[MIRROR] Reactions now use volume averaged purity (#803)

* Reactions now use volume averaged purity (#81246)

## About The Pull Request
Cause it only makes sense

Currently the purity of reagents created in a reaction is computed as
follows

`total sum of purity of all reagents present / total number of reagents`

This is incorrect because regardless of how much "volume" of an
impure/pure reagent is present the purity of the final solution is
unaffected. Logically if we have more amount of an impure reagent the
more impure the final solution should be & same for opposite case. This
is the case for ph, where if we have a large volume of say "acidic"
reagent then changes in other reagents have a small effect to the
overall "acidity" of the solution. The same concept now applies for
purity as well

`get_average_purity()`accounts for volume thus yielding more realistic
results. The effect becomes more significant with larger volumes of
reagents.

:cl:
fix: reactions now compute purity of reagents based on their volume,
meaning larger amounts of reagents created will have more significant
effects on the final purity of the solution
/:cl:

* Reactions now use volume averaged purity

* Merge #818

---------

Co-authored-by: SyncIt21 <[email protected]>
Co-authored-by: SomeRandomOwl <[email protected]>

code/modules/reagents/chemistry/equilibrium.dm

@@ -104,7 +104,7 @@
 		return FALSE
 
 	//To prevent reactions outside of the pH window from starting.
-	if(!((holder.ph >= (reaction.optimal_ph_min - reaction.determin_ph_range)) && (holder.ph <= (reaction.optimal_ph_max + reaction.determin_ph_range))))
+	if(holder.ph < (reaction.optimal_ph_min - reaction.determin_ph_range) || holder.ph > (reaction.optimal_ph_max + reaction.determin_ph_range))
 		return FALSE
 
 	//All checks pass. cache the product ratio
@@ -265,24 +265,23 @@
 	//Begin checks
 	//Calculate DeltapH (Deviation of pH from optimal)
 	//Within mid range
+	var/acceptable_ph
 	if (cached_ph >= reaction.optimal_ph_min  && cached_ph <= reaction.optimal_ph_max)
 		delta_ph = 1 //100% purity for this step
 	//Lower range
 	else if (cached_ph < reaction.optimal_ph_min) //If we're outside of the optimal lower bound
-		if (cached_ph < (reaction.optimal_ph_min - reaction.determin_ph_range)) //If we're outside of the deterministic bound
+		acceptable_ph = reaction.optimal_ph_min - reaction.determin_ph_range
+		if (cached_ph < acceptable_ph) //If we're outside of the deterministic bound
 			delta_ph = 0 //0% purity
 		else //We're in the deterministic phase
-			delta_ph = (((cached_ph - (reaction.optimal_ph_min - reaction.determin_ph_range)) ** reaction.ph_exponent_factor) / ((reaction.determin_ph_range ** reaction.ph_exponent_factor))) //main pH calculation
+			delta_ph = ((cached_ph - acceptable_ph) / reaction.determin_ph_range) ** reaction.ph_exponent_factor
 	//Upper range
 	else if (cached_ph > reaction.optimal_ph_max) //If we're above of the optimal lower bound
-		if (cached_ph > (reaction.optimal_ph_max + reaction.determin_ph_range))  //If we're outside of the deterministic bound
+		acceptable_ph = reaction.optimal_ph_max + reaction.determin_ph_range
+		if (cached_ph > acceptable_ph)  //If we're outside of the deterministic bound
 			delta_ph = 0 //0% purity
 		else  //We're in the deterministic phase
-			delta_ph = (((- cached_ph + (reaction.optimal_ph_max + reaction.determin_ph_range)) ** reaction.ph_exponent_factor) / (reaction.determin_ph_range ** reaction.ph_exponent_factor))//Reverse - to + to prevent math operation failures.
-
-	//This should never proc, but it's a catch incase someone puts in incorrect values
-	else
-		stack_trace("[holder.my_atom] attempted to determine FermiChem pH for '[reaction.type]' which had an invalid pH of [cached_ph] for set recipie pH vars. It's likely the recipe vars are wrong.")
+			delta_ph = ((acceptable_ph - cached_ph) / reaction.determin_ph_range) ** reaction.ph_exponent_factor
 
 	//Calculate DeltaT (Deviation of T from optimal)
 	if(!reaction.is_cold_recipe)
@@ -316,7 +315,7 @@
 	purity = delta_ph
 
 	//Then adjust purity of result with beaker reagent purity.
-	purity *= average_purity()
+	purity *= holder.get_average_purity()
 
