange = 0;
    return;
  }

  front = linedef->frontsector;
  back = linedef->backsector;

  if (front->ceilingheight < back->ceilingheight)
    opentop = front->ceilingheight;
  else
    opentop = back->ceilingheight;

  if (front->floorheight > back->floorheight) {
    openbottom = front->floorheight;
    lowfloor = back->floorheight;
  } else {
    openbottom = back->floorheight;
    lowfloor = front->floorheight;
  }

  openrange = opentop - openbottom;
}

//
// THING POSITION SETTING
//

//
// P_UnsetThingPosition
// Unlinks a thing from block map and sectors.
// On each position change, BLOCKMAP and other
// lookups maintaining lists ot things inside
// these structures need to be updated.
//
void P_UnsetThingPosition(mobj_t *thing) {
  int blockx;
  int blocky;

  if (!(thing->flags & MF_NOSECTOR)) {
    // inert things don't need to be in blockmap?
    // unlink from subsector
    if (thing->snext)
      thing->snext->sprev = thing->sprev;

    if (thing->sprev)
      thing->sprev->snext = thing->snext;
    else
      thing->subsector->sector->thinglist = thing->snext;
  }

  if (!(thing->flags & MF_NOBLOCKMAP)) {
    // inert things don't need to be in blockmap
    // unlink from block map
    if (thing->bnext)
      thing->bnext->bprev = thing->bprev;

    if (thing->bprev)
      thing->bprev->bnext = thing->bnext;
    else {
      blockx = (thing->x - bmaporgx) >> MAPBLOCKSHIFT;
      blocky = (thing->y - bmaporgy) >> MAPBLOCKSHIFT;

      if (blockx >= 0 && blockx < bmapwidth && blocky >= 0 &&
          blocky < bmapheight) {
        blocklinks[blocky * bmapwidth + blockx] = thing->bnext;
      }
    }
  }
}

//
// P_SetThingPosition
// Links a thing into both a block and a subsector
// based on it's x y.
// Sets thing->subsector properly
//
void P_SetThingPosition(mobj_t *thing) {
  subsector_t *ss;
  sector_t *sec;
  int blockx;
  int blocky;
  mobj_t **link;

  // link into subsector
  ss = R_PointInSubsector(thing->x, thing->y);
  thing->subsector = ss;

  if (!(thing->flags & MF_NOSECTOR)) {
    // invisible things don't go into the sector links
    sec = ss->sector;

    thing->sprev = NULL;
    thing->snext = sec->thinglist;

    if (sec->thinglist)
      sec->thinglist->sprev = thing;

    sec->thinglist = thing;
  }

  // link into blockmap
  if (!(thing->flags & MF_NOBLOCKMAP)) {
    // inert things don't need to be in blockmap
    blockx = (thing->x - bmaporgx) >> MAPBLOCKSHIFT;
    blocky = (thing->y - bmaporgy) >> MAPBLOCKSHIFT;

    if (blockx >= 0 && blockx < bmapwidth && blocky >= 0 &&
        blocky < bmapheight) {
      link = &blocklinks[blocky * bmapwidth + blockx];
      thing->bprev = NULL;
      thing->bnext = *link;
      if (*link)
        (*link)->bprev = thing;

      *link = thing;
    } else {
      // thing is off the map
      thing->bnext = thing->bprev = NULL;
    }
  }
}

//
// BLOCK MAP ITERATORS
// For each line/thing in the given mapblock,
// call the passed PIT_* function.
// If the function returns false,
// exit with false without checking anything else.
//

//
// P_BlockLinesIterator
// The validcount flags are used to avoid checking lines
// that are marked in multiple mapblocks,
// so increment validcount before the first call
// to P_BlockLinesIterator, then make one or more calls
// to it.
//
boolean P_BlockLinesIterator(int x, int y, boolean (*func)(line_t *)) {
  int offset;
  short *list;
  line_t *ld;

  if (x < 0 || y < 0 || x >= bmapwidth || y >= bmapheight) {
    return true;
  }

  offset = y * bmapwidth + x;

  offset = *(blockmap + offset);

  for (list = blockmaplump + offset; *list != -1; list++) {
    ld = &lines[*list];

    if (ld->validcount == validcount)
      continue; // line has already been checked

    ld->validcount = validcount;

    if (!func(ld))
      return false;
  }
  return true; // everything was checked
}

