game: add enemy modifier class

scenes/enemies/enemy_mod.gd

@@ -0,0 +1,27 @@
+class_name EnemyMod
+extends Resource
+
+enum ModType { ADDITIVE, MULTIPLICATIVE, ABSOLUTE, BOOL }
+
+@export var mod_property: String
+@export var mod_value: float
+@export var mod_value_bool: bool = false
+@export var mod_type: ModType = ModType.MULTIPLICATIVE
+
+func get_calculated(enemy: EnemyBase, key: String) -> Variant:
+	assert(enemy.has_property(key), "tried to calculate property '%s' where base value does not exist on %s" % [key, enemy])
+	var base_value = enemy.get(key)
+	var add = 0.0
+	var mul = 1.0
+	for mod in enemy.modifiers:
+		if mod.mod_property == key:
+			match mod.mod_type:
+				ModType.ADDITIVE:
+						add += mod.mod_value
+				ModType.MULTIPLICATIVE:
+						mul *= mod.mod_value
+				ModType.ABSOLUTE:
+						return mod.mod_value
+				ModType.BOOL:
+						return mod.mod_value_bool
+	return (base_value + add) * mul