/**
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Copyright (c) 2019, Vladyslav Usenko and Nikolaus Demmel.
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@file
@brief Helper for implementing Lie group and Euclidean b-splines in ceres.
*/

#pragma once

#include <basalt/spline/spline_common.h>
#include <Eigen/Dense>

namespace basalt {

/// @brief Helper for implementing Lie group and Euclidean b-splines in ceres of
/// order N
///
/// See [[arXiv:1911.08860]](https://arxiv.org/abs/1911.08860) for more details.
template <int _N>
struct CeresSplineHelper {
  static constexpr int N = _N;        // Order of the spline.
  static constexpr int DEG = _N - 1;  // Degree of the spline.

  using MatN = Eigen::Matrix<double, _N, _N>;
  using VecN = Eigen::Matrix<double, _N, 1>;

  static const MatN blending_matrix_;
  static const MatN cumulative_blending_matrix_;
  static const MatN base_coefficients_;

  /// @brief Vector of derivatives of time polynomial.
  ///
  /// Computes a derivative of \f$ \begin{bmatrix}1 & t & t^2 & \dots &
  /// t^{N-1}\end{bmatrix} \f$ with repect to time. For example, the first
  /// derivative would be \f$ \begin{bmatrix}0 & 1 & 2 t & \dots & (N-1)
  /// t^{N-2}\end{bmatrix} \f$.
  /// @param Derivative derivative to evaluate
  /// @param[out] res_const vector to store the result
  /// @param[in] t
  template <int Derivative, class Derived>
  static inline void baseCoeffsWithTime(
      const Eigen::MatrixBase<Derived>& res_const, double t) {
    EIGEN_STATIC_ASSERT_VECTOR_SPECIFIC_SIZE(Derived, N);
    Eigen::MatrixBase<Derived>& res =
        const_cast<Eigen::MatrixBase<Derived>&>(res_const);

    res.setZero();

    if (Derivative < N) {
      res[Derivative] = base_coefficients_(Derivative, Derivative);

      double _t = t;
      for (int j = Derivative + 1; j < N; j++) {
        res[j] = base_coefficients_(Derivative, j) * _t;
        _t = _t * t;
      }
    }
  }

  /// @brief Evaluate Lie group cummulative B-spline and time derivatives.
  ///
  /// @param[in] sKnots array of pointers of the spline knots. The size of each
  /// knot should be GroupT::num_parameters: 4 for SO(3) and 7 for SE(3).
  /// @param[in] u normalized time to compute value of the spline
  /// @param[in] inv_dt inverse of the time spacing in seconds between spline
  /// knots
  /// @param[out] transform_out if not nullptr return the value of the spline
  /// @param[out] vel_out if not nullptr velocity (first time derivative) in the
  /// body frame
  /// @param[out] accel_out if not nullptr acceleration (second time derivative)
  /// in the body frame
  template <class T, template <class> class GroupT>
  static inline void evaluate_lie(
      T const* const* sKnots, const double u, const double inv_dt,
      GroupT<T>* transform_out = nullptr,
      typename GroupT<T>::Tangent* vel_out = nullptr,
      typename GroupT<T>::Tangent* accel_out = nullptr,
      typename GroupT<T>::Tangent* jerk_out = nullptr) {
    using Group = GroupT<T>;
    using Tangent = typename GroupT<T>::Tangent;
    using Adjoint = typename GroupT<T>::Adjoint;

    VecN p, coeff, dcoeff, ddcoeff, dddcoeff;

    CeresSplineHelper<N>::template baseCoeffsWithTime<0>(p, u);
    coeff = CeresSplineHelper<N>::cumulative_blending_matrix_ * p;

    if (vel_out || accel_out || jerk_out) {
      CeresSplineHelper<N>::template baseCoeffsWithTime<1>(p, u);
      dcoeff = inv_dt * CeresSplineHelper<N>::cumulative_blending_matrix_ * p;

      if (accel_out || jerk_out) {
        CeresSplineHelper<N>::template baseCoeffsWithTime<2>(p, u);
        ddcoeff = inv_dt * inv_dt *
                  CeresSplineHelper<N>::cumulative_blending_matrix_ * p;

        if (jerk_out) {
          CeresSplineHelper<N>::template baseCoeffsWithTime<3>(p, u);
          dddcoeff = inv_dt * inv_dt * inv_dt *
                     CeresSplineHelper<N>::cumulative_blending_matrix_ * p;
        }
      }
    }

    if (transform_out) {
      Eigen::Map<Group const> const p00(sKnots[0]);
      *transform_out = p00;
    }

