#include "Model.hpp"
#include "Print.hpp"

namespace Slic3r {

// Add or remove support modifier ModelVolumes from model_object_dst to match the ModelVolumes of model_object_new
// in the exact order and with the same IDs.
// It is expected, that the model_object_dst already contains the non-support volumes of model_object_new in the correct order.
// Friend to ModelVolume to allow copying.
// static is not accepted by gcc if declared as a friend of ModelObject.
/* static */ void model_volume_list_update_supports(ModelObject &model_object_dst, const ModelObject &model_object_new)
{
    typedef std::pair<const ModelVolume*, bool> ModelVolumeWithStatus;
    std::vector<ModelVolumeWithStatus> old_volumes;
    old_volumes.reserve(model_object_dst.volumes.size());
    for (const ModelVolume *model_volume : model_object_dst.volumes)
        old_volumes.emplace_back(ModelVolumeWithStatus(model_volume, false));
    auto model_volume_lower = [](const ModelVolumeWithStatus &mv1, const ModelVolumeWithStatus &mv2){ return mv1.first->id() <  mv2.first->id(); };
    auto model_volume_equal = [](const ModelVolumeWithStatus &mv1, const ModelVolumeWithStatus &mv2){ return mv1.first->id() == mv2.first->id(); };
    std::sort(old_volumes.begin(), old_volumes.end(), model_volume_lower);
    model_object_dst.volumes.clear();
    model_object_dst.volumes.reserve(model_object_new.volumes.size());
    for (const ModelVolume *model_volume_src : model_object_new.volumes) {
        ModelVolumeWithStatus key(model_volume_src, false);
        auto it = std::lower_bound(old_volumes.begin(), old_volumes.end(), key, model_volume_lower);
        if (it != old_volumes.end() && model_volume_equal(*it, key)) {
            // The volume was found in the old list. Just copy it.
            assert(! it->second); // not consumed yet
            it->second = true;
            ModelVolume *model_volume_dst = const_cast<ModelVolume*>(it->first);
            // For support modifiers, the type may have been switched from blocker to enforcer and vice versa.
            assert((model_volume_dst->is_support_modifier() && model_volume_src->is_support_modifier()) || model_volume_dst->type() == model_volume_src->type());
            model_object_dst.volumes.emplace_back(model_volume_dst);
            if (model_volume_dst->is_support_modifier()) {
                // For support modifiers, the type may have been switched from blocker to enforcer and vice versa.
                model_volume_dst->set_type(model_volume_src->type());
                model_volume_dst->set_transformation(model_volume_src->get_transformation());
            }
            assert(model_volume_dst->get_matrix().isApprox(model_volume_src->get_matrix()));
        } else {
            // The volume was not found in the old list. Create a new copy.
            assert(model_volume_src->is_support_modifier());
            model_object_dst.volumes.emplace_back(new ModelVolume(*model_volume_src));
            model_object_dst.volumes.back()->set_model_object(&model_object_dst);
        }
    }
    // Release the non-consumed old volumes (those were deleted from the new list).
    for (ModelVolumeWithStatus &mv_with_status : old_volumes)
        if (! mv_with_status.second)
            delete mv_with_status.first;
}

static inline void model_volume_list_copy_configs(ModelObject &model_object_dst, const ModelObject &model_object_src, const ModelVolumeType type)
{
    size_t i_src, i_dst;
    for (i_src = 0, i_dst = 0; i_src < model_object_src.volumes.size() && i_dst < model_object_dst.volumes.size();) {
        const ModelVolume &mv_src = *model_object_src.volumes[i_src];
        ModelVolume       &mv_dst = *model_object_dst.volumes[i_dst];
        if (mv_src.type() != type) {
            ++ i_src;
            continue;
        }
        if (mv_dst.type() != type) {
            ++ i_dst;
            continue;
        }
        assert(mv_src.id() == mv_dst.id());
        // Copy the ModelVolume data.
        mv_dst.name   = mv_src.name;
		mv_dst.config.assign_config(mv_src.config);
        assert(mv_dst.supported_facets.id() == mv_src.supported_facets.id());
        mv_dst.supported_facets.assign(mv_src.supported_facets);
        assert(mv_dst.seam_facets.id() == mv_src.seam_facets.id());
        mv_dst.seam_facets.assign(mv_src.seam_facets);
        //FIXME what to do with the materials?
        // mv_dst.m_material_id = mv_src.m_material_id;
        ++ i_src;
        ++ i_dst;
    }
}

static inline void layer_height_ranges_copy_configs(t_layer_config_ranges &lr_dst, const t_layer_config_ranges &lr_src)
{
    assert(lr_dst.size() == lr_src.size());
    auto it_src = lr_src.cbegin();
    for (auto &kvp_dst : lr_dst) {
        const auto &kvp_src = *it_src ++;
        assert(std::abs(kvp_dst.first.first  - kvp_src.first.first ) <= EPSILON);
        assert(std::abs(kvp_dst.first.second - kvp_src.first.second) <= EPSILON);
        // Layer heights are allowed do differ in case the layer height table is being overriden by the smooth profile.
        // assert(std::abs(kvp_dst.second.option("layer_height")->getFloat() - kvp_src.second.option("layer_height")->getFloat()) <= EPSILON);
        kvp_dst.second = kvp_src.second;
    }
}

static inline bool transform3d_lower(const Transform3d &lhs, const Transform3d &rhs) 
{
    typedef Transform3d::Scalar T;
    const T *lv = lhs.data();
    const T *rv = rhs.data();
    for (size_t i = 0; i < 16; ++ i, ++ lv, ++ rv) {
        if (*lv < *rv)
            return true;
        else if (*lv > *rv)
            return false;
    }
    return false;
}

static inline bool transform3d_equal(const Transform3d &lhs, const Transform3d &rhs) 
{
    typedef Transform3d::Scalar T;
    const T *lv = lhs.data();
    const T *rv = rhs.data();
    for (size_t i = 0; i < 16; ++ i, ++ lv, ++ rv)
        if (*lv != *rv)
            return false;
    return true;
}

struct PrintObjectTrafoAndInstances
{
    Transform3d    	trafo;
    PrintInstances	instances;
    bool operator<(const PrintObjectTrafoAndInstances &rhs) const { return transform3d_lower(this->trafo, rhs.trafo); }
};

// Generate a list of trafos and XY offsets for instances of a ModelObject
static std::vector<PrintObjectTrafoAndInstances> print_objects_from_model_object(const ModelObject &model_object)
{
    std::set<PrintObjectTrafoAndInstances> trafos;
    PrintObjectTrafoAndInstances           trafo;
    for (ModelInstance *model_instance : model_object.instances)
        if (model_instance->is_printable()) {
            trafo.trafo = model_instance->get_matrix();
            auto shift = Point::new_scale(trafo.trafo.data()[12], trafo.trafo.data()[13]);
            // Reset the XY axes of the transformation.
            trafo.trafo.data()[12] = 0;
            trafo.trafo.data()[13] = 0;
            // Search or insert a trafo.
            auto it = trafos.emplace(trafo).first;
            const_cast<PrintObjectTrafoAndInstances&>(*it).instances.emplace_back(PrintInstance{ nullptr, model_instance, shift });
        }
    return std::vector<PrintObjectTrafoAndInstances>(trafos.begin(), trafos.end());
}

// Compare just the layer ranges and their layer heights, not the associated configs.
// Ignore the layer heights if check_layer_heights is false.
static bool layer_height_ranges_equal(const t_layer_config_ranges &lr1, const t_layer_config_ranges &lr2, bool check_layer_height)
{
    if (lr1.size() != lr2.size())
        return false;
    auto it2 = lr2.begin();
    for (const auto &kvp1 : lr1) {
        const auto &kvp2 = *it2 ++;
        if (std::abs(kvp1.first.first  - kvp2.first.first ) > EPSILON ||
            std::abs(kvp1.first.second - kvp2.first.second) > EPSILON ||
            (check_layer_height && std::abs(kvp1.second.option("layer_height")->getFloat() - kvp2.second.option("layer_height")->getFloat()) > EPSILON))
            return false;
    }
    return true;
}

