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 // This file is part of the ACTS project.
 //
 // Copyright (C) 2016 CERN for the benefit of the ACTS project
 //
 // This Source Code Form is subject to the terms of the Mozilla Public
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at https://mozilla.org/MPL/2.0/.
 
 #pragma once
 
 #include "Acts/Definitions/Tolerance.hpp"
 #include "Acts/EventData/ParticleHypothesis.hpp"
 #include "Acts/EventData/TrackParameterHelpers.hpp"
 #include "Acts/EventData/TransformationHelpers.hpp"
 #include "Acts/EventData/detail/PrintParameters.hpp"
 #include "Acts/Surfaces/CurvilinearSurface.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Utilities/UnitVectors.hpp"
 #include "Acts/Utilities/detail/periodic.hpp"
 
 #include <cassert>
 #include <cmath>
 #include <memory>
 
 namespace Acts {
 
 /// Track parameters bound to a reference surface for a single track.
 ///
 /// This is intended as a user-facing data class that adds additional accessors
 /// and charge/momentum interpretation on top of the pure parameters vector. All
 /// parameters and their corresponding covariance matrix are stored in bound
 /// parametrization. The specific definition of the local spatial parameters is
 /// defined by the associated surface.
 ///
 /// @note This class holds shared ownership on its reference surface.
 class BoundTrackParameters {
  public:
   /// Type alias for bound parameters vector
   using ParametersVector = BoundVector;
   /// Type alias for covariance matrix
   using CovarianceMatrix = BoundMatrix;
 
   /// Factory to construct from four-position, direction, absolute momentum, and
   /// charge.
   ///
   /// @param geoCtx Geometry context for the local-to-global transformation
   /// @param surface Reference surface the parameters are defined on
   /// @param pos4 Track position/time four-vector
   /// @param dir Track direction three-vector; normalization is ignored
   /// @param qOverP Charge over momentum
   /// @param cov Bound parameters covariance matrix
   /// @param particleHypothesis Particle hypothesis
   /// @param tolerance Tolerance used for globalToLocal
   ///
   /// @return Result containing the constructed bound track parameters or error
   /// @note The returned result indicates whether the free parameters could
   /// successfully be converted to on-surface parameters.
   static Result<BoundTrackParameters> create(
       const GeometryContext& geoCtx, std::shared_ptr<const Surface> surface,
       const Vector4& pos4, const Vector3& dir, double qOverP,
       std::optional<BoundMatrix> cov, ParticleHypothesis particleHypothesis,
       double tolerance = s_onSurfaceTolerance) {
     Result<BoundVector> bound =
         transformFreeToBoundParameters(pos4.segment<3>(ePos0), pos4[eTime], dir,
                                        qOverP, *surface, geoCtx, tolerance);
 
     if (!bound.ok()) {
       return bound.error();
     }
 
     return BoundTrackParameters{std::move(surface), *bound, std::move(cov),
                                 particleHypothesis};
   }
 
   /// Construct from four-position, direction, and qOverP.
   ///
   /// @param pos4 Track position/time four-vector
   /// @param dir Track direction three-vector; normalization is ignored.
   /// @param qOverP Charge over momentum
   /// @param cov Curvilinear bound parameters covariance matrix
   /// @param particleHypothesis Particle hypothesis
   /// @return Curvilinear bound track parameters
   static BoundTrackParameters createCurvilinear(
       const Vector4& pos4, const Vector3& dir, double qOverP,
       std::optional<BoundMatrix> cov, ParticleHypothesis particleHypothesis) {
     return BoundTrackParameters(
         CurvilinearSurface(pos4.segment<3>(ePos0), dir).surface(),
         transformFreeToCurvilinearParameters(pos4[eTime], dir, qOverP),
         std::move(cov), particleHypothesis);
   }
 
   /// Construct from four-position, angles, and qOverP.
   ///
   /// @param pos4 Track position/time four-vector
   /// @param phi Transverse track direction angle
   /// @param theta Longitudinal track direction angle
   /// @param qOverP Charge over momentum
   /// @param cov Curvilinear bound parameters covariance matrix
   /// @param particleHypothesis Particle hypothesis
   /// @return Curvilinear bound track parameters
   static BoundTrackParameters createCurvilinear(
       const Vector4& pos4, double phi, double theta, double qOverP,
       std::optional<BoundMatrix> cov, ParticleHypothesis particleHypothesis) {
     return BoundTrackParameters(
         CurvilinearSurface(pos4.segment<3>(ePos0),
                            makeDirectionFromPhiTheta(phi, theta))
             .surface(),
         transformFreeToCurvilinearParameters(pos4[eTime], phi, theta, qOverP),
         std::move(cov), particleHypothesis);
   }
 