    Tangent rot_vel, rot_accel, rot_jerk;

    if (vel_out || accel_out || jerk_out) rot_vel.setZero();
    if (accel_out || jerk_out) rot_accel.setZero();
    if (jerk_out) rot_jerk.setZero();

    for (int i = 0; i < DEG; i++) {
      Eigen::Map<Group const> const p0(sKnots[i]);
      Eigen::Map<Group const> const p1(sKnots[i + 1]);

      Group r01 = p0.inverse() * p1;
      Tangent delta = r01.log();

      Group exp_kdelta = Group::exp(delta * coeff[i + 1]);

      if (transform_out) (*transform_out) *= exp_kdelta;

      if (vel_out || accel_out || jerk_out) {
        Adjoint A = exp_kdelta.inverse().Adj();

        rot_vel = A * rot_vel;
        Tangent rot_vel_current = delta * dcoeff[i + 1];
        rot_vel += rot_vel_current;

        if (accel_out || jerk_out) {
          rot_accel = A * rot_accel;
          Tangent accel_lie_bracket =
              Group::lieBracket(rot_vel, rot_vel_current);
          rot_accel += ddcoeff[i + 1] * delta + accel_lie_bracket;

          if (jerk_out) {
            rot_jerk = A * rot_jerk;
            rot_jerk += dddcoeff[i + 1] * delta +
                        Group::lieBracket(ddcoeff[i + 1] * rot_vel +
                                              2 * dcoeff[i + 1] * rot_accel -
                                              dcoeff[i + 1] * accel_lie_bracket,
                                          delta);
          }
        }
      }
    }

    if (vel_out) *vel_out = rot_vel;
    if (accel_out) *accel_out = rot_accel;
    if (jerk_out) *jerk_out = rot_jerk;
  }

  /// @brief Evaluate Euclidean B-spline or time derivatives.
  ///
  /// @param[in] sKnots array of pointers of the spline knots. The size of each
  /// knot should be DIM.
  /// @param[in] u normalized time to compute value of the spline
  /// @param[in] inv_dt inverse of the time spacing in seconds between spline
  /// knots
  /// @param[out] vec_out if DERIV=0 returns value of the spline, otherwise
  /// corresponding derivative.
  template <class T, int DIM, int DERIV>
  static inline void evaluate(T const* const* sKnots, const double u,
                              const double inv_dt,
                              Eigen::Matrix<T, DIM, 1>* vec_out) {
    if (!vec_out) return;

    using VecD = Eigen::Matrix<T, DIM, 1>;

    VecN p, coeff;

    CeresSplineHelper<N>::template baseCoeffsWithTime<DERIV>(p, u);
    coeff =
        std::pow(inv_dt, DERIV) * CeresSplineHelper<N>::blending_matrix_ * p;

    vec_out->setZero();

    for (int i = 0; i < N; i++) {
      Eigen::Map<VecD const> const p(sKnots[i]);

      (*vec_out) += coeff[i] * p;
    }
  }
};

template <int _N>
const typename CeresSplineHelper<_N>::MatN
    CeresSplineHelper<_N>::base_coefficients_ =
        basalt::computeBaseCoefficients<_N, double>();

template <int _N>
const typename CeresSplineHelper<_N>::MatN
    CeresSplineHelper<_N>::blending_matrix_ =
        basalt::computeBlendingMatrix<_N, double, false>();

template <int _N>
const typename CeresSplineHelper<_N>::MatN
    CeresSplineHelper<_N>::cumulative_blending_matrix_ =
        basalt::computeBlendingMatrix<_N, double, true>();

}  // namespace basalt