From ad5c3885d8e6f3424ee9a168bb72bf5f8b95a001 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nicol=C3=B2=20Jacazio?= <nicolo.jacazio@cern.ch>
Date: Wed, 16 Sep 2026 21:15:55 +0200
Subject: [PATCH] Add DittoMC

---
 MC/config/ALICE3/ini/ditto_pp_136tev.ini     |  6 ++
 MC/config/ALICE3/pythia8/generator_DittoMC.C | 62 ++++++++++++++++++++
 2 files changed, 68 insertions(+)
 create mode 100644 MC/config/ALICE3/ini/ditto_pp_136tev.ini
 create mode 100644 MC/config/ALICE3/pythia8/generator_DittoMC.C

diff --git a/MC/config/ALICE3/ini/ditto_pp_136tev.ini b/MC/config/ALICE3/ini/ditto_pp_136tev.ini
new file mode 100644
index 000000000..cefe555d6
--- /dev/null
+++ b/MC/config/ALICE3/ini/ditto_pp_136tev.ini
@@ -0,0 +1,6 @@
+[Diamond]
+width[2]=6.0
+
+[GeneratorExternal]
+fileName=${O2DPG_MC_CONFIG_ROOT}/MC/config/ALICE3/pythia8/generator_DittoMC.C
+funcName=generator_DittoMC("Ditto_tune_pythia8_inel_136tev.root")
diff --git a/MC/config/ALICE3/pythia8/generator_DittoMC.C b/MC/config/ALICE3/pythia8/generator_DittoMC.C
new file mode 100644
index 000000000..d454a9383
--- /dev/null
+++ b/MC/config/ALICE3/pythia8/generator_DittoMC.C
@@ -0,0 +1,62 @@
+#include "Ditto.h"
+
+#include <algorithm>
+#include <cstdint>
+#include <cstdlib>
+#include <stdexcept>
+
+#if !defined(__CLING__) || defined(__ROOTCLING__)
+
+#include <SimulationDataFormat/MCGenProperties.h>
+
+#include <Generators/GeneratorPythia8.h>
+#include <Pythia8/Pythia.h>
+
+#include <FairGenerator.h>
+#include <FairPrimaryGenerator.h>
+
+#endif
+
+// Ditto event generator
+
+class GeneratorDittoMC : public o2::eventgen::GeneratorPythia8
+{
+ public:
+  /// Constructor
+  GeneratorDittoMC(const TString& tuneFile) : mGenerator(makeConfig(tuneFile))
+  {
+    mPythia.readString("ProcessLevel:all = off");
+  }
+
+  bool generateEvent() override
+  {
+    mGenerator.generate();
+    mGenerator.loadParticles(mPythia.event, true);
+    return true;
+  }
+
+  ///  Destructor
+  ~GeneratorDittoMC() = default;
+
+ private:
+  static Ditto::Config makeConfig(const TString& tuneFile)
+  {
+    Ditto::Config config;
+    if (tuneFile.IsNull()) {
+      throw std::runtime_error("DITTO_TUNE_FILE must point to a Ditto tune file");
+    }
+    config.tuneFile = tuneFile;
+
+    const char* alienProcId = std::getenv("ALIEN_PROC_ID");
+    config.seed = alienProcId ? static_cast<std::uint64_t>(std::atoll(alienProcId)) : 0;
+    Printf("Using Ditto tune: %s and seed: %lu\n", config.tuneFile.c_str(), config.seed);
+    return config;
+  }
+
+  Ditto::Generator mGenerator;
+};
+
+FairGenerator* generator_DittoMC(const TString& tuneFile)
+{
+  return new GeneratorDittoMC(tuneFile);
+}