   /// Construct from a parameters vector on the surface and particle charge.
   ///
   /// @param surface Reference surface the parameters are defined on
   /// @param params Bound parameters vector
   /// @param cov Bound parameters covariance matrix
   /// @param particleHypothesis Particle hypothesis
   ///
   /// In principle, only the charge magnitude is needed her to allow unambiguous
   /// extraction of the absolute momentum. The particle charge is required as
   /// an input here to be consistent with the other constructors below that
   /// that also take the charge as an input. The charge sign is only used in
   /// debug builds to check for consistency with the q/p parameter.
   BoundTrackParameters(std::shared_ptr<const Surface> surface,
                        const BoundVector& params,
                        std::optional<BoundMatrix> cov,
                        ParticleHypothesis particleHypothesis)
       : m_params(params),
         m_cov(std::move(cov)),
         m_surface(std::move(surface)),
         m_particleHypothesis(particleHypothesis) {
     // TODO set `validateAngleRange` to `true` after fixing caller code
     assert(isBoundVectorValid(m_params, false) &&
            "Invalid bound parameters vector");
     assert(m_surface != nullptr && "Reference surface must not be null");
     normalizePhiTheta();
   }
 
   /// Convert this track parameter object to the general type-erased one
   /// @return Type-erased bound track parameters
   [[deprecated(
       "You already have a universal bound track parameter at hand. You can "
       "drop `toBound()`.")]]
   BoundTrackParameters toBound() const {
     return BoundTrackParameters{*this};
   }
 
   /// Parameters vector.
   /// @return Mutable reference to the parameters vector
   BoundVector& parameters() { return m_params; }
   /// Parameters vector.
   /// @return Const reference to the parameters vector
   const BoundVector& parameters() const { return m_params; }
   /// Vector of spatial impact parameters (i.e., d0 and z0)
   /// @return Two-dimensional vector of spatial impact parameters
   Vector2 spatialImpactParameters() const { return m_params.head<2>(); }
   /// Vector of spatial and temporal impact parameters (i.e., d0, z0, and t)
   /// @return Three-dimensional vector of impact parameters
   Vector3 impactParameters() const {
     Vector3 ip;
     ip.template head<2>() = m_params.template head<2>();
     ip(2) = m_params(eBoundTime);
     return ip;
   }
 
   /// Optional covariance matrix.
   /// @return Mutable reference to the optional covariance matrix
   std::optional<BoundMatrix>& covariance() { return m_cov; }
   /// Optional covariance matrix.
   /// @return Const reference to the optional covariance matrix
   const std::optional<BoundMatrix>& covariance() const { return m_cov; }
   /// Covariance matrix of the spatial impact parameters (i.e., of d0 and z0)
   /// @return Optional 2x2 covariance matrix of spatial impact parameters
   std::optional<SquareMatrix<2>> spatialImpactParameterCovariance() const {
     if (!m_cov.has_value()) {
       return std::nullopt;
     }
 
     return m_cov.value().template topLeftCorner<2, 2>();
   }
 
   /// Covariance matrix of the spatial and temporal impact parameters (i.e., of
   /// d0, z0, and t)
   /// @return Optional 3x3 covariance matrix of impact parameters
   std::optional<SquareMatrix<3>> impactParameterCovariance() const {
     if (!m_cov.has_value()) {
       return std::nullopt;
     }
 
     SquareMatrix<3> ipCov;
     ipCov.template topLeftCorner<2, 2>() =
         m_cov.value().template topLeftCorner<2, 2>();
     ipCov.template block<2, 1>(0, 2) =
         m_cov.value().template block<2, 1>(0, eBoundTime);
     ipCov.template block<1, 2>(2, 0) =
         m_cov.value().template block<1, 2>(eBoundTime, 0);
     ipCov(2, 2) = m_cov.value()(eBoundTime, eBoundTime);
     return ipCov;
   }
 
   /// Access a single parameter value identified by its index.
   ///
   /// @tparam kIndex Track parameter index
   /// @return The parameter value at the specified index
   template <BoundIndices kIndex>
   double get() const {
     return m_params[kIndex];
   }
 
   /// Local spatial position two-vector.
   /// @return Two-dimensional local position vector on the reference surface
   Vector2 localPosition() const { return m_params.segment<2>(eBoundLoc0); }
   /// Space-time position four-vector.
   ///
   /// @param[in] geoCtx Geometry context for the local-to-global
   /// transformation
   ///
   /// @return Four-dimensional position vector (x, y, z, t) in global coordinates
   ///
   /// This uses the associated surface to transform the local position on
   /// the surface to globalcoordinates. This requires a geometry context to
   /// select the appropriate transformation and might be a computationally
   /// expensive operation.
   Vector4 fourPosition(const GeometryContext& geoCtx) const {
     Vector4 pos4;
     pos4.segment<3>(ePos0) =
         m_surface->localToGlobal(geoCtx, localPosition(), direction());
     pos4[eTime] = m_params[eBoundTime];
     return pos4;
   }
   /// Spatial position three-vector.
   ///
   /// @param[in] geoCtx Geometry context for the local-to-global
   /// transformation
   ///
   /// @return Three-dimensional position vector in global coordinates
   ///
   /// This uses the associated surface to transform the local position on
   /// the surface to globalcoordinates. This requires a geometry context to
   /// select the appropriate transformation and might be a computationally
   /// expensive operation.
   Vector3 position(const GeometryContext& geoCtx) const {
     return m_surface->localToGlobal(geoCtx, localPosition(), direction());
   }
   /// Time coordinate.
   /// @return The time coordinate value
   double time() const { return m_params[eBoundTime]; }
 
