/* SPDX-License-Identifier: GPL-2.0-or-later */

#include <algorithm>

#include "curves_sculpt_intern.hh"

#include "BLI_float4x4.hh"
#include "BLI_index_mask_ops.hh"
#include "BLI_kdtree.h"
#include "BLI_rand.hh"
#include "BLI_vector.hh"

#include "PIL_time.h"

#include "DEG_depsgraph.h"
#include "DEG_depsgraph_query.h"

#include "BKE_attribute_math.hh"
#include "BKE_brush.h"
#include "BKE_bvhutils.h"
#include "BKE_context.h"
#include "BKE_crazyspace.hh"
#include "BKE_curves.hh"
#include "BKE_geometry_set.hh"
#include "BKE_mesh.h"
#include "BKE_mesh_runtime.h"
#include "BKE_paint.h"

#include "DNA_brush_enums.h"
#include "DNA_brush_types.h"
#include "DNA_curves_types.h"
#include "DNA_mesh_types.h"
#include "DNA_meshdata_types.h"
#include "DNA_object_types.h"
#include "DNA_screen_types.h"
#include "DNA_space_types.h"

#include "ED_screen.h"
#include "ED_view3d.h"

#include "UI_interface.h"

#include "WM_api.h"

/**
 * The code below uses a prefix naming convention to indicate the coordinate space:
 * cu: Local space of the curves object that is being edited.
 * su: Local space of the surface object.
 * wo: World space.
 * re: 2D coordinates within the region.
 */

namespace blender::ed::sculpt_paint {

using blender::bke::CurvesGeometry;
using threading::EnumerableThreadSpecific;

/**
 * Moves individual points under the brush and does a length preservation step afterwards.
 */
class CombOperation : public CurvesSculptStrokeOperation {
 private:
  /** Last mouse position. */
  float2 brush_pos_last_re_;

  /** Only used when a 3D brush is used. */
  CurvesBrush3D brush_3d_;

  /** Length of each segment indexed by the index of the first point in the segment. */
  Array<float> segment_lengths_cu_;

  friend struct CombOperationExecutor;

 public:
  void on_stroke_extended(const bContext &C, const StrokeExtension &stroke_extension) override;
};

/**
 * Utility class that actually executes the update when the stroke is updated. That's useful
 * because it avoids passing a very large number of parameters between functions.
 */
struct CombOperationExecutor {
  CombOperation *self_ = nullptr;
  CurvesSculptCommonContext ctx_;

  const CurvesSculpt *curves_sculpt_ = nullptr;
  const Brush *brush_ = nullptr;
  float brush_radius_base_re_;
  float brush_radius_factor_;
  float brush_strength_;

  eBrushFalloffShape falloff_shape_;

  Object *curves_ob_orig_ = nullptr;
  Curves *curves_id_orig_ = nullptr;
  CurvesGeometry *curves_orig_ = nullptr;

  VArray<float> point_factors_;
  Vector<int64_t> selected_curve_indices_;
  IndexMask curve_selection_;

  float2 brush_pos_prev_re_;
  float2 brush_pos_re_;
  float2 brush_pos_diff_re_;

  CurvesSurfaceTransforms transforms_;

  CombOperationExecutor(const bContext &C) : ctx_(C)
  {
  }

  void execute(CombOperation &self, const bContext &C, const StrokeExtension &stroke_extension)
  {
    self_ = &self;

    BLI_SCOPED_DEFER([&]() { self_->brush_pos_last_re_ = stroke_extension.mouse_position; });

    curves_ob_orig_ = CTX_data_active_object(&C);
    curves_id_orig_ = static_cast<Curves *>(curves_ob_orig_->data);
    curves_orig_ = &CurvesGeometry::wrap(curves_id_orig_->geometry);
    if (curves_orig_->curves_num() == 0) {
      return;
    }

    curves_sculpt_ = ctx_.scene->toolsettings->curves_sculpt;
    brush_ = BKE_paint_brush_for_read(&curves_sculpt_->paint);
    brush_radius_base_re_ = BKE_brush_size_get(ctx_.scene, brush_);
    brush_radius_factor_ = brush_radius_factor(*brush_, stroke_extension);
    brush_strength_ = brush_strength_get(*ctx_.scene, *brush_, stroke_extension);

