Fix HUD conflicts and inappropriate HUD removals

The Odysseus's medical HUD and the RD hardsuit's diagnostic HUD no
longer conflict with wearing those HUDs as glasses.

HUDs from glasses are no longer removed inappropriately by taking off a
flightsuit's helmet.

code/datums/hud.dm

@@ -31,11 +31,10 @@ GLOBAL_LIST_INIT(huds, list(
 /datum/atom_hud/proc/remove_hud_from(mob/M)
 	if(!M)
 		return
-	if(src in M.permanent_huds)
-		return
-	for(var/atom/A in hudatoms)
-		remove_from_single_hud(M, A)
-	hudusers -= M
+	if (!--hudusers[M])
+		hudusers -= M
+		for(var/atom/A in hudatoms)
+			remove_from_single_hud(M, A)
 
 /datum/atom_hud/proc/remove_from_hud(atom/A)
 	if(!A)
@@ -54,9 +53,12 @@ GLOBAL_LIST_INIT(huds, list(
 /datum/atom_hud/proc/add_hud_to(mob/M)
 	if(!M)
 		return
-	hudusers[M] = TRUE
-	for(var/atom/A in hudatoms)
-		add_to_single_hud(M, A)
+	if (!hudusers[M])
+		hudusers[M] = 1
+		for(var/atom/A in hudatoms)
+			add_to_single_hud(M, A)
+	else
+		hudusers[M]++
 
 /datum/atom_hud/proc/add_to_hud(atom/A)
 	if(!A)

code/game/mecha/medical/odysseus.dm

@@ -9,25 +9,16 @@
 	internal_damage_threshold = 35
 	deflect_chance = 15
 	step_energy_drain = 6
-	var/builtin_hud_user = 0
 
 /obj/mecha/medical/odysseus/moved_inside(mob/living/carbon/human/H)
-	if(..())
-		if(H.glasses && istype(H.glasses, /obj/item/clothing/glasses/hud))
-			occupant_message("<span class='warning'>Your [H.glasses] prevent you from using the built-in medical hud.</span>")
-		else
-			var/datum/atom_hud/data/human/medical/advanced/A = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
-			A.add_hud_to(H)
-			builtin_hud_user = 1
-		return 1
-	else
-		return 0
+	. = ..()
+	if(.)
+		var/datum/atom_hud/hud = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
+		hud.add_hud_to(H)
 
 /obj/mecha/medical/odysseus/go_out()
-	if(ishuman(occupant) && builtin_hud_user)
+	if(ishuman(occupant))
 		var/mob/living/carbon/human/H = occupant
-		var/datum/atom_hud/data/human/medical/advanced/A = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
-		A.remove_hud_from(H)
+		var/datum/atom_hud/hud = GLOB.huds[DATA_HUD_MEDICAL_ADVANCED]
+		hud.remove_hud_from(H)
 	..()
-	return
-

code/modules/clothing/spacesuits/hardsuit.dm

@@ -444,7 +444,6 @@
 	icon_state = "hardsuit0-rd"
 	item_color = "rd"
 	resistance_flags = ACID_PROOF | FIRE_PROOF
-	var/onboard_hud_enabled = 0 //stops conflicts with another diag HUD
 	max_heat_protection_temperature = FIRE_SUIT_MAX_TEMP_PROTECT
 	armor = list(melee = 30, bullet = 5, laser = 10, energy = 5, bomb = 100, bio = 100, rad = 60, fire = 60, acid = 80)
 	var/obj/machinery/doppler_array/integrated/bomb_radar
@@ -457,16 +456,13 @@
 
 /obj/item/clothing/head/helmet/space/hardsuit/rd/equipped(mob/living/carbon/human/user, slot)
 	..()
-	if(user.glasses && istype(user.glasses, /obj/item/clothing/glasses/hud/diagnostic))
-		to_chat(user, ("<span class='warning'>Your [user.glasses] prevents you using [src]'s diagnostic visor HUD.</span>"))
-	else
-		onboard_hud_enabled = 1
+	if (slot == slot_head)
 		var/datum/atom_hud/DHUD = GLOB.huds[DATA_HUD_DIAGNOSTIC]
 		DHUD.add_hud_to(user)
 
 /obj/item/clothing/head/helmet/space/hardsuit/rd/dropped(mob/living/carbon/human/user)
 	..()
-	if(onboard_hud_enabled && !(user.glasses && istype(user.glasses, /obj/item/clothing/glasses/hud/diagnostic)))
+	if (user.head == src)
 		var/datum/atom_hud/DHUD = GLOB.huds[DATA_HUD_DIAGNOSTIC]
 		DHUD.remove_hud_from(user)
 

code/modules/mob/mob_defines.dm

@@ -134,8 +134,6 @@
 
 	var/turf/listed_turf = null	//the current turf being examined in the stat panel
 
-	var/list/permanent_huds = list()
-
 	var/resize = 1 //Badminnery resize
 
 	var/list/observers = null	//The list of people observing this mob.

code/modules/surgery/organs/augments_eyes.dm

@@ -19,12 +19,10 @@
 	if(HUD_type)
 		var/datum/atom_hud/H = GLOB.huds[HUD_type]
 		H.add_hud_to(M)
-		M.permanent_huds |= H
 
 /obj/item/organ/cyberimp/eyes/hud/Remove(var/mob/living/carbon/M, var/special = 0)
 	if(HUD_type)
 		var/datum/atom_hud/H = GLOB.huds[HUD_type]
-		M.permanent_huds ^= H
 		H.remove_hud_from(M)
 	..()