[MIRROR] Fixes a bug with the scope getting stuck on mobs that get du…

…sted or ghost [MDB IGNORE] (#24404)

* Fixes a bug with the scope getting stuck on mobs that get dusted or ghost (#78941)

## About The Pull Request

If you ghost while mid-scope (or similarly, if you get dusted/your mob
gets deleted) the mob's cursor would get all messed up due to some
oversights. This just clears up some of these logic errors and ensures
everything gets cleaned up properly.

Fixes Skyrat-SS13/Skyrat-tg#24189
Fixes tgstation/tgstation#78756

## Why It's Good For The Game

Fixes a bug. I don't think scopes are even in use here but they are
downstream.

<details>
<summary>Deleted and being dusted resets perspective and cursor
properly</summary>

![dreamseeker_SSU4YnEK4n](https://github.com/Skyrat-SS13/Skyrat-tg/assets/13398309/dcaa5238-0067-4923-a956-24c6ba4aa2b3)

![dreamseeker_GZEhuSJSGS](https://github.com/Skyrat-SS13/Skyrat-tg/assets/13398309/2b88db21-6560-486d-94d3-9773fa543c50)

</details>

<details>
<summary>So does ghosting</summary>

![dreamseeker_7n3uXZvDSI](https://github.com/tgstation/tgstation/assets/13398309/08f6272d-baba-4e8e-ae0b-db23331982f7)

</details>

## Changelog

:cl:
fix: being killed or ghosting while being scoped will no longer cause
the cursor offset to persist in a bugged state
/:cl:

---------

Co-authored-by: san7890 <the@ san7890.com>

* Fixes a bug with the scope getting stuck on mobs that get dusted or ghost

---------

Co-authored-by: Bloop <[email protected]>
Co-authored-by: san7890 <the@ san7890.com>

code/datums/components/scope.dm

@@ -3,6 +3,10 @@
 	var/range_modifier = 1
 	/// Fullscreen object we use for tracking the shots.
 	var/atom/movable/screen/fullscreen/cursor_catcher/scope/tracker
+	/// The owner of the tracker's ckey. For comparing with the current owner mob, in case the client has left it (e.g. ghosted).
+	var/tracker_owner_ckey
+	/// Are we zooming currently?
+	var/zooming
 
 /datum/component/scope/Initialize(range_modifier)
 	if(!isgun(parent))
@@ -101,21 +105,35 @@
 	return target_turf
 
 /**
- * We start zooming by hiding the mouse pointer, adding our tracker overlay and starting our processing.
+ * Wrapper for zoom(), so in case we runtime we do not get stuck in a bad state
  *
  * Arguments:
  * * user: The mob we are starting zooming on.
 */
 /datum/component/scope/proc/start_zooming(mob/user)
-	if(!user.client)
+	if(zoom(user))
+		zooming = TRUE
+
+/**
+ * We start zooming by hiding the mouse pointer, adding our tracker overlay and starting our processing.
+ *
+ * Arguments:
+ * * user: The mob we are starting zooming on.
+*/
+/datum/component/scope/proc/zoom(mob/user)
+	if(isnull(user.client))
+		return
+	if(zooming)
 		return
 	user.client.mouse_override_icon = 'icons/effects/mouse_pointers/scope_hide.dmi'
 	user.update_mouse_pointer()
 	user.playsound_local(parent, 'sound/weapons/scope.ogg', 75, TRUE)
 	tracker = user.overlay_fullscreen("scope", /atom/movable/screen/fullscreen/cursor_catcher/scope, 0)
 	tracker.assign_to_mob(user, range_modifier)
-	RegisterSignal(user, COMSIG_MOB_SWAP_HANDS, PROC_REF(stop_zooming))
+	tracker_owner_ckey = user.ckey
+	RegisterSignals(user, list(COMSIG_MOB_SWAP_HANDS, COMSIG_QDELETING), PROC_REF(stop_zooming))
 	START_PROCESSING(SSprojectiles, src)
+	return TRUE
 
 /**
  * We stop zooming, canceling processing, resetting stuff back to normal and deleting our tracker.
@@ -126,15 +144,31 @@
 /datum/component/scope/proc/stop_zooming(mob/user)
 	SIGNAL_HANDLER
 
+	if(!zooming)
+		return
+
 	STOP_PROCESSING(SSprojectiles, src)
-	UnregisterSignal(user, COMSIG_MOB_SWAP_HANDS)
+	UnregisterSignal(user, list(COMSIG_MOB_SWAP_HANDS, COMSIG_QDELETING))
+
+	zooming = FALSE
+
+	user.playsound_local(parent, 'sound/weapons/scope.ogg', 75, TRUE, frequency = -1)
+	user.clear_fullscreen("scope")
+
+	// if the client has ended up in another mob, find that mob so we can fix their cursor
+	var/mob/true_user
+	if(user.ckey != tracker_owner_ckey)
+		true_user = get_mob_by_ckey(tracker_owner_ckey)
+
+	if(!isnull(true_user))
+		user = true_user
+
 	if(user.client)
 		animate(user.client, 0.2 SECONDS, pixel_x = 0, pixel_y = 0)
 		user.client.mouse_override_icon = null
 		user.update_mouse_pointer()
-	user.playsound_local(parent, 'sound/weapons/scope.ogg', 75, TRUE, frequency = -1)
 	tracker = null
-	user.clear_fullscreen("scope")
+	tracker_owner_ckey = null
 
 /atom/movable/screen/fullscreen/cursor_catcher/scope
 	icon_state = "scope"