static func update_anchors(tree: SceneTree, position, acceptability) -> Anchor:
	""" Update anchor visual hint, and return selected one
	"""
	var anchors = tree.get_nodes_in_group("anchors")
	for anchor in anchors:
		anchor.selectable = position and acceptability.call_func(anchor)

	var selected_anchor = null
	var selected_distance = INF
	for anchor in anchors:
		if anchor.selectable:
			var distance = anchor.global_position.distance_to(position)
			if distance < 150 and distance < selected_distance:
				selected_anchor = anchor
				selected_distance = distance

	for anchor in anchors:
		anchor.selected = (anchor == selected_anchor)

	return selected_anchor

static func spawn_unit(name: String, anchor: Anchor, attacker: bool) -> Node:
	""" Spawn a unit on an empty anchor
	"""
	var scene = load("res://units/" + name + ".tscn")
	var node = scene.instance()
	anchor.set_content(node)
	node.attacker = attacker
	return node

static func list_units(tree: SceneTree):
	""" List all units in battle
	"""
	var units = []

	for anchor in tree.get_nodes_in_group("anchors"):
		var content = anchor.get_content()
		if content:
			units.append(content)

	return units

static func apply_combat(attacker: UnitPoints, defender: UnitPoints):
	""" Apply a unit combat to points
	"""
	while attacker.damage:
		attacker.damage -= 1

		if defender.shield:
			defender.shield -= 1
		elif defender.hull:
			defender.hull -= 1

	while defender.damage:
		defender.damage -= 1

		if attacker.shield:
			attacker.shield -= 1
		elif attacker.hull:
			attacker.hull -= 1

static func get_state(tree: SceneTree):
	""" Build the simple state associated with current battle scene
	"""
	var nodes = []
	var routes = []

	for anchor in tree.get_nodes_in_group("anchors"):
		pass

	for route in tree.get_nodes_in_group("routes"):
		pass

	return {
		"nodes": nodes,
		"routes": routes
	}