//
// P_BlockThingsIterator
//
boolean P_BlockThingsIterator(int x, int y, boolean (*func)(mobj_t *)) {
  mobj_t *mobj;

  if (x < 0 || y < 0 || x >= bmapwidth || y >= bmapheight) {
    return true;
  }

  for (mobj = blocklinks[y * bmapwidth + x]; mobj; mobj = mobj->bnext) {
    if (!func(mobj))
      return false;
  }
  return true;
}

//
// INTERCEPT ROUTINES
//
intercept_t intercepts[MAXINTERCEPTS];
intercept_t *intercept_p;

divline_t trace;
boolean earlyout;
int ptflags;

static void InterceptsOverrun(int num_intercepts, intercept_t *intercept);

//
// PIT_AddLineIntercepts.
// Looks for lines in the given block
// that intercept the given trace
// to add to the intercepts list.
//
// A line is crossed if its endpoints
// are on opposite sides of the trace.
// Returns true if earlyout and a solid line hit.
//
boolean PIT_AddLineIntercepts(line_t *ld) {
  int s1;
  int s2;
  fixed_t frac;
  divline_t dl;

  // avoid precision problems with two routines
  if (trace.dx > FRACUNIT * 16 || trace.dy > FRACUNIT * 16 ||
      trace.dx < -FRACUNIT * 16 || trace.dy < -FRACUNIT * 16) {
    s1 = P_PointOnDivlineSide(ld->v1->x, ld->v1->y, &trace);
    s2 = P_PointOnDivlineSide(ld->v2->x, ld->v2->y, &trace);
  } else {
    s1 = P_PointOnLineSide(trace.x, trace.y, ld);
    s2 = P_PointOnLineSide(trace.x + trace.dx, trace.y + trace.dy, ld);
  }

  if (s1 == s2)
    return true; // line isn't crossed

  // hit the line
  P_MakeDivline(ld, &dl);
  frac = P_InterceptVector(&trace, &dl);

  if (frac < 0)
    return true; // behind source

  // try to early out the check
  if (earlyout && frac < FRACUNIT && !ld->backsector) {
    return false; // stop checking
  }

  intercept_p->frac = frac;
  intercept_p->isaline = true;
  intercept_p->d.line = ld;
  InterceptsOverrun(intercept_p - intercepts, intercept_p);
  intercept_p++;

  return true; // continue
}

//
// PIT_AddThingIntercepts
//
boolean PIT_AddThingIntercepts(mobj_t *thing) {
  fixed_t x1;
  fixed_t y1;
  fixed_t x2;
  fixed_t y2;

  int s1;
  int s2;

  boolean tracepositive;

  divline_t dl;

  fixed_t frac;

  tracepositive = (trace.dx ^ trace.dy) > 0;

  // check a corner to corner crossection for hit
  if (tracepositive) {
    x1 = thing->x - thing->radius;
    y1 = thing->y + thing->radius;

    x2 = thing->x + thing->radius;
    y2 = thing->y - thing->radius;
  } else {
    x1 = thing->x - thing->radius;
    y1 = thing->y - thing->radius;

    x2 = thing->x + thing->radius;
    y2 = thing->y + thing->radius;
  }

  s1 = P_PointOnDivlineSide(x1, y1, &trace);
  s2 = P_PointOnDivlineSide(x2, y2, &trace);

  if (s1 == s2)
    return true; // line isn't crossed

  dl.x = x1;
  dl.y = y1;
  dl.dx = x2 - x1;
  dl.dy = y2 - y1;

  frac = P_InterceptVector(&trace, &dl);

  if (frac < 0)
    return true; // behind source

  intercept_p->frac = frac;
  intercept_p->isaline = false;
  intercept_p->d.thing = thing;
  InterceptsOverrun(intercept_p - intercepts, intercept_p);
  intercept_p++;