// Returns true if va == vb when all CustomGCode items that are not ToolChangeCode are ignored.
static bool custom_per_printz_gcodes_tool_changes_differ(const std::vector<CustomGCode::Item> &va, const std::vector<CustomGCode::Item> &vb)
{
	auto it_a = va.begin();
	auto it_b = vb.begin();
	while (it_a != va.end() || it_b != vb.end()) {
		if (it_a != va.end() && it_a->type != CustomGCode::ToolChange) {
			// Skip any CustomGCode items, which are not tool changes.
			++ it_a;
			continue;
		}
		if (it_b != vb.end() && it_b->type != CustomGCode::ToolChange) {
			// Skip any CustomGCode items, which are not tool changes.
			++ it_b;
			continue;
		}
		if (it_a == va.end() || it_b == vb.end())
			// va or vb contains more Tool Changes than the other.
			return true;
		assert(it_a->type == CustomGCode::ToolChange);
		assert(it_b->type == CustomGCode::ToolChange);
		if (*it_a != *it_b)
			// The two Tool Changes differ.
			return true;
		++ it_a;
		++ it_b;
	}
	// There is no change in custom Tool Changes.
	return false;
}

// Collect changes to print config, account for overrides of extruder retract values by filament presets.
static t_config_option_keys print_config_diffs(
    const PrintConfig        &current_config,
    const DynamicPrintConfig &new_full_config,
    DynamicPrintConfig       &filament_overrides)
{
    const std::vector<std::string> &extruder_retract_keys = print_config_def.extruder_retract_keys();
    const std::string               filament_prefix       = "filament_";
    t_config_option_keys            print_diff;
    for (const t_config_option_key &opt_key : current_config.keys()) {
        const ConfigOption *opt_old = current_config.option(opt_key);
        assert(opt_old != nullptr);
        const ConfigOption *opt_new = new_full_config.option(opt_key);
        // assert(opt_new != nullptr);
        if (opt_new == nullptr)
            //FIXME This may happen when executing some test cases.
            continue;
        const ConfigOption *opt_new_filament = std::binary_search(extruder_retract_keys.begin(), extruder_retract_keys.end(), opt_key) ? new_full_config.option(filament_prefix + opt_key) : nullptr;
        if (opt_new_filament != nullptr && ! opt_new_filament->is_nil()) {
            // An extruder retract override is available at some of the filament presets.
            if (*opt_old != *opt_new || opt_new->overriden_by(opt_new_filament)) {
                auto opt_copy = opt_new->clone();
                opt_copy->apply_override(opt_new_filament);
                if (*opt_old == *opt_copy)
                    delete opt_copy;
                else {
                    filament_overrides.set_key_value(opt_key, opt_copy);
                    print_diff.emplace_back(opt_key);
                }
            }
        } else if (*opt_new != *opt_old)
            print_diff.emplace_back(opt_key);
    }

    return print_diff;
 }

// Prepare for storing of the full print config into new_full_config to be exported into the G-code and to be used by the PlaceholderParser.
static t_config_option_keys full_print_config_diffs(const DynamicPrintConfig &current_full_config, const DynamicPrintConfig &new_full_config)
{
    t_config_option_keys full_config_diff;
    for (const t_config_option_key &opt_key : new_full_config.keys()) {
        const ConfigOption *opt_old = current_full_config.option(opt_key);
        const ConfigOption *opt_new = new_full_config.option(opt_key);
        if (opt_old == nullptr || *opt_new != *opt_old)
            full_config_diff.emplace_back(opt_key);
    }
    return full_config_diff;
}

bool model_volume_list_changed(const ModelObject &model_object_old, const ModelObject &model_object_new, const ModelVolumeType type)
{
    size_t i_old, i_new;
    for (i_old = 0, i_new = 0; i_old < model_object_old.volumes.size() && i_new < model_object_new.volumes.size();) {
        const ModelVolume &mv_old = *model_object_old.volumes[i_old];
        const ModelVolume &mv_new = *model_object_new.volumes[i_new];
        if (mv_old.type() != type) {
            ++ i_old;
            continue;
        }
        if (mv_new.type() != type) {
            ++ i_new;
            continue;
        }
        if (mv_old.id() != mv_new.id())
            return true;
        //FIXME test for the content of the mesh!

        if (!mv_old.get_matrix().isApprox(mv_new.get_matrix()))
            return true;

        ++ i_old;
        ++ i_new;
    }
    for (; i_old < model_object_old.volumes.size(); ++ i_old) {
        const ModelVolume &mv_old = *model_object_old.volumes[i_old];
        if (mv_old.type() == type)
            // ModelVolume was deleted.
            return true;
    }
    for (; i_new < model_object_new.volumes.size(); ++ i_new) {
        const ModelVolume &mv_new = *model_object_new.volumes[i_new];
        if (mv_new.type() == type)
            // ModelVolume was added.
            return true;
    }
    return false;
}

// Repository for solving partial overlaps of ModelObject::layer_config_ranges.
// Here the const DynamicPrintConfig* point to the config in ModelObject::layer_config_ranges.
class LayerRanges
{
public:
    struct LayerRange {
        t_layer_height_range        layer_height_range;
        // Config is owned by the associated ModelObject.
        const DynamicPrintConfig*   config { nullptr };
    };

    LayerRanges() = default;

    // Convert input config ranges into continuous non-overlapping sorted vector of intervals and their configs.
    void assign(const t_layer_config_ranges &in) {
        m_ranges.clear();
        m_ranges.reserve(in.size());
        // Input ranges are sorted lexicographically. First range trims the other ranges.
        coordf_t last_z = 0;
        for (const std::pair<const t_layer_height_range, ModelConfig> &range : in)
            if (range.first.second > last_z) {
                coordf_t min_z = std::max(range.first.first, 0.);
                if (min_z > last_z + EPSILON) {
                    m_ranges.push_back({ t_layer_height_range(last_z, min_z) });
                    last_z = min_z;
                }
                if (range.first.second > last_z + EPSILON) {
                    const DynamicPrintConfig *cfg = &range.second.get();
                    m_ranges.push_back({ t_layer_height_range(last_z, range.first.second), cfg });
                    last_z = range.layer_height_range.second;
                }
            }
        if (m_ranges.empty())
            m_ranges.push_back({ t_layer_height_range(0, DBL_MAX) });
        else if (m_ranges.back().config == nullptr)
            m_ranges.back().layer_height_range.second = DBL_MAX;
        else
            m_ranges.push_back({ t_layer_height_range(m_ranges.back().layer_height_range.second, DBL_MAX) });
    }

    const DynamicPrintConfig* config(const t_layer_height_range &range) const {
        auto it = std::lower_bound(m_ranges.begin(), m_ranges.end(), LayerRange { t_layer_height_range(range.first - EPSILON, range.second - EPSILON), nullptr });
        // #ys_FIXME_COLOR
        // assert(it != m_ranges.end());
        // assert(it == m_ranges.end() || std::abs(it->first.first  - range.first ) < EPSILON);
        // assert(it == m_ranges.end() || std::abs(it->first.second - range.second) < EPSILON);
        if (it == m_ranges.end() ||
            std::abs(it->first.first - range.first) > EPSILON ||
            std::abs(it->first.second - range.second) > EPSILON )
            return nullptr; // desired range doesn't found
        return (it == m_ranges.end()) ? nullptr : it->second;
    }
    std::vector<LayerRange>::const_iterator begin() const { return m_ranges.cbegin(); }
    std::vector<LayerRange>::const_iterator end  () const { return m_ranges.cend(); }
private:
    // Layer ranges with their config overrides and list of volumes with their snug bounding boxes in a given layer range.
    std::vector<LayerRange>  m_ranges;
};

