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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/Algebra.hpp"
 #include "Acts/Geometry/GeometryContext.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Utilities/AnyGridView.hpp"
 #include "Acts/Utilities/AxisDefinitions.hpp"
 #include "Acts/Utilities/Grid.hpp"
 #include "Acts/Utilities/IAxis.hpp"
 
 #include <iostream>
 #include <type_traits>
 #include <vector>
 
 namespace Acts {
 
 using SurfaceVector = std::vector<const Surface*>;
 
 /// @brief Provides Surface binning in N dimensions
 ///
 /// Uses @c Grid under the hood to implement the storage and lookup
 /// Contains a lookup struct which talks to the @c Grid
 /// and performs utility actions. This struct needs to be initialised
 /// externally and passed to @c SurfaceArray on construction.
 class SurfaceArray {
  public:
   /// @brief Base interface for all surface lookups.
   struct ISurfaceGridLookup {
     /// @brief Fill provided surfaces into the contained @c Grid.
     /// @param gctx The current geometry context object, e.g. alignment
 
     /// @param surfaces Input surface pointers
     virtual void fill(const GeometryContext& gctx,
                       const SurfaceVector& surfaces) = 0;
 
     /// @brief Attempts to fix sub-optimal binning by filling closest
     ///        Surfaces into empty bin
     ///
     /// @param gctx The current geometry context object, e.g. alignment
 
     /// @param surfaces The surface pointers to fill
     /// @return number of bins that were filled
     virtual std::size_t completeBinning(const GeometryContext& gctx,
                                         const SurfaceVector& surfaces) = 0;
 
     /// @brief Performs lookup at @c pos and returns bin content as reference
     /// @param position Lookup position
     /// @return @c SurfaceVector at given bin
     virtual SurfaceVector& lookup(const Vector3& position) = 0;
 
     /// @brief Performs lookup at @c pos and returns bin content as const
     /// reference
     /// @param position Lookup position
     /// @return @c SurfaceVector at given bin
     virtual const SurfaceVector& lookup(const Vector3& position) const = 0;
 
     /// @brief Performs lookup at global bin and returns bin content as
     /// reference
     /// @param bin Global lookup bin
     /// @return @c SurfaceVector at given bin
     virtual SurfaceVector& lookup(std::size_t bin) = 0;
 
     /// @brief Performs lookup at global bin and returns bin content as const
     /// reference
     /// @param bin Global lookup bin
     /// @return @c SurfaceVector at given bin
     virtual const SurfaceVector& lookup(std::size_t bin) const = 0;
 
     /// @brief Performs a lookup at @c pos, but returns neighbors as well
     ///
     /// @param position Lookup position
     /// @return @c SurfaceVector at given bin. Copy of all bins selected
     virtual const SurfaceVector& neighbors(const Vector3& position) const = 0;
 
     /// @brief Returns the total size of the grid (including under/overflow
     /// bins)
     /// @return Size of the grid data structure
     virtual std::size_t size() const = 0;
 
     /// @brief Gets the center position of bin @c bin in global coordinates
     /// @param bin the global bin index
     /// @return The bin center
     virtual Vector3 getBinCenter(std::size_t bin) const = 0;
 
     /// @brief Returns copies of the axes used in the grid as @c AnyAxis
     /// @return The axes
     /// @note This returns copies. Use for introspection and querying.
     virtual std::vector<const IAxis*> getAxes() const = 0;
 
     virtual std::optional<AnyGridConstView<SurfaceVector>> getGridView()
         const = 0;
 
     virtual const Transform3& getTransform() const = 0;
 
     virtual Surface::SurfaceType surfaceType() const = 0;
 
     /// @brief Get the number of dimensions of the grid.
     /// @return number of dimensions
     virtual std::size_t dimensions() const = 0;
 
     /// @brief Checks if global bin is valid
     /// @param bin the global bin index
     /// @return bool if the bin is valid
     /// @note Valid means that the index points to a bin which is not a under
     ///       or overflow bin or out of range in any axis.
     virtual bool isValidBin(std::size_t bin) const = 0;
 
     /// @brief The binning values described by this surface grid lookup
     /// They are in order of the axes (optional) and empty for eingle lookups
     virtual std::vector<AxisDirection> binningValues() const { return {}; };
 
     /// Pure virtual destructor
     virtual ~ISurfaceGridLookup() = 0;
   };
 
