/*
    Copyright (C) 1996-1997  Id Software, Inc.
    Copyright (C) 1997       Greg Lewis

    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

    See file, 'COPYING', for details.
*/

#include <qbsp/brushbsp.hh>

#include <climits>

#include <common/vectorutils.hh>
#include <qbsp/brush.hh>
#include <qbsp/csg.hh>
#include <qbsp/map.hh>
#include <qbsp/portals.hh>
#include <qbsp/qbsp.hh>
#include <qbsp/tree.hh>

#include <list>
#include <atomic>

#include "tbb/task_group.h"

// if a brush just barely pokes onto the other side,
// let it slide by without chopping
constexpr double PLANESIDE_EPSILON = 0.001;
// 0.1

constexpr int PSIDE_FRONT = 1;
constexpr int PSIDE_BACK = 2;
constexpr int PSIDE_BOTH = (PSIDE_FRONT | PSIDE_BACK);
// this gets OR'ed in in the return value of QuickTestBrushToPlanenum if one of the brush sides is on the input plane
constexpr int PSIDE_FACING = 4;

struct bspstats_t
{
    std::unique_ptr<content_stats_base_t> leafstats;
    // total number of nodes, includes c_nonvis
    std::atomic<int> c_nodes;
    // number of nodes created by splitting on a side_t which had !visible
    std::atomic<int> c_nonvis;
    // total number of nodes created by qbsp3 method
    std::atomic<int> c_qbsp3;
    // total number of nodes created by block splitting
    std::atomic<int> c_blocksplit;
    // total number of nodes created by midsplit
    std::atomic<int> c_midsplit;
    // total number of leafs
    std::atomic<int> c_leafs;
    // number of bogus brushes (beyond world extents)
    std::atomic<int> c_bogus;
    // number of brushes entirely removed from a split
    std::atomic<int> c_brushesremoved;
    // number of brushes half-removed from a split
    std::atomic<int> c_brushesonesided;
};

/*
==================
BrushFromBounds

Creates a new axial brush
==================
*/
std::unique_ptr<bspbrush_t> BrushFromBounds(const aabb3d &bounds)
{
    auto b = std::make_unique<bspbrush_t>();

    b->sides.resize(6);
    for (int i = 0; i < 3; i++) {
        {
            qplane3d plane{};
            plane.normal[i] = 1;
            plane.dist = bounds.maxs()[i];

            side_t &side = b->sides[i];
            side.planenum = map.add_or_find_plane(plane);
        }

        {
            qplane3d plane{};
            plane.normal[i] = -1;
            plane.dist = -bounds.mins()[i];

            side_t &side = b->sides[3 + i];
            side.planenum = map.add_or_find_plane(plane);
        }
    }

    CreateBrushWindings(b.get());

    return b;
}

/*
==================
BrushVolume

==================
*/
static vec_t BrushVolume(const bspbrush_t &brush)
{
    // grab the first valid point as the corner

    bool found = false;
    qvec3d corner;
    for (auto &face : brush.sides) {
        if (face.w.size() > 0) {
            corner = face.w[0];
            found = true;
        }
    }
    if (!found) {
        return 0;
    }

    // make tetrahedrons to all other faces

    vec_t volume = 0;
    for (auto &side : brush.sides) {
        if (!side.w.size()) {
            continue;
        }
        auto &plane = side.get_plane();
        vec_t d = -(qv::dot(corner, plane.get_normal()) - plane.get_dist());
        vec_t area = side.w.area();
        volume += d * area;
    }

    volume /= 3;
    return volume;
}

//========================================================

/*
==============
BoxOnPlaneSide

Returns PSIDE_FRONT, PSIDE_BACK, or PSIDE_BOTH
==============
*/
static int BoxOnPlaneSide(const aabb3d &bounds, const qbsp_plane_t &plane)
{
    // axial planes are easy
    if (plane.get_type() < plane_type_t::PLANE_ANYX) {
        int side = 0;
        if (bounds.maxs()[static_cast<int>(plane.get_type())] > plane.get_dist() + PLANESIDE_EPSILON)
            side |= PSIDE_FRONT;
        if (bounds.mins()[static_cast<int>(plane.get_type())] < plane.get_dist() - PLANESIDE_EPSILON)
            side |= PSIDE_BACK;
        return side;
    }

