Fixing embedding for projectiles. (#77674)

So, the main issue was that the variables for the embed element wouldn't
set when attached to a projectile but only on items for some
insignificant reason, which means it'll spawn the shrapnel yes, but
won't embed it since the chance is null/zero. I read the code over and
over and over with the assumption that something like this wouldn't have
been done, yet it was.

As for the secondary issue, because of how embedding works, the casing
types of arrows and harpoon aren't spawned when hitting a non-carbon or
reaching their maximum range. So, I'm re-enabling the reusable arg/var
for the caseless component of harpoons and arrows, and modifying the
`projectile_drop` to not drop their payload if the embedding component
would already do that, so we avoid duping.

code/datums/elements/embed.dm

@@ -40,23 +40,23 @@
 		RegisterSignal(target, COMSIG_ATOM_EXAMINE, PROC_REF(examined))
 		RegisterSignal(target, COMSIG_EMBED_TRY_FORCE, PROC_REF(tryForceEmbed))
 		RegisterSignal(target, COMSIG_ITEM_DISABLE_EMBED, PROC_REF(detachFromWeapon))
-		if(!initialized)
-			src.embed_chance = embed_chance
-			src.fall_chance = fall_chance
-			src.pain_chance = pain_chance
-			src.pain_mult = pain_mult
-			src.remove_pain_mult = remove_pain_mult
-			src.rip_time = rip_time
-			src.impact_pain_mult = impact_pain_mult
-			src.ignore_throwspeed_threshold = ignore_throwspeed_threshold
-			src.jostle_chance = jostle_chance
-			src.jostle_pain_mult = jostle_pain_mult
-			src.pain_stam_pct = pain_stam_pct
-			initialized = TRUE
 	else
 		payload_type = projectile_payload
 		RegisterSignal(target, COMSIG_PROJECTILE_SELF_ON_HIT, PROC_REF(checkEmbedProjectile))
 
+	if(!initialized)
+		src.embed_chance = embed_chance
+		src.fall_chance = fall_chance
+		src.pain_chance = pain_chance
+		src.pain_mult = pain_mult
+		src.remove_pain_mult = remove_pain_mult
+		src.rip_time = rip_time
+		src.impact_pain_mult = impact_pain_mult
+		src.ignore_throwspeed_threshold = ignore_throwspeed_threshold
+		src.jostle_chance = jostle_chance
+		src.jostle_pain_mult = jostle_pain_mult
+		src.pain_stam_pct = pain_stam_pct
+		initialized = TRUE
 
 /datum/element/embed/Detach(obj/target)
 	. = ..()
@@ -136,24 +136,25 @@
  * That's awful, and it'll limit us to drop-deletable shrapnels in the worry of stuff like
  * arrows and harpoons being embeddable even when not let loose by their weapons.
  */
-/datum/element/embed/proc/checkEmbedProjectile(obj/projectile/P, atom/movable/firer, atom/hit, angle, hit_zone)
+/datum/element/embed/proc/checkEmbedProjectile(obj/projectile/source, atom/movable/firer, atom/hit, angle, hit_zone)
 	SIGNAL_HANDLER
 
-	if(!iscarbon(hit) || HAS_TRAIT(hit, TRAIT_PIERCEIMMUNE))
-		Detach(P)
+	if(!source.can_embed_into(hit))
+		Detach(source)
 		return // we don't care
 
 	var/obj/item/payload = new payload_type(get_turf(hit))
 	if(istype(payload, /obj/item/shrapnel/bullet))
-		payload.name = P.name
-	SEND_SIGNAL(P, COMSIG_PROJECTILE_ON_SPAWN_EMBEDDED, payload)
+		payload.name = source.name
+	SEND_SIGNAL(source, COMSIG_PROJECTILE_ON_SPAWN_EMBEDDED, payload)
 	var/mob/living/carbon/C = hit
 	var/obj/item/bodypart/limb = C.get_bodypart(hit_zone)
 	if(!limb)
 		limb = C.get_bodypart()
 
-	tryForceEmbed(payload, limb)
-	Detach(P)
+	if(!tryForceEmbed(payload, limb))
+		payload.failedEmbed()
+	Detach(source)
 
 /**
  * tryForceEmbed() is called here when we fire COMSIG_EMBED_TRY_FORCE from [/obj/item/proc/tryEmbed]. Mostly, this means we're a piece of shrapnel from a projectile that just impacted something, and we're trying to embed in it.

