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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/.
 
 #include "ActsExamples/TrackFinding/HoughTransformSeeder.hpp"
 
 #include "Acts/Definitions/Algebra.hpp"
 #include "Acts/Definitions/Common.hpp"
 #include "Acts/Definitions/TrackParametrization.hpp"
 #include "Acts/EventData/SourceLink.hpp"
 #include "Acts/Geometry/TrackingGeometry.hpp"
 #include "Acts/Surfaces/Surface.hpp"
 #include "Acts/Utilities/Enumerate.hpp"
 #include "Acts/Utilities/MathHelpers.hpp"
 #include "ActsExamples/EventData/GeometryContainers.hpp"
 #include "ActsExamples/EventData/Index.hpp"
 #include "ActsExamples/EventData/IndexSourceLink.hpp"
 #include "ActsExamples/EventData/Measurement.hpp"
 #include "ActsExamples/EventData/ProtoTrack.hpp"
 #include "ActsExamples/Framework/AlgorithmContext.hpp"
 #include "ActsExamples/TrackFinding/DefaultHoughFunctions.hpp"
 #include "ActsExamples/Utilities/GroupBy.hpp"
 #include "ActsExamples/Utilities/Range.hpp"
 
 #include <algorithm>
 #include <cmath>
 #include <iterator>
 #include <ostream>
 #include <stdexcept>
 #include <variant>
 
 static inline int quant(double min, double max, unsigned nSteps, double val);
 static inline double unquant(double min, double max, unsigned nSteps, int step);
 template <typename T>
 static inline std::string to_string(std::vector<T> v);
 
 ActsExamples::HoughTransformSeeder::HoughTransformSeeder(
     ActsExamples::HoughTransformSeeder::Config cfg, Acts::Logging::Level lvl)
     : ActsExamples::IAlgorithm("HoughTransformSeeder", lvl),
       m_cfg(std::move(cfg)),
       m_logger(Acts::getDefaultLogger("HoughTransformSeeder", lvl)) {
   // require spacepoints or input measurements (or both), but at least one kind
   // of input
   bool foundInput = false;
   for (const auto& spName : m_cfg.inputSpacePoints) {
     if (!(spName.empty())) {
       foundInput = true;
     }
 
     auto& handle = m_inputSpacePoints.emplace_back(
         std::make_unique<ReadDataHandle<SimSpacePointContainer>>(
             this,
             "InputSpacePoints#" + std::to_string(m_inputSpacePoints.size())));
     handle->initialize(spName);
   }
   if (!(m_cfg.inputMeasurements.empty())) {
     foundInput = true;
   }
 
   if (!foundInput) {
     throw std::invalid_argument(
         "HoughTransformSeeder: Missing some kind of input (measurements of "
         "spacepoints)");
   }
 
   if (m_cfg.outputProtoTracks.empty()) {
     throw std::invalid_argument(
         "HoughTransformSeeder: Missing hough tracks output collection");
   }
   if (m_cfg.outputSeeds.empty()) {
     throw std::invalid_argument(
         "HoughTransformSeeder: Missing hough track seeds output collection");
   }
 
   m_outputProtoTracks.initialize(m_cfg.outputProtoTracks);
   m_inputMeasurements.initialize(m_cfg.inputMeasurements);
 
   if (!m_cfg.trackingGeometry) {
     throw std::invalid_argument(
         "HoughTransformSeeder: Missing tracking geometry");
   }
 
