extends SceneTree

# Headless gameplay test: run with
#   godot --headless -s res://tests/test_lopsided_formation_movement.gd
# Regression test for the fleet lurching the wrong way on the first frames
# of a move after the formation was edited at a command centre.
#
# Ships sit at anchor + offset, so the fleet CENTROID is anchor + the
# AVERAGE offset. Seeding the steering anchor from the centroid therefore
# displaced every slot by that average the moment the stick was pushed. The
# default wedge is balanced (average ~zero), so this was invisible; drag
# every slot into one corner and the average becomes large, and the fleet
# jerks towards that corner before the anchor catches up.
#
# Verifies, with every slot dragged to the top-right:
#   1. starting a move does NOT displace the ships' targets sideways
#   2. the fleet actually travels bottom-left from the outset - no frame in
#      which the centroid moves the wrong way
#   3. releasing the stick leaves the formation origin where the ships are,
#      so re-applying the layout does not teleport them

var scene: Node
var fleet: Node
var game_state: Node
var stage: int = 0
var elapsed: float = 0.0
var samples: Array = []
var start_centroid: Vector2 = Vector2.ZERO
var worst_backwards: float = 0.0

const HEADING: Vector2 = Vector2(-0.7071, 0.7071)   # bottom-left


func _initialize() -> void:
	game_state = root.get_node("GameState")
	game_state.reset_formation()
	# Every slot dragged into the top-right corner, as the command centre
	# allows. The layout keeps its shape; only its centre is offset.
	for i in range(game_state.formation.size()):
		game_state.formation[i] += Vector2(90.0, -70.0)

	scene = load("res://Main.tscn").instantiate()
	root.add_child(scene)
	fleet = scene.get_node("Fleet")


func _process(delta: float) -> bool:
	elapsed += delta
	match stage:
		0:
			scene.get_node("AsteroidField").set_process(false)
			scene.get_node("EnemySpawner").set_process(false)
			fleet.apply_formation()
			elapsed = 0.0
			stage = 1
			return false
		1:
			# Let the ships settle into the lopsided layout first.
			if elapsed < 1.0:
				return false

			start_centroid = fleet.get_centroid()
			var origin_before: Vector2 = fleet.get_formation_origin()
			fleet.move_in_direction(HEADING)

			# Direct assertion of the bug: the anchor steering starts from
			# must be the point the ships are already arranged around. Taking
			# the centroid instead puts it a whole average-offset away, which
			# is what yanked the fleet sideways.
			var drift: float = fleet.anchor.distance_to(origin_before)
			print("anchor is %.2f units from the formation origin (centroid is %.2f away)" % [
				drift, fleet.get_centroid().distance_to(origin_before)
			])
			if drift > 1.0:
				print("TEST_LOPSIDED_FORMATION_MOVEMENT: FAIL (steering anchored off the formation)")
				quit(1)
				return true

			elapsed = 0.0
			stage = 2
			return false
		2:
			# Watch the centroid every frame: it must make progress along the
			# heading from the very first one, never against it.
			var travelled: float = (fleet.get_centroid() - start_centroid).dot(HEADING)
			worst_backwards = minf(worst_backwards, travelled)
			samples.append(travelled)
			if elapsed < 0.6:
				return false

			print("progress along heading: first=%.2f last=%.2f worst=%.2f" % [
				samples[0], samples[-1], worst_backwards
			])
			if worst_backwards < -2.0:
				print("TEST_LOPSIDED_FORMATION_MOVEMENT: FAIL (fleet moved backwards before setting off)")
				quit(1)
				return true
			if samples[-1] < 50.0:
				print("TEST_LOPSIDED_FORMATION_MOVEMENT: FAIL (fleet did not travel along the heading)")
				quit(1)
				return true

			# --- releasing the stick --------------------------------------
			fleet.stop()
			var origin: Vector2 = fleet.fleet_target
			var expected: Vector2 = fleet.get_formation_origin()
			var settled_ok: bool = origin.distance_to(expected) < 0.01
			print("after stop: fleet_target=%s formation origin=%s ok=%s" % [
				origin, expected, settled_ok
			])
			if settled_ok:
				print("TEST_LOPSIDED_FORMATION_MOVEMENT: PASS")
				quit(0)
			else:
				print("TEST_LOPSIDED_FORMATION_MOVEMENT: FAIL (stop left the anchor off the formation)")
				quit(1)
			return true
	return false