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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/Layer.hpp"
 #include "Acts/Geometry/TrackingGeometry.hpp"
 #include "Acts/Geometry/TrackingVolume.hpp"
 #include "Acts/Propagator/NavigationTarget.hpp"
 #include "Acts/Propagator/NavigatorError.hpp"
 #include "Acts/Propagator/NavigatorOptions.hpp"
 #include "Acts/Propagator/NavigatorStatistics.hpp"
 #include "Acts/Propagator/detail/NavigationHelpers.hpp"
 #include "Acts/Surfaces/BoundaryTolerance.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Utilities/Enumerate.hpp"
 #include "Acts/Utilities/Intersection.hpp"
 #include "Acts/Utilities/Logger.hpp"
 #include "Acts/Utilities/StringHelpers.hpp"
 
 #include <algorithm>
 #include <cstdint>
 #include <limits>
 #include <memory>
 #include <vector>
 
 namespace Acts::Experimental {
 
 /// @brief Alternative @c Navigator which tries all possible intersections
 ///
 /// See @c Navigator for more general information about the Navigator concept.
 ///
 /// This Navigator tries all possible intersections with all surfaces in the
 /// current volume. It does not use any information about the geometry to
 /// optimise the search. It is therefore very slow, but can be used as a
 /// reference implementation.
 ///
 /// Additionally, this implementation tries to discover additional
 /// intersections after stepping forward and then checking for intersections
 /// based on the previous and current positions. This is slower, but more robust
 /// against bent tracks.
 class TryAllNavigator final {
  public:
   /// Configuration for this Navigator
   struct Config final {
     /// Tracking Geometry for this Navigator
     std::shared_ptr<const TrackingGeometry> trackingGeometry;
 
     /// stop at every sensitive surface (whether it has material or not)
     bool resolveSensitive = true;
     /// stop at every material surface (whether it is passive or not)
     bool resolveMaterial = true;
     /// stop at every surface regardless what it is
     bool resolvePassive = false;
 
     /// Which boundary checks to perform for surface approach
     BoundaryTolerance boundaryToleranceSurfaceApproach =
         BoundaryTolerance::None();
   };
 
   /// Options for this Navigator
   struct Options final : public NavigatorPlainOptions {
     /// @param gctx The geometry context for this navigator instance
     explicit Options(const GeometryContext& gctx)
         : NavigatorPlainOptions(gctx) {}
 
     /// The surface tolerance
     double surfaceTolerance = s_onSurfaceTolerance;
 
     /// The near limit to resolve surfaces
     double nearLimit = s_onSurfaceTolerance;
 
     /// The far limit to resolve surfaces
     double farLimit = std::numeric_limits<double>::max();
 
     /// @param options The plain options to copy
     void setPlainOptions(const NavigatorPlainOptions& options) {
       static_cast<NavigatorPlainOptions&>(*this) = options;
     }
   };
 
   /// Nested state struct
   struct State final {
     /// @param options_ Navigator options to initialise state with
     explicit State(const Options& options_) : options(options_) {}
 
     /// Navigation options containing configuration for this propagation
     Options options;
 
     // Starting geometry information of the navigation which should only be set
     // while initialization. NOTE: This information is mostly used by actors to
     // check if we are on the starting surface (e.g. MaterialInteraction).
     /// Surface where the propagation started
     const Surface* startSurface = nullptr;
 
     // Target geometry information of the navigation which should only be set
     // while initialization. NOTE: This information is mostly used by actors to
     // check if we are on the target surface (e.g. MaterialInteraction).
     /// Surface that is the target of the propagation
     const Surface* targetSurface = nullptr;
 
     // Current geometry information of the navigation which is set during
     // initialization and potentially updated after each step.
     /// Currently active surface during propagation
     const Surface* currentSurface = nullptr;
     /// Currently active tracking volume during propagation
     const TrackingVolume* currentVolume = nullptr;
 
     /// The vector of navigation candidates to work through
     std::vector<detail::NavigationObjectCandidate> navigationCandidates;
 
     /// If a break has been detected
     bool navigationBreak = false;
 
     /// Navigation statistics
     NavigatorStatistics statistics;
 