   if (m_cfg.geometrySelection.empty()) {
     throw std::invalid_argument(
         "HoughTransformSeeder: Missing geometry selection");
   }
   // ensure geometry selection contains only valid inputs
   for (const auto& geoId : m_cfg.geometrySelection) {
     if ((geoId.approach() != 0u) || (geoId.boundary() != 0u) ||
         (geoId.sensitive() != 0u)) {
       throw std::invalid_argument(
           "HoughTransformSeeder: Invalid geometry selection: only volume and "
           "layer are allowed to be set");
     }
   }
   // remove geometry selection duplicates
   //
   // the geometry selections must be mutually exclusive, i.e. if we have a
   // selection that contains both a volume and a layer within that same volume,
   // we would create the space points for the layer twice.
   auto isDuplicate = [](Acts::GeometryIdentifier ref,
                         Acts::GeometryIdentifier cmp) {
     // code assumes ref < cmp and that only volume and layer can be non-zero
     // root node always contains everything
     if (ref.volume() == 0) {
       return true;
     }
     // unequal volumes always means separate hierarchies
     if (ref.volume() != cmp.volume()) {
       return false;
     }
     // within the same volume hierarchy only consider layers
     return (ref.layer() == cmp.layer());
   };
   // sort geometry selection so the unique filtering works
   std::ranges::sort(m_cfg.geometrySelection,
                     std::less<Acts::GeometryIdentifier>{});
   auto geoSelBeg = m_cfg.geometrySelection.begin();
   auto geoSelEnd = m_cfg.geometrySelection.end();
   auto geoSelLastUnique = std::unique(geoSelBeg, geoSelEnd, isDuplicate);
   if (geoSelLastUnique != geoSelEnd) {
     ACTS_WARNING("Removed " << std::distance(geoSelLastUnique, geoSelEnd)
                             << " geometry selection duplicates");
     m_cfg.geometrySelection.erase(geoSelLastUnique, geoSelEnd);
   }
   ACTS_INFO("Hough geometry selection:");
   for (const auto& geoId : m_cfg.geometrySelection) {
     ACTS_INFO("  " << geoId);
   }
 
   // Fill convenience variables
   m_step_x = (m_cfg.xMax - m_cfg.xMin) / m_cfg.houghHistSize_x;
   m_step_y = (m_cfg.yMax - m_cfg.yMin) / m_cfg.houghHistSize_y;
   for (unsigned i = 0; i <= m_cfg.houghHistSize_x; i++) {
     m_bins_x.push_back(
         unquant(m_cfg.xMin, m_cfg.xMax, m_cfg.houghHistSize_x, i));
   }
   for (unsigned i = 0; i <= m_cfg.houghHistSize_y; i++) {
     m_bins_y.push_back(
         unquant(m_cfg.yMin, m_cfg.yMax, m_cfg.houghHistSize_y, i));
   }
 
   m_cfg.fieldCorrector
       .connect<&ActsExamples::DefaultHoughFunctions::fieldCorrectionDefault>();
   m_cfg.layerIDFinder
       .connect<&ActsExamples::DefaultHoughFunctions::findLayerIDDefault>();
   m_cfg.sliceTester
       .connect<&ActsExamples::DefaultHoughFunctions::inSliceDefault>();
 }
 
 ActsExamples::ProcessCode ActsExamples::HoughTransformSeeder::execute(
     const AlgorithmContext& ctx) const {
   // clear our Hough measurements out from the previous iteration, if at all
   houghMeasurementStructs.clear();
 
   // add SPs to the inputs
   addSpacePoints(ctx);
 
   // add ACTS measurements
   addMeasurements(ctx);
 
   static thread_local ProtoTrackContainer protoTracks;
   protoTracks.clear();
 
   // loop over our subregions and run the Hough Transform on each
   for (int subregion : m_cfg.subRegions) {
     ACTS_DEBUG("Processing subregion " << subregion);
     ActsExamples::HoughHist m_houghHist = createHoughHist(subregion);
 
     for (unsigned y = 0; y < m_cfg.houghHistSize_y; y++) {
       for (unsigned x = 0; x < m_cfg.houghHistSize_x; x++) {
         if (!passThreshold(m_houghHist, x, y)) {
           continue;
         }
 
