From c29fb407d5794089da62b7bf53049097fc74c725 Mon Sep 17 00:00:00 2001
From: Paul Romano <paul.k.romano@gmail.com>
Date: Wed, 31 Aug 2022 16:20:42 -0500
Subject: [PATCH] Add global configuration via openmc.config

---
 openmc/__init__.py |  1 +
 openmc/config.py   | 54 ++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+)
 create mode 100644 openmc/config.py

diff --git a/openmc/__init__.py b/openmc/__init__.py
index abcac899f6..214695e67f 100644
--- a/openmc/__init__.py
+++ b/openmc/__init__.py
@@ -32,6 +32,7 @@ from openmc.search import *
 from openmc.polynomial import *
 from openmc.tracks import *
 from . import examples
+from .config import *
 
 # Import a few names from the model module
 from openmc.model import rectangular_prism, hexagonal_prism, Model
diff --git a/openmc/config.py b/openmc/config.py
new file mode 100644
index 0000000000..a883c74cc9
--- /dev/null
+++ b/openmc/config.py
@@ -0,0 +1,54 @@
+from collections.abc import MutableMapping
+import os
+from pathlib import Path
+
+from openmc.data import DataLibrary
+
+
+class _Config(MutableMapping):
+    def __init__(self, data=()):
+        self._mapping = {}
+        self.update(data)
+
+    def __getitem__(self, key):
+        return self._mapping[key]
+
+    def __delitem__(self, key):
+        del self._mapping[key]
+
+    def __setitem__(self, key, value):
+        if key == 'cross_sections':
+            # Force environment variable to match
+            self._mapping[key] = Path(value)
+            os.environ['OPENMC_CROSS_SECTIONS'] = str(value)
+        elif key == 'chain_file':
+            self._mapping[key] = Path(value)
+        else:
+            raise KeyError(f'Unrecognized config key: {key}')
+
+    def __iter__(self):
+        return iter(self._mapping)
+
+    def __len__(self):
+        return len(self._mapping)
+
+    def __repr__(self):
+        return repr(self._mapping)
+
+
+# Create default configuration
+config = _Config()
+
+# Set cross sections using environment variable
+config['cross_sections'] = os.environ.get("OPENMC_CROSS_SECTIONS")
+
+# Check for depletion chain in cross_sections.xml
+# Set depletion chain
+chain_file = os.environ.get("OPENMC_DEPLETE_CHAIN")
+if chain_file is None and config['cross_sections'] is not None:
+    data = DataLibrary.from_xml(config['cross_sections'])
+    for lib in reversed(data.libraries):
+        if lib['type'] == 'depletion_chain':
+            chain_file = lib['path']
+            break
+config['chain_file'] = chain_file