/**
BSD 3-Clause License

This file is part of the Basalt project.
https://gitlab.com/VladyslavUsenko/basalt-headers.git

Copyright (c) 2019, Vladyslav Usenko and Nikolaus Demmel.
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@file
@brief Implementation of pinhole camera model
*/

#pragma once

#include <basalt/camera/camera_static_assert.hpp>

#include <basalt/utils/sophus_utils.hpp>

namespace basalt {

using std::sqrt;

/// @brief Pinhole camera model
///
/// This model has N=4 parameters \f$ \mathbf{i} = \left[f_x, f_y, c_x, c_y
/// \right]^T \f$ with. See \ref
/// project and \ref unproject functions for more details.
template <typename Scalar_ = double>
class PinholeCamera {
 public:
  using Scalar = Scalar_;
  static constexpr int N = 4;  ///< Number of intrinsic parameters.

  using Vec2 = Eigen::Matrix<Scalar, 2, 1>;
  using Vec4 = Eigen::Matrix<Scalar, 4, 1>;

  using VecN = Eigen::Matrix<Scalar, N, 1>;

  using Mat24 = Eigen::Matrix<Scalar, 2, 4>;
  using Mat2N = Eigen::Matrix<Scalar, 2, N>;

  using Mat42 = Eigen::Matrix<Scalar, 4, 2>;
  using Mat4N = Eigen::Matrix<Scalar, 4, N>;

  /// @brief Default constructor with zero intrinsics
  PinholeCamera() { param_.setZero(); }

  /// @brief Construct camera model with given vector of intrinsics
  ///
  /// @param[in] p vector of intrinsic parameters [fx, fy, cx, cy]
  explicit PinholeCamera(const VecN& p) { param_ = p; }

  /// @brief Cast to different scalar type
  template <class Scalar2>
  PinholeCamera<Scalar2> cast() const {
    return PinholeCamera<Scalar2>(param_.template cast<Scalar2>());
  }

  /// @brief Camera model name
  ///
  /// @return "pinhole"
  static std::string getName() { return "pinhole"; }

  /// @brief Project the point and optionally compute Jacobians
  ///
  /// Projection function is defined as follows:
  /// \f{align}{
  ///    \pi(\mathbf{x}, \mathbf{i}) &=
  ///    \begin{bmatrix}
  ///    f_x{\frac{x}{z}}
  ///    \\ f_y{\frac{y}{z}}
  ///    \\ \end{bmatrix}
  ///    +
  ///    \begin{bmatrix}
  ///    c_x
  ///    \\ c_y
  ///    \\ \end{bmatrix}.
  /// \f}
  /// A set of 3D points that results in valid projection is expressed as
  /// follows: \f{align}{
  ///    \Omega &= \{\mathbf{x} \in \mathbb{R}^3 ~|~ z > 0 \}
  /// \f}
  ///
  /// @param[in] p3d point to project
  /// @param[out] proj result of projection
  /// @param[out] d_proj_d_p3d if not nullptr computed Jacobian of projection
  /// with respect to p3d
  /// @param[out] d_proj_d_param point if not nullptr computed Jacobian of
  /// projection with respect to intrinsic parameters
  /// @return if projection is valid
  template <class DerivedPoint3D, class DerivedPoint2D,
            class DerivedJ3D = std::nullptr_t,
            class DerivedJparam = std::nullptr_t>
  inline bool project(const Eigen::MatrixBase<DerivedPoint3D>& p3d,
                      Eigen::MatrixBase<DerivedPoint2D>& proj,
                      DerivedJ3D d_proj_d_p3d = nullptr,
                      DerivedJparam d_proj_d_param = nullptr) const {
    checkProjectionDerivedTypes<DerivedPoint3D, DerivedPoint2D, DerivedJ3D,
                                DerivedJparam, N>();

    const typename EvalOrReference<DerivedPoint3D>::Type p3d_eval(p3d);

