/*
 * 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

#include "BLI_array.hh"
#include "BLI_span.hh"

#include "FN_generic_virtual_array.hh"

#include "BKE_spline.hh"

using blender::float3;
using blender::IndexRange;
using blender::MutableSpan;
using blender::Span;

Spline::Type Spline::type() const
{
  return type_;
}

void Spline::translate(const blender::float3 &translation)
{
  for (float3 &position : this->positions()) {
    position += translation;
  }
  this->mark_cache_invalid();
}

void Spline::transform(const blender::float4x4 &matrix)
{
  for (float3 &position : this->positions()) {
    position = matrix * position;
  }
  this->mark_cache_invalid();
}

int Spline::evaluated_edges_size() const
{
  const int eval_size = this->evaluated_points_size();
  if (eval_size == 1) {
    return 0;
  }

  return this->is_cyclic_ ? eval_size : eval_size - 1;
}

float Spline::length() const
{
  return this->evaluated_lengths().last();
}

int Spline::segments_size() const
{
  const int points_len = this->size();

  return is_cyclic_ ? points_len : points_len - 1;
}

bool Spline::is_cyclic() const
{
  return is_cyclic_;
}

void Spline::set_cyclic(const bool value)
{
  is_cyclic_ = value;
}

static void accumulate_lengths(Span<float3> positions,
                               const bool is_cyclic,
                               MutableSpan<float> lengths)
{
  float length = 0.0f;
  for (const int i : IndexRange(positions.size() - 1)) {
    length += float3::distance(positions[i], positions[i + 1]);
    lengths[i] = length;
  }
  if (is_cyclic) {
    lengths.last() = length + float3::distance(positions.last(), positions.first());
  }
}

/**
 * Return non-owning access to the cache of accumulated lengths along the spline. Each item is the
 * length of the subsequent segment, i.e. the first value is the length of the first segment rather
 * than 0. This calculation is rather trivial, and only depends on the evaluated positions.
 * However, the results are used often, so it makes sense to cache it.
 */
Span<float> Spline::evaluated_lengths() const
{
  if (!length_cache_dirty_) {
    return evaluated_lengths_cache_;
  }

  std::lock_guard lock{length_cache_mutex_};
  if (!length_cache_dirty_) {
    return evaluated_lengths_cache_;
  }

  const int total = evaluated_edges_size();
  evaluated_lengths_cache_.resize(total);

  Span<float3> positions = this->evaluated_positions();
  accumulate_lengths(positions, is_cyclic_, evaluated_lengths_cache_);

  length_cache_dirty_ = false;
  return evaluated_lengths_cache_;
}

static float3 direction_bisect(const float3 &prev, const float3 &middle, const float3 &next)
{
  const float3 dir_prev = (middle - prev).normalized();
  const float3 dir_next = (next - middle).normalized();

  return (dir_prev + dir_next).normalized();
}

static void calculate_tangents(Span<float3> positions,
                               const bool is_cyclic,
                               MutableSpan<float3> tangents)
{
  if (positions.size() == 1) {
    return;
  }

  for (const int i : IndexRange(1, positions.size() - 2)) {
    tangents[i] = direction_bisect(positions[i - 1], positions[i], positions[i + 1]);
  }

  if (is_cyclic) {
    const float3 &second_to_last = positions[positions.size() - 2];
    const float3 &last = positions.last();
    const float3 &first = positions.first();
    const float3 &second = positions[1];
    tangents.first() = direction_bisect(last, first, second);
    tangents.last() = direction_bisect(second_to_last, last, first);
  }
  else {
    tangents.first() = (positions[1] - positions[0]).normalized();
    tangents.last() = (positions.last() - positions[positions.size() - 2]).normalized();
  }
}

/**
 * Return non-owning access to the direction of the curve at each evaluated point.
 */
Span<float3> Spline::evaluated_tangents() const
{
  if (!tangent_cache_dirty_) {
    return evaluated_tangents_cache_;
  }

  std::lock_guard lock{tangent_cache_mutex_};
  if (!tangent_cache_dirty_) {
    return evaluated_tangents_cache_;
  }

  const int eval_size = this->evaluated_points_size();
  evaluated_tangents_cache_.resize(eval_size);

  Span<float3> positions = this->evaluated_positions();

  if (eval_size == 1) {
    evaluated_tangents_cache_.first() = float3(1.0f, 0.0f, 0.0f);
  }
  else {
    calculate_tangents(positions, is_cyclic_, evaluated_tangents_cache_);
    this->correct_end_tangents();
  }

  tangent_cache_dirty_ = false;
  return evaluated_tangents_cache_;
}

static float3 rotate_direction_around_axis(const float3 &direction,
                                           const float3 &axis,
                                           const float angle)
{
  BLI_ASSERT_UNIT_V3(direction);
  BLI_ASSERT_UNIT_V3(axis);

  const float3 axis_scaled = axis * float3::dot(direction, axis);
  const float3 diff = direction - axis_scaled;
  const float3 cross = float3::cross(axis, diff);

  return axis_scaled + diff * std::cos(angle) + cross * std::sin(angle);
}

static void calculate_normals_z_up(Span<float3> tangents, MutableSpan<float3> normals)
{
  for (const int i : normals.index_range()) {
    normals[i] = float3::cross(tangents[i], float3(0.0f, 0.0f, 1.0f)).normalized();
  }
}

/**
 * Return non-owning access to the direction vectors perpendicular to the tangents at every
 * evaluated point. The method used to generate the normal vectors depends on Spline.normal_mode.
 */
Span<float3> Spline::evaluated_normals() const
{
  if (!normal_cache_dirty_) {
    return evaluated_normals_cache_;
  }

  std::lock_guard lock{normal_cache_mutex_};
  if (!normal_cache_dirty_) {
    return evaluated_normals_cache_;
  }

  const int eval_size = this->evaluated_points_size();
  evaluated_normals_cache_.resize(eval_size);

  Span<float3> tangents = evaluated_tangents();
  MutableSpan<float3> normals = evaluated_normals_cache_;

  /* Only Z up normals are supported at the moment. */
  calculate_normals_z_up(tangents, normals);

  /* Rotate the generated normals with the interpolated tilt data. */
  blender::fn::GVArray_Typed<float> tilts{
      this->interpolate_to_evaluated_points(blender::fn::GVArray_For_Span(this->tilts()))};
  for (const int i : normals.index_range()) {
    normals[i] = rotate_direction_around_axis(normals[i], tangents[i], tilts[i]);
  }

  normal_cache_dirty_ = false;
  return evaluated_normals_cache_;
}

Spline::LookupResult Spline::lookup_evaluated_factor(const float factor) const
{
  return this->lookup_evaluated_length(this->length() * factor);
}

/**
 * \note This does not support extrapolation currently.
 */
Spline::LookupResult Spline::lookup_evaluated_length(const float length) const
{
  BLI_assert(length >= 0.0f && length <= this->length());

  Span<float> lengths = this->evaluated_lengths();

  const float *offset = std::lower_bound(lengths.begin(), lengths.end(), length);
  const int index = offset - lengths.begin();
  const int next_index = (index == this->size() - 1) ? 0 : index + 1;

  const float previous_length = (index == 0) ? 0.0f : lengths[index - 1];
  const float factor = (length - previous_length) / (lengths[index] - previous_length);

  return LookupResult{index, next_index, factor};
}

void Spline::bounds_min_max(float3 &min, float3 &max, const bool use_evaluated) const
{
  Span<float3> positions = use_evaluated ? this->evaluated_positions() : this->positions();
  for (const float3 &position : positions) {
    minmax_v3v3_v3(min, max, position);
  }
}