// To track Model / ModelObject updates between the front end and back end, including layer height ranges, their configs,
// and snug bounding boxes of ModelVolumes.
struct ModelObjectStatus {
    enum Status {
        Unknown,
        Old,
        New,
        Moved,
        Deleted,
    };

    enum class PrintObjectRegionsStatus {
        Invalid,
        Valid,
        PartiallyValid,
    };

    ModelObjectStatus(ObjectID id, Status status = Unknown) : id(id), status(status) {}
    ~ModelObjectStatus() { if (print_object_regions) print_object_regions.ref_cnt_dec(); }

    // Key of the set.
    ObjectID                                    id;
    // Status of this ModelObject with id on apply().
    Status                                      status;
    // PrintObjects to be generated for this ModelObject including their base transformation.
    std::vector<PrintObjectTrafoAndInstances>   print_instances;
    // Regions shared by the associated PrintObjects.
    PrintObjectRegions                         *print_object_regions { nullptr };
    // Status of the above.
    PrintObjectRegionsStatus                    print_object_regions_status { PrintObjectRegionsStatus::Invalid };

    // Search by id.
    bool operator<(const ModelObjectStatus &rhs) const { return id < rhs.id; }
};

struct ModelObjectStatusDB
{
    void add(const ModelObject &model_object, const ModelObjectStatus status) {
        db.emplace(model_object.id(), status);
    }

    bool add_if_new(const ModelObject &model_object, const ModelObjectStatus status) {
        auto it = db.find(ModelObjectStatus(model_object.id()));
        assert(it != db.end());
        if (it == db.end()) {
            db.emplace_hint(it, model_object.id(), status);
            return true;
        }
        return false;
    }

    const ModelObjectStatus& get(const ModelObject &model_object) {
        auto it = db.find(ModelObjectStatus(model_object.id()));
        assert(it != db.end());
        return *it;
    }

    const ModelObjectStatus& reuse(const ModelObject &model_object) {
        const ModelObjectStatus &result = this->get(model_object);
        assert(result.status != ModelObjectStatus::Deleted);
        return result;
    }

    std::set<ModelObjectStatus> db;
}

struct PrintObjectStatus {
    enum Status {
        Unknown,
        Deleted,
        Reused,
        New
    };
    PrintObjectStatus(PrintObject *print_object, Status status = Unknown) : 
        id(print_object->model_object()->id()),
        print_object(print_object),
        trafo(print_object->trafo()),
        status(status) {}
    PrintObjectStatus(ObjectID id) : id(id), print_object(nullptr), trafo(Transform3d::Identity()), status(Unknown) {}
    // ID of the ModelObject & PrintObject
    ObjectID          id;
    // Pointer to the old PrintObject
    PrintObject     *print_object;
    // Trafo generated with model_object->world_matrix(true) 
    Transform3d      trafo;
    Status           status;
    // Search by id.
    bool operator<(const PrintObjectStatus &rhs) const { return id < rhs.id; }
};

template <typename I>
iter_pair<I> make_range(std::pair<I, I> p) {
    return iter_pair<I>(p);
}

class PrintObjectStatusDB {
public:
    using iterator          = std::multiset<PrintObjectStatus>::iterator;
    using const_iterator    = std::multiset<PrintObjectStatus>::const_iterator;

    PrintObjectStatusDB(const PrintObjects &print_objects) {
        for (PrintObject *print_object : m_objects)
            db.emplace(PrintObjectStatus(print_object));
    }

    struct iterator_range : std::pair<const_iterator, const_iterator>
    { 
        using std::pair<const_iterator, const_iterator>::pair;

        const_iterator begin() throw() { return this->first; }
        const_iterator end() throw() { return this->second; }
    };

    iterator_range get_range(const ModelObject &model_object) {
        return print_object_status.equal_range(PrintObjectStatus(model_object.id()));
    }

    iterator_range get_range(const ModelObjectStatus &model_object_status) {
        return print_object_status.equal_range(PrintObjectStatus(model_object_status.id));
    }

    size_t count(const ModelObject &model_object) {
        return db.count(PrintObjectStatus(model_object.id()));
    }

    void clear() {
        db.clear();
    }

    const_iterator begin() throw() { return this->first; }
    const_iterator end() throw() { return this->second; }

private:
    std::multiset<PrintObjectStatus> db;
};

static inline bool model_volume_needs_bbox(const ModelVolume &mv)
{
    ModelVolumeType type = mv.type();
    return type == ModelVolumeType::MODEL_PART || type == ModelVolumeType::NEGATIVE_VOLUME || type == ModelVolumeType::PARAMETER_MODIFIER;
}

static inline Matrix3f trafo_for_bbox(const Transform3d &object_trafo, const Transform3d &volume_trafo)
{
    Matrix3d m = object_trafo.matrix().block<3,3>(0,0) * volume_trafo.matrix().block<3,3>(0,0);
    return m.cast<float>();
}

static inline bool trafos_differ_in_rotation_and_mirroring_by_z_only(const Transform3d &t1, const Transform3d &t2)
{
    Matrix3d m1 = t1.matrix().block<3, 3>(0, 0);
    Matrix3d m2 = t2.matrix().block<3, 3>(0, 0);
    Matrix3d m = m2.inverse() * m1;
    Vec3d    z = m.block<3, 1>(0, 2);
    if (std::abs(z.x()) > EPSILON || std::abs(z.y()) > EPSILON || std::abs(z.z() - 1.) > EPSILON)
        // Z direction or length changed.
        return false;
    // Z still points in the same direction and it has the same length.
    Vec3d    x = m.block<3, 1>(0, 0);
    Vec3d    y = m.block<3, 1>(0, 1);
    if (std::abs(x.z()) > EPSILON || std::abs(y.z()) > EPSILON)
        return false;
    double   lx2 = x.squaredNorm();
    double   ly2 = y.squaredNorm();
    if (lx2 - 1. > EPSILON * EPSILON || ly2 - 1. > EPSILON * EPSILON)
        return false;
    // Verify whether the vectors x, y are still perpendicular.
    double   d   = x.dot(y);
    return std::abs(d) > EPSILON;
}

static BoundingBoxf3 transformed_its_bbox2d(const stl_triangle_vertex_indices &its, const Matrix3f &m)
{
    BoundingBoxf3 bbox;
    for (const stl_triangle_vertex_indices &tri : its.indices)
        for (int i = 0; i < 3; ++ i)
            bbox.merge(m * its.vertices[tri(i)]);
    return bbox;
}

static void transformed_its_bboxes_in_z_ranges(
    const stl_triangle_vertex_indices       &its, 
    const Matrix3f                          &m, 
    const std::vector<t_layer_height_range> &z_ranges,
    std::vector<BoundingBoxf3>              &bboxes)
{
    bboxes.assign(z_ranges.size(), BoundingBoxf());
    for (const stl_triangle_vertex_indices &tri : its.indices) {
        const Vec3f pts[3] = { m * its.vertices[tri(0)], m * its.vertices[tri(1)], m * its.vertices[tri(2)] };
        for (size_t irange = 0; irange < z_ranges.size(); ++ irange) {
            t_layer_height_range &z_range = z_ranges[irange];
            BoundingBoxf3        &bbox    = bboxes[irange];
            int iprev = 3;
            for (int iedge = 0; iedge < 3; ++ iedge) {
                const Vec3f *p1 = &pts[iprev];
                const Vec3f *p2 = &pts[iedge];
                // Sort the edge points by Z.
                if (p1->z() > p2->z())
                    std::swap(p1, p2);
                if (p2->z() <= z_range.first || p1->z() >= z_range.second) {
                    // Out of this slab.
                } else if (p1->z() < z_range.first) {
                    if (p1->z() > z_range.second) {
                        // Two intersections.
                        float zspan = p2->z() - p1->z();
                        float t1 = z_range.first  / zspan;
                        float t2 = z_range.second / zspan;
                        Vec2f p = to_2d(*p1);
                        Vec2f v(p2->x() - p1->x(), p2->y() - p1->y());
                        bbox.merge(to_3d(p + v * t1, z_range.first));
                        bbox.merge(to_3d(p + v * t2, z_range.second));
                    } else {
                        // Single intersection with the lower limit.
                        float t = z_range.first / (p2->z() - p1->z());
                        Vec2f v(p2->x() - p1->x(), p2->y() - p1->y());
                        bbox.merge(to_3d(to_2d(*p1) + v * t), z_range.first);
                        bbox.merge(*p2);
                    }
                } else if (p2->z() > z_range.second) {
                    // Single intersection with the upper limit.
                    float t = z_range.second / (p2->z() - p1->z());
                    Vec2f v(p2->x() - p1->x(), p2->y() - p1->y());
                    bbox.merge(to_3d(to_2d(*p1) + v * t), z_range.second);
                    bbox.merge(*p1);
                } else {
                    // Both points are inside.
                    bbox.merge(*p1);
                    bbox.merge(*p2);
                }
                iprev = iedge;
            }
        }
    }
}