    // create the proper leading and trailing verts for the box
    std::array<qvec3d, 2> corners;
    for (int i = 0; i < 3; i++) {
        if (plane.get_normal()[i] < 0) {
            corners[0][i] = bounds.mins()[i];
            corners[1][i] = bounds.maxs()[i];
        } else {
            corners[1][i] = bounds.mins()[i];
            corners[0][i] = bounds.maxs()[i];
        }
    }

    double dist1 = qv::dot(plane.get_normal(), corners[0]) - plane.get_dist();
    double dist2 = qv::dot(plane.get_normal(), corners[1]) - plane.get_dist();
    int side = 0;
    if (dist1 >= PLANESIDE_EPSILON)
        side = PSIDE_FRONT;
    if (dist2 < PLANESIDE_EPSILON)
        side |= PSIDE_BACK;

    return side;
}

#if 0
static int SphereOnPlaneSide(const qvec3d &sphere_origin, double sphere_radius, const qplane3d &plane)
{
    const double sphere_dist = plane.dist_above(sphere_origin);
    if (sphere_dist > sphere_radius) {
        return PSIDE_FRONT;
    }
    if (sphere_dist < -sphere_radius) {
        return PSIDE_BACK;
    }
    return PSIDE_BOTH;
}
#endif

#if 0
/*
============
QuickTestBrushToPlanenum

Returns PSIDE_BACK, PSIDE_FRONT, PSIDE_BOTH depending on how the brush is split by planenum
============
*/
static int QuickTestBrushToPlanenum(const bspbrush_t &brush, int planenum, int *numsplits)
{
    *numsplits = 0;

    // if the brush actually uses the planenum,
    // we can tell the side for sure
    for (auto& side : brush.sides) {
        int num = FindPlane(side.plane, nullptr);
        if (num == planenum) {
            if (side.plane_flipped == SIDE_FRONT) {
                return PSIDE_BACK|PSIDE_FACING;
            } else {
                return PSIDE_FRONT|PSIDE_FACING;
            }
        }
    }

    // box on plane side
    auto plane = map.get_plane(planenum);
    int s = BoxOnPlaneSide(brush.bounds, plane);

    // if both sides, count the visible faces split
    if (s == PSIDE_BOTH) {
        *numsplits += 3;
    }

    return s;
}
#endif

/*
============
TestBrushToPlanenum

============
*/
static int TestBrushToPlanenum(
    const bspbrush_t &brush, size_t planenum, int *numsplits, bool *hintsplit, int *epsilonbrush)
{
    if (numsplits) {
        *numsplits = 0;
    }
    if (hintsplit) {
        *hintsplit = false;
    }

    // if the brush actually uses the planenum,
    // we can tell the side for sure
    for (auto &side : brush.sides) {
		if (side.planenum == planenum) {
			return PSIDE_BACK | PSIDE_FACING;
        } else if (side.planenum == (planenum ^ 1)) {
			return PSIDE_FRONT|PSIDE_FACING;
        }
    }

    // box on plane side
    // int s = SphereOnPlaneSide(brush.sphere_origin, brush.sphere_radius, plane);
    const qbsp_plane_t &plane = map.get_plane(planenum);
    int s = BoxOnPlaneSide(brush.bounds, plane);
    if (s != PSIDE_BOTH)
        return s;

    if (numsplits && hintsplit && epsilonbrush) {
        // if both sides, count the visible faces split
        vec_t d_front = 0;
        vec_t d_back = 0;

        for (const side_t &side : brush.sides) {
            if (side.onnode)
                continue; // on node, don't worry about splits
            if (!side.visible)
                continue; // we don't care about non-visible
            auto &w = side.w;
            if (!w)
                continue;
            int front = 0;
            int back = 0;
            for (auto &point : w) {
                const double d = qv::dot(point, plane.get_normal()) - plane.get_dist();
                if (d > d_front)
                    d_front = d;
                if (d < d_back)
                    d_back = d;

                if (d > 0.1) // PLANESIDE_EPSILON)
                    front = 1;
                if (d < -0.1) // PLANESIDE_EPSILON)
                    back = 1;
            }
            if (front && back) {
                if (!(side.get_texinfo().flags.is_hintskip)) {
                    (*numsplits)++;
                    if (side.get_texinfo().flags.is_hint) {
                        *hintsplit = true;
                    }
                }
            }
        }