code/datums/elements/projectile_drop.dm

@@ -1,4 +1,8 @@
-///A simple element that spawns an atom when the bullet hits an object or reaches the end of its range
+/**
+ * A simple element that spawns an atom when the bullet hits an object or reaches the end of its range
+ * If the projectile has embedding and it can embed into the target, then it won't spawn the drop,
+ * since embedding the embed element already handles that.
+ */
 /datum/element/projectile_drop
 	element_flags = ELEMENT_BESPOKE
 	argument_hash_start_idx = 2
@@ -9,7 +13,12 @@
 	if(!isprojectile(target))
 		return ELEMENT_INCOMPATIBLE
 	src.drop_type = drop_type
-	RegisterSignals(target, list(COMSIG_PROJECTILE_RANGE_OUT, COMSIG_PROJECTILE_SELF_ON_HIT), PROC_REF(spawn_drop))
+	RegisterSignal(target, COMSIG_PROJECTILE_RANGE_OUT, PROC_REF(spawn_drop))
+	RegisterSignal(target, COMSIG_PROJECTILE_SELF_ON_HIT, PROC_REF(spawn_drop_if_not_embeddable))
+
+/datum/element/projectile_drop/Detach(datum/source)
+	UnregisterSignal(source, list(COMSIG_PROJECTILE_RANGE_OUT, COMSIG_PROJECTILE_SELF_ON_HIT))
+	return ..()
 
 /datum/element/projectile_drop/proc/spawn_drop(obj/projectile/source)
 	SIGNAL_HANDLER
@@ -17,4 +26,11 @@
 	var/atom/new_drop = new drop_type(turf)
 	SEND_SIGNAL(source, COMSIG_PROJECTILE_ON_SPAWN_DROP, new_drop)
 	//Just to be safe, knowing it won't be spawned multiple times.
-	UnregisterSignal(source, list(COMSIG_PROJECTILE_RANGE_OUT, COMSIG_PROJECTILE_SELF_ON_HIT, COMSIG_QDELETING))
+	Detach(source)
+
+/datum/element/projectile_drop/proc/spawn_drop_if_not_embeddable(obj/projectile/source, atom/movable/firer, atom/hit, angle, hit_zone)
+	SIGNAL_HANDLER
+	if(source.can_embed_into(hit))
+		Detach(source)
+		return
+	spawn_drop(source)

code/modules/projectiles/ammunition/ballistic/harpoon.dm

@@ -7,7 +7,7 @@
 
 /obj/item/ammo_casing/harpoon/Initialize(mapload)
 	. = ..()
-	AddElement(/datum/element/caseless)
+	AddElement(/datum/element/caseless, TRUE)
 
 /obj/item/ammo_casing/harpoon/update_icon_state()
 	. = ..()

code/modules/projectiles/guns/ballistic/bows/bow_arrows.dm

@@ -12,11 +12,13 @@
 	firing_effect_type = null
 	caliber = CALIBER_ARROW
 	is_cased_ammo = FALSE
+	///Whether the bullet type spawns another casing of the same type or not.
+	var/reusable = TRUE
 
 /obj/item/ammo_casing/arrow/Initialize(mapload)
 	. = ..()
 	AddElement(/datum/element/envenomable_casing)
-	AddElement(/datum/element/caseless)
+	AddElement(/datum/element/caseless, reusable)
 
 /obj/item/ammo_casing/arrow/update_icon_state()
 	. = ..()
@@ -58,7 +60,7 @@
 	desc = "Here it comes, cultist scum!"
 	icon_state = "holy_arrow_projectile"
 	damage = 20 //still a lot but this is roundstart gear so far less
-	shrapnel_type =/obj/projectile/bullet/arrow/holy
+	shrapnel_type =/obj/item/ammo_casing/arrow/holy
 	embedding = list(
 		embed_chance = 50,
 		fall_chance = 2,
@@ -80,6 +82,7 @@
 	name = "blazing star arrow"
 	desc = "A holy diver seeking its target, blessed with fire. Will ignite on hit, destroying the arrow. But if you hit an already ignited target...?"
 	projectile_type = /obj/projectile/bullet/arrow/blazing
+	reusable = FALSE
 
 /obj/projectile/bullet/arrow/blazing
 	name = "blazing arrow"

code/modules/projectiles/projectile.dm

@@ -740,9 +740,6 @@
 		SEND_SIGNAL(fired_from, COMSIG_PROJECTILE_BEFORE_FIRE, src, original)
 	if(firer)
 		SEND_SIGNAL(firer, COMSIG_PROJECTILE_FIRER_BEFORE_FIRE, src, fired_from, original)
-	//If no angle needs to resolve it from xo/yo!
-	if(shrapnel_type && LAZYLEN(embedding))
-		AddElement(/datum/element/embed, projectile_payload = shrapnel_type)
 	if(!log_override && firer && original)
 		log_combat(firer, original, "fired at", src, "from [get_area_name(src, TRUE)]")
 			//note: mecha projectile logging is handled in /obj/item/mecha_parts/mecha_equipment/weapon/action(). try to keep these messages roughly the sameish just for consistency's sake.
@@ -1129,6 +1126,10 @@
 
 	return FALSE
 
+///Checks if the projectile can embed into someone
+/obj/projectile/proc/can_embed_into(atom/hit)
+	return embedding && shrapnel_type && iscarbon(hit) && !HAS_TRAIT(hit, TRAIT_PIERCEIMMUNE)
+
 #undef MOVES_HITSCAN
 #undef MUZZLE_EFFECT_PIXEL_INCREMENT