   /// Phi direction.
   /// @return The azimuthal angle phi in radians
   double phi() const { return m_params[eBoundPhi]; }
   /// Theta direction.
   /// @return The polar angle theta in radians
   double theta() const { return m_params[eBoundTheta]; }
   /// Charge over momentum.
   /// @return The charge over momentum ratio
   double qOverP() const { return m_params[eBoundQOverP]; }
 
   /// Unit direction three-vector, i.e. the normalized momentum
   /// three-vector.
   /// @return Normalized direction vector
   Vector3 direction() const {
     return makeDirectionFromPhiTheta(m_params[eBoundPhi],
                                      m_params[eBoundTheta]);
   }
   /// Absolute momentum.
   /// @return The absolute momentum magnitude
   double absoluteMomentum() const {
     return m_particleHypothesis.extractMomentum(m_params[eBoundQOverP]);
   }
   /// Transverse momentum.
   /// @return The transverse momentum magnitude
   double transverseMomentum() const {
     return std::sin(m_params[eBoundTheta]) * absoluteMomentum();
   }
   /// Momentum three-vector.
   /// @return Three-dimensional momentum vector
   Vector3 momentum() const { return absoluteMomentum() * direction(); }
 
   /// Particle electric charge.
   /// @return The particle electric charge
   double charge() const {
     return m_particleHypothesis.extractCharge(get<eBoundQOverP>());
   }
 
   /// Particle hypothesis.
   /// @return Reference to the particle hypothesis
   const ParticleHypothesis& particleHypothesis() const {
     return m_particleHypothesis;
   }
 
   /// Reference surface onto which the parameters are bound.
   /// @return Reference to the bound reference surface
   const Surface& referenceSurface() const { return *m_surface; }
   /// Reference frame in which the local error is defined.
   ///
   /// @param[in] geoCtx Geometry context for the local-to-global
   /// transformation
   ///
   /// @return The reference frame rotation matrix
   ///
   /// For planar surfaces, this is the transformation local-to-global
   /// rotation matrix. For non-planar surfaces, it is the local-to-global
   /// rotation matrix of the tangential plane at the track position.
   RotationMatrix3 referenceFrame(const GeometryContext& geoCtx) const {
     return m_surface->referenceFrame(geoCtx, position(geoCtx), momentum());
   }
 
   /// Reflect the parameters in place.
   void reflectInPlace() { m_params = reflectBoundParameters(m_params); }
 
   /// Reflect the parameters.
   /// @return Reflected parameters.
   BoundTrackParameters reflect() const {
     BoundTrackParameters reflected = *this;
     reflected.reflectInPlace();
     return reflected;
   }
 
  private:
   BoundVector m_params;
   std::optional<BoundMatrix> m_cov;
   /// reference surface
   std::shared_ptr<const Surface> m_surface;
   // TODO use [[no_unique_address]] once we switch to C++20
   ParticleHypothesis m_particleHypothesis;
 
   /// Ensure phi and theta angles are within bounds.
   void normalizePhiTheta() {
     auto [phi, theta] =
         detail::normalizePhiTheta(m_params[eBoundPhi], m_params[eBoundTheta]);
     m_params[eBoundPhi] = phi;
     m_params[eBoundTheta] = theta;
   }
 
   /// Compare two bound track parameters for bitwise equality.
   ///
   /// @note Comparing track parameters for bitwise equality is not a good
   /// idea.
   ///   Depending on the context you might want to compare only the
   ///   parameter values, or compare them for compatibility instead of
   ///   equality; you might also have different (floating point) thresholds
   ///   of equality in different contexts. None of that can be handled by
   ///   this operator. Users should think really hard if this is what they
   ///   want and we might decided that we will remove this in the future.
   friend bool operator==(const BoundTrackParameters& lhs,
                          const BoundTrackParameters& rhs) = default;
 
   /// Print information to the output stream.
   friend std::ostream& operator<<(std::ostream& os,
                                   const BoundTrackParameters& tp) {
     detail::printBoundParameters(
         os, tp.referenceSurface(), tp.particleHypothesis(), tp.parameters(),
         tp.covariance().has_value() ? &tp.covariance().value() : nullptr);
     return os;
   }
 };
 
 }  // namespace Acts

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