        if ((d_front > 0.0 && d_front < 1.0) || (d_back < 0.0 && d_back > -1.0)) {
            (*epsilonbrush)++;
        }
    }

    return s;
}

//========================================================

/*
================
WindingIsTiny

Returns true if the winding would be crunched out of
existance by the vertex snapping.
================
*/
bool WindingIsTiny(const winding_t &w, double size)
{
    int edges = 0;
    for (size_t i = 0; i < w.size(); i++) {
        size_t j = (i + 1) % w.size();
        const qvec3d delta = w[j] - w[i];
        const double len = qv::length(delta);
        if (len > size) {
            if (++edges == 3)
                return false;
        }
    }
    return true;
}

/*
================
WindingIsHuge

Returns true if the winding still has one of the points
from basewinding for plane
================
*/
bool WindingIsHuge(const winding_t &w)
{
    for (size_t i = 0; i < w.size(); i++) {
        for (size_t j = 0; j < 3; j++) {
            if (fabs(w[i][j]) > qbsp_options.worldextent.value())
                return true;
        }
    }
    return false;
}

//============================================================================

/*
==================
LeafNode

Creates a leaf node.

Called in parallel.
==================
*/
static void LeafNode(node_t *leafnode, std::vector<std::unique_ptr<bspbrush_t>> brushes, bspstats_t &stats)
{
    leafnode->facelist.clear();
    leafnode->is_leaf = true;

    leafnode->contents = qbsp_options.target_game->create_empty_contents();
    for (auto &brush : brushes) {
        leafnode->contents = qbsp_options.target_game->combine_contents(leafnode->contents, brush->contents);
    }
    for (auto &brush : brushes) {
        Q_assert(brush->original != nullptr);
        leafnode->original_brushes.insert(brush->original);
        leafnode->original_mapbrushes.insert(brush->original->mapbrush);
    }

    qbsp_options.target_game->count_contents_in_stats(leafnode->contents, *stats.leafstats);
}

//============================================================

/*
==================
BrushMostlyOnSide

==================
*/
planeside_t BrushMostlyOnSide(const bspbrush_t &brush, const qplane3d &plane)
{
    vec_t max = 0;
    planeside_t side = SIDE_FRONT;
    for (auto &face : brush.sides) {
        for (size_t j = 0; j < face.w.size(); j++) {
            vec_t d = qv::dot(face.w[j], plane.normal) - plane.dist;
            if (d > max) {
                max = d;
                side = SIDE_FRONT;
            }
            if (-d > max) {
                max = -d;
                side = SIDE_BACK;
            }
        }
    }
    return side;
}

/*
================
SplitBrush

Note, it's useful to take/return std::unique_ptr so it can quickly return the
input.

https://github.com/id-Software/Quake-2-Tools/blob/master/bsp/qbsp3/brushbsp.c#L935
================
*/
static twosided<std::unique_ptr<bspbrush_t>> SplitBrush(std::unique_ptr<bspbrush_t> brush, size_t planenum, bspstats_t &stats)
{
    const qplane3d &split = map.planes[planenum];
    twosided<std::unique_ptr<bspbrush_t>> result;

    // check all points
    vec_t d_front = 0;
    vec_t d_back = 0;
    for (auto &face : brush->sides) {
        for (int j = 0; j < face.w.size(); j++) {
            vec_t d = qv::dot(face.w[j], split.normal) - split.dist;
            if (d > 0 && d > d_front)
                d_front = d;
            if (d < 0 && d < d_back)
                d_back = d;
        }
    }
    if (d_front < 0.1) // PLANESIDE_EPSILON)
    { // only on back
        result.back = std::move(brush);
        return result;
    }
    if (d_back > -0.1) // PLANESIDE_EPSILON)
    { // only on front
        result.front = std::move(brush);
        return result;
    }

    // create a new winding from the split plane
    auto w = std::optional<winding_t>{BaseWindingForPlane(split)};
    for (auto &face : brush->sides) {
        if (!w) {
            break;
        }
        auto [frontOpt, backOpt] = w->clip(face.get_plane());
        w = backOpt;
    }

    if (!w || WindingIsTiny(*w)) { // the brush isn't really split
        planeside_t side = BrushMostlyOnSide(*brush, split);
        if (side == SIDE_FRONT)
            result.front = std::move(brush);
        else
            result.back = std::move(brush);
        return result;
    }

    if (WindingIsHuge(*w)) {
        logging::print("WARNING: huge winding\n");
    }

    winding_t midwinding = *w;