  return true; // keep going
}

//
// P_TraverseIntercepts
// Returns true if the traverser function returns true
// for all lines.
//
boolean P_TraverseIntercepts(traverser_t func, fixed_t maxfrac) {
  int count;
  fixed_t dist;
  intercept_t *scan;
  intercept_t *in;

  count = intercept_p - intercepts;

  in = 0; // shut up compiler warning

  while (count--) {
    dist = INT_MAX;
    for (scan = intercepts; scan < intercept_p; scan++) {
      if (scan->frac < dist) {
        dist = scan->frac;
        in = scan;
      }
    }

    if (dist > maxfrac)
      return true; // checked everything in range

#if 0 // UNUSED
    {
	// don't check these yet, there may be others inserted
	in = scan = intercepts;
	for ( scan = intercepts ; scan<intercept_p ; scan++)
	    if (scan->frac > maxfrac)
		*in++ = *scan;
	intercept_p = in;
	return false;
    }
#endif

    if (!func(in))
      return false; // don't bother going farther

    in->frac = INT_MAX;
  }

  return true; // everything was traversed
}

extern fixed_t bulletslope;

// Intercepts Overrun emulation, from PrBoom-plus.
// Thanks to Andrey Budko (entryway) for researching this and his
// implementation of Intercepts Overrun emulation in PrBoom-plus
// which this is based on.

typedef struct {
  int len;
  void *addr;
  boolean int16_array;
} intercepts_overrun_t;

// Intercepts memory table.  This is where various variables are located
// in memory in Vanilla Doom.  When the intercepts table overflows, we
// need to write to them.
//
// Almost all of the values to overwrite are 32-bit integers, except for
// playerstarts, which is effectively an array of 16-bit integers and
// must be treated differently.

static intercepts_overrun_t intercepts_overrun[] = {
    {4, NULL, false},
    {4, NULL, /* &earlyout, */ false},
    {4, NULL, /* &intercept_p, */ false},
    {4, &lowfloor, false},
    {4, &openbottom, false},
    {4, &opentop, false},
    {4, &openrange, false},
    {4, NULL, false},
    {120, NULL, /* &activeplats, */ false},
    {8, NULL, false},
    {4, &bulletslope, false},
    {4, NULL, /* &swingx, */ false},
    {4, NULL, /* &swingy, */ false},
    {4, NULL, false},
    {40, &playerstarts, true},
    {4, NULL, /* &blocklinks, */ false},
    {4, &bmapwidth, false},
    {4, NULL, /* &blockmap, */ false},
    {4, &bmaporgx, false},
    {4, &bmaporgy, false},
    {4, NULL, /* &blockmaplump, */ false},
    {4, &bmapheight, false},
    {0, NULL, false},
};

// Overwrite a specific memory location with a value.

static void InterceptsMemoryOverrun(int location, int value) {
  int i, offset;
  int index;
  void *addr;

  i = 0;
  offset = 0;

  // Search down the array until we find the right entry

  while (intercepts_overrun[i].len != 0) {
    if (offset + intercepts_overrun[i].len > location) {
      addr = intercepts_overrun[i].addr;

      // Write the value to the memory location.
      // 16-bit and 32-bit values are written differently.

      if (addr != NULL) {
        if (intercepts_overrun[i].int16_array) {
          index = (location - offset) / 2;
          ((short *)addr)[index] = value & 0xffff;
          ((short *)addr)[index + 1] = (value >> 16) & 0xffff;
        } else {
          index = (location - offset) / 4;
          ((int *)addr)[index] = value;
        }
      }

      break;
    }

    offset += intercepts_overrun[i].len;
    ++i;
  }
}

// Emulate overruns of the intercepts[] array.

static void InterceptsOverrun(int num_intercepts, intercept_t *intercept) {
  int location;

  if (num_intercepts <= MAXINTERCEPTS_ORIGINAL) {
    // No overrun

    return;
  }

  location = (num_intercepts - MAXINTERCEPTS_ORIGINAL - 1) * 12;

  // Overwrite memory that is overwritten in Vanilla Doom, using
  // the values from the intercept structure.
  //
  // Note: the ->d.{thing,line} member should really have its
  // address translated into the correct address value for
  // Vanilla Doom.

