#include "fesa/loads/shell_surface_pressure.h"

#include <algorithm>
#include <array>
#include <cmath>
#include <cstddef>
#include <string>
#include <utility>
#include "math/vector3_operations.h"

namespace fesa {
namespace {

using math_internal::WeightedSum;

constexpr std::size_t kNodeCount = 4U;
constexpr std::size_t kDofsPerNode = 6U;
constexpr std::size_t kDofCount = kNodeCount * kDofsPerNode;
constexpr double kGeometryThreshold = 1.0e-12;

struct ShapeData {
  std::array<double, kNodeCount> values;
  std::array<double, kNodeCount> xi_derivatives;
  std::array<double, kNodeCount> eta_derivatives;
};

struct GeometryData {
  ShapeData shape;
  Vector3 xi_tangent;
  Vector3 eta_tangent;
  Vector3 area_vector;
};

struct ValidatedGeometry {
  std::array<GeometryData, 4> gauss_points;
};

/// @brief Creates one deterministic evaluator failure diagnostic.
Status Failure(const FailureCategory category,
               const ShellSurfacePressureInput& input,
               std::string code, std::string message) {
  return Status::Failure(
      category,
      {{Severity::kError, std::move(code), input.location, "DSLOAD",
        input.entity_identity, std::move(message)}});
}

/// @brief Evaluates four-node bilinear shape data in source connectivity order.
ShapeData ShapeAt(const double xi, const double eta) noexcept {
  return {{{0.25 * (1.0 - xi) * (1.0 - eta),
           0.25 * (1.0 + xi) * (1.0 - eta),
           0.25 * (1.0 + xi) * (1.0 + eta),
           0.25 * (1.0 - xi) * (1.0 + eta)}},
          {{-0.25 * (1.0 - eta), 0.25 * (1.0 - eta),
            0.25 * (1.0 + eta), -0.25 * (1.0 + eta)}},
          {{-0.25 * (1.0 - xi), -0.25 * (1.0 + xi),
            0.25 * (1.0 + xi), 0.25 * (1.0 - xi)}}};
}

/// @brief Evaluates finite bilinear surface data at one natural point.
bool EvaluateGeometry(const std::array<Vector3, kNodeCount>& coordinates,
                      const double xi, const double eta,
                      GeometryData& geometry) {
  geometry.shape = ShapeAt(xi, eta);
  geometry.xi_tangent =
      WeightedSum(geometry.shape.xi_derivatives, coordinates);
  geometry.eta_tangent =
      WeightedSum(geometry.shape.eta_derivatives, coordinates);
  geometry.area_vector = geometry.xi_tangent.Cross(geometry.eta_tangent);
  if (!geometry.xi_tangent.IsFinite() || !geometry.eta_tangent.IsFinite() ||
      !geometry.area_vector.IsFinite()) {
    return false;
  }
  for (const double value : geometry.shape.values) {
    if (!std::isfinite(value)) {
      return false;
    }
  }
  for (const double value : geometry.shape.xi_derivatives) {
    if (!std::isfinite(value)) {
      return false;
    }
  }
  for (const double value : geometry.shape.eta_derivatives) {
    if (!std::isfinite(value)) {
      return false;
    }
  }
  return true;
}

/// @brief Returns the exact reference or current coordinates selected by input.
bool SelectCoordinates(const ShellSurfacePressureInput& input,
                       std::array<Vector3, kNodeCount>& coordinates) {
  for (std::size_t node = 0U; node < kNodeCount; ++node) {
    coordinates[node] = input.reference_coordinates[node];
    if (input.configuration == SurfacePressureConfiguration::kCurrent) {
      coordinates[node] =
          coordinates[node] + input.translational_displacements[node];
    }
    if (!coordinates[node].IsFinite()) {
      return false;
    }
  }
  return true;
}