    // split it for real

    // start with 2 empty brushes

    for (int i = 0; i < 2; i++) {
        result[i] = std::make_unique<bspbrush_t>();
        result[i]->original = brush->original;
        // fixme-brushbsp: add a bspbrush_t copy constructor to make sure we get all fields
        result[i]->contents = brush->contents;
        result[i]->lmshift = brush->lmshift;
        result[i]->func_areaportal = brush->func_areaportal;
        result[i]->sides.reserve(brush->sides.size() + 1);
    }

    // split all the current windings

    for (const auto &face : brush->sides) {
        auto cw = face.w.clip(split, 0 /*PLANESIDE_EPSILON*/);
        for (size_t j = 0; j < 2; j++) {
            if (!cw[j])
                continue;
#if 0
			if (WindingIsTiny (cw[j]))
			{
				FreeWinding (cw[j]);
				continue;
			}
#endif

            // add the clipped face to result[j]
            side_t faceCopy = face;
            faceCopy.w = *cw[j];

            // fixme-brushbsp: configure any settings on the faceCopy?
            // Q2 does `cs->tested = false;`, why?

            result[j]->sides.push_back(std::move(faceCopy));
        }
    }

    // see if we have valid polygons on both sides

    for (int i = 0; i < 2; i++) {
        result[i]->update_bounds();

        bool bogus = false;
        for (int j = 0; j < 3; j++) {
            if (result[i]->bounds.mins()[j] < -qbsp_options.worldextent.value() || result[i]->bounds.maxs()[j] > qbsp_options.worldextent.value()) {
                stats.c_bogus++;
                bogus = true;
                break;
            }
        }

        if (result[i]->sides.size() < 3 || bogus) {
            result[i] = nullptr;
        }
    }

    if (!result[0] && !result[1]) {
        stats.c_brushesremoved++;

        return result;
    } else if (!result[0] || !result[1]) {
        stats.c_brushesonesided++;

        if (result[0]) {
            result.front = std::move(brush);
        } else {
            result.back = std::move(brush);
        }

        return result;
    }

    // add the midwinding to both sides
    for (int i = 0; i < 2; i++) {
        side_t cs{};

        const bool brushOnFront = (i == 0);

        // for the brush on the front side of the plane, the `midwinding`
        // (the face that is touching the plane) should have a normal opposite the plane's normal
        cs.planenum = planenum ^ i ^ 1;
        cs.texinfo = map.skip_texinfo;
        cs.visible = false;
        cs.tested = false;
        cs.onnode = true;
        // fixme-brushbsp: configure any other settings on the face?

        cs.w = brushOnFront ? midwinding.flip() : midwinding;

        result[i]->sides.push_back(std::move(cs));
    }

    {
        vec_t v1;
        int i;

        for (i = 0; i < 2; i++) {
            v1 = BrushVolume(*result[i]);
            if (v1 < 1.0) {
                result[i] = nullptr;
                //			qprintf ("tiny volume after clip\n");
            }
        }
    }

    return result;
}

inline void CheckPlaneAgainstParents(size_t planenum, node_t *node)
{
    for (node_t *p = node->parent; p; p = p->parent) {
        if (p->planenum == planenum) {
            Error("Tried parent");
        }
    }
}

static bool CheckPlaneAgainstVolume(size_t planenum, const node_t *node, bspstats_t &stats)
{
    auto [front, back] = SplitBrush(node->volume->copy_unique(), planenum, stats);

    bool good = (front && back);

    return good;
}

/*
 * Split a bounding box by a plane; The front and back bounds returned
 * are such that they completely contain the portion of the input box
 * on that side of the plane. Therefore, if the split plane is
 * non-axial, then the returned bounds will overlap.
 */
inline void DivideBounds(const aabb3d &in_bounds, const qbsp_plane_t &split, aabb3d &front_bounds, aabb3d &back_bounds)
{
    int a, b, c, i, j;
    vec_t dist1, dist2, mid, split_mins, split_maxs;
    qvec3d corner;

    front_bounds = back_bounds = in_bounds;

    if (split.get_type() < plane_type_t::PLANE_ANYX) {
        front_bounds[0][static_cast<size_t>(split.get_type())] = back_bounds[1][static_cast<size_t>(split.get_type())] = split.get_dist();
        return;
    }