// Update from scratch.
void update_model_object_status_layers_bboxes(
    const ModelObject &model_object,
    ModelObjectStatus &model_object_status)
{
    assert(! model_object_status.print_instances.empty());
    assert(! model_object_status.layer_ranges.m_ranges.empty());

    // Use the trafo of the 1st newly created PrintObject.
    model_object_status.layer_ranges.m_trafo = model_object_status.print_instances.front().trafo;

    if (model_object_status.layer_ranges.m_ranges.size() == 1) {
        LayerRange &layer_range = model_object_status.layer_ranges.m_ranges.front();
        assert(layer_range.volumes.empty());
        layer_range.reserve(model_object.volumes.size());
        for (const ModelVolume *model_volume : model_object.volumes)
            if (model_volume_needs_bbox(*model_volume))
                layer_range.volumes.emplace_back(model_volume->id(), 
                    transformed_its_bbox2d(model_volume.mesh().its, trafo_for_bbox(model_object_status.layer_ranges.m_trafo, model_volume->get_matrix(false))));
    } else {
        std::vector<BoundingBoxf>           bboxes;
        std::vector<t_layer_height_range>   ranges;
        ranges.reserve(model_object_status.layer_ranges.m_ranges.size());
        for (const LayerRange &layer_range : model_object_status.layer_ranges.m_ranges) {
            assert(layer_range.volumes.empty());
            t_layer_height_range r = layer_range.layer_height_range;
            r.first -= EPSILON;
            r.second += EPSILON;
            ranges.emplace_back(r);
        }
        double offset = print_object.config().xy_size_compensation();
        for (const ModelVolume *model_volume : model_object.volumes)
            if (model_volume_needs_bbox(*model_volume)) {
                transformed_its_bbox2ds_in_z_ranges(model_volume.mesh().its, trafo_for_bbox(model_object_status.layer_ranges.m_trafo, model_volume->get_matrix(false)), 
                    ranges, bboxes);
                size_t i = 0;
                for (LayerRange &layer_range : model_object_status.layer_ranges.m_ranges) {
                    if (bboxes[i].defined) {
                        bboxes.min.x() -= offset;
                        bboxes.min.y() -= offset;
                        bboxes.max.x() += offset;
                        bboxes.max.y() += offset;
                        layer_range.volumes.emplace_back(model_volume->id(), bboxes[i]);
                    }
                    ++ i;
                }
            }
}

// Update by reusing everything.
void update_model_object_status_layers_bboxes(
    const ModelObject    &model_object,
    PrintObject         &&print_object,
    ModelObjectStatus    &model_object_status)
{
    assert(! model_object_status.print_instances.empty());
    assert(! model_object_status.layer_ranges.m_ranges.empty());

    for (print_object.m_volumes_ranges
}

// Try to extract layer ranges and snug bounding boxes from some existing PrintObject.
void update_model_object_status_layers_bboxes(
    const ModelObject &model_object_old,
    const ModelObject &model_object_new,
    PrintObject      &&print_object,
    ModelObjectStatus &model_object_status)
{
    assert(! print_object.m_region_volumes.empty());

    // 1) Verify that the trafo is still applicable.
    if (trafos_differ_in_rotation_and_mirroring_by_z_only(model_object_status.layer_ranges.m_trafo, model_object_status.print_instances.front().trafo)) {
        update_model_object_status_layers_bboxes(model_object_new, model_object_status);
        return;
    }

    // 2) Try to recover some of the trafos from print_object.

}

void print_objects_regions_update_volumes(PrintObjectRegions &print_object_regions, ModelVolumePtrs old_volumes, ModelVolumePtrs new_volumes)
{
    print_object_regions.all_regions.clear();

    model_volumes_sort_by_id(old_volumes);
    model_volumes_sort_by_id(new_volumes);
    {
        size_t last = 0;
        size_t i_old = 0;
        for (size_t i_new = 0; i_new < new_volumes.size(); ++ i_new) {
            for (; i_old < old_volumes.size(); ++ i_old)
                if (old_volumes[i_old]->id() == new_volumes[i_new]->id())
                    break;
            if (i_old == old_volumes.size())
                break;
            if (old_volumes[i_old]->get_matrix().isApprox(new_volumes[i_new]->get_matrix())) {
                // Reuse the volume.
                new_volumes[last ++] = new_volumes[i_new];
            } else {
                // Don't reuse the volume.
            }
        }
        old_volumes.clear();
        new_volumes.erase(new_volumes.begin() + last, new_volumes.end());
    }

    for (PrintObjectRegions::LayerRangeRegions &layer_regions : print_object_regions.layer_ranges) {
        auto it = std::remove_if(layer_regions.volumes.begin(), layer_regions.volumes.end(), 
            [](const PrintObjectRegions::VolumeExtents &v) { return model_volume_find_by_id(new_volumes, v.volume_id) == nullptr; });
        layer_regions.volumes.erase(it, layer_regions.volumes.end());
        layer_regions.volume_regions.clear();
        layer_regions.volume_regions.clear();
        layer_regions.painted_regions.clear();
    }
}

const BoundingBoxf3* find_volume(const PrintObjectLayerRange &layer_range, const ModelVolume &volume)
{
    auto it = lower_bound_by_predicate(layer_range.volumes.begin(), layer_range.volumes.end(), [&volume](const PrintVolumeExtents &v){ return v.volume_id < volume.id(); });
    retun it != layer_range.volumes.end() && it->volume_id == volume.id() ? &it->bbox : nullptr;
}

// Returns false if this object needs to be resliced.
static bool verify_update_print_object_regions(
    ModelVolumePtrs                                              model_volumes,
    const PrintRegionConfig                                     &default_region_config,
    size_t                                                       num_extruders,
    const std::vector<unsigned int>                             &painting_extruders,
    const PrintObjectRegions                                    &print_object_regions,
    std::function<>                                              callback_invalidate)
{
    // Sort by ModelVolume ID.
    std::sort(model_volumes.begin(), model_volumes.end(), [](const ModelVolume *l, const ModelVolume *r){ return l->id() < r->id(); });

    for (std::unique_ptr<PrintRegion> &region : all_regions)
        region->m_ref_cnt = 0;

    // Verify and / or update PrintRegions produced by ModelVolumes, layer range modifiers, modifier volumes.
    for (const PrintObjectRegions::LayerRangeRegions &layer_range : print_object_regions.layer_ranges)
        for (const PrintObjectRegions::VolumeRegion &region : layer_range.volume_regions) {
            auto it_model_volume = lower_bound_by_predicate(model_volumes.begin(), model_volumes.end(), [&region](const ModelVolume *v){ return v->id() < region.volume_id});
            assert(it_model_volume != model_volumes.begin() && it_model_volume->id() == region.volume_id);
            PrintRegionConfig cfg = region.parent == -1 ?
                PrintObject::region_config_from_model_volume(default_region_config, region.config, *it_model_volume, num_extruders) :
                PrintObject::region_config_from_model_volume(parent_region.region->config(), nullptr, *it_model_volume, num_extruders);
            if (cfg != region.region->config()) {
                // Region configuration changed.
                if (region.region->m_ref_cnt == 0) {
                    // Region is referenced for the first time. Just change its parameters.
                    // Stop the background process before assigning new configuration to the regions.
                    t_config_option_keys diff = override.region->config().diff(cfg);
                    callback_invalidate(override.region->config(), cfg, diff);
                    override.region->config().config_apply_only(cfg, diff, false);
                } else {
                    // Region is referenced multiple times, thus the region is being split. We need to reslice.
                    return false;
                }
            }
            ++ region.region->m_ref_cnt;
        }

