//-----------------------------------------------------------
// Description:
//      Pulseshape from an APFEL ASIC preamplifier shaper
//      Circuit is described in EMC TDR and consists of charge-sensitive preamplifier,
//      with the following pole-zero cancelation of its feedback ad 3rd order integrator.
//		  The pulseshape is determined by the integration time of single intagrator stage 
//      and scintillation time of the crystal, with exponential input convoluted with
//      response of the circuit  
//
//-----------------------------------------------------------


// This Class' Header ------------------
#include "PndEmcAsicPulseshape.h"

// C/C++ Headers ----------------------
#include "assert.h"
#include "math.h"

// Collaborating Class Headers --------


// Class Member definitions -----------

PndEmcAsicPulseshape::PndEmcAsicPulseshape(double Tint, double Tsig) 
  : fTint(Tint), fTsig(Tsig)    
{
  assert(fTint!=fTsig);
}

double 
PndEmcAsicPulseshape::operator() (const double t, 
	    const double amp, const double toffset) const {
  if(fTsig==0)return degenerate_solution(t,amp,toffset);
  
  return general_solution(t,amp,toffset);
}


double 
PndEmcAsicPulseshape::general_solution(const double t, 
				    const double amp, 
				    const double toffset) const 
{
	double dt=t-toffset;
	if(dt<0) return 0;                           // piecewise definition!
	
	double l_int=1.0/fTint;
	double l_sig=1.0/fTsig;

	double term1=exp(-dt*l_int)*dt*dt*dt/(6*(l_sig-l_int));
	double term2=exp(-dt*l_int)*dt*dt/(2*pow(l_sig-l_int,2));
	double term3=exp(-dt*l_int)*dt/(pow(l_sig-l_int,3));
	double term4=exp(-dt*l_int)/(pow(l_sig-l_int,4));
	double term5=exp(-dt*l_sig)/(pow(l_sig-l_int,4));
	
	return amp*(term1-term2+term3-term4+term5); 
}


double 
PndEmcAsicPulseshape::degenerate_solution(const double t,  // for Tsig=0
				       const double amp, 
				       const double toffset) const 
{
	double dt=t-toffset;
	if(dt<0) return 0;                           // piecewise definition!
	
	double l_shaper=1.0/fTint;
   
	double term1 = exp(-l_shaper*dt)*pow(dt,3);

	return amp*term1;
}

ClassImp(PndEmcAsicPulseshape);