     /// The vector of active targets ahead of the current position
     std::vector<NavigationTarget> activeTargetsAhead;
     /// The vector of active targets behind the current position
     std::vector<NavigationTarget> activeTargetsBehind;
     /// Index to keep track of which target behind the current position is
     /// currently active
     std::int32_t activeTargetBehindIndex = -1;
 
     /// The position before the last step
     std::optional<Vector3> lastPosition;
 
     /// Provides easy access to the current active targets, prioritizing targets
     /// behind the current position.
     /// @return Reference to the vector of currently active intersection
     /// candidates, prioritizing targets behind the current position
     const std::vector<NavigationTarget>& currentTargets() const {
       if (hasTargetsBehind()) {
         return activeTargetsBehind;
       }
       return activeTargetsAhead;
     }
 
     /// Provides easy access to the active intersection target
     /// @return Reference to the currently active intersection candidate
     const NavigationTarget& activeTargetBehind() const {
       return activeTargetsBehind.at(activeTargetBehindIndex);
     }
 
     /// Checks if there are still active targets behind the current position
     /// that have not been tried yet
     /// @return True if there are still active targets behind the current position, false otherwise
     bool hasTargetsBehind() const {
       return !activeTargetsBehind.empty() &&
              activeTargetBehindIndex <
                  static_cast<std::int32_t>(activeTargetsBehind.size());
     }
   };
 
   /// Constructor with configuration object
   ///
   /// @param cfg The navigator configuration
   /// @param logger a logger instance
   explicit TryAllNavigator(Config cfg, std::unique_ptr<const Logger> logger =
                                            getDefaultLogger("TryAllNavigator",
                                                             Logging::INFO))
       : m_cfg(std::move(cfg)), m_logger(std::move(logger)) {}
 
   /// Creates a new navigator state
   /// @param options Navigator options for state initialization
   /// @return Initialized navigator state with current candidates storage
   State makeState(const Options& options) const {
     State state(options);
     return state;
   }
 
   /// Get the current surface from the navigation state
   /// @param state The navigation state
   /// @return Pointer to the current surface, or nullptr if none
   const Surface* currentSurface(const State& state) const {
     return state.currentSurface;
   }
 
   /// Get the current tracking volume from the navigation state
   /// @param state The navigation state
   /// @return Pointer to the current tracking volume, or nullptr if none
   const TrackingVolume* currentVolume(const State& state) const {
     return state.currentVolume;
   }
 
   /// Get the material of the current tracking volume
   /// @param state The navigation state
   /// @return Pointer to the volume material, or nullptr if no volume or no material
   const IVolumeMaterial* currentVolumeMaterial(const State& state) const {
     if (state.currentVolume == nullptr) {
       return nullptr;
     }
     return state.currentVolume->volumeMaterial();
   }
 
   /// Get the start surface from the navigation state
   /// @param state The navigation state
   /// @return Pointer to the start surface, or nullptr if none
   const Surface* startSurface(const State& state) const {
     return state.startSurface;
   }
 
   /// Get the target surface from the navigation state
   /// @param state The navigation state
   /// @return Pointer to the target surface, or nullptr if none
   const Surface* targetSurface(const State& state) const {
     return state.targetSurface;
   }
 
   /// Check if the end of the world has been reached
   /// @param state The navigation state
   /// @return True if no current volume is set (end of world reached)
   bool endOfWorldReached(State& state) const {
     return state.currentVolume == nullptr;
   }
 
   /// Check if navigation has been interrupted
   /// @param state The navigation state
   /// @return True if navigation break flag is set
   bool navigationBreak(const State& state) const {
     return state.navigationBreak;
   }
 
   /// @brief Initialize the navigator
   ///
   /// This method initializes the navigator for a new propagation. It sets the
   /// current volume and surface to the start volume and surface, respectively.
   ///
   /// @param state The navigation state
   /// @param position The starting position
   /// @param direction The starting direction
   /// @param propagationDirection The propagation direction
   /// @return Result indicating success or failure of initialization
   [[nodiscard]] Result<void> initialize(State& state, const Vector3& position,
                                         const Vector3& direction,
                                         Direction propagationDirection) const {
     static_cast<void>(propagationDirection);
 