   /// @brief Lookup helper which encapsulates a @c Grid
   /// @tparam Axes The axes used for the grid
   template <class... Axes>
   struct SurfaceGridLookup : ISurfaceGridLookup {
     static constexpr std::size_t DIM = sizeof...(Axes);
 
    public:
     /// @brief Specifies the local coordinate type.
     /// This resolves to @c ActsVector<DIM> for DIM > 1, else @c
     /// std::array<double, 1>
     using point_t =
         std::conditional_t<DIM == 1, std::array<double, 1>, ActsVector<DIM>>;
     using Grid_t = Grid<SurfaceVector, Axes...>;
 
     /// @brief Default constructor
     ///
     /// @param type The surface type, this determines the local to global calculation
     /// @param transform The transform to apply to the surface`
     /// @param R the radius (interpretation depends on @p type)
     /// @param Z the z position (interpretation depends on @p type)
     /// @param axes The axes to build the grid data structure.
     /// @param bValues What the axes represent (optional)
     /// @note Signature of localToGlobal and globalToLocal depends on @c DIM.
     ///       If DIM > 1, local coords are @c ActsVector<DIM> else
     ///       @c std::array<double, 1>.
     SurfaceGridLookup(Surface::SurfaceType type, const Transform3& transform,
                       double R, double Z, std::tuple<Axes...> axes,
                       std::vector<AxisDirection> bValues = {})
         : m_type(type),
           m_transform(transform),
           m_itransform(transform.inverse()),
           m_grid(std::move(axes)),
           m_binValues(std::move(bValues)) {
       m_neighborMap.resize(m_grid.size());
 
       using namespace VectorHelpers;
 
       switch (type) {
         using enum Surface::SurfaceType;
         case Cylinder:
           m_globalToLocal = [](const Vector3& pos) {
             return Vector2(phi(pos), pos.z());
           };
           m_localToGlobal = [R](const Vector2& loc) {
             // Technically, this is not correct, the radius is arbitrary
             return Vector3(R * std::cos(loc[0]), R * std::sin(loc[0]), loc[1]);
           };
           break;
         case Disc:
           m_globalToLocal = [](const Vector3& pos) {
             return Vector2(perp(pos), phi(pos));
           };
           m_localToGlobal = [Z](const Vector2& loc) {
             // Technically, this is not correct, the z position is arbitrary
             return Vector3(loc[0] * std::cos(loc[1]), loc[0] * std::sin(loc[1]),
                            Z);
           };
           break;
         case Plane:
           m_globalToLocal = [](const Vector3& pos) {
             return Vector2(perp(pos), phi(pos));
           };
           m_localToGlobal = [](const Vector2& loc) {
             return Vector3(loc.x(), loc.y(), 0.);
           };
           break;
         default:
           throw std::invalid_argument("Surface type not supported");
       }
     }
 
     /// @brief Fill provided surfaces into the contained @c Grid.
     ///
     /// This is done by iterating, accessing the referencePosition, lookup
     /// and append.
     /// Also populates the neighbor map by combining the filled bins of
     /// all bins around a given one.
     ///
     /// @param gctx The current geometry context object, e.g. alignment
     /// @param surfaces Input surface pointers
     void fill(const GeometryContext& gctx,
               const SurfaceVector& surfaces) override {
       for (const auto& srf : surfaces) {
         Vector3 pos = srf->referencePosition(gctx, AxisDirection::AxisR);
         lookup(pos).push_back(srf);
       }
 
       populateNeighborCache();
     }
 
     /// @brief Attempts to fix sub-optimal binning by filling closest
     ///        Surfaces into empty bins
     /// @note This does not always do what you want.
     ///
     /// @param gctx The current geometry context object, e.g. alignment
     /// @param surfaces The surface pointers to fill
     /// @return number of bins that were filled
     std::size_t completeBinning(const GeometryContext& gctx,
                                 const SurfaceVector& surfaces) override {
       std::size_t binCompleted = 0;
       std::size_t nBins = size();
       double minPath = 0;
       double curPath = 0;
       const Surface* minSrf = nullptr;
 
       for (std::size_t b = 0; b < nBins; ++b) {
         if (!isValidBin(b)) {
           continue;
         }
         std::vector<const Surface*>& binContent = lookup(b);
         // only complete if we have an empty bin
         if (!binContent.empty()) {
           continue;
         }
 
         Vector3 binCtr = getBinCenter(b);
         minPath = std::numeric_limits<double>::max();
         for (const auto& srf : surfaces) {
           curPath =
               (binCtr - srf->referencePosition(gctx, AxisDirection::AxisR))
                   .norm();
 
           if (curPath < minPath) {
             minPath = curPath;
             minSrf = srf;
           }
         }
 
         binContent.push_back(minSrf);
         ++binCompleted;
       }
 
       // recreate neighborcache
       populateNeighborCache();
       return binCompleted;
     }
 