    /* Make proper sloping cuts... */
    for (a = 0; a < 3; ++a) {
        /* Check for parallel case... no intersection */
        if (fabs(split.get_normal()[a]) < NORMAL_EPSILON)
            continue;

        b = (a + 1) % 3;
        c = (a + 2) % 3;

        split_mins = in_bounds.maxs()[a];
        split_maxs = in_bounds.mins()[a];
        for (i = 0; i < 2; ++i) {
            corner[b] = in_bounds[i][b];
            for (j = 0; j < 2; ++j) {
                corner[c] = in_bounds[j][c];

                corner[a] = in_bounds[0][a];
                dist1 = split.distance_to(corner);

                corner[a] = in_bounds[1][a];
                dist2 = split.distance_to(corner);

                mid = in_bounds[1][a] - in_bounds[0][a];
                mid *= (dist1 / (dist1 - dist2));
                mid += in_bounds[0][a];

                split_mins = max(min(mid, split_mins), in_bounds.mins()[a]);
                split_maxs = min(max(mid, split_maxs), in_bounds.maxs()[a]);
            }
        }
        if (split.get_normal()[a] > 0) {
            front_bounds[0][a] = split_mins;
            back_bounds[1][a] = split_maxs;
        } else {
            back_bounds[0][a] = split_mins;
            front_bounds[1][a] = split_maxs;
        }
    }
}

inline vec_t SplitPlaneMetric(const qbsp_plane_t &p, const aabb3d &bounds)
{
    aabb3d f, b;

    DivideBounds(bounds, p, f, b);

    // i.e. a good split will have equal volumes on front and back.
    // a bad split will have all of the volume on one side.
    return fabs(f.volume() - b.volume());
}

/*
==================
ChooseMidPlaneFromList

The clipping hull BSP doesn't worry about avoiding splits
==================
*/
static std::optional<size_t> ChooseMidPlaneFromList(const std::vector<std::unique_ptr<bspbrush_t>> &brushes, const node_t *node, bspstats_t &stats)
{
    vec_t bestaxialmetric = VECT_MAX;
    std::optional<size_t> bestaxialplane;

    vec_t bestanymetric = VECT_MAX;
    std::optional<size_t> bestanyplane;

    for (auto &brush : brushes) {
        for (auto &side : brush->sides) {
            if (side.bevel) {
                continue; // never use a bevel as a spliter
            }
            if (side.onnode) {
                continue; // allready a node splitter
            }

            size_t positive_planenum = side.planenum & ~1;
            const qbsp_plane_t &plane = side.get_positive_plane();

            if (!CheckPlaneAgainstVolume(positive_planenum, node, stats)) {
                continue; // would produce a tiny volume
            }

            /* calculate the split metric, smaller values are better */
            const vec_t metric = SplitPlaneMetric(plane, node->bounds);

            if (metric < bestanymetric) {
                bestanymetric = metric;
                bestanyplane = side.planenum & ~1;
            }

            /* check for axis aligned surfaces */
            if (plane.get_type() < plane_type_t::PLANE_ANYX) {
                if (metric < bestaxialmetric) {
                    bestaxialmetric = metric;
                    bestaxialplane = side.planenum & ~1;
                }
            }
        }
    }

    // prefer the axial split
    return bestaxialplane ? bestaxialplane : bestanyplane;
}


/*
================
SelectSplitPlane

Using heuristics, chooses a plane to partition the brushes with.
Returns nullopt if there are no valid planes to split with.
================
*/
static std::optional<size_t> SelectSplitPlane(const std::vector<std::unique_ptr<bspbrush_t>> &brushes, node_t *node, std::optional<bool> forced_quick_tree, bspstats_t &stats)
{
    // no brushes left to split, so we can't use any plane.
    if (!brushes.size()) {
        return std::nullopt;
    }

    // if forced_quick_tree is nullopt, we will choose fast/slow based on
    // certain parameters.
    if (!forced_quick_tree.has_value() || forced_quick_tree.value() == true) {
        if (!forced_quick_tree.has_value()) {

