Pattern for numerical stats that can have buffs or debuffs applied.

stat.gd

extends Resource
class_name Stat
# keeps track a a numerical stat and connected buffs / debuffs

# name of stat, also used as a matching ID for buffs
@export var name:String = ""

# whether value needs to be recalculated
var dirty:bool = false

# value of the stat after all buffs are added to base_value
var value:float:
	get:
		if dirty:
			recalculate()
		return value

# starting value without buffs
@export var base_value:float = 0:
	set(new_value):
		base_value = new_value
		dirty = true

# list of buffs attached to this stat
var buffs:Array[StatBuff] = []

func _init(new_name:String, start_value:float = 0.0) -> void:
	name = new_name
	base_value = start_value

# recalculates value based on current list of buffs
func recalculate() -> void:
	var temp_value = base_value
	var unstacked:Dictionary = {} # list of buff changes that need special handling
	for buff in buffs:
		if buff.no_stacking:
			# use the highest change instead of letting them add together
			if unstacked.has(buff.source):
				unstacked[buff.source] = max(buff.change, unstacked[buff.source])
			else:
				unstacked[buff.source] = buff.change
		else: # handle normally
			temp_value += buff.change
	
	for change in unstacked:
		temp_value += change
	
	value = temp_value
	dirty = false
	
# adds a buff
func add_buff(new_buff:StatBuff) -> void:
	# TODO should we prevent duplicate buffs?
	buffs.append(new_buff)
	dirty = true

# removes a given buff	
# returns whether it had the buff to remove
func remove_buff(old_buff:StatBuff) -> bool:
	if buffs.has(old_buff):
		buffs.remove_at(buffs.find(old_buff))
		dirty = true
		return true
	else:
		return false

# clears all buffs
func clear_buffs() -> void:
	buffs.clear()
	dirty = true

# remove any buffs that came from a named source
# int is how many were found
func remove_buff_source(source:String) -> int:
	var remove_list:Array[StatBuff] = []
	for buff in buffs:
		if buff.source == source:
			remove_list.append(buff)
			dirty = true
	for buff in remove_list:
		if buffs.has(buff):
			buffs.remove_at(buffs.find(buff))
	return remove_list.size()

stat_buff.gd

extends Resource
class_name StatBuff
# adds a value to a given stat, can easily be debuff if change is negative

# name of the stat this will be applied to
@export var stat_name:String = ""

# name of how much it changes the underlying stat
@export var change:float = 0.0

# name of the source of this buff
@export var source:String = ""


func _init(new_name:String, new_change:float, new_source:String = "") -> void:
	stat_name = new_name
	change = new_change
	source = new_source

stat_container.gd

extends Resource
class_name StatContainer
# contains any number of stats

@export var stats:Array[Stat]

var dirty:bool = false

var baked_stats:Dictionary = {}

# adds a stat
func add_stat(stat_name:String, stat_value:float = 0.0) -> void:
	# if the stat alredy exists, just update base value
	for stat in stats:
		if stat.name == stat_name:
			stat.base_value = stat_value
			dirty = true
			return
	# otherwise, create the stat and add it to the list
	var new_stat:Stat = Stat.new(stat_name, stat_value)
	stats.append(new_stat)
	# since this stat has no buffs yet, we can just directly set the baked value and not bother with dirty
	if !baked_stats.has(stat_name):
		baked_stats[stat_name] = stat_value

# removes a stat
func remove_stat(stat_name:String) -> void:
	for stat in stats:
		if stat.name == stat_name:
			stats.remove_at(stats.find(stat))
			# remove it from the baked stats
			if baked_stats.has(stat_name):
				baked_stats.erase(stat_name)
			# that is the only bake change required so we don't bother setting dirty
			return

# applies a buff to the matching stat
# returns True or False based on whether a matching stat is found
func apply_buff(buff:StatBuff) -> bool:
	if buff == null:
		return false
	# search stats for matching name
	for stat in stats:
		if stat.name == buff.stat_name:
			stat.add_buff(buff)
			dirty = true
			return true
	return false

# applies a list of buffs a returns count of how many were applied
func apply_buffs(buffs:Array[StatBuff]) -> int:
	var count:int = 0
	for buff in buffs:
		if apply_buff(buff):
			count += 1
	return count

# applies a buff to the matching stat
# returns true or false based on whether a matching stat is found
func remove_buff(buff:StatBuff) -> bool:
	if buff == null:
		return false
	# search stats for matching name
	for stat in stats:
		if stat.name == buff.stat_name:
			if stat.remove_buff(buff):
				dirty = true
				return true
			else:
				return false
	return false

# removes a list of buffs
func remove_buffs(buffs:Array[StatBuff]) -> void:
	for buff in buffs:
		remove_buff(buff)


# removes all buffs from a named source
func remove_buff_source(source:String) -> void:
	for stat in stats:
		if stat.remove_buff_source(source) > 0:
			dirty = true

# fetches the value of a given stat by name
func get_value(stat_name:String) -> float:
	if dirty:
		rebake_stats()
	if baked_stats.has(stat_name):
		return baked_stats[stat_name]
	return 0.0


# bakes stats into a dictionary for easy reference by name
func rebake_stats() -> void:
	dirty = false
	baked_stats.clear()
	for stat in stats:
		baked_stats[stat.name] = stat.value