TreeTraversal.h

/**************************************************************************
 * basf2 (Belle II Analysis Software Framework)                           *
 * Author: The Belle II Collaboration                                     *
 *                                                                        *
 * See git log for contributors and copyright holders.                    *
 * This file is licensed under LGPL-3.0, see LICENSE.md.                  *
 **************************************************************************/
#pragma once
 
#include <tracking/trackFindingCDC/findlets/base/Findlet.h>
 
#include <tracking/trackFindingCDC/utilities/Relation.h>
#include <tracking/trackFindingCDC/utilities/Range.h>
 
#include <framework/logging/Logger.h>
 
#include <vector>
#include <string>
 
namespace Belle2 {
  class ModuleParamList;
  namespace TrackFindingCDC {
    template <class AStateRejecter, class AState, class AResult = std::vector<const AState*> >
    class TreeTraversal : public Findlet<const AState* const, const Relation<AState>, AResult> {
    private:
      using Super = Findlet<const AState* const, const Relation<AState>, AResult>;
 
    public:
      TreeTraversal()
        : Super()
      {
        Super::addProcessingSignalListener(&m_stateRejecter);
      }

      void exposeParameters(ModuleParamList* moduleParamList, const std::string& prefix) final
      {
        m_stateRejecter.exposeParameters(moduleParamList, prefix);
      }

      void apply(const std::vector<const AState*>& seededStates,
                 const std::vector<Relation<AState>>& stateRelations,
                 std::vector<AResult>& results) override;
 
    private:
      void traverseTree(std::vector<const AState*>& path,
                        const std::vector<Relation<AState>>& stateRelations,
                        std::vector<AResult>& results);
 
    private:
      AStateRejecter m_stateRejecter;
    };
 
    template <class AStateRejecter, class AState, class AResult>
    void TreeTraversal<AStateRejecter, AState, AResult>::apply(
      const std::vector<const AState*>& seededStates,
      const std::vector<Relation<AState>>& stateRelations,
      std::vector<AResult>& results)
    {
      B2ASSERT("Expected relation to be sorted",
               std::is_sorted(stateRelations.begin(), stateRelations.end()));
 
      std::vector<const AState*> path;
      for (const AState* state : seededStates) {
        B2DEBUG(25, "Starting with new seed...");
        path.push_back(state);
        traverseTree(path, stateRelations, results);
        path.pop_back();
        B2DEBUG(25, "... finished with seed");
      }
      assert(path.empty());
    }
 
    template <class AStateRejecter, class AState, class AResult>
    void TreeTraversal<AStateRejecter, AState, AResult>::traverseTree(
      std::vector<const AState*>& path,
      const std::vector<Relation<AState>>& stateRelations,
      std::vector<AResult>& results)
    {
      // Implement only graph traversal logic and leave the extrapolation and selection to the
      // rejecter.
      const AState* currentState = path.back();
      auto continuations =
        std::equal_range(stateRelations.begin(), stateRelations.end(), currentState);
 
      std::vector<AState*> childStates;
      for (const Relation<AState>& continuation : asRange(continuations)) {
        AState* childState = continuation.getTo();
        childStates.push_back(childState);
      }
 
      // Do everything with child states, linking, extrapolation, teaching, discarding, what have
      // you.
      const std::vector<const AState*>& constPath = path;
      m_stateRejecter.apply(constPath, childStates);
 
      if (childStates.empty()) {
        B2DEBUG(25, "Terminating this route, as there are no possible child states.");
        results.emplace_back(path);
        return;
      }
 
      // Traverse the tree from each new state on
      B2DEBUG(25, "Having found " << childStates.size() << " child states.");
      for (const AState* childState : childStates) {
        if (std::count(path.begin(), path.end(), childState)) {
          // Cycle detected -- is this the best handling?
          // Other options: Raise and exception and bail out of this seed
          continue;
        }
        path.push_back(childState);
        traverseTree(path, stateRelations, results);
        path.pop_back();
      }
    }
  }
}