CompactSegmentFinderTool.h

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/*
  Copyright (C) 2002-2026 CERN for the benefit of the ATLAS collaboration
*/
 
#ifndef L0MuonMDTTools_COMPACTSEGMENTFINDERTOOL_H
#define L0MuonMDTTools_COMPACTSEGMENTFINDERTOOL_H
#include "AthenaBaseComps/AthAlgTool.h"
 
// local includes
#include "xAODMuonPrepData/MdtDriftCircleContainer.h"
#include "L0MuonMDTTools/IL0MDTSegmentFinderTool.h"
#include "L0MuonMDTTools/L0MDTSegment.h"
#include "MuonIdHelpers/IMuonIdHelperSvc.h"
#include "ActsGeometryInterfaces/GeometryContext.h"
#include "MuonReadoutGeometryR4/MdtReadoutElement.h"
#include <optional>
 
// namespace for the L0MDTS related classes
namespace L0MDT {

class CompactSegmentFinderTool : public extends<AthAlgTool, IL0MDTSegmentFinderTool> {
 
public:
  using base_class::base_class;
  virtual ~CompactSegmentFinderTool() override = default;

  virtual StatusCode initialize() override;

  virtual StatusCode findSegments(const std::vector<const xAOD::MdtDriftCircle*>& driftCircles,
                                  const ActsTrk::GeometryContext& gctx, float m, float b,
                                  std::vector<L0MDT::Segment>& segments) const override;
 
private:

  Gaudi::Property<float> m_clusterTolerance{this, "ClusterTolerance", 5.f,
      "Maximum allowed distance in intercept space when attaching a hit to an existing cluster"};

  Gaudi::Property<int> m_maxClusters{this, "MaxClusters", 6,
      "Maximum number of temporary clusters allowed during clustering"};

  Gaudi::Property<bool> m_debugClusters{this, "DebugClusters", false,
      "Enable debug printout of cluster content and selection"};

  struct HitInfo {
    const xAOD::MdtDriftCircle* dc{nullptr};
    float z{0.f};
    float r{0.f};
    float driftRadius{0.f};
    float bPlus{0.f};
    float bMinus{0.f};
    float deltaZ{0.f};
    float deltaR{0.f};
    int multilayer{0};
  };

  struct Cluster {
    float refB{0.f};
    std::vector<std::size_t> hitIndices;
    std::vector<bool> plusFlags;
  };

  struct FitResult {
    float m{0.f};
    float b{0.f};
    float chi2{0.f};
    bool valid{false};
  };

  virtual StatusCode buildHitInfo(const std::vector<const xAOD::MdtDriftCircle*>& driftCircles,
                                  const ActsTrk::GeometryContext& gctx, float m,
                                  std::vector<HitInfo>& hitInfos) const;

  void clusterHits(const std::vector<HitInfo>& hitInfos,
                   const std::vector<std::size_t>& orderedIndices,
                   std::vector<Cluster>& clusters) const;

  ServiceHandle<Muon::IMuonIdHelperSvc> m_idHelperSvc{
      this, "MuonIdHelperSvc", "Muon::MuonIdHelperSvc/MuonIdHelperSvc"};

  std::optional<Cluster> chooseBestCluster(const std::vector<Cluster>& clusters, float b) const;

  FitResult fitLine(const std::vector<float>& zVals,
                    const std::vector<float>& rVals,
                    float sigma = 1.f / 8.f) const;
};
 
} // end of namespace
#endif