    // Verify and / or update PrintRegions produced by color painting. 
    for (const PrintObjectRegions::LayerRangeRegions &layer_range : print_object_regions.layer_ranges)
        size_t painted_region_idx = 0;
        for (unsigned int painted_extruder_id : painting_extruders)
            for (int parent_region_id = 0; parent_region_id < int(layer_range.volume_regions.size()); ++ parent_region_id) {
                const PrintVolumeRegion  &parent_region  = layer_range.volume_regions[parent_region_id];
                const PrintPaintedRegion &region         = layer_range.painted_regions[painted_region_idx ++];
                PrintRegionConfig cfg = parent_region.region->config();
                cfg.external_perimeter_extruder = painted_extruder_id;
                cfg.perimeter_extruder          = painted_extruder_id;
                cfg.infill_extruder             = painted_extruder_id;
                if (cfg != region.region->config()) {
                    // Region configuration changed.
                    if (region->m_ref_cnt == 0) {
                        // Region is referenced for the first time. Just change its parameters.
                        // Stop the background process before assigning new configuration to the regions.
                        t_config_option_keys diff = override.region->config().diff(cfg);
                        callback_invalidate(override.region->config(), cfg, diff);
                        override.region->config().config_apply_only(cfg, diff, false);
                    } else {
                        // Region is referenced multiple times, thus the region is being split. We need to reslice.
                        return false;
                    }
                }
                ++ region.region->m_ref_cnt;
            }
    }

    // Lastly verify, whether some regions were not merged.
    {
        std::vector<const PrintRegion*> regions;
        regions.reserve(all_regions.size());
        for (std::unique_ptr<PrintRegion> &region : all_regions) {
            assert(region->m_ref_cnt > 0);
            regions.emplace_back(&(*region));
        }
        std::sort(regions.begin(), regions.end(), [](const PrintRegion *l, const PrintRegion *r){ return l->config_hash() < r->config_hash(); });
        for (size_t i = 0; i < regions.size(); ++ i) {
            size_t hash = regions[i]->config_hash();
            size_t j = i;
            for (++ j; j < regions.size() && regions[j]->config_hash() == hash; ++ j)
                if (regions[i]->config() == regions[j]->config()) {
                    // Regions were merged. We need to reslice.
                    return false;
                }
        }
    }

    return out;
}

// Either a fresh PrintObject, or PrintObject regions were invalidated (merged, split).
// Generate PrintRegions from scratch.
static PrintObjectRegions generate_print_object_regions(
    const ModelVolumePtrs                       &model_volumes,
    const std::vector<PrintObjectLayerRange>    &layer_ranges,
    const PrintRegionConfig                     &default_region_config,
    size_t                                       num_extruders,
    const std::vector<unsigned int>             &painting_extruders)
{
    PrintObjectRegions out;
    auto &all_regions          = all_regions;
    auto &layer_ranges_regions = layer_ranges;

    layer_ranges_regions.assign(layer_ranges.size(), PrintObjectLayerRangeRegions{});
    for (PrintObjectLayerRangeRegions &lrr : layer_ranges_regions)
        lrr = layer_ranges[&lrr - layer_ranges_regions.data()];

    std::set<const PrintRegion*, > region_set;
    auto get_create_region = [&region_set](PrintRegionConfig &&config) {

    };

    // Chain the regions in the order they are stored in the volumes list.
    for (int volume_id = 0; volume_id < int(model_volumes.size()); ++ volume_id) {
        const ModelVolume &volume = model_volumes[volume_id];
        if (volume.type() == ModelVolumeType::MODEL_PART || volume.type() == ModelVolumeType::PARAMETER_MODIFIER) {
            for (const PrintObjectLayerRangeRegions &layer_range : layer_ranges_regions)
                if (const BoundingBoxf3 *bbox = find_volume(layer_range, volume); bbox) {
                    if (volume.type() == MODEL_PART)
                        layer_range.regions.push_back( {
                            volume.id(), -1,
                            get_create_region(PrintObject::region_config_from_model_volume(default_region_config, layer_range.config, volume, num_extruders))
                        });
                    else {
                        assert(volume.type() == ModelVolumeType::PARAMETER_MODIFIER);
                        // Modifiers may be chained one over the other. Check for overlap, merge DynamicPrintConfigs.
                        for (int parent_region_id = int(layer_range.regions.size()) - 1; parent_region_id >= 0; -- parent_region_id) {
                            const PrintVolumeRegion &parent_region = layer_range.regions[parent_region_id];
                            const BoundingBoxf3     *parent_bbox   = find_volume(layer_range, parent_region.volume_id);
                            assert(parent_bbox != nullptr);
                            if (parent_bbox->overlap(*bbox))
                                layer_range.regions.push_back( {
                                    volume.id(), parent_region_id,
                                    get_create_region(PrintObject::region_config_from_model_volume(parent_region.region->config(), nullptr, volume, num_extruders))
                                });
                        }
                    }
                }
            }
    }

    // Finally add painting regions.
    for (const PrintObjectLayerRangeRegions &layer_range : layer_ranges_regions) {
        for (unsigned int painted_extruder_id : painting_extruders)
            for (int parent_region_id = 0; parent_region_id < int(layer_range.regions.size()); ++ parent_region_id) {
                const PrintVolumeRegion &parent_region = layer_range.regions[parent_region_id];
                PrintRegionConfig cfg = parent_region.region->config();
                cfg.external_perimeter_extruder = painted_extruder_id;
                cfg.perimeter_extruder          = painted_extruder_id;
                cfg.infill_extruder             = painted_extruder_id;
                layer_range.painted_regions.push_back({ painted_extruder_id, parent_region_id, get_create_region(std::move(cfg))});
            }
    }

    return out;
}

Print::ApplyStatus Print::apply(const Model &model, DynamicPrintConfig new_full_config)
{
#ifdef _DEBUG
    check_model_ids_validity(model);
#endif /* _DEBUG */

    // Normalize the config.
	new_full_config.option("print_settings_id",            true);
	new_full_config.option("filament_settings_id",         true);
	new_full_config.option("printer_settings_id",          true);
    new_full_config.option("physical_printer_settings_id", true);
    new_full_config.normalize_fdm();

    // Find modified keys of the various configs. Resolve overrides extruder retract values by filament profiles.
    DynamicPrintConfig   filament_overrides;
    t_config_option_keys print_diff       = print_config_diffs(m_config, new_full_config, filament_overrides);
    t_config_option_keys full_config_diff = full_print_config_diffs(m_full_print_config, new_full_config);
    // Collect changes to object and region configs.
    t_config_option_keys object_diff      = m_default_object_config.diff(new_full_config);
    t_config_option_keys region_diff      = m_default_region_config.diff(new_full_config);

    // Do not use the ApplyStatus as we will use the max function when updating apply_status.
    unsigned int apply_status = APPLY_STATUS_UNCHANGED;
    auto update_apply_status = [&apply_status](bool invalidated)
        { apply_status = std::max<unsigned int>(apply_status, invalidated ? APPLY_STATUS_INVALIDATED : APPLY_STATUS_CHANGED); };
    if (! (print_diff.empty() && object_diff.empty() && region_diff.empty()))
        update_apply_status(false);

    // Grab the lock for the Print / PrintObject milestones.
	tbb::mutex::scoped_lock lock(this->state_mutex());

    // The following call may stop the background processing.
    if (! print_diff.empty())
        update_apply_status(this->invalidate_state_by_config_options(new_full_config, print_diff));