    falloff_shape_ = static_cast<eBrushFalloffShape>(brush_->falloff_shape);

    transforms_ = CurvesSurfaceTransforms(*curves_ob_orig_, curves_id_orig_->surface);

    point_factors_ = get_point_selection(*curves_id_orig_);
    curve_selection_ = retrieve_selected_curves(*curves_id_orig_, selected_curve_indices_);

    brush_pos_prev_re_ = self_->brush_pos_last_re_;
    brush_pos_re_ = stroke_extension.mouse_position;
    brush_pos_diff_re_ = brush_pos_re_ - brush_pos_prev_re_;

    if (stroke_extension.is_first) {
      if (falloff_shape_ == PAINT_FALLOFF_SHAPE_SPHERE) {
        this->initialize_spherical_brush_reference_point();
      }
      this->initialize_segment_lengths();
      /* Combing does nothing when there is no mouse movement, so return directly. */
      return;
    }

    EnumerableThreadSpecific<Vector<int>> changed_curves;

    if (falloff_shape_ == PAINT_FALLOFF_SHAPE_TUBE) {
      this->comb_projected_with_symmetry(changed_curves);
    }
    else if (falloff_shape_ == PAINT_FALLOFF_SHAPE_SPHERE) {
      this->comb_spherical_with_symmetry(changed_curves);
    }
    else {
      BLI_assert_unreachable();
    }

    this->restore_segment_lengths(changed_curves);

    curves_orig_->tag_positions_changed();
    DEG_id_tag_update(&curves_id_orig_->id, ID_RECALC_GEOMETRY);
    WM_main_add_notifier(NC_GEOM | ND_DATA, &curves_id_orig_->id);
    ED_region_tag_redraw(ctx_.region);
  }

  /**
   * Do combing in screen space.
   */
  void comb_projected_with_symmetry(EnumerableThreadSpecific<Vector<int>> &r_changed_curves)
  {
    const Vector<float4x4> symmetry_brush_transforms = get_symmetry_brush_transforms(
        eCurvesSymmetryType(curves_id_orig_->symmetry));
    for (const float4x4 &brush_transform : symmetry_brush_transforms) {
      this->comb_projected(r_changed_curves, brush_transform);
    }
  }

  void comb_projected(EnumerableThreadSpecific<Vector<int>> &r_changed_curves,
                      const float4x4 &brush_transform)
  {
    const float4x4 brush_transform_inv = brush_transform.inverted();

    MutableSpan<float3> positions_cu_orig = curves_orig_->positions_for_write();
    const bke::crazyspace::GeometryDeformation deformation =
        bke::crazyspace::get_evaluated_curves_deformation(*ctx_.depsgraph, *curves_ob_orig_);

    float4x4 projection;
    ED_view3d_ob_project_mat_get(ctx_.rv3d, curves_ob_orig_, projection.values);

    const float brush_radius_re = brush_radius_base_re_ * brush_radius_factor_;
    const float brush_radius_sq_re = pow2f(brush_radius_re);

    threading::parallel_for(curve_selection_.index_range(), 256, [&](const IndexRange range) {
      Vector<int> &local_changed_curves = r_changed_curves.local();
      for (const int curve_i : curve_selection_.slice(range)) {
        bool curve_changed = false;
        const IndexRange points = curves_orig_->points_for_curve(curve_i);
        for (const int point_i : points.drop_front(1)) {
          const float3 old_pos_cu = deformation.positions[point_i];
          const float3 old_symm_pos_cu = brush_transform_inv * old_pos_cu;

