From f58272feb970374dd5092fc4582fd2f5cd1aa721 Mon Sep 17 00:00:00 2001
From: Christopher Dilks <c-dilks@users.noreply.github.com>
Date: Sun, 1 Dec 2024 00:59:18 -0500
Subject: [PATCH] feat: `particle::get` utility function

---
 src/iguana/algorithms/TypeDefs.h              | 33 +++++++++++++++++++
 .../clas12/PhotonGBTFilter/Algorithm.cc       | 15 ++-------
 .../clas12/PhotonGBTFilter/Algorithm.h        |  7 ----
 3 files changed, 36 insertions(+), 19 deletions(-)

diff --git a/src/iguana/algorithms/TypeDefs.h b/src/iguana/algorithms/TypeDefs.h
index d97e4e08..95a0fca4 100644
--- a/src/iguana/algorithms/TypeDefs.h
+++ b/src/iguana/algorithms/TypeDefs.h
@@ -3,6 +3,7 @@
 #pragma once
 
 #include <string>
+#include <optional>
 #include <unordered_map>
 
 namespace iguana {
@@ -92,6 +93,38 @@ namespace iguana {
       { kaon_minus, 0.493677 }
     };
 
+    /// @brief get a particle property given a PDG code
+    ///
+    /// Example:
+    /// ```cpp
+    /// auto mass = particle::get(particle::mass, particle::PDG::photon); // mass => 0.0
+    /// ```
+    /// @param property the particle property, such as `particle::name`, `particle::title`, or `particle::mass`
+    /// @param pdg_code the `particle::PDG` value
+    /// @returns the value of the property, if defined for this `pdg_code`
+    template <typename VALUE_TYPE>
+    std::optional<VALUE_TYPE> const get(std::unordered_map<PDG,VALUE_TYPE> const& property, PDG const& pdg_code)
+    {
+      if(auto const& it = property.find(pdg_code); it != property.end())
+        return it->second;
+      return std::nullopt;
+    }
+
+    /// @brief get a particle property given a PDG code
+    ///
+    /// Example:
+    /// ```cpp
+    /// auto mass = particle::get(particle::mass, 22); // mass => 0.0
+    /// ```
+    /// @param property the particle property, such as `particle::name`, `particle::title`, or `particle::mass`
+    /// @param pdg_code the `particle::PDG` value
+    /// @returns the value of the property, if defined for this `pdg_code`
+    template <typename VALUE_TYPE>
+    std::optional<VALUE_TYPE> const get(std::unordered_map<PDG,VALUE_TYPE> const& property, int const& pdg_code)
+    {
+      return get(property, static_cast<particle::PDG>(pdg_code));
+    }
+
     // clang-format on
   }
 
diff --git a/src/iguana/algorithms/clas12/PhotonGBTFilter/Algorithm.cc b/src/iguana/algorithms/clas12/PhotonGBTFilter/Algorithm.cc
index 51ddc500..72c7ff23 100644
--- a/src/iguana/algorithms/clas12/PhotonGBTFilter/Algorithm.cc
+++ b/src/iguana/algorithms/clas12/PhotonGBTFilter/Algorithm.cc
@@ -160,15 +160,15 @@ namespace iguana::clas12 {
           auto calo_PART = calo_map.at(inner_row);
           
           auto pid = particleBank.getInt("pid",inner_row);
-          auto mass = GetMass(pid);
+          auto mass = particle::get(particle::mass, pid);
           
           // Skip over particle if its mass was undefined
-          if (mass == -1.0) continue;
+          if (!mass.value()) continue;
           auto px = particleBank.getFloat("px",inner_row);
           auto py = particleBank.getFloat("py",inner_row);
           auto pz = particleBank.getFloat("pz",inner_row);
           auto p  = sqrt(px*px+py*py+pz*pz);
-          auto E  = sqrt(p*p+mass*mass);
+          auto E  = sqrt(p*p+mass.value()*mass.value());
           auto th = acos(pz/p);
           // Skip over particle if it is not in the forward detector (necessary for model compatibility)
           if (ForwardDetectorFilter(th)==false) continue;
@@ -367,15 +367,6 @@ namespace iguana::clas12 {
       return v;
   }
 
-  double PhotonGBTFilter::GetMass(int pid) const {
-      auto it = particle::mass.find(static_cast<particle::PDG>(pid));
-      if (it != particle::mass.end()) {
-        return it->second;
-      } else {
-        return -1.0; // Default mass if pid not found
-      }
-  }
-    
   std::function<double(std::vector<float> const &)> PhotonGBTFilter::getModelFunction(int runnum) const {
 
     for (const auto &entry : modelMap) {
diff --git a/src/iguana/algorithms/clas12/PhotonGBTFilter/Algorithm.h b/src/iguana/algorithms/clas12/PhotonGBTFilter/Algorithm.h
index fb87f499..9c68442a 100644
--- a/src/iguana/algorithms/clas12/PhotonGBTFilter/Algorithm.h
+++ b/src/iguana/algorithms/clas12/PhotonGBTFilter/Algorithm.h
@@ -101,13 +101,6 @@ namespace iguana::clas12 {
       /// @returns a ROOT::Math::XYZVector with the coordinates of the particle in the calorimeter
       ROOT::Math::XYZVector GetParticleCaloVector(PhotonGBTFilter::calo_row_data calo_row) const;
       
-      
-      /// Gets the mass of a particle given its PID
-      /// @param pid the particle ID to get the mass for
-      /// @returns the mass of the particle in GeV; returns -1.0 if the PID is not recognized
-      double GetMass(int pid) const;
-      
-      
       /// Gets the model function for the run number
       /// @param runnum the run of the associated event
       /// @returns GBT function for the run period