            // decide if we should switch to the midsplit method
            if (qbsp_options.midsplitbrushfraction.value() != 0.0) {
                // new way (opt-in)
                // how much of the map are we partitioning?
                double fractionOfMap = brushes.size() / (double) map.total_brushes;
                forced_quick_tree = (fractionOfMap > qbsp_options.midsplitbrushfraction.value());
            } else {
                // old way (ericw-tools 0.15.2+)
                if (qbsp_options.maxnodesize.value() >= 64) {
                    const vec_t maxnodesize = qbsp_options.maxnodesize.value() - qbsp_options.epsilon.value();

                    forced_quick_tree = (node->bounds.maxs()[0] - node->bounds.mins()[0]) > maxnodesize
                                || (node->bounds.maxs()[1] - node->bounds.mins()[1]) > maxnodesize
                                || (node->bounds.maxs()[2] - node->bounds.mins()[2]) > maxnodesize;
                }
            }
        }

        if (forced_quick_tree.value()) {
            if (auto mid_plane = ChooseMidPlaneFromList(brushes, node, stats)) {
                stats.c_midsplit++;

                for (auto &b : brushes) {
                    b->side = TestBrushToPlanenum(*b, mid_plane.value(), nullptr, nullptr, nullptr);
                }

                return mid_plane;
            }
        }
    }

    side_t *bestside = nullptr;
    int bestvalue = -99999;

    // the search order goes: visible-structural, visible-detail,
    // nonvisible-structural, nonvisible-detail.
    // If any valid plane is available in a pass, no further
    // passes will be tried.
    constexpr int numpasses = 4;
    for (int pass = 0; pass < numpasses; pass++) {
        for (auto &brush : brushes) {
            if ((pass & 1) && !brush->original->contents.is_any_detail(qbsp_options.target_game))
                continue;
            if (!(pass & 1) && brush->original->contents.is_any_detail(qbsp_options.target_game))
                continue;
            for (auto &side : brush->sides) {
                if (side.bevel)
                    continue; // never use a bevel as a spliter
                if (!side.w)
                    continue; // nothing visible, so it can't split
                if (side.onnode)
                    continue; // allready a node splitter
                if (side.tested)
                    continue; // we allready have metrics for this plane
                if (side.get_texinfo().flags.is_hintskip)
                    continue; // skip surfaces are never chosen
                if (side.visible ^ (pass < 2))
                    continue; // only check visible faces on first pass

                size_t positive_planenum = side.planenum & ~1;
                const qbsp_plane_t &plane = side.get_positive_plane(); // always use positive facing plane

                CheckPlaneAgainstParents(positive_planenum, node);

                if (!CheckPlaneAgainstVolume(positive_planenum, node, stats))
                    continue; // would produce a tiny volume

                int front = 0;
                int back = 0;
                int both = 0;
                int facing = 0;
                int splits = 0;
                int epsilonbrush = 0;
                bool hintsplit = false;

                for (auto &test : brushes) {
                    int bsplits;
                    int s = TestBrushToPlanenum(*test, positive_planenum, &bsplits, &hintsplit, &epsilonbrush);

                    splits += bsplits;
                    if (bsplits && (s & PSIDE_FACING))
                        Error("PSIDE_FACING with splits");

                    test->testside = s;
                    // if the brush shares this face, don't bother
                    // testing that facenum as a splitter again
                    if (s & PSIDE_FACING) {
                        facing++;
                        for (auto &testside : test->sides) {
                            if ((testside.planenum & ~1) == (side.planenum & ~1)) {
                                testside.tested = true;
                            }
                        }
                    }
                    if (s & PSIDE_FRONT)
                        front++;
                    if (s & PSIDE_BACK)
                        back++;
                    if (s == PSIDE_BOTH)
                        both++;
                }

                // give a value estimate for using this plane

                int value = 5 * facing - 5 * splits - abs(front - back);
                //					value =  -5*splits;
                //					value =  5*facing - 5*splits;
                if (plane.get_type() < plane_type_t::PLANE_ANYX)
                    value += 5; // axial is better
                value -= epsilonbrush * 1000; // avoid!