     /// @brief Performs lookup at @c pos and returns bin content as reference
     /// @param position Lookup position
     /// @return @c SurfaceVector at given bin
     SurfaceVector& lookup(const Vector3& position) override {
       return m_grid.atPosition(m_globalToLocal(m_transform * position));
     }
 
     /// @brief Performs lookup at @c pos and returns bin content as const
     /// reference
     /// @param position Lookup position
     /// @return @c SurfaceVector at given bin
     const SurfaceVector& lookup(const Vector3& position) const override {
       return m_grid.atPosition(m_globalToLocal(m_transform * position));
     }
 
     /// @brief Performs lookup at global bin and returns bin content as
     /// reference
     /// @param bin Global lookup bin
     /// @return @c SurfaceVector at given bin
     SurfaceVector& lookup(std::size_t bin) override { return m_grid.at(bin); }
 
     /// @brief Performs lookup at global bin and returns bin content as const
     /// reference
     /// @param bin Global lookup bin
     /// @return @c SurfaceVector at given bin
     const SurfaceVector& lookup(std::size_t bin) const override {
       return m_grid.at(bin);
     }
 
     /// @brief Performs a lookup at @c pos, but returns neighbors as well
     ///
     /// @param position Lookup position
     /// @return @c SurfaceVector at given bin. Copy of all bins selected
     const SurfaceVector& neighbors(const Vector3& position) const override {
       auto lposition = m_globalToLocal(m_transform * position);
       return m_neighborMap.at(m_grid.globalBinFromPosition(lposition));
     }
 
     /// @brief Returns the total size of the grid (including under/overflow
     /// bins)
     /// @return Size of the grid data structure
     std::size_t size() const override { return m_grid.size(); }
 
     /// @brief The binning values described by this surface grid lookup
     /// They are in order of the axes
     std::vector<AxisDirection> binningValues() const override {
       return m_binValues;
     }
 
     /// @brief Gets the center position of bin @c bin in global coordinates
     /// @param bin the global bin index
     /// @return The bin center
     Vector3 getBinCenter(std::size_t bin) const override {
       return getBinCenterImpl(bin);
     }
 
     /// @brief Returns copies of the axes used in the grid as @c AnyAxis
     /// @return The axes
     /// @note This returns copies. Use for introspection and querying.
     std::vector<const IAxis*> getAxes() const override {
       auto arr = m_grid.axes();
       return std::vector<const IAxis*>(arr.begin(), arr.end());
     }
 
     std::optional<AnyGridConstView<SurfaceVector>> getGridView()
         const override {
       return AnyGridConstView<SurfaceVector>{m_grid};
     }
 
     const Transform3& getTransform() const override { return m_transform; }
 
     Surface::SurfaceType surfaceType() const override { return m_type; }
 
     /// @brief Get the number of dimensions of the grid.
     /// @return number of dimensions
     std::size_t dimensions() const override { return DIM; }
 
     /// @brief Checks if global bin is valid
     /// @param bin the global bin index
     /// @return bool if the bin is valid
     /// @note Valid means that the index points to a bin which is not a under
     ///       or overflow bin or out of range in any axis.
     bool isValidBin(std::size_t bin) const override {
       std::array<std::size_t, DIM> indices = m_grid.localBinsFromGlobalBin(bin);
       std::array<std::size_t, DIM> nBins = m_grid.numLocalBins();
       for (std::size_t i = 0; i < indices.size(); ++i) {
         std::size_t idx = indices.at(i);
         if (idx <= 0 || idx >= nBins.at(i) + 1) {
           return false;
         }
       }
 
       return true;
     }
 
    private:
     void populateNeighborCache() {
       // calculate neighbors for every bin and store in map
       for (std::size_t i = 0; i < m_grid.size(); i++) {
         if (!isValidBin(i)) {
           continue;
         }
         typename Grid_t::index_t loc = m_grid.localBinsFromGlobalBin(i);
         auto neighborIdxs = m_grid.neighborHoodIndices(loc, 1u);
         std::vector<const Surface*>& neighbors = m_neighborMap.at(i);
         neighbors.clear();
 
         for (const auto idx : neighborIdxs) {
           const std::vector<const Surface*>& binContent = m_grid.at(idx);
           std::copy(binContent.begin(), binContent.end(),
                     std::back_inserter(neighbors));
         }
       }
     }
 