    // Apply variables to placeholder parser. The placeholder parser is used by G-code export,
    // which should be stopped if print_diff is not empty.
    size_t num_extruders = m_config.nozzle_diameter.size();
    bool   num_extruders_changed = false;
    if (! full_config_diff.empty()) {
        update_apply_status(this->invalidate_step(psGCodeExport));
        // Set the profile aliases for the PrintBase::output_filename()
		m_placeholder_parser.set("print_preset",              new_full_config.option("print_settings_id")->clone());
		m_placeholder_parser.set("filament_preset",           new_full_config.option("filament_settings_id")->clone());
		m_placeholder_parser.set("printer_preset",            new_full_config.option("printer_settings_id")->clone());
        m_placeholder_parser.set("physical_printer_preset",   new_full_config.option("physical_printer_settings_id")->clone());
		// We want the filament overrides to be applied over their respective extruder parameters by the PlaceholderParser.
		// see "Placeholders do not respect filament overrides." GH issue #3649
		m_placeholder_parser.apply_config(filament_overrides);
	    // It is also safe to change m_config now after this->invalidate_state_by_config_options() call.
	    m_config.apply_only(new_full_config, print_diff, true);
	    //FIXME use move semantics once ConfigBase supports it.
	    m_config.apply(filament_overrides);
	    // Handle changes to object config defaults
	    m_default_object_config.apply_only(new_full_config, object_diff, true);
	    // Handle changes to regions config defaults
	    m_default_region_config.apply_only(new_full_config, region_diff, true);
        m_full_print_config = std::move(new_full_config);
        if (num_extruders != m_config.nozzle_diameter.size()) {
        	num_extruders = m_config.nozzle_diameter.size();
        	num_extruders_changed = true;
        }
    }
    
    ModelObjectStatusDB model_object_status_db;

    // 1) Synchronize model objects.
    bool print_regions_reshuffled = false;
    if (model.id() != m_model.id()) {
        // Kill everything, initialize from scratch.
        // Stop background processing.
        this->call_cancel_callback();
        update_apply_status(this->invalidate_all_steps());
        for (PrintObject *object : m_objects) {
            model_object_status_db.add(*object->model_object(), ModelObjectStatus::Deleted);
			update_apply_status(object->invalidate_all_steps());
			delete object;
        }
        m_objects.clear();
        print_regions_reshuffled = true;
        m_model.assign_copy(model);
		for (const ModelObject *model_object : m_model.objects)
			model_object_status_db.add(*model_object, ModelObjectStatus::New);
    } else {
        if (m_model.custom_gcode_per_print_z != model.custom_gcode_per_print_z) {
            update_apply_status(num_extruders_changed || 
            	// Tool change G-codes are applied as color changes for a single extruder printer, no need to invalidate tool ordering.
            	//FIXME The tool ordering may be invalidated unnecessarily if the custom_gcode_per_print_z.mode is not applicable
            	// to the active print / model state, and then it is reset, so it is being applicable, but empty, thus the effect is the same.
            	(num_extruders > 1 && custom_per_printz_gcodes_tool_changes_differ(m_model.custom_gcode_per_print_z.gcodes, model.custom_gcode_per_print_z.gcodes)) ?
            	// The Tool Ordering and the Wipe Tower are no more valid.
            	this->invalidate_steps({ psWipeTower, psGCodeExport }) :
            	// There is no change in Tool Changes stored in custom_gcode_per_print_z, therefore there is no need to update Tool Ordering.
            	this->invalidate_step(psGCodeExport));
            m_model.custom_gcode_per_print_z = model.custom_gcode_per_print_z;
        }
        if (model_object_list_equal(m_model, model)) {
            // The object list did not change.
			for (const ModelObject *model_object : m_model.objects)
				model_object_status_db.add(*model_object, ModelObjectStatus::Old);
        } else if (model_object_list_extended(m_model, model)) {
            // Add new objects. Their volumes and configs will be synchronized later.
            update_apply_status(this->invalidate_step(psGCodeExport));
            for (const ModelObject *model_object : m_model.objects)
                model_object_status_db.add(*model_object, ModelObjectStatus::Old);
            for (size_t i = m_model.objects.size(); i < model.objects.size(); ++ i) {
                model_object_status_db.add(*model.objects[i], ModelObjectStatus::New);
                m_model.objects.emplace_back(ModelObject::new_copy(*model.objects[i]));
				m_model.objects.back()->set_model(&m_model);
            }
        } else {
            // Reorder the objects, add new objects.
            // First stop background processing before shuffling or deleting the PrintObjects in the object list.
            this->call_cancel_callback();
            update_apply_status(this->invalidate_step(psGCodeExport));
            // Second create a new list of objects.
            std::vector<ModelObject*> model_objects_old(std::move(m_model.objects));
            m_model.objects.clear();
            m_model.objects.reserve(model.objects.size());
            auto by_id_lower = [](const ModelObject *lhs, const ModelObject *rhs){ return lhs->id() < rhs->id(); };
            std::sort(model_objects_old.begin(), model_objects_old.end(), by_id_lower);
            for (const ModelObject *mobj : model.objects) {
                auto it = std::lower_bound(model_objects_old.begin(), model_objects_old.end(), mobj, by_id_lower);
                if (it == model_objects_old.end() || (*it)->id() != mobj->id()) {
                    // New ModelObject added.
					m_model.objects.emplace_back(ModelObject::new_copy(*mobj));
					m_model.objects.back()->set_model(&m_model);
                    model_object_status_db.add(*mobj, ModelObjectStatus::New);
                } else {
                    // Existing ModelObject re-added (possibly moved in the list).
                    m_model.objects.emplace_back(*it);
                    model_object_status_db.add(*mobj, ModelObjectStatus::Moved);
                }
            }
            bool deleted_any = false;
			for (ModelObject *&model_object : model_objects_old)
                if (model_object_status_db.add_if_new(*model_object, ModelObjectStatus::Deleted))
                    deleted_any = true;
                else
                    // Do not delete this ModelObject instance.
                    model_object = nullptr;
            if (deleted_any) {
                // Delete PrintObjects of the deleted ModelObjects.
                PrintObjectPtrs print_objects_old = std::move(m_objects);
                m_objects.clear();
                m_objects.reserve(print_objects_old.size());
                for (PrintObject *print_object : print_objects_old) {
                    const ModelObjectStatus &status = model_object_status_db.get(*print_object->model_object());
                    if (status.status == ModelObjectStatus::Deleted) {
                        update_apply_status(print_object->invalidate_all_steps());
                        delete print_object;
                    } else
                        m_objects.emplace_back(print_object);
                }
                for (ModelObject *model_object : model_objects_old)
                    delete model_object;
                print_regions_reshuffled = true;
            }
        }
    }

    // 2) Map print objects including their transformation matrices.
    PrintObjectStatusDB print_object_status_db(m_objects);

