Allow planets to have fuel-based atmospheres

code/__DEFINES/mobs.dm

@@ -347,6 +347,7 @@
 // / Breathing types. Lungs can access either by these or by a string, which will be considered a gas ID.
 #define BREATH_OXY		/datum/breathing_class/oxygen
 #define BREATH_PLASMA	/datum/breathing_class/plasma
+#define BREATH_METHANE	/datum/breathing_class/methane
 
 //Gremlins
 #define NPC_TAMPER_ACT_FORGET 1 //Don't try to tamper with this again

code/datums/atmosphere/planetary.dm

@@ -13,7 +13,7 @@
 	)
 	restricted_gases = list(
 		GAS_BZ=0.1,
-		GAS_METHYL_BROMIDE=0.1,
+		GAS_BROMINE=0.1
 	)
 	restricted_chance = 30
 
@@ -23,6 +23,23 @@
 	minimum_temp = 281
 	maximum_temp = 320
 
+/datum/atmosphere/lavaland/generate_gas_string()
+	if(prob(restricted_chance))
+		base_gases = list(
+			GAS_METHANE=5,
+			GAS_N2=10
+		)
+		normal_gases = list(
+			GAS_METHANE=5,
+			GAS_N2=5,
+		)
+		restricted_gases = list(
+			GAS_AMMONIA = 0.1,
+			GAS_METHYL_BROMIDE = 0.1,
+			GAS_HYDROGEN = 0.1
+		)
+	return ..()
+
 /datum/atmosphere/lavaland/check_for_sanity(datum/gas_mixture/mix)
 	var/datum/breathing_class/o2_class = GLOB.gas_data.breathing_classes[BREATH_OXY]
 	while(o2_class.get_effective_pp(mix) < 10)
@@ -33,16 +50,16 @@
 	id = ICEMOON_DEFAULT_ATMOS
 
 	base_gases = list(
-		GAS_O2=5,
+		GAS_METHANE=5,
 		GAS_N2=10,
 	)
 	normal_gases = list(
-		GAS_O2=10,
-		GAS_N2=10,
-		GAS_CO2=10,
+		GAS_METHANE=5,
+		GAS_N2=10
 	)
 	restricted_gases = list(
 		GAS_METHYL_BROMIDE=0.1,
+		GAS_HYDROGEN=0.1
 	)
 	restricted_chance = 10
 
@@ -52,3 +69,18 @@
 	minimum_temp = 180
 	maximum_temp = 180
 
+/datum/atmosphere/icemoon/generate_gas_string()
+	if(prob(restricted_chance))
+		base_gases = list(
+			GAS_O2=5,
+			GAS_N2=10,
+		)
+		normal_gases = list(
+			GAS_O2=5,
+			GAS_N2=10,
+		)
+		restricted_gases = list(
+			GAS_BZ = 0.1,
+			GAS_METHYL_BROMIDE = 0.1,
+		)
+	return ..()

code/modules/atmospherics/auxgm/breathing_classes.dm

@@ -41,3 +41,18 @@
 	low_alert_datum = /atom/movable/screen/alert/not_enough_tox
 	high_alert_category = "too_much_tox"
 	high_alert_datum = /atom/movable/screen/alert/too_much_tox
+
+/datum/breathing_class/methane
+	gases = list(
+		GAS_METHANE = 1,
+		GAS_METHYL_BROMIDE = -0.7
+		GAS_OXYGEN = -0.1,
+		GAS_PLUOXIUM = -0.8
+	)
+	products = list(
+		GAS_METHYL_BROMIDE = 1
+	)
+	low_alert_category = "not_enough_ch4"
+	low_alert_datum = /atom/movable/screen/alert/not_enough_ch4
+	high_alert_category = "too_much_ch4"
+	high_alert_datum = /atom/movable/screen/alert/too_much_ch4

code/modules/surgery/organs/lungs.dm

@@ -440,7 +440,7 @@
 			owner.adjust_bodytemperature(30*TEMPERATURE_DAMAGE_COEFFICIENT)
 		if(50 to INFINITY)
 			owner.adjust_bodytemperature(100*TEMPERATURE_DAMAGE_COEFFICIENT)
-	
+
 /obj/item/organ/lungs/ipc/ui_action_click(mob/user, actiontype)
 	if(!owner)
 		return
@@ -494,7 +494,7 @@
 	if(owner.blood_volume <= next_warn)
 		to_chat(owner, "[owner.blood_volume > BLOOD_VOLUME_BAD ? "<span class='notice'>" : "<span class='warning'>"]Coolant level passed threshold - now [round(owner.blood_volume / BLOOD_VOLUME_NORMAL * 100, 0.1)] percent.</span>")
 		next_warn -= (BLOOD_VOLUME_NORMAL * 0.1)
-			
+
 /obj/item/organ/lungs/plasmaman
 	name = "plasma filter"
 	desc = "A spongy rib-shaped mass for filtering plasma from the air."
@@ -574,6 +574,8 @@
 	// humans usually breathe 21 but require 16/17, so 80% - 1, which is more lenient but it's fine
 	#define SAFE_THRESHOLD_RATIO 0.8
 	var/datum/gas_mixture/breath = SSair.planetary[LAVALAND_DEFAULT_ATMOS] // y'all know
+	if(breath.get_moles(GAS_METHANE) > 0.1)
+		breathing_class = BREATH_METHANE
 	var/pressure = breath.return_pressure()
 	var/total_moles = breath.total_moles()
 	for(var/id in breath.get_gases())