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// G4VoxelisationHelper
//
// Class description:
//
// A helper class to undertake voxelisation in parallel, aiding
// and off-loading the work of G4GeometryManager.  
// 
// Only one instance must exist, and it must be owned by G4GeometryManager 
// -- by the master thread's instance for the time being.
//
// It is designed to be thread safe, and its methods re-entrant.  
// The following methods are expected to be called asynchronously 
// by threads safely.

// Author: John Apostolakis (CERN), 10.02.2025
// -------------------------------------------------------------------
#ifndef G4VOXELISATIONHELPER_HH
#define G4VOXELISATIONHELPER_HH

#include <vector>

#include "G4Types.hh"
#include "G4SmartVoxelStat.hh"
#include "G4ios.hh"

class G4VPhysicalVolume;
class G4Timer;

/**
 * @brief G4VoxelisationHelper is a helper class to undertake voxelisation
 * in parallel, aiding and off-loading the work of G4GeometryManager.
 */

class G4VoxelisationHelper
{
  public:

    /**
     * Constructor & Destructor.
     */
    G4VoxelisationHelper();
    ~G4VoxelisationHelper();

    /**
     * Key method that creates a list of volumes and resets the state
     * to prepare for the parallel optimisation.
     */
    void PrepareParallelOptimisation(G4bool allOpts, G4bool verbose);

    /**
     * Contributes to voxel optimisation until all work is done.
     * To be called by a worker thread initialisation, not by the user.
     */
    void UndertakeOptimisation();

    // Methods that can be used by this Helper, Geometry Manager and others
    // --------------------------------------------------------------------

    /**
     * Methods to report statistics on the voxelisation process.
     */
    static void ReportVoxelStats( std::vector<G4SmartVoxelStat>& stats,
                                  G4double totalCpuTime,
                                  std::ostream &os = G4cout );
    void ReportVoxelInfo(G4LogicalVolume* logVolume, std::ostream& os);

    /**
     * Sets verbosity mode.
     */
    inline void SetVerbosity(G4bool verbose) { fVerboseParallel = verbose; }

    /**
     * Returns true if all workers are finished (or all work is done).
     */
    G4bool IsParallelOptimisationFinished();

    // Auxiliary method - may be useful elsewhere

    /**
     * Check that volumes marked to optimise are done, and report number
     * of those that are missing voxel header.
     */
    G4int CheckOptimisation();

  private: // Methods used to implement the parallel optimisation

    /**
     * Builds a vector of relevant volumes.
     */
    void CreateListOfVolumesToOptimise(G4bool allOpts, G4bool verbose);
    
    /**
     * Returns a pointer to the logical volume to optimise.
     */
    G4LogicalVolume* ObtainVolumeToOptimise();

    /**
     * Prepares for doing the work in parallel.
     * Called in preparation (not MT safe).
     */
    void ReSetParallelOptimisation(G4bool verbose); 

    /**
     * Resets (empties) the list of candidate volumes for optimisation.
     * Must be called when optimisation is finished.
     */
    void ResetListOfVolumesToOptimise();

    /**
     * Thread-safe method for a worker to report it's finished its work.
     * It counts the number of workers that finished, and returns count.
     * It counts the number of volumes optimised; if all workers have
     * reported, it results in a 'Finished' state.
     */
    G4int ReportWorkerIsDoneOptimising(unsigned int numVolumesOptimised);

    /**
     * Method called when all work is done -- all workers are finished.
     */
    void RecordOptimisationIsFinished(G4bool verbose);

    /**
     * Waits until the voxelisation is all done.
     */
    void WaitForVoxelisationFinish(G4bool verbose = false);

  private:

    /** The list of volumes which threads need to optimise. */
    std::vector<G4LogicalVolume*> fVolumesToOptimise;

    /** Iterator used by UndertakeOptimisation(). */
    std::vector<G4LogicalVolume*>::const_iterator fLogVolumeIterator;

    /** Statistics container shared by all workers. */
    std::vector<G4SmartVoxelStat> fGlobVoxelStats;
  
    // Flags for parallel initialization
    // ---------------------------------

    G4bool fVerboseParallel = false;
    G4bool fParallelVoxelOptimisationUnderway = false; // It has started
    G4bool fParallelVoxelOptimisationFinished = false; // It is done

    // Statistics for parallel Optimisation - used in 'verbose' mode
    // ------------------------------------

    /** Counters. */
    G4double fSumVoxelTime = -9999999.9999;
    G4int fNumberThreadsReporting = -99999; // Must be set correctly later
    unsigned long fTotalNumberVolumesOptimised = -9999999;
  
    /** For Wall Clock time in parallel mode ... */
    G4Timer* fWallClockTimer = nullptr;
    G4bool fWallClockStarted = false;
};

#endif