  InterceptsMemoryOverrun(location, intercept->frac);
  InterceptsMemoryOverrun(location + 4, intercept->isaline);
  InterceptsMemoryOverrun(location + 8, (intptr_t)intercept->d.thing);
}

//
// P_PathTraverse
// Traces a line from x1,y1 to x2,y2,
// calling the traverser function for each.
// Returns true if the traverser function returns true
// for all lines.
//
boolean P_PathTraverse(fixed_t x1, fixed_t y1, fixed_t x2, fixed_t y2,
                       int flags, boolean (*trav)(intercept_t *)) {
  fixed_t xt1;
  fixed_t yt1;
  fixed_t xt2;
  fixed_t yt2;

  fixed_t xstep;
  fixed_t ystep;

  fixed_t partial;

  fixed_t xintercept;
  fixed_t yintercept;

  int mapx;
  int mapy;

  int mapxstep;
  int mapystep;

  int count;

  earlyout = (flags & PT_EARLYOUT) != 0;

  validcount++;
  intercept_p = intercepts;

  if (((x1 - bmaporgx) & (MAPBLOCKSIZE - 1)) == 0)
    x1 += FRACUNIT; // don't side exactly on a line

  if (((y1 - bmaporgy) & (MAPBLOCKSIZE - 1)) == 0)
    y1 += FRACUNIT; // don't side exactly on a line

  trace.x = x1;
  trace.y = y1;
  trace.dx = x2 - x1;
  trace.dy = y2 - y1;

  x1 -= bmaporgx;
  y1 -= bmaporgy;
  xt1 = x1 >> MAPBLOCKSHIFT;
  yt1 = y1 >> MAPBLOCKSHIFT;

  x2 -= bmaporgx;
  y2 -= bmaporgy;
  xt2 = x2 >> MAPBLOCKSHIFT;
  yt2 = y2 >> MAPBLOCKSHIFT;

  if (xt2 > xt1) {
    mapxstep = 1;
    partial = FRACUNIT - ((x1 >> MAPBTOFRAC) & (FRACUNIT - 1));
    ystep = FixedDiv(y2 - y1, abs(x2 - x1));
  } else if (xt2 < xt1) {
    mapxstep = -1;
    partial = (x1 >> MAPBTOFRAC) & (FRACUNIT - 1);
    ystep = FixedDiv(y2 - y1, abs(x2 - x1));
  } else {
    mapxstep = 0;
    partial = FRACUNIT;
    ystep = 256 * FRACUNIT;
  }

  yintercept = (y1 >> MAPBTOFRAC) + FixedMul(partial, ystep);

  if (yt2 > yt1) {
    mapystep = 1;
    partial = FRACUNIT - ((y1 >> MAPBTOFRAC) & (FRACUNIT - 1));
    xstep = FixedDiv(x2 - x1, abs(y2 - y1));
  } else if (yt2 < yt1) {
    mapystep = -1;
    partial = (y1 >> MAPBTOFRAC) & (FRACUNIT - 1);
    xstep = FixedDiv(x2 - x1, abs(y2 - y1));
  } else {
    mapystep = 0;
    partial = FRACUNIT;
    xstep = 256 * FRACUNIT;
  }
  xintercept = (x1 >> MAPBTOFRAC) + FixedMul(partial, xstep);

  // Step through map blocks.
  // Count is present to prevent a round off error
  // from skipping the break.
  mapx = xt1;
  mapy = yt1;

  for (count = 0; count < 64; count++) {
    if (flags & PT_ADDLINES) {
      if (!P_BlockLinesIterator(mapx, mapy, PIT_AddLineIntercepts))
        return false; // early out
    }

    if (flags & PT_ADDTHINGS) {
      if (!P_BlockThingsIterator(mapx, mapy, PIT_AddThingIntercepts))
        return false; // early out
    }

    if (mapx == xt2 && mapy == yt2) {
      break;
    }

    if ((yintercept >> FRACBITS) == mapy) {
      yintercept += ystep;
      mapx += mapxstep;
    } else if ((xintercept >> FRACBITS) == mapx) {
      xintercept += xstep;
      mapy += mapystep;
    }
  }
  // go through the sorted list
  return P_TraverseIntercepts(trav, FRACUNIT);
}