     ACTS_VERBOSE("initialize");
 
     state.startSurface = state.options.startSurface;
     state.targetSurface = state.options.targetSurface;
 
     const TrackingVolume* startVolume = nullptr;
 
     if (state.startSurface != nullptr &&
         state.startSurface->associatedLayer() != nullptr) {
       ACTS_VERBOSE(
           "Fast start initialization through association from Surface.");
       const auto* startLayer = state.startSurface->associatedLayer();
       startVolume = startLayer->trackingVolume();
     } else {
       ACTS_VERBOSE("Slow start initialization through search.");
       ACTS_VERBOSE("Starting from position " << toString(position)
                                              << " and direction "
                                              << toString(direction));
       startVolume =
           m_cfg.trackingGeometry
               ->resolveLowestTrackingVolume(state.options.geoContext, position)
               .value();
     }
 
     // Initialize current volume, layer and surface
     {
       state.currentVolume = startVolume;
       if (state.currentVolume != nullptr) {
         ACTS_VERBOSE(volInfo(state) << "Start volume resolved.");
       } else {
         ACTS_DEBUG("Start volume not resolved.");
         state.navigationBreak = true;
         return NavigatorError::NoStartVolume;
       }
 
       state.currentSurface = state.startSurface;
       if (state.currentSurface != nullptr) {
         ACTS_VERBOSE(volInfo(state) << "Current surface set to start surface "
                                     << state.currentSurface->geometryId());
       } else {
         ACTS_VERBOSE(volInfo(state) << "No start surface set.");
       }
     }
 
     // Initialize navigation candidates for the start volume
     reinitializeCandidates(state);
 
     state.lastPosition.reset();
 
     return Result<void>::success();
   }
 
   /// @brief Get the next target surface
   ///
   /// This method gets the next target surface based on the current
   /// position and direction. It returns a none target if no target can be
   /// found.
   ///
   /// @param state The navigation state
   /// @param position The current position
   /// @param direction The current direction
   ///
   /// @return The next target surface
   NavigationTarget nextTarget(State& state, const Vector3& position,
                               const Vector3& direction) const {
     // Navigator preStep always resets the current surface
     state.currentSurface = nullptr;
 
     // Check if the navigator is inactive
     if (state.navigationBreak) {
       return NavigationTarget::None();
     }
 
     ACTS_VERBOSE(volInfo(state) << "nextTarget");
 
     if (state.lastPosition.has_value() && !state.hasTargetsBehind()) {
       ACTS_VERBOSE(volInfo(state) << "Evaluate blind step");
 
       const Vector3 stepStart = state.lastPosition.value();
       state.lastPosition.reset();
       const Vector3 stepEnd = position;
       const Vector3 step = stepEnd - stepStart;
       const double stepDistance = step.norm();
 
       ACTS_VERBOSE("- from: " << stepStart.transpose());
       ACTS_VERBOSE("- to: " << stepEnd.transpose());
       ACTS_VERBOSE("- distance: " << stepDistance);
 
       if (stepDistance < std::numeric_limits<double>::epsilon()) {
         ACTS_DEBUG(volInfo(state) << "Step distance is zero: " << stepDistance
                                   << ". Retry to resolve the next target.");
         return nextTarget(state, position, direction);
       }
 
       const Vector3 stepDirection = step.normalized();
 
       const double nearLimit = -stepDistance + state.options.surfaceTolerance;
       const double farLimit = 0;
 
       state.activeTargetsBehind =
           resolveTargets(state, stepEnd, stepDirection, nearLimit, farLimit);
       state.activeTargetBehindIndex = -1;
 
       ACTS_VERBOSE(volInfo(state)
                    << "Found " << state.activeTargetsBehind.size()
                    << " intersections behind");
 
       for (const auto& target : state.activeTargetsBehind) {
         ACTS_VERBOSE("Found target behind " << target.surface().geometryId());
       }
     }
 
     // Prioritize targets behind the current position
     ++state.activeTargetBehindIndex;
     if (state.hasTargetsBehind()) {
       ACTS_VERBOSE(volInfo(state) << "Handle active candidates behind");
 