     /// Internal method.
     /// This is here, because apparently Eigen doesn't like Vector1.
     /// So SurfaceGridLookup internally uses std::array<double, 1> instead
     /// of Vector1 (see the point_t typedef). This needs to be switched here,
     /// so as not to
     /// attempt an initialization of Vector1 that Eigen will complain about.
     /// The SFINAE is hidden in this private method so the public
     /// interface stays the same, since we don't care what happens
     /// here on the callers end
     /// This is the version for DIM>1
     Vector3 getBinCenterImpl(std::size_t bin) const
       requires(DIM != 1)
     {
       return m_itransform *
              m_localToGlobal(ActsVector<DIM>(
                  m_grid.binCenter(m_grid.localBinsFromGlobalBin(bin)).data()));
     }
 
     /// Internal method, see above.
     /// This is the version for DIM==1
     Vector3 getBinCenterImpl(std::size_t bin) const
       requires(DIM == 1)
     {
       point_t pos = m_grid.binCenter(m_grid.localBinsFromGlobalBin(bin));
       return m_itransform * m_localToGlobal(pos);
     }
 
     Surface::SurfaceType m_type;
     Transform3 m_transform;
     Transform3 m_itransform;
     std::function<point_t(const Vector3&)> m_globalToLocal;
     std::function<Vector3(const point_t&)> m_localToGlobal;
     Grid_t m_grid;
     std::vector<AxisDirection> m_binValues;
     std::vector<SurfaceVector> m_neighborMap;
   };
 
   /// @brief Lookup implementation which wraps one element and always returns
   ///        this element when lookup is called
   struct SingleElementLookup : ISurfaceGridLookup {
     /// @brief Default constructor.
     /// @param element the one and only element.
     explicit SingleElementLookup(SurfaceVector::value_type element)
         : m_element({element}) {}
 
     /// @brief Default constructor.
     /// @param elements the surfaces that are provided through a single lookup
     explicit SingleElementLookup(const SurfaceVector& elements)
         : m_element(elements) {}
 
     /// @brief Lookup, always returns @c element
     /// @return reference to vector containing only @c element
     SurfaceVector& lookup(const Vector3& /*position*/) override {
       return m_element;
     }
 
     /// @brief Lookup, always returns @c element
     /// @return reference to vector containing only @c element
     const SurfaceVector& lookup(const Vector3& /*position*/) const override {
       return m_element;
     }
 
     /// @brief Lookup, always returns @c element
     /// @return reference to vector containing only @c element
     SurfaceVector& lookup(std::size_t /*bin*/) override { return m_element; }
 
     /// @brief Lookup, always returns @c element
     /// @return reference to vector containing only @c element
     const SurfaceVector& lookup(std::size_t /*bin*/) const override {
       return m_element;
     }
 
     /// @brief Lookup, always returns @c element
     /// @return reference to vector containing only @c element
     const SurfaceVector& neighbors(const Vector3& /*position*/) const override {
       return m_element;
     }
 
     /// @brief returns 1
     /// @return 1
     std::size_t size() const override { return 1; }
 
     /// @brief Gets the bin center, but always returns (0, 0, 0)
     /// @return (0, 0, 0)
     Vector3 getBinCenter(std::size_t /*bin*/) const override {
       return Vector3(0, 0, 0);
     }
 
     /// @brief Returns an empty vector of @c AnyAxis
     /// @return empty vector
     std::vector<const IAxis*> getAxes() const override { return {}; }
 
     std::optional<AnyGridConstView<SurfaceVector>> getGridView()
         const override {
       return std::nullopt;
     }
 
     const Transform3& getTransform() const override {
       static const Transform3 identityTransform = Transform3::Identity();
       return identityTransform;
     }
 
     Surface::SurfaceType surfaceType() const override {
       return Surface::SurfaceType::Other;
     }
 
     /// @brief Get the number of dimensions
     /// @return always 0
     std::size_t dimensions() const override { return 0; }
 
     /// @brief Comply with concept and provide fill method
     /// @note Does nothing
     void fill(const GeometryContext& /*gctx*/,
               const SurfaceVector& /*surfaces*/) override {}
 
     /// @brief Comply with concept and provide completeBinning method
     /// @note Does nothing
     std::size_t completeBinning(const GeometryContext& /*gctx*/,
                                 const SurfaceVector& /*surfaces*/) override {
       return 0;
     }
 
     /// @brief Returns if the bin is valid (it is)
     /// @return always true
     bool isValidBin(std::size_t /*bin*/) const override { return true; }
 
    private:
     SurfaceVector m_element;
   };
 