/// @brief Validates all required geometry points before contribution assembly.
Result<ValidatedGeometry> ValidateGeometry(
    const ShellSurfacePressureInput& input,
    const std::array<Vector3, kNodeCount>& coordinates) {
  const FailureCategory category =
      input.configuration == SurfacePressureConfiguration::kReference
          ? FailureCategory::kModel
          : FailureCategory::kSolver;
  const std::string code =
      input.configuration == SurfacePressureConfiguration::kReference
          ? "invalid-reference-surface-geometry"
          : "invalid-current-surface-geometry";

  double chord_length = 0.0;
  for (std::size_t first = 0U; first < kNodeCount; ++first) {
    for (std::size_t second = first + 1U; second < kNodeCount; ++second) {
      const double chord = (coordinates[first] - coordinates[second]).Norm();
      if (!std::isfinite(chord)) {
        return Result<ValidatedGeometry>::Failure(
            Failure(category, input, code, "Surface chord is nonfinite."));
      }
      chord_length = (std::max)(chord_length, chord);
    }
  }
  if (!(chord_length > 0.0)) {
    return Result<ValidatedGeometry>::Failure(
        Failure(category, input, code, "Surface chord scale is zero."));
  }
  const double chord_squared = chord_length * chord_length;
  if (!std::isfinite(chord_squared)) {
    return Result<ValidatedGeometry>::Failure(
        Failure(category, input, code, "Surface chord scale is nonfinite."));
  }

  constexpr double kGauss = 0.57735026918962576450914878050196;
  constexpr std::array<std::array<double, 2>, 4> kGaussLocations{{
      {{-kGauss, -kGauss}},
      {{kGauss, -kGauss}},
      {{kGauss, kGauss}},
      {{-kGauss, kGauss}},
  }};
  constexpr std::array<std::array<double, 2>, 4> kCorners{{
      {{-1.0, -1.0}},
      {{1.0, -1.0}},
      {{1.0, 1.0}},
      {{-1.0, 1.0}},
  }};

  ValidatedGeometry result{};
  Vector3 mean_area{};
  for (std::size_t point = 0U; point < kGaussLocations.size(); ++point) {
    if (!EvaluateGeometry(coordinates, kGaussLocations[point][0U],
                          kGaussLocations[point][1U],
                          result.gauss_points[point])) {
      return Result<ValidatedGeometry>::Failure(Failure(
          category, input, code, "Surface geometry is nonfinite at Gauss point."));
    }
    mean_area = mean_area + result.gauss_points[point].area_vector;
  }
  mean_area = 0.25 * mean_area;
  const double mean_norm = mean_area.Norm();
  if (!mean_area.IsFinite() || !std::isfinite(mean_norm) ||
      !(mean_norm / chord_squared > kGeometryThreshold)) {
    return Result<ValidatedGeometry>::Failure(
        Failure(category, input, code,
                "Mean surface area is collapsed or below the geometry threshold."));
  }
  const Vector3 mean_normal = mean_area / mean_norm;
  if (!mean_normal.IsFinite()) {
    return Result<ValidatedGeometry>::Failure(
        Failure(category, input, code, "Mean surface normal is nonfinite."));
  }

  for (const auto& corner : kCorners) {
    GeometryData corner_geometry{};
    if (!EvaluateGeometry(coordinates, corner[0U], corner[1U],
                          corner_geometry)) {
      return Result<ValidatedGeometry>::Failure(
          Failure(category, input, code,
                  "Surface geometry is nonfinite at corner point."));
    }
    const double signed_scale =
        corner_geometry.area_vector.Dot(mean_normal) / chord_squared;
    if (!std::isfinite(signed_scale) ||
        !(signed_scale > kGeometryThreshold)) {
      return Result<ValidatedGeometry>::Failure(
          Failure(category, input, code,
                  "Surface orientation is invalid at corner point."));
    }
  }
  for (const auto& point : result.gauss_points) {
    const double signed_scale = point.area_vector.Dot(mean_normal) / chord_squared;
    if (!std::isfinite(signed_scale) ||
        !(signed_scale > kGeometryThreshold)) {
      return Result<ValidatedGeometry>::Failure(
          Failure(category, input, code,
                  "Surface orientation is invalid at Gauss point."));
    }
  }
  return Result<ValidatedGeometry>::Success(result);
}

/// @brief Returns one row-major entry of the cross-product matrix [value]_x.
double SkewEntry(const Vector3& value, const std::size_t row,
                 const std::size_t column) noexcept {
  constexpr std::array<std::array<int, 3>, 3> kSigns{{
      {{0, -1, 1}},
      {{1, 0, -1}},
      {{-1, 1, 0}},
  }};
  constexpr std::array<std::array<std::size_t, 3>, 3> kComponents{{
      {{0U, 2U, 1U}},
      {{2U, 0U, 0U}},
      {{1U, 0U, 0U}},
  }};
  const int sign = kSigns[row][column];
  if (sign == 0) {
    return 0.0;
  }
  return static_cast<double>(sign) * value[kComponents[row][column]];
}

