PrimaryVertexDecoratorAlg.cxx

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/*
  Copyright (C) 2002-2026 CERN for the benefit of the ATLAS collaboration
*/
 
#include "PrimaryVertexDecoratorAlg.h"
 
#include "StoreGate/WriteDecorHandle.h"
 
#include "xAODTracking/VertexContainer.h"
#include "xAODTracking/TrackingPrimitives.h"
 
#include <cmath>
#include <limits>
 
namespace FlavorTagJetDecorators {
 
  PrimaryVertexDecoratorAlg::PrimaryVertexDecoratorAlg(
    const std::string& name, ISvcLocator* loc)
    : AthReentrantAlgorithm(name, loc) {}
 
  StatusCode PrimaryVertexDecoratorAlg::initialize() {
    ATH_MSG_DEBUG("Initializing " << name() << "...");
 
    ATH_CHECK(m_vertexContainerKey.initialize());
    ATH_CHECK(m_eventInfoKey.initialize());
    ATH_CHECK(m_dec_nPrimaryVertices.initialize());
    ATH_CHECK(m_dec_primaryVertexZ.initialize());
 
    return StatusCode::SUCCESS;
  }
 
  StatusCode PrimaryVertexDecoratorAlg::execute(
      const EventContext& ctx) const {
    ATH_MSG_DEBUG("Executing " << name() << "...");
 
    constexpr float NaN = std::numeric_limits<float>::quiet_NaN();
 
    SG::ReadHandle<xAOD::VertexContainer> vertices(
      m_vertexContainerKey, ctx);
    ATH_CHECK(vertices.isValid());
 
    auto eventInfo = SG::makeHandle(m_eventInfoKey, ctx);
    ATH_CHECK(eventInfo.isValid());
 
    SG::WriteDecorHandle<xAOD::EventInfo, int> dec_nPV(
      m_dec_nPrimaryVertices, ctx);
    SG::WriteDecorHandle<xAOD::EventInfo, float> dec_pvZ(
      m_dec_primaryVertexZ, ctx);
 
    if (vertices->empty()) {
      ATH_MSG_WARNING("Empty PrimaryVertices container — writing defaults");
      dec_nPV(*eventInfo) = 0;
      dec_pvZ(*eventInfo) = NaN;
      return StatusCode::SUCCESS;
    }
 
    // Find the primary vertex: first with vertexType == PriVtx,
    // fallback to front().  Matches TDD's primary() function exactly.
    const xAOD::Vertex* pv = nullptr;
    for (const auto* vertex : *vertices) {
      if (vertex->vertexType() == xAOD::VxType::PriVtx) {
        pv = vertex;
        break;
      }
    }
    if (!pv) {
      pv = vertices->front();
    }
 
    dec_nPV(*eventInfo) = static_cast<int>(vertices->size());
    dec_pvZ(*eventInfo) = static_cast<float>(pv->z());
 
    ATH_MSG_DEBUG("nPrimaryVertices=" << vertices->size()
                  << " primaryVertexZ=" << pv->z());
 
    return StatusCode::SUCCESS;
  }
 
}  // namespace FlavorTagJetDecorators