#ifndef __JDETECTOR__JK40DEFAULTSIMULATORINTERFACE__
#define __JDETECTOR__JK40DEFAULTSIMULATORINTERFACE__

#include "TRandom3.h"

#include "JDetector/JK40Simulator.hh"
#include "JDetector/JModuleIdentifier.hh"
#include "JDetector/JPMTIdentifier.hh"
#include "JDetector/JTimeRange.hh"

#include "JMath/JMathToolkit.hh"
#include "JLang/JException.hh"
#include "JLang/JCC.hh"


/**
 * \author mdejong
 */

namespace JDETECTOR {}
namespace JPP { using namespace JDETECTOR; }

namespace JDETECTOR {

  using JLANG::JNumericalPrecision;


  /**
   * Default K40 simulator interface.
   *
   * This class provides for a default implementation of the JK40Simulator interface
   * which is based on a set of virtual methods.
   * These methods constitute a user interface to the K40 background simulation.
   */
  class JK40DefaultSimulatorInterface :
    public JK40Simulator
  {
  protected:
    /**
     * 1D-linear buffer.
     */
    struct JBuffer1D_t : 
      public std::vector<double>
    {};


    /**
     * 2D-square buffer.
     */
    struct JBuffer2D_t : 
      public std::vector<JBuffer1D_t>
    {
      /**
       * Resize.
       *
       * \param  size    size
       */
      void resize(size_t size)
      {
	std::vector<JBuffer1D_t>::resize(size);

	for (iterator i = begin(); i != end(); ++i) {
	  i->resize(size);
	}
      }
    };


    /**
     * Default constructor.
     */
    JK40DefaultSimulatorInterface()
    {}


  public:
    /**
     * Get singles rate as a function of PMT.
     *
     * \param  pmt            PMT identifier
     * \return                rate [Hz]
     */
    virtual double getSinglesRate(const JPMTIdentifier& pmt) const = 0;

    
    /**
     * Get multiples rate as a function of optical module.
     *
     * \param  module         optical module identifier
     * \param  M              multiplicity (M >= 2)
     * \return                rate [Hz]
     */
    virtual double getMultiplesRate(const JModuleIdentifier& module, const int M) const = 0;


    /**
     * Get probability of coincidence.
     *
     * \param  ct             cosine space angle between PMT axes
     * \return                probability
     */
    virtual double getProbability(const double ct) const = 0;


    /**
     * Generate hits.
     *
     * \param  module         module
     * \param  period         time window [ns]
     * \param  output         background data
     */
    virtual void generateHits(const JModule&    module,
			      const JTimeRange& period,
			      JModuleData&      output) const
    {

      // resize internal buffers
      
      const int N = module.size();

      probability2D.resize(N);
      probability1D.resize(N);
      probabilityND.resize(N);

      rateL1_Hz.resize(N);


      // generate singles

      for (int pmt = 0; pmt != N; ++pmt) {

	const double rateL0_Hz = getSinglesRate(JPMTIdentifier(module.getID(), pmt));

	if (rateL0_Hz > 0.0) {
	      
	  const double t_ns = 1.0e9 / rateL0_Hz;          // [ns]
	      
	  for (double t1 = period.getLowerLimit() + gRandom->Exp(t_ns); t1 < period.getUpperLimit(); t1 += gRandom->Exp(t_ns)) {
	    output[pmt].push_back(JPMTSignal(t1, 1));
	  }
	}
      }


      // generate coincidences

      double totalRateL1_Hz = 0.0;

      for (int i = 0; i != N; ++i) {
	totalRateL1_Hz += rateL1_Hz[i] = getMultiplesRate(module.getID(), i + 2);
      }

      if (totalRateL1_Hz > 0.0) {

	const double t_ns = 1.0e9 / totalRateL1_Hz;       // [ns]

	double t1 = period.getLowerLimit() + gRandom->Exp(t_ns);

	if (t1 < period.getUpperLimit()) {


	  // configure correlation matrix

	  for (int i = 0; i != N; ++i) {
	    
	    probability2D[i][i] = 0.0;

	    for (int j = i + 1; j != N; ++j) {
	      
	      const double ct = JMATH::getDot(module[i], module[j]);
	      const double p  = getProbability(ct);
	      