                // never split a hint side except with another hint
                if (hintsplit && !(side.get_texinfo().flags.is_hint))
                    value = -9999999;

                // save off the side test so we don't need
                // to recalculate it when we actually seperate
                // the brushes
                if (value > bestvalue) {
                    bestvalue = value;
                    bestside = &side;
                    for (auto &test : brushes) {
                        test->side = test->testside;
                    }
                }
            }
        }

        // if we found a good plane, don't bother trying any
        // other passes
        if (bestside) {
            if (pass > 0)
                node->detail_separator = true; // not needed for vis
            break;
        }
    }

    //
    // clear all the tested flags we set
    //
    for (auto &brush : brushes) {
        for (auto &side : brush->sides) {
            side.tested = false;
        }
    }

    if (!bestside) {
        return std::nullopt;
    }

    if (!bestside->visible) {
        stats.c_nonvis++;
    }

    stats.c_qbsp3++;

    return bestside->planenum & ~1;
}

/*
================
SplitBrushList
================
*/
static std::array<std::vector<std::unique_ptr<bspbrush_t>>, 2> SplitBrushList(
    std::vector<std::unique_ptr<bspbrush_t>> brushes, size_t planenum, bspstats_t &stats)
{
    std::array<std::vector<std::unique_ptr<bspbrush_t>>, 2> result;

    for (auto &brush : brushes) {
        int sides = brush->side;

        if (sides == PSIDE_BOTH) {
            // split into two brushes (destructively)
            auto [front, back] = SplitBrush(std::move(brush), planenum, stats);

            if (front) {
                result[0].push_back(std::move(front));
            }

            if (back) {
                result[1].push_back(std::move(back));
            }
            continue;
        }

        // if the planenum is actually a part of the brush
        // find the plane and flag it as used so it won't be tried
        // as a splitter again
        if (sides & PSIDE_FACING) {
            for (auto &side : brush->sides) {
                if ((side.planenum & ~1) == planenum) {
                    side.onnode = true;
                }
            }
        }

        if (sides & PSIDE_FRONT) {
            result[0].push_back(std::move(brush));
            continue;
        }
        if (sides & PSIDE_BACK) {
            result[1].push_back(std::move(brush));
            continue;
        }
    }

    return result;
}

/*
==================
BuildTree_r

Called in parallel.
==================
*/
static void BuildTree_r(node_t *node, std::vector<std::unique_ptr<bspbrush_t>> brushes, std::optional<bool> forced_quick_tree, bspstats_t &stats)
{
    // find the best plane to use as a splitter
    auto bestplane = SelectSplitPlane(brushes, node, forced_quick_tree, stats);

    if (!bestplane) {
        // this is a leaf node
        node->is_leaf = true;

        stats.c_leafs++;
        LeafNode(node, std::move(brushes), stats);

        return;
    }

    // this is a splitplane node
    stats.c_nodes++;

    // make sure this was a positive-facing split
    Q_assert(!(bestplane.value() & 1));

    node->planenum = bestplane.value();
    
    auto &plane = map.get_plane(bestplane.value());
    auto children = SplitBrushList(std::move(brushes), bestplane.value(), stats);

    // allocate children before recursing
    for (int i = 0; i < 2; i++) {
        auto &newnode = node->children[i] = std::make_unique<node_t>();
        newnode->parent = node;
        newnode->bounds = node->bounds;
    }

	for (int i = 0; i < 3; i++) {
		if (plane.get_normal()[i] == 1.0) {
            node->children[0]->bounds[0][i] = plane.get_dist();
			node->children[1]->bounds[1][i] = plane.get_dist();
			break;
		}
	}

    auto children_volumes = SplitBrush(node->volume->copy_unique(), bestplane.value(), stats);
    node->children[0]->volume = std::move(children_volumes[0]);
    node->children[1]->volume = std::move(children_volumes[1]);

    // recursively process children
    tbb::task_group g;
    g.run([&]() { BuildTree_r(node->children[0].get(), std::move(children[0]), forced_quick_tree, stats); });
    g.run([&]() { BuildTree_r(node->children[1].get(), std::move(children[1]), forced_quick_tree, stats); });
    g.wait();
}

/*
==================
BrushBSP
==================
*/
static std::unique_ptr<tree_t> BrushBSP_internal(mapentity_t *entity, std::vector<std::unique_ptr<bspbrush_t>> brushlist, std::optional<bool> forced_quick_tree)
{
    auto tree = std::make_unique<tree_t>();

    logging::funcheader();

    size_t c_faces = 0;
    size_t c_nonvisfaces = 0;
    size_t c_brushes = 0;

    for (const auto &b : brushlist) {
        c_brushes++;