    const Scalar& fx = param_[0];
    const Scalar& fy = param_[1];
    const Scalar& cx = param_[2];
    const Scalar& cy = param_[3];

    const Scalar& x = p3d_eval[0];
    const Scalar& y = p3d_eval[1];
    const Scalar& z = p3d_eval[2];

    proj[0] = fx * x / z + cx;
    proj[1] = fy * y / z + cy;

    const bool is_valid = z >= Sophus::Constants<Scalar>::epsilonSqrt();

    if constexpr (!std::is_same_v<DerivedJ3D, std::nullptr_t>) {
      BASALT_ASSERT(d_proj_d_p3d);

      d_proj_d_p3d->setZero();
      const Scalar z2 = z * z;

      (*d_proj_d_p3d)(0, 0) = fx / z;
      (*d_proj_d_p3d)(0, 2) = -fx * x / z2;

      (*d_proj_d_p3d)(1, 1) = fy / z;
      (*d_proj_d_p3d)(1, 2) = -fy * y / z2;
    } else {
      UNUSED(d_proj_d_p3d);
    }

    if constexpr (!std::is_same_v<DerivedJparam, std::nullptr_t>) {
      BASALT_ASSERT(d_proj_d_param);
      d_proj_d_param->setZero();
      (*d_proj_d_param)(0, 0) = x / z;
      (*d_proj_d_param)(0, 2) = Scalar(1);
      (*d_proj_d_param)(1, 1) = y / z;
      (*d_proj_d_param)(1, 3) = Scalar(1);
    } else {
      UNUSED(d_proj_d_param);
    }

    return is_valid;
  }

  /// @brief Unproject the point and optionally compute Jacobians
  ///
  /// The unprojection function is computed as follows: \f{align}{
  ///    \pi^{-1}(\mathbf{u}, \mathbf{i}) &=
  ///    \frac{1}{m_x^2 + m_y^2 + 1}
  ///    \begin{bmatrix}
  ///    m_x \\ m_y \\ 1
  ///    \\ \end{bmatrix}
  ///    \\ m_x &= \frac{u - c_x}{f_x},
  ///    \\ m_y &= \frac{v - c_y}{f_y}.
  /// \f}
  ///
  ///
  /// @param[in] proj point to unproject
  /// @param[out] p3d result of unprojection
  /// @param[out] d_p3d_d_proj if not nullptr computed Jacobian of
  /// unprojection with respect to proj
  /// @param[out] d_p3d_d_param point if not nullptr computed Jacobian of
  /// unprojection with respect to intrinsic parameters
  /// @return if unprojection is valid
  template <class DerivedPoint2D, class DerivedPoint3D,
            class DerivedJ2D = std::nullptr_t,
            class DerivedJparam = std::nullptr_t>
  inline bool unproject(const Eigen::MatrixBase<DerivedPoint2D>& proj,
                        Eigen::MatrixBase<DerivedPoint3D>& p3d,
                        DerivedJ2D d_p3d_d_proj = nullptr,
                        DerivedJparam d_p3d_d_param = nullptr) const {
    checkUnprojectionDerivedTypes<DerivedPoint2D, DerivedPoint3D, DerivedJ2D,
                                  DerivedJparam, N>();

    const typename EvalOrReference<DerivedPoint2D>::Type proj_eval(proj);

    const Scalar& fx = param_[0];
    const Scalar& fy = param_[1];
    const Scalar& cx = param_[2];
    const Scalar& cy = param_[3];

    const Scalar mx = (proj_eval[0] - cx) / fx;
    const Scalar my = (proj_eval[1] - cy) / fy;

    const Scalar r2 = mx * mx + my * my;

    const Scalar norm = sqrt(Scalar(1) + r2);
    const Scalar norm_inv = Scalar(1) / norm;

    p3d.setZero();
    p3d[0] = mx * norm_inv;
    p3d[1] = my * norm_inv;
    p3d[2] = norm_inv;

