From 265d3b0111f5abb136d1b6d31aab7f839fb22c39 Mon Sep 17 00:00:00 2001
From: Pim Nelissen <pim.nelissen@protonmail.com>
Date: Fri, 20 Feb 2026 11:46:45 +0100
Subject: [PATCH] Add isotope lookup dictionary, so isotopes can be loaded from
 string in config.

---
 src/pg_rad/isotopes/__init__.py |  7 +++----
 src/pg_rad/isotopes/isotope.py  | 23 +++++++++++++++++++++++
 src/pg_rad/isotopes/presets.py  | 10 ----------
 src/pg_rad/objects/sources.py   | 19 ++++++++++---------
 4 files changed, 36 insertions(+), 23 deletions(-)
 delete mode 100644 src/pg_rad/isotopes/presets.py

diff --git a/src/pg_rad/isotopes/__init__.py b/src/pg_rad/isotopes/__init__.py
index 6f000c0..b926aa8 100644
--- a/src/pg_rad/isotopes/__init__.py
+++ b/src/pg_rad/isotopes/__init__.py
@@ -2,9 +2,8 @@
 __ignore__ = ["logger"]
 
 from pg_rad.isotopes import isotope
-from pg_rad.isotopes import presets
 
-from pg_rad.isotopes.isotope import (Isotope,)
-from pg_rad.isotopes.presets import (CS137,)
+from pg_rad.isotopes.isotope import (CS137, Isotope, get_isotope,
+                                     preset_isotopes,)
 
-__all__ = ['CS137', 'Isotope', 'isotope', 'presets']
+__all__ = ['CS137', 'Isotope', 'get_isotope', 'isotope', 'preset_isotopes']
diff --git a/src/pg_rad/isotopes/isotope.py b/src/pg_rad/isotopes/isotope.py
index 5706acd..218b36f 100644
--- a/src/pg_rad/isotopes/isotope.py
+++ b/src/pg_rad/isotopes/isotope.py
@@ -1,3 +1,5 @@
+from typing import Dict, Type
+
 from pg_rad.physics.attenuation import get_mass_attenuation_coeff
 
 
@@ -25,3 +27,24 @@ class Isotope:
         self.E = E
         self.b = b
         self.mu_mass_air = get_mass_attenuation_coeff(E / 1000)
+
+
+class CS137(Isotope):
+    def __init__(self):
+        super().__init__(
+            name="Cs-137",
+            E=661.66,
+            b=0.851
+        )
+
+
+preset_isotopes: Dict[str, Type[Isotope]] = {
+    "CS137": CS137
+}
+
+
+def get_isotope(isotope_str: str) -> Isotope:
+    """Lazy factory function to create isotope objects."""
+    if isotope_str not in preset_isotopes:
+        raise ValueError(f"Unknown isotope: {isotope_str}")
+    return preset_isotopes[isotope_str]()
diff --git a/src/pg_rad/isotopes/presets.py b/src/pg_rad/isotopes/presets.py
deleted file mode 100644
index d8135d6..0000000
--- a/src/pg_rad/isotopes/presets.py
+++ /dev/null
@@ -1,10 +0,0 @@
-from .isotope import Isotope
-
-
-class CS137(Isotope):
-    def __init__(self):
-        super().__init__(
-            name="Cs-137",
-            E=661.66,
-            b=0.851
-        )
diff --git a/src/pg_rad/objects/sources.py b/src/pg_rad/objects/sources.py
index 7659704..74a0ad3 100644
--- a/src/pg_rad/objects/sources.py
+++ b/src/pg_rad/objects/sources.py
@@ -1,7 +1,7 @@
 import logging
 
 from .objects import BaseObject
-from pg_rad.isotopes.isotope import Isotope
+from pg_rad.isotopes.isotope import Isotope, get_isotope
 
 logger = logging.getLogger(__name__)
 
@@ -11,16 +11,16 @@ class PointSource(BaseObject):
 
     def __init__(
             self,
-            activity: int,
-            isotope: Isotope,
-            pos: tuple[float, float, float] = (0, 0, 0),
+            activity_MBq: int,
+            isotope: str,
+            position: tuple[float, float, float] = (0, 0, 0),
             name: str | None = None,
             color: str = 'red'
             ):
         """A point source.
 
         Args:
-            activity (int): Activity A in MBq.
+            activity_MBq (int): Activity A in MBq.
             isotope (Isotope): The isotope.
             pos (tuple[float, float, float], optional):
                 Position of the PointSource.
@@ -37,16 +37,17 @@ class PointSource(BaseObject):
         if name is None:
             name = f"Source {self.id}"
 
-        super().__init__(pos, name, color)
+        super().__init__(position, name, color)
 
-        self.activity = activity
-        self.isotope = isotope
+        self.activity = activity_MBq
+        self.isotope: Isotope = get_isotope(isotope)
 
         logger.debug(f"Source created: {self.name}")
 
     def __repr__(self):
+        x, y, z = self.position
         repr_str = (f"PointSource(name={self.name}, "
-                    + f"pos={(self.x, self.y, self.z)}, "
+                    + f"pos={(x, y, z)}, "
                     + f"A={self.activity} MBq), "
                     + f"isotope={self.isotope.name}.")