completely overhauls chemistry dispensers (#5132)

Co-authored-by: silicons <no@you.cat>

code/controllers/subsystem/processing/chemistry.dm

@@ -3,13 +3,17 @@ PROCESSING_SUBSYSTEM_DEF(chemistry)
 	wait = 10
 	subsystem_flags = SS_BACKGROUND|SS_POST_FIRE_TIMING
 	init_order = INIT_ORDER_CHEMISTRY
+
+	/// id to instance dict of reagents
+	var/list/reagent_lookup = list()
+
 	var/list/chemical_reactions = list()
 	var/list/chemical_reactions_by_reagent = list()
-	var/list/chemical_reagents = list()
+
 
 /datum/controller/subsystem/processing/chemistry/Recover()
 	chemical_reactions = SSchemistry.chemical_reactions
-	chemical_reagents = SSchemistry.chemical_reagents
+	reagent_lookup = SSchemistry.reagent_lookup
 
 // honestly hate that we have to do this but some things INITIALIZE_IMMEDIATE so uh fuck me I guess!
 /datum/controller/subsystem/processing/chemistry/PreInit(recovering)
@@ -41,9 +45,19 @@ PROCESSING_SUBSYSTEM_DEF(chemistry)
 /// Chemical Reagents - Initialises all /datum/reagent into a list indexed by reagent id
 /datum/controller/subsystem/processing/chemistry/proc/initialize_chemical_reagents()
 	var/paths = typesof(/datum/reagent) - /datum/reagent
-	chemical_reagents = list()
-	for(var/path in paths)
+	reagent_lookup = list()
+	for(var/datum/reagent/path as anything in paths)
+		if(initial(path.abstract_type) == path)
+			continue
 		var/datum/reagent/D = new path()
 		if(!D.name)
 			continue
-		chemical_reagents[D.id] = D
+		reagent_lookup[D.id] = D
+
+/**
+ * fetches the instance of a reagent
+ *
+ * do not edit the returned instance, it is global!
+ */
+/datum/controller/subsystem/processing/chemistry/proc/get_reagent(datum/reagent/id_or_path)
+	return reagent_lookup[ispath(id_or_path)? initial(id_or_path.id) : id_or_path]