   /// @brief Default constructor which takes a @c SurfaceLookup and a vector of
   /// surfaces
   /// @param gridLookup The grid storage. @c SurfaceArray does not fill it on
   /// its own
   /// @param surfaces The input vector of surfaces. This is only for
   /// bookkeeping, so we can ask
   /// @param transform Optional additional transform for this SurfaceArray
   explicit SurfaceArray(std::unique_ptr<ISurfaceGridLookup> gridLookup,
                         std::vector<std::shared_ptr<const Surface>> surfaces,
                         const Transform3& transform = Transform3::Identity());
 
   /// @brief Constructor with a single surface
   /// @param srf The one and only surface
   explicit SurfaceArray(std::shared_ptr<const Surface> srf);
 
   /// @brief Get all surfaces in bin given by position.
   /// @param position the lookup position
   /// @return reference to @c SurfaceVector contained in bin at that position
   SurfaceVector& at(const Vector3& position) {
     return p_gridLookup->lookup(position);
   }
 
   /// @brief Get all surfaces in bin given by position @p pos.
   /// @param position the lookup position
   /// @return const reference to @c SurfaceVector contained in bin at that
   /// position
   const SurfaceVector& at(const Vector3& position) const {
     return p_gridLookup->lookup(position);
   }
 
   /// @brief Get all surfaces in bin given by global bin index @p bin.
   /// @param bin the global bin index
   /// @return reference to @c SurfaceVector contained in bin
   SurfaceVector& at(std::size_t bin) { return p_gridLookup->lookup(bin); }
 
   /// @brief Get all surfaces in bin given by global bin index.
   /// @param bin the global bin index
   /// @return const reference to @c SurfaceVector contained in bin
   const SurfaceVector& at(std::size_t bin) const {
     return p_gridLookup->lookup(bin);
   }
 
   /// @brief Get all surfaces in bin at @p pos and its neighbors
   /// @param position The position to lookup as nominal
   /// @return Merged @c SurfaceVector of neighbors and nominal
   /// @note The @c SurfaceVector will be combined. For technical reasons, the
   ///       different bin content vectors have to be copied, so the resulting
   ///       vector contains copies.
   const SurfaceVector& neighbors(const Vector3& position) const {
     return p_gridLookup->neighbors(position);
   }
 
   /// @brief Get the size of the underlying grid structure including
   /// under/overflow bins
   /// @return the size
   std::size_t size() const { return p_gridLookup->size(); }
 
   /// @brief Get the center of the bin identified by global bin index @p bin
   /// @param bin the global bin index
   /// @return Center position of the bin in global coordinates
   Vector3 getBinCenter(std::size_t bin) const {
     return p_gridLookup->getBinCenter(bin);
   }
 
   /// @brief Get all surfaces attached to this @c SurfaceArray
   /// @return Reference to @c SurfaceVector containing all surfaces
   /// @note This does not reflect the actual state of the grid. It only
   ///       returns what was given in the constructor, without any checks
   ///       if that is actually what's in the grid.
   const SurfaceVector& surfaces() const { return m_surfacesRawPointers; }
 
   /// @brief Get vector of axes spanning the grid as @c AnyAxis
   /// @return vector of @c AnyAxis
   /// @note The axes in the vector are copies. Only use for introspection and
   ///       querying.
   std::vector<const IAxis*> getAxes() const { return p_gridLookup->getAxes(); }
 
   /// @brief Checks if global bin is valid
   /// @param bin the global bin index
   /// @return bool if the bin is valid
   /// @note Valid means that the index points to a bin which is not a under
   ///       or overflow bin or out of range in any axis.
   bool isValidBin(std::size_t bin) const {
     return p_gridLookup->isValidBin(bin);
   }
 
   const Transform3& transform() const { return m_transform; }
 
   /// @brief The binning values described by this surface grid lookup
   /// They are in order of the axes
   std::vector<AxisDirection> binningValues() const {
     return p_gridLookup->binningValues();
   };
 
   /// @brief String representation of this @c SurfaceArray
   /// @param gctx The current geometry context object, e.g. alignment
   /// @param sl Output stream to write to
   /// @return the output stream given as @p sl
   std::ostream& toStream(const GeometryContext& gctx, std::ostream& sl) const;
 
   /// Return the lookup object
   const ISurfaceGridLookup& gridLookup() const { return *p_gridLookup; }
 
  private:
   std::unique_ptr<ISurfaceGridLookup> p_gridLookup;
   // this vector makes sure we have shared ownership over the surfaces
   std::vector<std::shared_ptr<const Surface>> m_surfaces;
   // this vector is returned, so that (expensive) copying of the shared_ptr
   // vector does not happen by default
   SurfaceVector m_surfacesRawPointers;
   // this is only used to keep info on transform applied
   // by l2g and g2l
   Transform3 m_transform;
 };
 
 }  // namespace Acts

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