         // Now we need to unpack the hits; there should be multiple track
         // candidates if we have multiple hits in a given layer. So the first
         // thing is to unpack the indices (which is what we need) by layer
 
         std::vector<std::vector<std::vector<Index>>> hitIndicesAll(
             m_cfg.nLayers);
         std::vector<std::size_t> nHitsPerLayer(m_cfg.nLayers);
         for (auto measurementIndex : m_houghHist.atLocalBins({y, x}).second) {
           HoughMeasurementStruct* meas =
               houghMeasurementStructs[measurementIndex].get();
           hitIndicesAll[meas->layer].push_back(meas->indices);
           nHitsPerLayer[meas->layer]++;
         }
 
         std::vector<std::vector<int>> combs = getComboIndices(nHitsPerLayer);
 
         // Loop over all combinations.
         for (auto [icomb, hit_indices] : Acts::enumerate(combs)) {
           ProtoTrack protoTrack;
           for (unsigned layer = 0; layer < m_cfg.nLayers; layer++) {
             if (hit_indices[layer] >= 0) {
               for (auto index : hitIndicesAll[layer][hit_indices[layer]]) {
                 protoTrack.push_back(index);
               }
             }
           }
           protoTracks.push_back(protoTrack);
         }
       }
     }
   }
   ACTS_DEBUG("Created " << protoTracks.size() << " proto track");
 
   m_outputProtoTracks(ctx, ProtoTrackContainer{protoTracks});
   // clear the vector
   houghMeasurementStructs.clear();
   return ActsExamples::ProcessCode::SUCCESS;
 }
 
 ActsExamples::HoughHist
 ActsExamples::HoughTransformSeeder::createLayerHoughHist(unsigned layer,
                                                          int subregion) const {
   ActsExamples::HoughHist houghHist(
       Axis(0, m_cfg.houghHistSize_y, m_cfg.houghHistSize_y),
       Axis(0, m_cfg.houghHistSize_x, m_cfg.houghHistSize_x));
   for (unsigned index = 0; index < houghMeasurementStructs.size(); index++) {
     HoughMeasurementStruct* meas = houghMeasurementStructs[index].get();
     if (meas->layer != layer) {
       continue;
     }
     if (!(m_cfg.sliceTester(meas->z, meas->layer, subregion)).value()) {
       continue;
     }
 
     // This scans over y (pT) because that is more efficient in memory
     for (unsigned y_ = 0; y_ < m_cfg.houghHistSize_y; y_++) {
       unsigned y_bin_min = y_;
       unsigned y_bin_max = (y_ + 1);
 
       // Find the min/max x bins
       auto xBins =
           yToXBins(y_bin_min, y_bin_max, meas->radius, meas->phi, meas->layer);
       // Update the houghHist
       for (unsigned y = y_bin_min; y < y_bin_max; y++) {
         for (unsigned x = xBins.first; x < xBins.second; x++) {
           houghHist.atLocalBins({y, x}).first++;
           houghHist.atLocalBins({y, x}).second.insert(index);
         }
       }
     }
   }
 
   return houghHist;
 }
 
 ActsExamples::HoughHist ActsExamples::HoughTransformSeeder::createHoughHist(
     int subregion) const {
   ActsExamples::HoughHist houghHist(
       Axis(0, m_cfg.houghHistSize_y, m_cfg.houghHistSize_y),
       Axis(0, m_cfg.houghHistSize_x, m_cfg.houghHistSize_x));
 
   for (unsigned i = 0; i < m_cfg.nLayers; i++) {
     HoughHist layerHoughHist = createLayerHoughHist(i, subregion);
     for (unsigned x = 0; x < m_cfg.houghHistSize_x; ++x) {
       for (unsigned y = 0; y < m_cfg.houghHistSize_y; ++y) {
         if (layerHoughHist.atLocalBins({y, x}).first > 0) {
           houghHist.atLocalBins({y, x}).first++;
           houghHist.atLocalBins({y, x}).second.insert(
               layerHoughHist.atLocalBins({y, x}).second.begin(),
               layerHoughHist.atLocalBins({y, x}).second.end());
         }
       }
     }
   }
 