       ACTS_VERBOSE(volInfo(state)
                    << (state.activeTargetsBehind.size() -
                        state.activeTargetBehindIndex)
                    << " out of " << state.activeTargetsBehind.size()
                    << " surfaces remain to try.");
 
       const NavigationTarget& nextTarget = state.activeTargetBehind();
 
       ACTS_VERBOSE(volInfo(state) << "Next target behind selected: "
                                   << nextTarget.surface().geometryId());
 
       return nextTarget;
     }
 
     // No more targets behind, now try to find targets ahead as usual
 
     state.lastPosition = position;
     state.activeTargetsBehind.clear();
     state.activeTargetBehindIndex = -1;
 
     ACTS_VERBOSE(volInfo(state)
                  << "No targets behind, try to find targets ahead");
 
     const double nearLimit = state.options.nearLimit;
     const double farLimit = state.options.farLimit;
 
     state.activeTargetsAhead =
         resolveTargets(state, position, direction, nearLimit, farLimit);
 
     NavigationTarget nextTarget = NavigationTarget::None();
 
     for (const auto& target : state.activeTargetsAhead) {
       const Intersection3D& intersection = target.intersection();
 
       if (intersection.status() == IntersectionStatus::onSurface) {
         ACTS_ERROR(volInfo(state)
                    << "We are on surface " << target.surface().geometryId()
                    << " before trying to reach it. This should not happen. "
                       "Good luck.");
         continue;
       }
 
       if (intersection.status() == IntersectionStatus::reachable) {
         nextTarget = target;
         break;
       }
     }
 
     if (nextTarget.isNone()) {
       ACTS_VERBOSE(volInfo(state)
                    << "No target ahead found. Step blindly forward.");
     } else {
       ACTS_VERBOSE(volInfo(state) << "Next target ahead selected: "
                                   << nextTarget.surface().geometryId());
     }
 
     return nextTarget;
   }
 
   /// @brief Check if the target is still valid
   ///
   /// This method checks if the target is valid based on the current position
   /// and direction. It returns true if the target is still valid.
   ///
   /// For the TryAllNavigator, the target is always invalid since we do not want
   /// to assume any specific surface sequence over multiple steps.
   ///
   /// @param state The navigation state
   /// @param position The current position
   /// @param direction The current direction
   ///
   /// @return True if the target is still valid
   bool checkTargetValid(const State& state, const Vector3& position,
                         const Vector3& direction) const {
     static_cast<void>(state);
     static_cast<void>(position);
     static_cast<void>(direction);
 
     return false;
   }
 
   /// @brief Handle the surface reached
   ///
   /// This method is called when a surface is reached. It sets the current
   /// surface in the navigation state and updates the navigation candidates.
   ///
   /// @param state The navigation state
   /// @param position The current position
   /// @param direction The current direction
   void handleSurfaceReached(State& state, const Vector3& position,
                             const Vector3& direction,
                             const Surface& /*surface*/) const {
     // Check if the navigator is inactive
     if (state.navigationBreak) {
       return;
     }
 
     ACTS_VERBOSE(volInfo(state) << "handleSurfaceReached");
 
     const std::vector<NavigationTarget>& currentTargets =
         state.currentTargets();
 
     if (currentTargets.empty()) {
       ACTS_VERBOSE(volInfo(state) << "No current target set.");
       return;
     }
 
     assert(state.currentSurface == nullptr && "Current surface must be reset.");
 
     // handle multiple surface intersections due to increased bounds
 
     std::vector<NavigationTarget> hitTargets;
 
     for (const auto& target : currentTargets) {
       const std::uint8_t index = target.intersectionIndex();
       const Surface& surface = target.surface();
       const BoundaryTolerance boundaryTolerance = BoundaryTolerance::None();
 
       const Intersection3D intersection =
           surface
               .intersect(state.options.geoContext, position, direction,
                          boundaryTolerance, state.options.surfaceTolerance)
               .at(index);
 
       if (intersection.status() == IntersectionStatus::onSurface) {
         hitTargets.emplace_back(target);
       }
     }
 
     ACTS_VERBOSE(volInfo(state)
                  << "Found " << hitTargets.size()
                  << " intersections on surface with bounds check.");
 
