// Copyright 2019-2026 CERN and copyright holders of ALICE O2.

// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.

// All rights not expressly granted are reserved.

//

// This software is distributed under the terms of the GNU General Public

// License v3 (GPL Version 3), copied verbatim in the file "COPYING".

//

// In applying this license CERN does not waive the privileges and immunities

// granted to it by virtue of its status as an Intergovernmental Organization

// or submit itself to any jurisdiction.

#include "FastSim/ToyAbsorberFastSim.h"

#include <cmath>

namespace o2::fastsim

{

namespace

{

/// Attenuation length of the toy transformation.

constexpr double kAbsorptionLengthCm = 60.;

} // namespace

//_____________________________________________________________________________

std::vector<FastSimOutput> ToyAbsorberFastSim::sample(const FastSimInput& input) const

{

// A toy transformation, not a physics model: the incident particle carries on

// in its direction with the energy attenuated over the path through the

// envelope. A trained model returns a shower here instead.

// Always positive: ModelTrigger only calls a model above its threshold, and

// an exponential of a finite path cannot reach zero.

const double kinetic = input.kineticEnergy * std::exp(-input.exitDistance / kAbsorptionLengthCm);

const double momentum = std::sqrt(kinetic * (kinetic + 2. * input.mass));

FastSimOutput out;

out.pdg = input.pdg;

out.time = input.time;

for (int i = 0; i < 3; ++i) {

out.position[i] =

input.position[i] + (input.exitDistance + kSurfaceEpsilonCm) * input.direction[i];

out.momentum[i] = momentum * input.direction[i];

}

return {out};

}

} // namespace o2::fastsim