Add disease resistance effects for spaceacillin (#67448)

About The Pull Request

Spaceacillin is currently an under utilized medical chem. Its only effect is to stop a person who is already infected from spreading an airborne disease.

My changes add the following when someone has taken spaceacillin:

    Infected mobs slow down disease progression by 50%
    Uninfected mobs have a 75% chance to block being infected
    Uninfected mobs have a 75% chance to block zombie infection when attacked
    Impregnated mobs that have an alien larva slow down larva growth by 50%

Why It's Good For The Game

Gives spaceacillin more utility since it was such a niche thing.
Changelog

cl
add: Add disease resistance to spaceacillin. It now gives 50% disease progression slowdown, 75% to block disease infection, 75% to block zombie infection when attacked, and 50% alien larva growth slowdown.
/cl

code/datums/diseases/_MobProcs.dm

@@ -64,6 +64,9 @@
 	if(ishuman(src))
 		var/mob/living/carbon/human/infecting_human = src
 
+		if(infecting_human.reagents.has_reagent(/datum/reagent/medicine/spaceacillin) && prob(75))
+			return
+
 		switch(target_zone)
 			if(BODY_ZONE_HEAD)
 				if(isobj(infecting_human.head))
@@ -92,6 +95,11 @@
 		disease.try_infect(src)
 
 /mob/living/proc/AirborneContractDisease(datum/disease/disease, force_spread)
+	if(ishuman(src))
+		var/mob/living/carbon/human/infecting_human = src
+		if(infecting_human.reagents.has_reagent(/datum/reagent/medicine/spaceacillin) && prob(75))
+			return
+
 	if(((disease.spread_flags & DISEASE_SPREAD_AIRBORNE) || force_spread) && prob((50*disease.spreading_modifier) - 1))
 		ForceContractDisease(disease)
 

code/datums/diseases/_disease.dm

@@ -64,6 +64,8 @@
 
 ///Proc to process the disease and decide on whether to advance, cure or make the sympthoms appear. Returns a boolean on whether to continue acting on the symptoms or not.
 /datum/disease/proc/stage_act(delta_time, times_fired)
+	var/slowdown = affected_mob.reagents.has_reagent(/datum/reagent/medicine/spaceacillin) ? 0.5 : 1 // spaceacillin slows stage speed by 50%
+
 	if(has_cure())
 		if(DT_PROB(cure_chance, delta_time))
 			update_stage(max(stage - 1, 1))
@@ -71,8 +73,7 @@
 		if(disease_flags & CURABLE && DT_PROB(cure_chance, delta_time))
 			cure()
 			return FALSE
-
-	else if(DT_PROB(stage_prob, delta_time))
+	else if(DT_PROB(stage_prob*slowdown, delta_time))
 		update_stage(min(stage + 1, max_stages))
 
 	return !carrier

code/modules/mob/living/carbon/alien/special/alien_embryo.dm

@@ -60,7 +60,11 @@
 		return
 	if(++stage < 6)
 		INVOKE_ASYNC(src, .proc/RefreshInfectionImage)
-		addtimer(CALLBACK(src, .proc/advance_embryo_stage), growth_time)
+		var/slowdown = 1
+		if(ishuman(owner))
+			var/mob/living/carbon/human/baby_momma = owner
+			slowdown = baby_momma.reagents.has_reagent(/datum/reagent/medicine/spaceacillin) ? 2 : 1 // spaceacillin doubles the time it takes to grow
+		addtimer(CALLBACK(src, .proc/advance_embryo_stage), growth_time*slowdown)
 
 /obj/item/organ/internal/body_egg/alien_embryo/egg_process()
 	if(stage == 6 && prob(50))

code/modules/reagents/chemistry/reagents/medicine_reagents.dm

@@ -271,7 +271,7 @@
 
 /datum/reagent/medicine/spaceacillin
 	name = "Spaceacillin"
-	description = "Spaceacillin will prevent a patient from conventionally spreading any diseases they are currently infected with. Also reduces infection in serious burns."
+	description = "Spaceacillin will provide limited resistance against disease and parasites. Also reduces infection in serious burns."
 	color = "#E1F2E6"
 	metabolization_rate = 0.1 * REAGENTS_METABOLISM
 	ph = 8.1

code/modules/zombie/items.dm

@@ -48,6 +48,10 @@
 		// zombies)
 		return
 
+	// spaceacillin has a 75% chance to block infection
+	if(istype(target) && target.reagents.has_reagent(/datum/reagent/medicine/spaceacillin) && prob(75))
+		return
+
 	var/obj/item/organ/internal/zombie_infection/infection
 	infection = target.getorganslot(ORGAN_SLOT_ZOMBIE)
 	if(!infection)