     // reset stored targets
     state.lastPosition.reset();
     state.activeTargetsAhead.clear();
     state.activeTargetsBehind.clear();
     state.activeTargetBehindIndex = -1;
 
     if (hitTargets.empty()) {
       ACTS_VERBOSE(volInfo(state) << "No hit targets found.");
       return;
     }
 
     if (hitTargets.size() > 1) {
       ACTS_VERBOSE(volInfo(state)
                    << "Only using first intersection within bounds.");
     }
 
     // we can only handle a single surface hit so we pick the first one
     const NavigationTarget& target = hitTargets.front();
     const Surface& surface = target.surface();
 
     ACTS_VERBOSE(volInfo(state) << "Surface " << surface.geometryId()
                                 << " successfully hit, storing it.");
     state.currentSurface = &surface;
 
     if (target.isSurfaceTarget()) {
       ACTS_VERBOSE(volInfo(state) << "This is a surface");
     } else if (target.isLayerTarget()) {
       ACTS_VERBOSE(volInfo(state) << "This is a layer");
     } else if (target.isPortalTarget()) {
       ACTS_VERBOSE(volInfo(state)
                    << "This is a boundary. Reinitialize navigation");
 
       const BoundarySurface& boundary = target.boundarySurface();
 
       state.currentVolume = boundary.attachedVolume(state.options.geoContext,
                                                     position, direction);
 
       ACTS_VERBOSE(volInfo(state) << "Switched volume");
 
       reinitializeCandidates(state);
     } else {
       ACTS_ERROR(volInfo(state) << "Unknown intersection type");
     }
   }
 
  private:
   /// Configuration object for this navigator
   Config m_cfg;
 
   /// Logger instance for this navigator
   std::unique_ptr<const Logger> m_logger;
 
   /// @brief Get the logger instance
   /// @return Reference to the logger instance
   const Logger& logger() const { return *m_logger; }
 
   /// Helper method to reset and reinitialize the navigation candidates.
   void reinitializeCandidates(State& state) const {
     state.navigationCandidates.clear();
     state.activeTargetsAhead.clear();
     state.activeTargetsBehind.clear();
     state.activeTargetBehindIndex = -1;
 
     initializeVolumeCandidates(state);
   }
 
   /// Helper method to initialise navigation candidates for the current volume.
   /// @param state Navigation state to initialise candidates for
   void initializeVolumeCandidates(State& state) const {
     const TrackingVolume* volume = state.currentVolume;
     ACTS_VERBOSE(volInfo(state) << "Initialize volume");
 
     if (volume == nullptr) {
       state.navigationBreak = true;
       ACTS_VERBOSE(volInfo(state) << "No volume set. Good luck.");
       return;
     }
 
     emplaceAllVolumeCandidates(
         state.navigationCandidates, *volume, m_cfg.resolveSensitive,
         m_cfg.resolveMaterial, m_cfg.resolvePassive,
         m_cfg.boundaryToleranceSurfaceApproach, logger());
   }
 
   std::vector<NavigationTarget> resolveTargets(State& state,
                                                const Vector3& position,
                                                const Vector3& direction,
                                                double nearLimit,
                                                double farLimit) const {
     std::vector<NavigationTarget> targets;
 
     // Find intersections with all candidates
     for (const auto& candidate : state.navigationCandidates) {
       auto intersections =
           candidate.intersect(state.options.geoContext, position, direction,
                               state.options.surfaceTolerance);
       for (auto [intersectionIndex, intersection] :
            Acts::enumerate(intersections)) {
         // exclude invalid intersections
         if (!intersection.isValid() ||
             !detail::checkPathLength(intersection.pathLength(), nearLimit,
                                      farLimit)) {
           continue;
         }
         // store candidate
         targets.emplace_back(candidate.target(intersection, intersectionIndex));
       }
     }
 
     std::ranges::sort(targets, NavigationTarget::pathLengthOrder);
 
     return targets;
   }
 
   /// @brief Get volume information string for logging
   /// @param state The navigation state
   /// @return String containing volume name or "No Volume" followed by separator
   std::string volInfo(const State& state) const {
     return (state.currentVolume != nullptr ? state.currentVolume->volumeName()
                                            : "No Volume") +
            " | ";
   }
 };
 
 }  // namespace Acts::Experimental

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