    // 3) Synchronize ModelObjects & PrintObjects.
    for (size_t idx_model_object = 0; idx_model_object < model.objects.size(); ++ idx_model_object) {
        ModelObject       &model_object        = *m_model.objects[idx_model_object];
        ModelObjectStatus &model_object_status = const_cast<ModelObjectStatus&>(model_object_status.reuse(model_object));
		const ModelObject &model_object_new    = *model.objects[idx_model_object];
        model_object_status.print_instances    = print_objects_from_model_object(*model_object_new);
        if (it_status->status == ModelObjectStatus::New)
            // PrintObject instances will be added in the next loop.
            continue;
        // Update the ModelObject instance, possibly invalidate the linked PrintObjects.
        assert(it_status->status == ModelObjectStatus::Old || it_status->status == ModelObjectStatus::Moved);
        // Check whether a model part volume was added or removed, their transformations or order changed.
        // Only volume IDs, volume types, transformation matrices and their order are checked, configuration and other parameters are NOT checked.
        bool model_parts_differ         = model_volume_list_changed(model_object, model_object_new, ModelVolumeType::MODEL_PART);
        bool modifiers_differ           = model_volume_list_changed(model_object, model_object_new, ModelVolumeType::PARAMETER_MODIFIER);
        bool supports_differ            = model_volume_list_changed(model_object, model_object_new, ModelVolumeType::SUPPORT_BLOCKER) ||
                                          model_volume_list_changed(model_object, model_object_new, ModelVolumeType::SUPPORT_ENFORCER);
        bool layer_height_ranges_differ = ! layer_height_ranges_equal(model_object.layer_config_ranges, model_object_new.layer_config_ranges, model_object_new.layer_height_profile.empty());
        auto print_objects_range        = print_object_status_db.get_range(&model_object);
        assert(print_objects_range.begin() != print_objects_range.end());
        model_object_status.prints_objects_regions = (*print_objects_range.begin())->prints_objects_regions;
        model_object_status.prints_objects_regions->ref_cnt_inc();
        if (model_parts_differ || modifiers_differ || 
            model_object.origin_translation != model_object_new.origin_translation   ||
            ! model_object.layer_height_profile.timestamp_matches(model_object_new.layer_height_profile) ||
            layer_height_ranges_differ) {
            // The very first step (the slicing step) is invalidated. One may freely remove all associated PrintObjects.
            model_object_status.prints_objects_regions_status = 
                model_object.origin_translation == model_object_new.origin_translation && ! layer_height_ranges_differ ? 
                    // Drop print_objects_regions.
                    ModelObjectStatus::PrintObjectRegionsStatus::Invalid :
                    // Reuse bounding boxes of print_objects_regions for ModelVolumes with unmodified transformation.
                    ModelObjectStatus::PrintObjectRegionsStatus::PartiallyValid;
            for (auto it : print_objects_range) {
                update_apply_status(it->print_object->invalidate_all_steps());
                const_cast<PrintObjectStatus&>(*it).status = PrintObjectStatus::Deleted;
            }
            if (model_object_status.prints_objects_regions_status == ModelObjectStatus::PrintObjectRegionsStatus::PartiallyValid)
                print_objects_regions_update_volumes(*model_object_status.prints_objects_regions, model_object.volumes, model_object_new.volumes);
            // Copy content of the ModelObject including its ID, do not change the parent.
            model_object.assign_copy(model_object_new);
        } else if (supports_differ || model_custom_supports_data_changed(model_object, model_object_new)) {
            // First stop background processing before shuffling or deleting the ModelVolumes in the ModelObject's list.
            if (supports_differ) {
                this->call_cancel_callback();
                update_apply_status(false);
            }
            // Invalidate just the supports step.
            for (auto it : print_objects_range)
                update_apply_status(it->print_object->invalidate_step(posSupportMaterial));
            if (supports_differ) {
                // Copy just the support volumes.
                model_volume_list_update_supports(model_object, model_object_new);
            }
        } else if (model_custom_seam_data_changed(model_object, model_object_new)) {
            update_apply_status(this->invalidate_step(psGCodeExport));
        }
        if (! model_parts_differ && ! modifiers_differ) {
            // Synchronize Object's config.
            bool object_config_changed = ! model_object.config.timestamp_matches(model_object_new.config);
			if (object_config_changed)
				model_object.config.assign_config(model_object_new.config);
            if (! object_diff.empty() || object_config_changed || num_extruders_changed) {
                PrintObjectConfig new_config = PrintObject::object_config_from_model_object(m_default_object_config, model_object, num_extruders);
                for (auto it : print_object_status_db.get_range(model_object)) {
                    t_config_option_keys diff = it->print_object->config().diff(new_config);
                    if (! diff.empty()) {
                        update_apply_status(it->print_object->invalidate_state_by_config_options(it->print_object->config(), new_config, diff));
                        it->print_object->config_apply_only(new_config, diff, true);
                    }
                }
            }
            // Synchronize (just copy) the remaining data of ModelVolumes (name, config, custom supports data).
            //FIXME What to do with m_material_id?
			model_volume_list_copy_configs(model_object /* dst */, model_object_new /* src */, ModelVolumeType::MODEL_PART);
			model_volume_list_copy_configs(model_object /* dst */, model_object_new /* src */, ModelVolumeType::PARAMETER_MODIFIER);
            layer_height_ranges_copy_configs(model_object.layer_config_ranges /* dst */, model_object_new.layer_config_ranges /* src */);
            // Copy the ModelObject name, input_file and instances. The instances will be compared against PrintObject instances in the next step.
            model_object.name       = model_object_new.name;
            model_object.input_file = model_object_new.input_file;
            // Only refresh ModelInstances if there is any change.
            if (model_object.instances.size() != model_object_new.instances.size() || 
            	! std::equal(model_object.instances.begin(), model_object.instances.end(), model_object_new.instances.begin(), [](auto l, auto r){ return l->id() == r->id(); })) {
            	// G-code generator accesses model_object.instances to generate sequential print ordering matching the Plater object list.
            	update_apply_status(this->invalidate_step(psGCodeExport));
	            model_object.clear_instances();
	            model_object.instances.reserve(model_object_new.instances.size());
	            for (const ModelInstance *model_instance : model_object_new.instances) {
	                model_object.instances.emplace_back(new ModelInstance(*model_instance));
	                model_object.instances.back()->set_model_object(&model_object);
	            }
	        } else if (! std::equal(model_object.instances.begin(), model_object.instances.end(), model_object_new.instances.begin(), 
	        		[](auto l, auto r){ return l->print_volume_state == r->print_volume_state && l->printable == r->printable && 
	        						           l->get_transformation().get_matrix().isApprox(r->get_transformation().get_matrix()); })) {
	        	// If some of the instances changed, the bounding box of the updated ModelObject is likely no more valid.
	        	// This is safe as the ModelObject's bounding box is only accessed from this function, which is called from the main thread only.
	 			model_object.invalidate_bounding_box();
	        	// Synchronize the content of instances.
	        	auto new_instance = model_object_new.instances.begin();
				for (auto old_instance = model_object.instances.begin(); old_instance != model_object.instances.end(); ++ old_instance, ++ new_instance) {
					(*old_instance)->set_transformation((*new_instance)->get_transformation());
                    (*old_instance)->print_volume_state = (*new_instance)->print_volume_state;
                    (*old_instance)->printable 		    = (*new_instance)->printable;
  				}
	        }
        }
    }

