/afs/cern.ch/work/a/aaltunda/public/www/CMSSW_6_2_7/src/RecoTauTag/RecoTau/src/PFTauDecayModeTools.cc

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#include <map>
#include <boost/assign.hpp>
#include "RecoTauTag/RecoTau/interface/PFTauDecayModeTools.h"
#include "DataFormats/JetReco/interface/GenJet.h"
#include "PhysicsTools/JetMCUtils/interface/JetMCTag.h"

namespace reco { namespace tau {

namespace {
  struct entry {
    char const *label;
    reco::PFTau::hadronicDecayMode mode;
  };

  // Convert the string decay mode from PhysicsTools to the
  // PFTau::hadronicDecayMode format
  constexpr entry dmTranslatorMap[] = {
    {"unknown", reco::PFTau::kNull},
    {"rare", reco::PFTau::kRareDecayMode},
    {"oneProng0Pi0", reco::PFTau::kOneProng0PiZero},
    {"oneProng1Pi0", reco::PFTau::kOneProng1PiZero},
    {"oneProng2Pi0", reco::PFTau::kOneProng2PiZero},
    {"oneProngOther", reco::PFTau::kOneProngNPiZero},
    {"threeProng0Pi0", reco::PFTau::kThreeProng0PiZero},
    {"threeProng1Pi0", reco::PFTau::kThreeProng1PiZero},
    {"threeProngOther", reco::PFTau::kThreeProngNPiZero},
    {"electron", reco::PFTau::kNull},
    {"muon", reco::PFTau::kNull},
    {0,reco::PFTau::kNull}
  };
  
  constexpr bool same(char const *x, char const *y) {
    return !*x && !*y ? true : (*x == *y && same(x+1, y+1));
  }

  constexpr enum reco::PFTau::hadronicDecayMode decayModeStringToId(char const *label, entry const *entries) {
    return !entries->label ? reco::PFTau::kRareDecayMode : same(entries->label, label) ? entries->mode : decayModeStringToId(label, entries+1);
  }

  constexpr char const *decayModeIdToString(reco::PFTau::hadronicDecayMode mode, entry const *entries) {
    return !entries->label ? "unknown" : (entries->mode == mode ? entries->label : decayModeIdToString(mode, entries+1));
  }
}

unsigned int chargedHadronsInDecayMode(PFTau::hadronicDecayMode mode) {
   int modeAsInt = static_cast<int>(mode);
   return (modeAsInt / PFTau::kOneProngNPiZero) + 1;
}

unsigned int piZerosInDecayMode(PFTau::hadronicDecayMode mode) {
   int modeAsInt = static_cast<int>(mode);
   return (modeAsInt % PFTau::kOneProngNPiZero);
}

PFTau::hadronicDecayMode translateDecayMode(
    unsigned int nCharged, unsigned int nPiZeros) {
   // If no tracks exist, this is definitely not a tau!
   if(!nCharged) return PFTau::kNull;
   // Find the maximum number of PiZeros our parameterization can hold
   const unsigned int maxPiZeros = PFTau::kOneProngNPiZero;
   // Determine our track index
   unsigned int trackIndex = (nCharged-1)*(maxPiZeros+1);
   // Check if we handle the given number of tracks
   if(trackIndex >= PFTau::kRareDecayMode) return PFTau::kRareDecayMode;

   nPiZeros = (nPiZeros <= maxPiZeros) ? nPiZeros : maxPiZeros;
   return static_cast<PFTau::hadronicDecayMode>(trackIndex + nPiZeros);
}

PFTau::hadronicDecayMode translateGenDecayModeToReco(
    const std::string& name) {
  return decayModeStringToId(name.c_str(), dmTranslatorMap);
}

std::string translateRecoDecayModeToGen(PFTau::hadronicDecayMode decayMode) {
  return decayModeIdToString(decayMode, dmTranslatorMap);
}


PFTau::hadronicDecayMode getDecayMode(const reco::GenJet* genJet) {
  if (!genJet)
    return reco::PFTau::kNull;
  return translateGenDecayModeToReco(JetMCTagUtils::genTauDecayMode(*genJet));
}

}} // end namespace reco::tau