   return houghHist;
 }
 
 bool ActsExamples::HoughTransformSeeder::passThreshold(
     HoughHist const& houghHist, unsigned x, unsigned y) const {
   // Pass window threshold
   unsigned width = m_cfg.threshold.size() / 2;
   if (x < width || m_cfg.houghHistSize_x - x < width) {
     return false;
   }
   for (unsigned i = 0; i < m_cfg.threshold.size(); i++) {
     if (houghHist.atLocalBins({y, x - width + i}).first < m_cfg.threshold[i]) {
       return false;
     }
   }
 
   // Pass local-maximum check, if used
   if (m_cfg.localMaxWindowSize != 0) {
     for (int j = -m_cfg.localMaxWindowSize; j <= m_cfg.localMaxWindowSize;
          j++) {
       for (int i = -m_cfg.localMaxWindowSize; i <= m_cfg.localMaxWindowSize;
            i++) {
         if (i == 0 && j == 0) {
           continue;
         }
         if (y + j < m_cfg.houghHistSize_y && x + i < m_cfg.houghHistSize_x) {
           if (houghHist.atLocalBins({y + j, x + i}).first >
               houghHist.atLocalBins({y, x}).first) {
             return false;
           }
           if (houghHist.atLocalBins({y + j, x + i}).first ==
               houghHist.atLocalBins({y, x}).first) {
             if (houghHist.atLocalBins({y + j, x + i}).second.size() >
                 houghHist.atLocalBins({y, x}).second.size()) {
               return false;
             }
             if (houghHist.atLocalBins({y + j, x + i}).second.size() ==
                     houghHist.atLocalBins({y, x}).second.size() &&
                 j <= 0 && i <= 0) {
               return false;  // favor bottom-left (low phi, low neg q/pt)
             }
           }
         }
       }
     }
   }
 
   return true;
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 // Helpers
 
 // Quantizes val, given a range [min, max) split into nSteps. Returns the bin
 // below.
 static inline int quant(double min, double max, unsigned nSteps, double val) {
   return static_cast<int>((val - min) / (max - min) * nSteps);
 }
 
 // Returns the lower bound of the bin specified by step
 static inline double unquant(double min, double max, unsigned nSteps,
                              int step) {
   return min + (max - min) * step / nSteps;
 }
 
 template <typename T>
 static inline std::string to_string(std::vector<T> v) {
   std::ostringstream oss;
   oss << "[";
   if (!v.empty()) {
     std::copy(v.begin(), v.end() - 1, std::ostream_iterator<T>(oss, ", "));
     oss << v.back();
   }
   oss << "]";
   return oss.str();
 }
 
 double ActsExamples::HoughTransformSeeder::yToX(double y, double r,
                                                 double phi) const {
   double d0 = 0;  // d0 correction TO DO allow for this
   double x =
       asin(r * ActsExamples::HoughTransformSeeder::m_cfg.kA * y - d0 / r) + phi;
 
   if (m_cfg.fieldCorrector.connected()) {
     x += (m_cfg.fieldCorrector(0, y, r)).value();
   }
 
   return x;
 }
 
 // Find the min/max x bins of the hit's line, in each y bin. Max is exclusive.
 // Note this assumes yToX is monotonic. Returns {0, 0} if hit lies out of
 // bounds.
 std::pair<unsigned, unsigned> ActsExamples::HoughTransformSeeder::yToXBins(
     std::size_t yBin_min, std::size_t yBin_max, double r, double phi,
     unsigned layer) const {
   double x_min = yToX(m_bins_y[yBin_min], r, phi);
   double x_max = yToX(m_bins_y[yBin_max], r, phi);
   if (x_min > x_max) {
     std::swap(x_min, x_max);
   }
   if (x_max < m_cfg.xMin || x_min > m_cfg.xMax) {
     return {0, 0};  // out of bounds
   }
 