          /* Find the position of the point in screen space. */
          float2 old_symm_pos_re;
          ED_view3d_project_float_v2_m4(
              ctx_.region, old_symm_pos_cu, old_symm_pos_re, projection.values);

          const float distance_to_brush_sq_re = dist_squared_to_line_segment_v2(
              old_symm_pos_re, brush_pos_prev_re_, brush_pos_re_);
          if (distance_to_brush_sq_re > brush_radius_sq_re) {
            /* Ignore the point because it's too far away. */
            continue;
          }

          const float distance_to_brush_re = std::sqrt(distance_to_brush_sq_re);
          /* A falloff that is based on how far away the point is from the stroke. */
          const float radius_falloff = BKE_brush_curve_strength(
              brush_, distance_to_brush_re, brush_radius_re);
          /* Combine the falloff and brush strength. */
          const float weight = brush_strength_ * radius_falloff * point_factors_[point_i];

          /* Offset the old point position in screen space and transform it back into 3D space.
           */
          const float2 new_symm_pos_re = old_symm_pos_re + brush_pos_diff_re_ * weight;
          float3 new_symm_pos_wo;
          ED_view3d_win_to_3d(ctx_.v3d,
                              ctx_.region,
                              transforms_.curves_to_world * old_symm_pos_cu,
                              new_symm_pos_re,
                              new_symm_pos_wo);
          const float3 new_pos_cu = brush_transform *
                                    (transforms_.world_to_curves * new_symm_pos_wo);

          const float3 translation_eval = new_pos_cu - old_pos_cu;
          const float3 translation_orig = deformation.translation_from_deformed_to_original(
              point_i, translation_eval);
          positions_cu_orig[point_i] += translation_orig;

          curve_changed = true;
        }
        if (curve_changed) {
          local_changed_curves.append(curve_i);
        }
      }
    });
  }

  /**
   * Do combing in 3D space.
   */
  void comb_spherical_with_symmetry(EnumerableThreadSpecific<Vector<int>> &r_changed_curves)
  {
    float4x4 projection;
    ED_view3d_ob_project_mat_get(ctx_.rv3d, curves_ob_orig_, projection.values);

    float3 brush_start_wo, brush_end_wo;
    ED_view3d_win_to_3d(ctx_.v3d,
                        ctx_.region,
                        transforms_.curves_to_world * self_->brush_3d_.position_cu,
                        brush_pos_prev_re_,
                        brush_start_wo);
    ED_view3d_win_to_3d(ctx_.v3d,
                        ctx_.region,
                        transforms_.curves_to_world * self_->brush_3d_.position_cu,
                        brush_pos_re_,
                        brush_end_wo);
    const float3 brush_start_cu = transforms_.world_to_curves * brush_start_wo;
    const float3 brush_end_cu = transforms_.world_to_curves * brush_end_wo;

    const float brush_radius_cu = self_->brush_3d_.radius_cu * brush_radius_factor_;

    const Vector<float4x4> symmetry_brush_transforms = get_symmetry_brush_transforms(
        eCurvesSymmetryType(curves_id_orig_->symmetry));
    for (const float4x4 &brush_transform : symmetry_brush_transforms) {
      this->comb_spherical(r_changed_curves,
                           brush_transform * brush_start_cu,
                           brush_transform * brush_end_cu,
                           brush_radius_cu);
    }
  }

  void comb_spherical(EnumerableThreadSpecific<Vector<int>> &r_changed_curves,
                      const float3 &brush_start_cu,
                      const float3 &brush_end_cu,
                      const float brush_radius_cu)
  {
    MutableSpan<float3> positions_cu = curves_orig_->positions_for_write();
    const float brush_radius_sq_cu = pow2f(brush_radius_cu);
    const float3 brush_diff_cu = brush_end_cu - brush_start_cu;

    const bke::crazyspace::GeometryDeformation deformation =
        bke::crazyspace::get_evaluated_curves_deformation(*ctx_.depsgraph, *curves_ob_orig_);

    threading::parallel_for(curve_selection_.index_range(), 256, [&](const IndexRange range) {
      Vector<int> &local_changed_curves = r_changed_curves.local();
      for (const int curve_i : curve_selection_.slice(range)) {
        bool curve_changed = false;
        const IndexRange points = curves_orig_->points_for_curve(curve_i);
        for (const int point_i : points.drop_front(1)) {
          const float3 pos_old_cu = deformation.positions[point_i];

