auto-config BField flags based on DCS database

MagneticField/MagFieldConfig/python/BFieldConfigFlags.py

-# Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
+# Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
 
 from AthenaConfiguration.AthConfigFlags import AthConfigFlags
+from CoolConvUtilities.MagFieldUtils import getFieldForRun
 
+
+#So far no attempt to auto-config field for MC or online-running
+#
+#The old-style config did auto-config the field for online based on IS
+#(see https://gitlab.cern.ch/atlas/athena/-/blame/1802605a4ab69cab7ee3e53d75f162c7da99a944/Reconstruction/RecExample/RecExOnline/python/OnlineISConfiguration.py#L52)
+#
+#The old-sytle config tried to auto-config the field based on in-file metadata, falling back to Geometry and Conditions tags. See  
+#(see https://gitlab.cern.ch/atlas/athena/-/blame/1802605a4ab69cab7ee3e53d75f162c7da99a944/Reconstruction/RecExample/RecExConfig/python/AutoConfiguration.py#L181
+
+def _toroidFieldAutoCfg(prevFlags):
+    if prevFlags.Input.isMC or prevFlags.Common.isOnline:
+        return True
+
+    lbs=prevFlags.Input.LumiBlockNumbers
+    fieldStat=getFieldForRun(run=prevFlags.Input.RunNumbers[0],lumiblock=0 if len(lbs)==0 else lbs[0],quiet=True)
+    return (fieldStat.toroidCurrent()>1)
+
+def _solenoidFieldAutoCfg(prevFlags):
+    if prevFlags.Input.isMC or prevFlags.Common.isOnline:
+        return True
+
+    lbs=prevFlags.Input.LumiBlockNumbers
+    fieldStat=getFieldForRun(run=prevFlags.Input.RunNumbers[0],lumiblock=0 if len(lbs)==0 else lbs[0],quiet=True)
+    return (fieldStat.solenoidCurrent()>1)
+    
+                              
 def createBFieldConfigFlags(): 
     bcf=AthConfigFlags()
-    # True when magnetic filed is taken from these flags rather than cond db (when available)
-    bcf.addFlag("BField.override", True)
     # True when solenoid is on
-    bcf.addFlag("BField.solenoidOn", True)
+    bcf.addFlag("BField.solenoidOn", _solenoidFieldAutoCfg)
     # True when barrel toroid is on
-    bcf.addFlag("BField.barrelToroidOn", True)
+    bcf.addFlag("BField.barrelToroidOn", _toroidFieldAutoCfg)
     # True when endcap toroid is on
-    bcf.addFlag("BField.endcapToroidOn", True)
+    bcf.addFlag("BField.endcapToroidOn", _toroidFieldAutoCfg)
     return bcf