#include "PrimaryGeneratorAction.hh"
#include "DetectorConstruction.hh"

#include "G4Event.hh"
#include "G4ParticleGun.hh"
#include "G4ParticleTable.hh"
#include "G4ParticleDefinition.hh"
#include "G4ThreeVector.hh"
#include "G4SystemOfUnits.hh"
#include "Randomize.hh"

// Toggle this to true if you want to place primaries uniformly in the crystal
static const bool kUniformInVolume = false;

PrimaryGeneratorAction::PrimaryGeneratorAction(DetectorConstruction* det)
    : G4VUserPrimaryGeneratorAction(),
    fDetector(det),
    fParticleGun(new G4ParticleGun(1))            // 1 primary per event
{
    auto* eMinus = G4ParticleTable::GetParticleTable()->FindParticle("e-");
    fParticleGun->SetParticleDefinition(eMinus);
    fParticleGun->SetParticleEnergy(500. * keV);

    const G4double L = fDetector->GetScintillatorSize();

    // Start just INSIDE the -X face, shoot along +X so track crosses the crystal
    const G4double eps = 0.5 * mm;
    fParticleGun->SetParticlePosition(G4ThreeVector(0.,0.,0.));
    fParticleGun->SetParticleMomentumDirection(G4ThreeVector(0., 0., +1.));
}

PrimaryGeneratorAction::~PrimaryGeneratorAction() {
    delete fParticleGun;
}

void PrimaryGeneratorAction::GeneratePrimaries(G4Event* anEvent)
{
    if (kUniformInVolume) {
        // Optional: uniformly distribute the source inside the scintillator
        const G4double L = fDetector->GetScintillatorSize();
        const auto rU = []() { return 2. * G4UniformRand() - 1.; };
        const G4ThreeVector pos(0.5 * L * rU(), 0.5 * L * rU(), 0.5 * L * rU());
        fParticleGun->SetParticlePosition(pos);
    }
    fParticleGun->GeneratePrimaryVertex(anEvent);
}