          /* Compute distance to the brush. */
          const float distance_to_brush_sq_cu = dist_squared_to_line_segment_v3(
              pos_old_cu, brush_start_cu, brush_end_cu);
          if (distance_to_brush_sq_cu > brush_radius_sq_cu) {
            /* Ignore the point because it's too far away. */
            continue;
          }

          const float distance_to_brush_cu = std::sqrt(distance_to_brush_sq_cu);

          /* A falloff that is based on how far away the point is from the stroke. */
          const float radius_falloff = BKE_brush_curve_strength(
              brush_, distance_to_brush_cu, brush_radius_cu);
          /* Combine the falloff and brush strength. */
          const float weight = brush_strength_ * radius_falloff * point_factors_[point_i];

          const float3 translation_eval_cu = weight * brush_diff_cu;
          const float3 translation_orig_cu = deformation.translation_from_deformed_to_original(
              point_i, translation_eval_cu);

          /* Update the point position. */
          positions_cu[point_i] += translation_orig_cu;
          curve_changed = true;
        }
        if (curve_changed) {
          local_changed_curves.append(curve_i);
        }
      }
    });
  }

  /**
   * Sample depth under mouse by looking at curves and the surface.
   */
  void initialize_spherical_brush_reference_point()
  {
    std::optional<CurvesBrush3D> brush_3d = sample_curves_3d_brush(*ctx_.depsgraph,
                                                                   *ctx_.region,
                                                                   *ctx_.v3d,
                                                                   *ctx_.rv3d,
                                                                   *curves_ob_orig_,
                                                                   brush_pos_re_,
                                                                   brush_radius_base_re_);
    if (brush_3d.has_value()) {
      self_->brush_3d_ = *brush_3d;
    }
  }

  /**
   * Remember the initial length of all curve segments. This allows restoring the length after
   * combing.
   */
  void initialize_segment_lengths()
  {
    const Span<float3> positions_cu = curves_orig_->positions();
    self_->segment_lengths_cu_.reinitialize(curves_orig_->points_num());
    threading::parallel_for(curves_orig_->curves_range(), 128, [&](const IndexRange range) {
      for (const int curve_i : range) {
        const IndexRange points = curves_orig_->points_for_curve(curve_i);
        for (const int point_i : points.drop_back(1)) {
          const float3 &p1_cu = positions_cu[point_i];
          const float3 &p2_cu = positions_cu[point_i + 1];
          const float length_cu = math::distance(p1_cu, p2_cu);
          self_->segment_lengths_cu_[point_i] = length_cu;
        }
      }
    });
  }

  /**
   * Restore previously stored length for each segment in the changed curves.
   */
  void restore_segment_lengths(EnumerableThreadSpecific<Vector<int>> &changed_curves)
  {
    const Span<float> expected_lengths_cu = self_->segment_lengths_cu_;
    MutableSpan<float3> positions_cu = curves_orig_->positions_for_write();

    threading::parallel_for_each(changed_curves, [&](const Vector<int> &changed_curves) {
      threading::parallel_for(changed_curves.index_range(), 256, [&](const IndexRange range) {
        for (const int curve_i : changed_curves.as_span().slice(range)) {
          const IndexRange points = curves_orig_->points_for_curve(curve_i);
          for (const int segment_i : points.drop_back(1)) {
            const float3 &p1_cu = positions_cu[segment_i];
            float3 &p2_cu = positions_cu[segment_i + 1];
            const float3 direction = math::normalize(p2_cu - p1_cu);
            const float expected_length_cu = expected_lengths_cu[segment_i];
            p2_cu = p1_cu + direction * expected_length_cu;
          }
        }
      });
    });
  }
};

void CombOperation::on_stroke_extended(const bContext &C, const StrokeExtension &stroke_extension)
{
  CombOperationExecutor executor{C};
  executor.execute(*this, C, stroke_extension);
}

std::unique_ptr<CurvesSculptStrokeOperation> new_comb_operation()
{
  return std::make_unique<CombOperation>();
}

}  // namespace blender::ed::sculpt_paint