    // 4) Generate PrintObjects from ModelObjects and their instances.
    {
        PrintObjectPtrs print_objects_new;
        print_objects_new.reserve(std::max(m_objects.size(), m_model.objects.size()));
        bool new_objects = false;
        // Walk over all new model objects and check, whether there are matching PrintObjects.
        for (ModelObject *model_object : m_model.objects) {
            ModelObjectStatus &model_object_status = const_cast<ModelObjectStatus&>(model_object_status.reuse(model_object));
            std::vector<const PrintObjectStatus*> old;
            old.reserve(print_object_status.count(*model_object));
            for (auto it : print_object_status.get_range(*model_object))
                if (it->status != PrintObjectStatus::Deleted)
                    old.emplace_back(&(*it));
            // Generate a list of trafos and XY offsets for instances of a ModelObject
            // Producing the config for PrintObject on demand, caching it at print_object_last.
            const PrintObject *print_object_last = nullptr;
            auto print_object_apply_config = [this, &print_object_last, model_object, num_extruders](PrintObject* print_object) {
                print_object->config_apply(print_object_last ?
                    print_object_last->config() :
                    PrintObject::object_config_from_model_object(m_default_object_config, *model_object, num_extruders));
                print_object_last = print_object;
            };
            if (old.empty()) {
                // Simple case, just generate new instances.
                for (PrintObjectTrafoAndInstances &print_instances : model_object_status.print_instances) {
                    PrintObject *print_object = new PrintObject(this, model_object, print_instances.trafo, std::move(print_instances.instances));
                    print_object_apply_config(print_object);
                    print_objects_new.emplace_back(print_object);
                    // print_object_status.emplace(PrintObjectStatus(print_object, PrintObjectStatus::New));
                    new_objects = true;
                }
                continue;
            }
            // Complex case, try to merge the two lists.
            // Sort the old lexicographically by their trafos.
            std::sort(old.begin(), old.end(), [](const PrintObjectStatus *lhs, const PrintObjectStatus *rhs){ return transform3d_lower(lhs->trafo, rhs->trafo); });
            // Merge the old / new lists.
            auto it_old = old.begin();
            size_t num_old = old.size();
            for (PrintObjectTrafoAndInstances &new_instances : model_object_status.print_instances) {
				for (; it_old != old.end() && transform3d_lower((*it_old)->trafo, new_instances.trafo); ++ it_old);
				if (it_old == old.end() || ! transform3d_equal((*it_old)->trafo, new_instances.trafo)) {
                    // This is a new instance (or a set of instances with the same trafo). Just add it.
                    PrintObject *print_object = new PrintObject(this, model_object, new_instances.trafo, std::move(new_instances.instances));
                    print_object_apply_config(print_object);
                    print_objects_new.emplace_back(print_object);
                    // print_object_status.emplace(PrintObjectStatus(print_object, PrintObjectStatus::New));
                    new_objects = true;
                    if (it_old != old.end()) {
                        if (-- num_old == 0)
                            update_model_object_status_layers_bboxes(*model_object, model_object_status, std::move(*old.front()->print_object));
                        const_cast<PrintObjectStatus*>(*it_old)->status = PrintObjectStatus::Deleted;
                    }
                } else {
                    // The PrintObject already exists and the copies differ.
					PrintBase::ApplyStatus status = (*it_old)->print_object->set_instances(std::move(new_instances.instances));
                    if (status != PrintBase::APPLY_STATUS_UNCHANGED)
						update_apply_status(status == PrintBase::APPLY_STATUS_INVALIDATED);
					print_objects_new.emplace_back((*it_old)->print_object);
					const_cast<PrintObjectStatus*>(*it_old)->status = PrintObjectStatus::Reused;
				}
            }
        }
        if (m_objects != print_objects_new) {
            this->call_cancel_callback();
			update_apply_status(this->invalidate_all_steps());
            m_objects = print_objects_new;
            // Delete the PrintObjects marked as Unknown or Deleted.
            bool deleted_objects = false;
            for (auto &pos : print_object_status_db)
                if (pos.status == PrintObjectStatus::Unknown || pos.status == PrintObjectStatus::Deleted) {
                    update_apply_status(pos.print_object->invalidate_all_steps());
                    delete pos.print_object;
					deleted_objects = true;
                }
			if (new_objects || deleted_objects)
				update_apply_status(this->invalidate_steps({ psSkirt, psBrim, psWipeTower, psGCodeExport }));
			if (new_objects)
	            update_apply_status(false);
            print_regions_reshuffled = true;
        }
        print_object_status.clear();
    }

    // All regions now have distinct settings.
    // Check whether applying the new region config defaults we would get different regions.
    const std::vector<unsigned int> painting_extruders;
    for (auto it_print_object = m_objects.begin(); it_print_object != m_objects.end();) {
        // Find the range of PrintObjects sharing the same associated ModelObject.
        auto                it_print_object_end  = m_objects.begin();
        PrintObject        &print_object         = *(*it_print_object);
        const ModelObject  &model_object         = *print_object.model_object();
        ModelObjectStatus  &model_object_status  = const_cast<ModelObjectStatus&>(model_object_status.reuse(model_object));
        PrintObjectRegions *print_object_regions = model_object_status.print_object_regions;
        for (++ it_print_object_end; it_print_object != m_objects.end() && (*it_print_object)->model_object() == (*it_print_object_end)->model_object(); ++ it_print_object_end)
            assert((*it_print_object_end)->m_shared_regions == nullptr || (*it_print_object_end)->m_shared_regions == print_object_regions);
        if (print_object_regions == nullptr)
            print_object_regions = new PrintObjectRegions {};
        if (model_object_status.print_object_regions_status == ModelObjectStatus::PrintObjectRegionsStatus::Valid) {
            if (verify_update_print_object_regions(
                    print_object.model_object()->volumes,
                    m_default_region_config,
                    num_extruders,
                    painting_extruders,
                    *print_object_regions,
                    [](){
                        // Stop the background process before assigning new configuration to the regions.
                        t_config_option_keys diff = region.config().diff(region_config);
                        update_apply_status(print_object->invalidate_state_by_config_options(region.config(), region_config, diff));
                        region.config_apply_only(region_config, diff, false);
                    })) {
                // Regions are valid, assign them to the other PrintObjects.
                for (auto it = it_print_object; it != it_print_object_end; ++ it)
                    if ((*it)->m_shared_regions == nullptr) {
                        (*it)->m_shared_regions = print_object_regions;
                        print_object_regions->ref_cnt_inc();
                    }
            } else {
                // Regions were reshuffled.
                for (auto it = it_print_object; it != it_print_object_end; ++ it)
                    if ((*it)->m_shared_regions != nullptr) {
                        assert(print_object_regions == (*it)->m_shared_regions);
                        update_apply_status((*it)->invalidate_all_steps());
                        (*it)->m_shared_regions = nullptr;
                        print_object_regions->ref_cnt_dec();
                    }
                // At least reuse layer ranges and bounding boxes of ModelVolumes.
                model_object_status.print_object_regions_status = ModelObjectStatus::PrintObjectRegionsStatus::PartiallyValid;
                print_regions_reshuffled = true;
            }
        }
        if (model_object_status.print_object_regions_status == ModelObjectStatus::PrintObjectRegionsStatus::PartiallyValid) {
            // Reuse layer ranges and bounding boxes of ModelVolumes.
        } else {
            assert(model_object_status.print_object_regions_status == ModelObjectStatus::PrintObjectRegionsStatus::Invalid);
            // Layer ranges with their associated configurations.
            LayerRanges layer_ranges;
            layer_ranges.assign(print_object.model_object()->layer_config_ranges);
            print_object_regions = new PrintObjectRegions(generate_print_object_regions(
                print_object.model_object()->volumes,
                layer_ranges,
                m_default_region_config,
                num_extruders,
                painting_extruders));
            for (auto it = it_print_object; it != it_print_object_end; ++ it) {
                (*it)->m_shared_regions = print_object_regions;
                print_object_regions->ref_cnt_inc();
            }
        }
        it_print_object = it_print_object_end;
    }

    if (print_regions_reshuffled) {
        // Update Print::m_print_regions from objects.
        struct cmp { bool operator() (const PrintRegion *l, const PrintRegion *r) const { return l->config_hash() == r->config_hash() && l->config() == r->config(); } };
        std::set<const PrintRegion*, cmp> region_set;
        m_print_regions.clear();
        PrintObjectRegions *print_object_regions = nullptr;
        for (PrintObject *print_object : m_objects) {
            if (print_object_regions != print_object->m_shared_regions) {
                print_object_regions = print_object->m_shared_regions;
                for (std::unique_ptr<Slic3r::PrintRegion> &print_region : print_object_regions->all_regions)
                    if (auto it = region_set.find(print_region.get()); it == region_set.end()) {
                        int print_region_id = int(m_print_regions.size());
                        m_print_regions.emplace_back(print_region.get());
                        print_region->m_print_region_id = print_region_id;
                    } else {
                        print_region->m_print_region_id = (*it)->print_region_id();
                    }
            }
    }

    // Update SlicingParameters for each object where the SlicingParameters is not valid.
    // If it is not valid, then it is ensured that PrintObject.m_slicing_params is not in use
    // (posSlicing and posSupportMaterial was invalidated).
    for (PrintObject *object : m_objects)
        object->update_slicing_parameters();

#ifdef _DEBUG
    check_model_ids_equal(m_model, model);
#endif /* _DEBUG */

	return static_cast<ApplyStatus>(apply_status);
}

} // namespace Slic3r