#include "PrimaryGeneratorAction.hh"

#include "G4Box.hh"
#include "G4LogicalVolume.hh"
#include "G4LogicalVolumeStore.hh"
#include "G4ParticleDefinition.hh"
#include "G4ParticleGun.hh"
#include "G4ParticleTable.hh"
#include "G4RunManager.hh"
#include "G4SystemOfUnits.hh"
#include "Randomize.hh"

namespace B1 {

PrimaryGeneratorAction::PrimaryGeneratorAction() {
    // 初始化粒子枪，每个 event 有 n_particle 个粒子
    G4int n_particle = 1;
    fParticleGun = new G4ParticleGun(n_particle);

    // default particle kinematic
    // 粒子列表的查找器
    G4ParticleTable* particleTable = G4ParticleTable::GetParticleTable();
    // 设置为 6 MeV 沿 z 轴正方向的 gamma 源
    G4ParticleDefinition* particle = particleTable->FindParticle("gamma");
    fParticleGun->SetParticleDefinition(particle);
    fParticleGun->SetParticleMomentumDirection(G4ThreeVector(0., 0., 1.));
    fParticleGun->SetParticleEnergy(6. * MeV);
}

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

// 每次 event 调用一次 this function is called at the begining of ecah event
// 可以设置粒子能谱分布、角度分布、源的位置分布
void PrimaryGeneratorAction::GeneratePrimaries(G4Event* anEvent) {
    G4double envSizeXY = 0;
    G4double envSizeZ = 0;

    // 避免引入 DetectorConstruction 类
    // 从 G4LogicalVolumeStore 获取 Envelope volume
    if (!fEnvelopeBox) {
        G4LogicalVolume* envLV = G4LogicalVolumeStore::GetInstance()->GetVolume("Envelope");
        if (envLV) fEnvelopeBox = dynamic_cast<G4Box*>(envLV->GetSolid());
    }

    // 获取几何参数
    if (fEnvelopeBox) {
        envSizeXY = fEnvelopeBox->GetXHalfLength() * 2.;
        envSizeZ = fEnvelopeBox->GetZHalfLength() * 2.;
    } else {
        G4ExceptionDescription msg;
        msg << "Envelope volume of box shape not found.\n";
        msg << "Perhaps you have changed geometry.\n";
        msg << "The gun will be place at the center.";
        G4Exception("PrimaryGeneratorAction::GeneratePrimaries()", "MyCode0002", JustWarning, msg);
    }

    // 几何参数用于调整源的空间分布
    G4double size = 0.8;
    G4double x0 = size * envSizeXY * (G4UniformRand() - 0.5);
    G4double y0 = size * envSizeXY * (G4UniformRand() - 0.5);
    G4double z0 = -0.5 * envSizeZ;

    fParticleGun->SetParticlePosition(G4ThreeVector(x0, y0, z0));  // 设置此次发射的位置
    fParticleGun->GeneratePrimaryVertex(anEvent);                  // 发射粒子
}

}  // namespace B1