	      probability2D[i][j] = p;
	      probability2D[j][i] = p;
	    }
	  }


	  // determine probability of a coincidence as a function of the PMT number
	  
	  for (int i = 0; i != N; ++i) {

	    probability1D[i] = 0.0;

	    for (int j = 0; j != N; ++j) {
	      probability1D[i] += probability2D[i][j];
	    }
	  }


	  for ( ; t1 < period.getUpperLimit(); t1 += gRandom->Exp(t_ns)) {


	    // generate two-fold coincidence

	    const unsigned int pmt1 = getRandomIndex(probability1D,       gRandom->Rndm());
	    const unsigned int pmt2 = getRandomIndex(probability2D[pmt1], gRandom->Rndm());

	    output[pmt1].insert(JPMTSignal(gRandom->Gaus(t1, getSigma()), 1));
	    output[pmt2].insert(JPMTSignal(gRandom->Gaus(t1, getSigma()), 1));


	    try {

	      // generate larger than two-fold coincidences, if any

	      unsigned int M = getRandomIndex(rateL1_Hz, gRandom->Rndm());

	      if (M != 0) {

		probabilityND = probability2D[pmt1];

		for (unsigned int pmtN = pmt2; M != 0; --M) {

		  for (int i = 0; i != N; ++i) {
		    probabilityND[i] *= probability2D[pmtN][i];
		  }

		  probabilityND[pmtN] = 0.0;
		  
		  pmtN = getRandomIndex(probabilityND, gRandom->Rndm());
		  
		  output[pmtN].insert(JPMTSignal(gRandom->Gaus(t1, getSigma()), 1));
		}
	      }
	    }
	    catch (const JNumericalPrecision&) {}
	  }
	}
      }
    }


    /**
     * Get index based on random value.
     *
     * It is assumed that the values of the input buffer monotonously decrease or increase.
     * This method throws an exception when the summed values in the input buffer is zero.
     *
     * \param  buffer         input  values
     * \param  random         random value <0,1]
     * \return                index
     */
    static inline unsigned int getRandomIndex(const JBuffer1D_t& buffer, const double random)
    {
      double x = 0.0;

      for (JBuffer1D_t::const_iterator i = buffer.begin(); i != buffer.end(); ++i) {
	x += *i;
      }

      if (x > 0.0) {

	x *= random;

	unsigned int index = 0;

	for (JBuffer1D_t::const_iterator i = buffer.begin(); i != buffer.end() && (x -= *i) > 0.0; ++i, ++index) {}

	if (index == buffer.size()) {
	  --index;
	}

	return index;

      } else {

	THROW(JNumericalPrecision, "getRandomIndex(): zero or negative probability.");
      }
    }


    /**
     * Get intrinsic time smearing of K40 coincidences.
     *
     * \return                sigma [ns]
     */
    static double getSigma()
    {
      return get_sigma();
    }


    /**
     * Set intrinsic time smearing of K40 coincidences.
     *
     * \param  sigma          sigma [ns]
     */
    static void setSigma(const double sigma)
    {
      get_sigma() = sigma;
    }

  private:
    /**
     * Get intrinsic time smearing of K40 coincidences.
     *
     * \return                sigma [ns]
     */
    static double& get_sigma()
    {
      static double sigma = 0.5;

      return sigma;
    }


    /**
     * This correlation matrix is a two-dimensional array in which element [i][j] 
     * corresponds to the probability of a genuine coincidence due to K40 decays, 
     * where i and j refer to the indices of the PMTs in the optical module.
     */
    mutable JBuffer2D_t probability2D;

    /**
     * This probability vector is a one-dimensional array in which element [i] 
     * corresponds to the probability of a genuine coincidence due to K40 decays, 
     * where i refers to the index of the PMT in the optical module.
     */
    mutable JBuffer1D_t probability1D;

    /**
     * This probability vector is a one-dimensional array in which element [i] 
     * corresponds to the probability of an additional hit,
     * where i refers to the index of the PMT in the optical module.
     */
    mutable JBuffer1D_t probabilityND;

    /**
     * Multiples rate as a function of the multiplicity.
     * The index i corresponds to multiplicity M = i + 2.
     */
    mutable JBuffer1D_t rateL1_Hz;
  }; 
}

#endif