        // fixme-brushbsp: why does this just print and do nothing? should
        // the brush be removed?
        double volume = BrushVolume(*b);
        if (volume < qbsp_options.microvolume.value()) {
            logging::print("WARNING: {}: microbrush\n",
                b->original->mapbrush->line);
        }

        for (side_t &side : b->sides) {
            if (side.bevel)
                continue;
            if (!side.w)
                continue;
            if (side.onnode)
                continue;
            if (side.visible)
                c_faces++;
            else
                c_nonvisfaces++;
        }

        tree->bounds += b->bounds;
    }

    if (brushlist.empty()) {
        /*
         * We allow an entity to be constructed with no visible brushes
         * (i.e. all clip brushes), but need to construct a simple empty
         * collision hull for the engine. Probably could be done a little
         * smarter, but this works.
         */
        auto headnode = std::make_unique<node_t>();
        headnode->bounds = entity->bounds;
        // The choice of plane is mostly unimportant, but having it at (0, 0, 0) affects
        // the node bounds calculation.
        headnode->planenum = 0;
        headnode->children[0] = std::make_unique<node_t>();
        headnode->children[0]->is_leaf = true;
        headnode->children[0]->contents = qbsp_options.target_game->create_empty_contents();
        headnode->children[0]->parent = headnode.get();
        headnode->children[1] = std::make_unique<node_t>();
        headnode->children[1]->is_leaf = true;
        headnode->children[1]->contents = qbsp_options.target_game->create_empty_contents();
        headnode->children[1]->parent = headnode.get();

        tree->bounds = headnode->bounds;
        tree->headnode = std::move(headnode);

        return tree;
    }

    logging::print(logging::flag::STAT, "     {:8} brushes\n", c_brushes);
    logging::print(logging::flag::STAT, "     {:8} visible faces\n", c_faces);
    logging::print(logging::flag::STAT, "     {:8} nonvisible faces\n", c_nonvisfaces);

    auto node = std::make_unique<node_t>();

    node->volume = BrushFromBounds(tree->bounds.grow(SIDESPACE));
    node->bounds = tree->bounds.grow(SIDESPACE);

    tree->headnode = std::move(node);

    bspstats_t stats{};
    stats.leafstats = qbsp_options.target_game->create_content_stats();
    BuildTree_r(tree->headnode.get(), std::move(brushlist), forced_quick_tree, stats);

    logging::print(logging::flag::STAT, "     {:8} visible nodes\n", stats.c_nodes - stats.c_nonvis);
    if (stats.c_nonvis) {
        logging::print(logging::flag::STAT, "     {:8} nonvis nodes\n", stats.c_nonvis);
    }
    if (stats.c_blocksplit) {
        logging::print(logging::flag::STAT, "     {:8} block split nodes\n", stats.c_blocksplit);
    }
    if (stats.c_qbsp3) {
        logging::print(logging::flag::STAT, "     {:8} expensive split nodes\n", stats.c_qbsp3);
    }
    if (stats.c_midsplit) {
        logging::print(logging::flag::STAT, "     {:8} midsplit nodes\n", stats.c_midsplit);
    }
    logging::print(logging::flag::STAT, "     {:8} leafs\n", stats.c_leafs);
    if (stats.c_bogus) {
        logging::print(logging::flag::STAT, "     {:8} bogus brushes\n", stats.c_bogus);
    }
    if (stats.c_brushesremoved) {
        logging::print(logging::flag::STAT, "     {:8} brushes removed from a split\n", stats.c_brushesremoved);
    }
    if (stats.c_brushesonesided) {
        logging::print(logging::flag::STAT, "     {:8} brushes split only on one side\n", stats.c_brushesonesided);
    }

    logging::header("CountLeafs");
    qbsp_options.target_game->print_content_stats(*stats.leafstats, "leafs");

    return tree;
}

std::unique_ptr<tree_t> BrushBSP(mapentity_t *entity, const std::vector<std::unique_ptr<bspbrush_t>> &brushlist, std::optional<bool> forced_quick_tree)
{
    return BrushBSP_internal(entity, MakeBspBrushList(brushlist), forced_quick_tree);
}