}  // namespace

Result<ShellSurfacePressureContribution> EvaluateShellSurfacePressure(
    const ShellSurfacePressureInput& input) {
  if (!std::isfinite(input.pressure_magnitude) ||
      !std::isfinite(input.load_factor)) {
    return Result<ShellSurfacePressureContribution>::Failure(Failure(
        FailureCategory::kSolver, input, "nonfinite-pressure-contribution",
        "Pressure magnitude or load factor is nonfinite."));
  }
  const double pressure_factor = input.pressure_magnitude * input.load_factor;
  if (!std::isfinite(pressure_factor)) {
    return Result<ShellSurfacePressureContribution>::Failure(Failure(
        FailureCategory::kSolver, input, "nonfinite-pressure-contribution",
        "Pressure magnitude and load factor have a nonfinite product."));
  }

  std::array<Vector3, kNodeCount> coordinates{};
  if (!SelectCoordinates(input, coordinates)) {
    const FailureCategory category =
        input.configuration == SurfacePressureConfiguration::kReference
            ? FailureCategory::kModel
            : FailureCategory::kSolver;
    const std::string code =
        input.configuration == SurfacePressureConfiguration::kReference
            ? "invalid-reference-surface-geometry"
            : "invalid-current-surface-geometry";
    return Result<ShellSurfacePressureContribution>::Failure(
        Failure(category, input, code, "Surface coordinate is nonfinite."));
  }
  const auto geometry = ValidateGeometry(input, coordinates);
  if (!geometry.HasValue()) {
    return Result<ShellSurfacePressureContribution>::Failure(
        geometry.GetStatus());
  }

  ShellSurfacePressureContribution contribution{};
  if (pressure_factor == 0.0) {
    return Result<ShellSurfacePressureContribution>::Success(contribution);
  }
  const double side_multiplier =
      input.side == ShellSurfaceSide::kSpos ? 1.0 : -1.0;
  const double force_scale = -pressure_factor * side_multiplier;
  const double tangent_scale = pressure_factor * side_multiplier;
  for (const auto& point : geometry.Value().gauss_points) {
    for (std::size_t node = 0U; node < kNodeCount; ++node) {
      const Vector3 force_increment =
          force_scale * point.shape.values[node] * point.area_vector;
      if (!force_increment.IsFinite()) {
        return Result<ShellSurfacePressureContribution>::Failure(Failure(
            FailureCategory::kSolver, input, "nonfinite-pressure-contribution",
            "Pressure force integrand is nonfinite."));
      }
      const std::size_t row_offset = node * kDofsPerNode;
      for (std::size_t component = 0U; component < 3U; ++component) {
        contribution.force[row_offset + component] += force_increment[component];
        if (!std::isfinite(contribution.force[row_offset + component])) {
          return Result<ShellSurfacePressureContribution>::Failure(Failure(
              FailureCategory::kSolver, input, "nonfinite-pressure-contribution",
              "Accumulated pressure force is nonfinite."));
        }
      }
    }

    if (input.configuration == SurfacePressureConfiguration::kReference) {
      continue;
    }
    for (std::size_t row_node = 0U; row_node < kNodeCount; ++row_node) {
      for (std::size_t column_node = 0U; column_node < kNodeCount;
           ++column_node) {
        for (std::size_t row_component = 0U; row_component < 3U;
             ++row_component) {
          for (std::size_t column_component = 0U; column_component < 3U;
               ++column_component) {
            const double derivative =
                point.shape.xi_derivatives[column_node] *
                    SkewEntry(point.eta_tangent, row_component,
                              column_component) -
                point.shape.eta_derivatives[column_node] *
                    SkewEntry(point.xi_tangent, row_component,
                              column_component);
            const double tangent_increment =
                tangent_scale * point.shape.values[row_node] * derivative;
            const std::size_t index =
                (row_node * kDofsPerNode + row_component) * kDofCount +
                column_node * kDofsPerNode + column_component;
            contribution.external_tangent[index] += tangent_increment;
            if (!std::isfinite(contribution.external_tangent[index])) {
              return Result<ShellSurfacePressureContribution>::Failure(Failure(
                  FailureCategory::kSolver, input,
                  "nonfinite-pressure-tangent",
                  "Accumulated pressure tangent is nonfinite."));
            }
          }
        }
      }
    }
  }
  return Result<ShellSurfacePressureContribution>::Success(contribution);
}

}  // namespace fesa