//
// 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 "doomdef.h"
#include "doomstat.h"
#include "m_bbox.h"
#include "p_local.h"

#include <stdlib.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, (int) 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;

    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);
}