   // Get bins
   int x_bin_min = quant(m_cfg.xMin, m_cfg.xMax, m_cfg.houghHistSize_x, x_min);
   int x_bin_max = quant(m_cfg.xMin, m_cfg.xMax, m_cfg.houghHistSize_x, x_max) +
                   1;  // exclusive
 
   // Extend bins
   unsigned extend = getExtension(yBin_min, layer);
   x_bin_min -= extend;
   x_bin_max += extend;
 
   // Clamp bins
   if (x_bin_min < 0) {
     x_bin_min = 0;
   }
   if (x_bin_max > static_cast<int>(m_cfg.houghHistSize_x)) {
     x_bin_max = m_cfg.houghHistSize_x;
   }
 
   return {x_bin_min, x_bin_max};
 }
 
 // We allow variable extension based on the size of m_hitExtend_x. See comments
 // below.
 unsigned ActsExamples::HoughTransformSeeder::getExtension(
     unsigned y, unsigned layer) const {
   if (m_cfg.hitExtend_x.size() == m_cfg.nLayers) {
     return m_cfg.hitExtend_x[layer];
   }
 
   if (m_cfg.hitExtend_x.size() == m_cfg.nLayers * 2) {
     // different extension for low pt vs high pt, split in half but irrespective
     // of sign first nLayers entries of m_hitExtend_x is for low pt half, rest
     // are for high pt half
     if (y < m_cfg.houghHistSize_y / 4 || y > 3 * m_cfg.houghHistSize_y / 4) {
       return m_cfg.hitExtend_x[layer];
     }
 
     return m_cfg.hitExtend_x[m_cfg.nLayers + layer];
   }
   return 0;
 }
 
 /**
  * Given a list of sizes (of arrays), generates a list of all combinations of
  * indices to index one element from each array.
  *
  * For example, given [2 3], generates [(0 0) (1 0) (0 1) (1 1) (0 2) (1 2)].
  *
  * This basically amounts to a positional number system of where each digit has
  * its own base. The number of digits is sizes.size(), and the base of digit i
  * is sizes[i]. Then all combinations can be uniquely represented just by
  * counting from [0, nCombs).
  *
  * For a decimal number like 1357, you get the thousands digit with n / 1000 = n
  * / (10 * 10 * 10). So here, you get the 0th digit with n / (base_1 * base_2 *
  * base_3);
  */
 std::vector<std::vector<int>>
 ActsExamples::HoughTransformSeeder::getComboIndices(
     std::vector<std::size_t>& sizes) const {
   std::size_t nCombs = 1;
   std::vector<std::size_t> nCombs_prior(sizes.size());
   std::vector<int> temp(sizes.size(), 0);
 
   for (std::size_t i = 0; i < sizes.size(); i++) {
     if (sizes[i] > 0) {
       nCombs_prior[i] = nCombs;
       nCombs *= sizes[i];
     } else {
       temp[i] = -1;
     }
   }
 
   std::vector<std::vector<int>> combos(nCombs, temp);
 
   for (std::size_t icomb = 0; icomb < nCombs; icomb++) {
     std::size_t index = icomb;
     for (std::size_t isize = sizes.size() - 1; isize < sizes.size(); isize--) {
       if (sizes[isize] == 0) {
         continue;
       }
       combos[icomb][isize] = static_cast<int>(index / nCombs_prior[isize]);
       index = index % nCombs_prior[isize];
     }
   }
 
