[MIRROR] Converts the enemies list to weakrefs (#6453)

* Converts the enemies list to weakrefs (#59694)

This has some minor overhead, but listtargets isn't exactly a hot proc, so we should be just fine

* Converts the enemies list to weakrefs

Co-authored-by: LemonInTheDark <58055496+LemonInTheDark@users.noreply.github.com>

code/modules/mob/living/simple_animal/friendly/farm_animals.dm

@@ -49,7 +49,7 @@
 			Retaliate()
 
 		if(enemies.len && DT_PROB(5, delta_time))
-			clear_enemies()
+			enemies.Cut()
 			LoseTarget()
 			src.visible_message(span_notice("[src] calms down."))
 	if(stat != CONSCIOUS)

code/modules/mob/living/simple_animal/friendly/snake.dm

@@ -53,10 +53,19 @@
 			living_mobs += HM
 
 	// if no tasty mice to chase, lets chase any living mob enemies in our vision range
-	if(length(mice) == 0)
-		//Filter living mobs (in range mobs) by those we consider enemies (retaliate behaviour)
-		return  living_mobs & enemies
-	return mice
+	if(length(mice))
+		return mice
+
+	var/list/actual_enemies = list()
+	for(var/datum/weakref/enemy as anything in enemies)
+		var/mob/flesh_and_blood = enemy.resolve()
+		if(!flesh_and_blood)
+			enemies -= enemy
+			continue
+		actual_enemies += flesh_and_blood
+
+	//Filter living mobs (in range mobs) by those we consider enemies (retaliate behaviour)
+	return  living_mobs & actual_enemies
 
 /mob/living/simple_animal/hostile/retaliate/snake/AttackingTarget()
 	if(istype(target, /mob/living/simple_animal/mouse))

code/modules/mob/living/simple_animal/hostile/retaliate/retaliate.dm

@@ -1,4 +1,5 @@
 /mob/living/simple_animal/hostile/retaliate
+	///A list of weakrefs pointing at things that we consider targets
 	var/list/enemies = list()
 
 /mob/living/simple_animal/hostile/retaliate/Found(atom/A)
@@ -7,7 +8,7 @@
 		if(!L.stat)
 			return L
 		else
-			remove_enemy(L)
+			enemies -= WEAKREF(L)
 	else if(ismecha(A))
 		var/obj/vehicle/sealed/mecha/M = A
 		if(LAZYLEN(M.occupants))
@@ -17,7 +18,15 @@
 	if(!enemies.len)
 		return list()
 	var/list/see = ..()
-	see &= enemies // Remove all entries that aren't in enemies
+	var/list/actual_enemies = list()
+	for(var/datum/weakref/enemy as anything in enemies)
+		var/mob/flesh_and_blood = enemy.resolve()
+		if(!flesh_and_blood)
+			enemies -= enemy
+			continue
+		actual_enemies += flesh_and_blood
+
+	see &= actual_enemies // Remove all entries that aren't in enemies
 	return see
 
 /mob/living/simple_animal/hostile/retaliate/proc/Retaliate()
@@ -29,37 +38,22 @@
 		if(isliving(A))
 			var/mob/living/M = A
 			if(faction_check_mob(M) && attack_same || !faction_check_mob(M))
-				add_enemy(M)
+				enemies |= WEAKREF(M)
 		else if(ismecha(A))
 			var/obj/vehicle/sealed/mecha/M = A
 			if(LAZYLEN(M.occupants))
-				add_enemy(M)
+				enemies |= WEAKREF(M)
 				add_enemies(M.occupants)
 
 	for(var/mob/living/simple_animal/hostile/retaliate/H in around)
 		if(faction_check_mob(H) && !attack_same && !H.attack_same)
-			H.add_enemies(enemies)
+			H.enemies |= enemies
 
 /mob/living/simple_animal/hostile/retaliate/adjustHealth(amount, updating_health = TRUE, forced = FALSE)
 	. = ..()
 	if(. > 0 && stat == CONSCIOUS)
 		Retaliate()
 
-/mob/living/simple_animal/hostile/retaliate/proc/add_enemy(new_enemy)
-	RegisterSignal(new_enemy, COMSIG_PARENT_QDELETING, .proc/remove_enemy, override = TRUE)
-	enemies |= new_enemy
-
 /mob/living/simple_animal/hostile/retaliate/proc/add_enemies(new_enemies)
 	for(var/new_enemy in new_enemies)
-		RegisterSignal(new_enemy, COMSIG_PARENT_QDELETING, .proc/remove_enemy, override = TRUE)
-		enemies |= new_enemy
-
-/mob/living/simple_animal/hostile/retaliate/proc/clear_enemies()
-	for(var/enemy in enemies)
-		UnregisterSignal(enemy, COMSIG_PARENT_QDELETING)
-	enemies.Cut()
-
-/mob/living/simple_animal/hostile/retaliate/proc/remove_enemy(datum/enemy_to_remove)
-	SIGNAL_HANDLER
-	UnregisterSignal(enemy_to_remove, COMSIG_PARENT_QDELETING)
-	enemies -= enemy_to_remove
+		enemies |= WEAKREF(new_enemy)