 	//Then adjust it from the input modifier
 	purity *= purity_modifier
@@ -399,23 +398,3 @@
 	//i.e. we have created all the reagents needed for this reaction
 	if(total_step_added >= step_target_vol)
 		to_delete = TRUE
-
-/*
-* Calculates the total sum normalised purity of ALL reagents in a holder
-* Currently calculates it irrespective of required reagents at the start, but this should be changed if this is powergamed to required reagents
-* It's not currently because overly_impure affects all reagents
-*/
-/datum/equilibrium/proc/average_purity()
-	PRIVATE_PROC(TRUE)
-
-	var/list/cached_reagents = holder.reagent_list
-
-	var/num_of_reagents = cached_reagents.len
-	if(!num_of_reagents)//I've never seen it get here with 0, but in case - it gets here when it blows up from overheat
-		stack_trace("No reactants found mid reaction for [reaction.type]. Beaker: [holder.my_atom]")
-		return 0 //we exploded and cleared reagents - but lets not kill the process
-
-	var/cached_purity
-	for(var/datum/reagent/reagent as anything in cached_reagents)
-		cached_purity += reagent.purity
-	return cached_purity / num_of_reagents

code/modules/reagents/chemistry/holder/reactions.dm

@@ -308,36 +308,39 @@
 	var/list/cached_required_reagents = selected_reaction.required_reagents
 	var/list/cached_results = selected_reaction.results
 	var/datum/cached_my_atom = my_atom
-	var/multiplier = INFINITY
-	for(var/reagent in cached_required_reagents)
-		multiplier = round(min(multiplier, get_reagent_amount(reagent) / cached_required_reagents[reagent]))
 
-	if(!multiplier)//Incase we're missing reagents - usually from on_reaction being called in an equlibrium when the results.len == 0 handlier catches a misflagged reaction
+	//find how much ration of products to create
+	var/multiplier = INFINITY
+	for(var/datum/reagent/requirement as anything in cached_required_reagents)
+		multiplier = min(multiplier, get_reagent_amount(requirement) / cached_required_reagents[requirement])
+	multiplier = round(multiplier, CHEMICAL_QUANTISATION_LEVEL)
+	if(!multiplier)//Incase we're missing reagents - usually from on_reaction being called in an equlibrium when the results.len == 0 handler catches a misflagged reaction
 		return FALSE
-	var/sum_purity = 0
-	for(var/_reagent in cached_required_reagents)//this is not an object
-		var/datum/reagent/reagent = has_reagent(_reagent)
-		if (!reagent)
-			continue
-		sum_purity += reagent.purity
-		remove_reagent(_reagent, (multiplier * cached_required_reagents[_reagent]))
-	sum_purity /= cached_required_reagents.len
 
-	for(var/product in selected_reaction.results)
-		multiplier = max(multiplier, 1) //this shouldn't happen ...
-		var/yield = (cached_results[product]*multiplier)*sum_purity
+	//average purity to be used in scaling the yield of products formed
+	var/average_purity = get_average_purity()
+
+	//remove the required reagents
+	for(var/datum/reagent/requirement as anything in cached_required_reagents)//this is not an object
+		remove_reagent(requirement, cached_required_reagents[requirement] * multiplier)
+
+	//add the result reagents whose yield depend on the average purity
+	var/yield
+	for(var/datum/reagent/product as anything in cached_results)
+		yield = cached_results[product] * multiplier * average_purity
 		SSblackbox.record_feedback("tally", "chemical_reaction", yield, product)
-		add_reagent(product, yield, null, chem_temp, sum_purity)
+		add_reagent(product, yield, null, chem_temp, average_purity)
 
+	//play sounds on the target atom
 	var/list/seen = viewers(4, get_turf(my_atom))
 	var/iconhtml = icon2html(cached_my_atom, seen)
 	if(cached_my_atom)
 		if(!ismob(cached_my_atom)) // No bubbling mobs
 			if(selected_reaction.mix_sound)
 				playsound(get_turf(cached_my_atom), selected_reaction.mix_sound, 80, TRUE)
-
 			my_atom.audible_message(span_notice("[iconhtml] [selected_reaction.mix_message]"))
 
+		//use slime extract
 		if(istype(cached_my_atom, /obj/item/slime_extract))
 			var/obj/item/slime_extract/extract = my_atom
 			extract.extract_uses--
@@ -353,4 +356,5 @@
 			my_turf.pollute_turf(selected_reaction.pollutant_type, selected_reaction.pollutant_amount * multiplier)
 	//NOVA EDIT END
 
+	//finish the reaction
 	selected_reaction.on_reaction(src, null, multiplier)