    if constexpr (!std::is_same_v<DerivedJ2D, std::nullptr_t> ||
                  !std::is_same_v<DerivedJparam, std::nullptr_t>) {
      const Scalar d_norm_inv_d_r2 =
          -Scalar(0.5) * norm_inv * norm_inv * norm_inv;

      constexpr int SIZE_3D = DerivedPoint3D::SizeAtCompileTime;
      Eigen::Matrix<Scalar, SIZE_3D, 1> c0, c1;

      c0.setZero();
      c0(0) = (norm_inv + 2 * mx * mx * d_norm_inv_d_r2) / fx;
      c0(1) = (2 * my * mx * d_norm_inv_d_r2) / fx;
      c0(2) = 2 * mx * d_norm_inv_d_r2 / fx;

      c1.setZero();
      c1(0) = (2 * my * mx * d_norm_inv_d_r2) / fy;
      c1(1) = (norm_inv + 2 * my * my * d_norm_inv_d_r2) / fy;
      c1(2) = 2 * my * d_norm_inv_d_r2 / fy;

      if constexpr (!std::is_same_v<DerivedJ2D, std::nullptr_t>) {
        BASALT_ASSERT(d_p3d_d_proj);
        d_p3d_d_proj->col(0) = c0;
        d_p3d_d_proj->col(1) = c1;
      } else {
        UNUSED(d_p3d_d_proj);
      }

      if constexpr (!std::is_same_v<DerivedJparam, std::nullptr_t>) {
        BASALT_ASSERT(d_p3d_d_param);
        d_p3d_d_param->col(2) = -c0;
        d_p3d_d_param->col(3) = -c1;

        d_p3d_d_param->col(0) = -c0 * mx;
        d_p3d_d_param->col(1) = -c1 * my;
      } else {
        UNUSED(d_p3d_d_param);
      }
    } else {
      UNUSED(d_p3d_d_proj);
      UNUSED(d_p3d_d_param);
    }

    return true;
  }

  /// @brief Set parameters from initialization
  ///
  /// Initializes the camera model to  \f$ \left[f_x, f_y, c_x, c_y, \right]^T
  /// \f$
  ///
  /// @param[in] init vector [fx, fy, cx, cy]
  inline void setFromInit(const Vec4& init) {
    param_[0] = init[0];
    param_[1] = init[1];
    param_[2] = init[2];
    param_[3] = init[3];
  }

  /// @brief Increment intrinsic parameters by inc
  ///
  /// @param[in] inc increment vector
  void operator+=(const VecN& inc) { param_ += inc; }

  /// @brief Returns a const reference to the intrinsic parameters vector
  ///
  /// The order is following: \f$ \left[f_x, f_y, c_x, c_y, \right]^T \f$
  /// @return const reference to the intrinsic parameters vector
  const VecN& getParam() const { return param_; }

  /// @brief Projections used for unit-tests
  static Eigen::aligned_vector<PinholeCamera> getTestProjections() {
    Eigen::aligned_vector<PinholeCamera> res;

    VecN vec1;

    // Euroc
    vec1 << 460.76484651566468, 459.4051018049483, 365.8937161309615,
        249.33499869752445;
    res.emplace_back(vec1);

    // TUM VI 512
    vec1 << 191.14799816648748, 191.13150946585135, 254.95857715233118,
        256.8815466235898;
    res.emplace_back(vec1);

    return res;
  }

  /// @brief Resolutions used for unit-tests
  static Eigen::aligned_vector<Eigen::Vector2i> getTestResolutions() {
    Eigen::aligned_vector<Eigen::Vector2i> res;

    res.emplace_back(752, 480);
    res.emplace_back(512, 512);

    return res;
  }

  EIGEN_MAKE_ALIGNED_OPERATOR_NEW
 private:
  VecN param_;
};

}  // namespace basalt