   return combos;
 }
 
 void ActsExamples::HoughTransformSeeder::addSpacePoints(
     const AlgorithmContext& ctx) const {
   // construct the combined input container of space point pointers from all
   // configured input sources.
   for (const auto& isp : m_inputSpacePoints) {
     const auto& spContainer = (*isp)(ctx);
     ACTS_DEBUG("Inserting " << spContainer.size() << " space points from "
                             << isp->key());
     for (auto& sp : spContainer) {
       double r = Acts::fastHypot(sp.x(), sp.y());
       double z = sp.z();
       float phi = std::atan2(sp.y(), sp.x());
       ResultUnsigned hitlayer = m_cfg.layerIDFinder(r).value();
       if (!(hitlayer.ok())) {
         continue;
       }
       std::vector<Index> indices;
       for (const auto& slink : sp.sourceLinks()) {
         const auto& islink = slink.get<IndexSourceLink>();
         indices.push_back(islink.index());
       }
 
       auto meas =
           std::shared_ptr<HoughMeasurementStruct>(new HoughMeasurementStruct(
               hitlayer.value(), phi, r, z, indices, HoughHitType::SP));
       houghMeasurementStructs.push_back(meas);
     }
   }
 }
 
 void ActsExamples::HoughTransformSeeder::addMeasurements(
     const AlgorithmContext& ctx) const {
   const auto& measurements = m_inputMeasurements(ctx);
 
   ACTS_DEBUG("Inserting " << measurements.size() << " space points from "
                           << m_cfg.inputMeasurements);
 
   for (Acts::GeometryIdentifier geoId : m_cfg.geometrySelection) {
     // select volume/layer depending on what is set in the geometry id
     auto range =
         selectLowestNonZeroGeometryObject(measurements.orderedIndices(), geoId);
     // groupByModule only works with geometry containers, not with an
     // arbitrary range. do the equivalent grouping manually
     auto groupedByModule = makeGroupBy(range, detail::GeometryIdGetter());
 
     for (const auto& [moduleGeoId, moduleSourceLinks] : groupedByModule) {
       // find corresponding surface
       const Acts::Surface* surface =
           m_cfg.trackingGeometry->findSurface(moduleGeoId);
       if (surface == nullptr) {
         ACTS_ERROR("Could not find surface " << moduleGeoId);
         return;
       }
 
       for (auto& sourceLink : moduleSourceLinks) {
         // extract a local position/covariance independent of the concrete
         // measurement content. since we do not know if and where the local
         // parameters are contained in the measurement parameters vector, they
         // are transformed to the bound space where we do know their location.
         // if the local parameters are not measured, this results in a
         // zero location, which is a reasonable default fall-back.
         const ConstVariableBoundMeasurementProxy measurement =
             measurements.getMeasurement(sourceLink.index());
 
         assert(measurement.contains(Acts::eBoundLoc0) &&
                "Measurement does not contain the required bound loc0");
         assert(measurement.contains(Acts::eBoundLoc1) &&
                "Measurement does not contain the required bound loc1");
 
         auto boundLoc0 = measurement.indexOf(Acts::eBoundLoc0);
         auto boundLoc1 = measurement.indexOf(Acts::eBoundLoc1);
 
         Acts::Vector2 localPos{measurement.parameters()[boundLoc0],
                                measurement.parameters()[boundLoc1]};
 
         // transform local position to global coordinates
         Acts::Vector3 globalFakeMom(1, 1, 1);
         Acts::Vector3 globalPos =
             surface->localToGlobal(ctx.geoContext, localPos, globalFakeMom);
         double r = globalPos.head<2>().norm();
         double phi = std::atan2(globalPos[Acts::ePos1], globalPos[Acts::ePos0]);
         double z = globalPos[Acts::ePos2];
         ResultUnsigned hitlayer = m_cfg.layerIDFinder(r);
         if (hitlayer.ok()) {
           std::vector<Index> index;
           index.push_back(sourceLink.index());
           auto houghMeas = std::shared_ptr<HoughMeasurementStruct>(
               new HoughMeasurementStruct(hitlayer.value(), phi, r, z, index,
                                          HoughHitType::MEASUREMENT));
           houghMeasurementStructs.push_back(houghMeas);
         }
       }
     }
   }
 }

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