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// Authors: Lucio Santi, Rodrigo Castro (Univ. Buenos Aires), 2018-2021
// --------------------------------------------------------------------

template <class T>
G4QSSDriver<T>::G4QSSDriver(T* pStepper) : G4InterpolationDriver<T, true>(0, pStepper)
{
  // TODO: Remove additional stepper instances - should be a separate Driver class
  this->fSteppers.resize(1);
}

template <class T>
void G4QSSDriver<T>::OnStartTracking()
{
  Base::OnStartTracking();
  if (! initializedOnFirstRun)
  {
    G4double dqRel = G4QSSMessenger::instance()->Get_dQRel();
    G4double dQMin = G4QSSMessenger::instance()->Get_dQMin();
    if (dqRel == 0) { dqRel = 0.001; }
    if (dQMin == 0) { dQMin = 0.0001; }
    this->SetPrecision(dqRel, dQMin);

    initializedOnFirstRun = true;
  }
}

template <class T>
void G4QSSDriver<T>::OnComputeStep(const G4FieldTrack* track)
{
  Base::OnComputeStep(track);
}

template <class T>
void G4QSSDriver<T>::SetPrecision(G4double dq_rel, G4double dq_min)
{
  G4cout << "Setting QSS precision parameters: "
         << "dQRel = " << dq_rel << " - "
         << "dQMin = " << dq_min << G4endl;

  for (const auto& item : this->fSteppers)
  {
    item.stepper->SetPrecision(dq_rel, dq_min);
  }
}

template <class T>
G4double G4QSSDriver<T>::AdvanceChordLimited(
  G4FieldTrack& track, G4double hstep, G4double epsStep, G4double chordDistance)
{
  // For now, just extract functionality that we don't use from G4InterpolationDriver
  // We should probably end up making  a custom G4QSSDriver separated from it
  ++this->fTotalStepsForTrack;
  this->fLastStepper = this->fSteppers.begin();

  const G4double preCurveLength = track.GetCurveLength();
  G4double postCurveLength = preCurveLength;
  auto it = this->fSteppers.begin();

  it->stepper->reset(const_cast<const G4FieldTrack*>(&track));

  field_utils::State yBegin, y;
  track.DumpToArray(yBegin);
  track.DumpToArray(y);

  G4double hdid = OneGoodStep(it, y, this->fdydx, hstep, epsStep, preCurveLength, &track);
  postCurveLength += hdid;

  G4double dChordStep = this->DistChord(yBegin, preCurveLength, y, postCurveLength);

  // update chord step estimate
  hdid = this->FindNextChord(
    yBegin, preCurveLength, y, postCurveLength, dChordStep, chordDistance);

  track.LoadFromArray(y, this->fSteppers[0].stepper->GetNumberOfVariables());
  track.SetCurveLength(preCurveLength + hdid);

  return hdid;
}

template <class T>
G4double G4QSSDriver<T>::OneGoodStep(typename G4InterpolationDriver<T, true>::StepperIterator it,
  field_utils::State& y, field_utils::State& dydx, G4double& hstep, G4double /*epsStep*/,
  G4double curveLength, G4FieldTrack* /*track*/)
{
  G4double yerr[G4FieldTrack::ncompSVEC], ytemp[G4FieldTrack::ncompSVEC];
  it->stepper->Stepper(y, dydx, hstep, ytemp, yerr);
  G4double h = it->stepper->GetLastStepLength();

  // set interpolation interval
  it->begin = curveLength;
  it->end = curveLength + h;
  it->inverseLength = 1. / h;

  field_utils::copy(y, ytemp);

  return h;
}