extends SceneTree

# Headless gameplay test: run with
#   godot --headless -s res://tests/test_fleet_agility.gd
# The fleet handled with too much inertia: flipping the stick left while
# cruising right took most of a second to take effect, and letting go coasted
# the ships several lengths further.
#
# The cause was every vessel's acceleration sitting at roughly its own top
# speed - a time constant of about a second to change velocity at all, while
# the formation anchor the ships chase turns instantly. Acceleration is now
# ~3x top speed, measured rather than guessed: past 3x the reversal time stops
# improving, because max_speed becomes the limit instead of acceleration.
#
# Feel is not directly assertable, but the three things that PRODUCE it are,
# so this measures them:
#   A. how long after the stick reverses before a ship is actually travelling
#      the new way
#   B. how far past the turn it drifts first
#   C. how far it coasts after the stick is released
#
# Plus D: the same measurement at the OLD acceleration must BREACH these
# bounds. Without that, quietly restoring the sluggish handling would still
# pass, and so would bounds so loose they mean nothing.
#
# The bounds are roughly double what the tuned values measure. This suite runs
# several Godot processes at once on a phone, and a physics-timing measurement
# under that load strays (see the note in test_space_time_distorder.gd); real
# regression here means going back towards a second, which is far outside this
# margin.

const MAX_REVERSE_TIME: float = 0.35
const MAX_OVERSHOOT: float = 45.0
const MAX_STOP_COAST: float = 60.0
# What the acceleration was before, as a fraction of what it is now.
const OLD_ACCELERATION_FRACTION: float = 1.0 / 3.0

var main: Node
var fleet: Node
var elapsed: float = 0.0
var stage: int = 0
var flip_x: float = 0.0
var reverse_time: float = -1.0
var overshoot: float = 0.0
var stop_x: float = 0.0
# Second pass re-runs the identical measurement with the old acceleration.
var measuring_old: bool = false
var tuned: Dictionary = {}


func _initialize() -> void:
	var game_state: Node = root.get_node("GameState")
	game_state.reset_progression()
	main = load("res://world/Main.tscn").instantiate()
	root.add_child(main)
	current_scene = main
	fleet = main.get_node("Fleet")


func _process(delta: float) -> bool:
	elapsed += delta
	match stage:
		0:
			if elapsed < 0.3:
				return false
			main.get_node("AsteroidField").set_process(false)
			main.get_node("EnemySpawner").set_process(false)
			# A rock or an enemy destroying the ship being measured would
			# read as a handling failure. Same clean-slate idiom as
			# test_space_time_distorder.gd.
			for hazard in get_nodes_in_group("asteroids") + get_nodes_in_group("enemies"):
				if is_instance_valid(hazard):
					hazard.queue_free()
			_begin_pass()
			return false
		1:
			# Reach steady state travelling right before disturbing anything.
			if elapsed < 2.0:
				return false
			if fleet.ships.is_empty():
				return _fail("the fleet lost its ships before anything could be measured")
			flip_x = fleet.ships[0].position.x
			fleet.move_in_direction(Vector2(-1.0, 0.0))
			stage = 2
			elapsed = 0.0
			return false
		2:
			var ship: Node2D = fleet.ships[0]
			overshoot = maxf(overshoot, ship.position.x - flip_x)
			if reverse_time < 0.0 and ship.velocity.x < 0.0:
				reverse_time = elapsed
			if elapsed < 2.0:
				return false
			if reverse_time < 0.0:
				return _fail("the fleet never reversed at all within 2s of the stick flipping")
			# Settle going one way again, so the coast below is measured from
			# a steady cruise rather than mid-catch-up.
			fleet.move_in_direction(Vector2(1.0, 0.0))
			stage = 3
			elapsed = 0.0
			return false
		3:
			if elapsed < 2.0:
				return false
			stop_x = fleet.ships[0].position.x
			fleet.stop()
			stage = 4
			elapsed = 0.0
			return false
		4:
			if elapsed < 2.5:
				return false
			var result: Dictionary = {
				"reverse_time": reverse_time,
				"overshoot": overshoot,
				"coast": fleet.ships[0].position.x - stop_x,
			}
			if not measuring_old:
				tuned = result
				if not _check_tuned(result):
					return true
				# --- D: the same measurement, sluggish again ----------------
				measuring_old = true
				_begin_pass()
				return false
			return _check_old_breaches(result)
	return false


func _begin_pass() -> void:
	reverse_time = -1.0
	overshoot = 0.0
	for ship in fleet.ships:
		# apply_vessel_stats() has already put the definition's value on the
		# ship, so the old handling is reproduced by scaling that field
		# directly - no need to edit a resource mid-test.
		if measuring_old:
			ship.acceleration *= OLD_ACCELERATION_FRACTION
		ship.position = Vector2.ZERO
		ship.velocity = Vector2.ZERO
	fleet.move_to(Vector2.ZERO)
	fleet.move_in_direction(Vector2(1.0, 0.0))
	stage = 1
	elapsed = 0.0


func _check_tuned(r: Dictionary) -> bool:
	print("tuned (acceleration %.0f): reversed in %.3fs, overshot %.1f, coasted %.1f" \
		% [fleet.ships[0].acceleration, r.reverse_time, r.overshoot, r.coast])
	if r.reverse_time > MAX_REVERSE_TIME:
		return _fail("the fleet took %.3fs to obey a reversed stick (allowed %.2f)" \
			% [r.reverse_time, MAX_REVERSE_TIME])
	if r.overshoot > MAX_OVERSHOOT:
		return _fail("the fleet drifted %.1f units past the turn (allowed %.1f)" \
			% [r.overshoot, MAX_OVERSHOOT])
	if r.coast > MAX_STOP_COAST:
		return _fail("the fleet coasted %.1f units after the stick was released (allowed %.1f)" \
			% [r.coast, MAX_STOP_COAST])
	return true


func _check_old_breaches(r: Dictionary) -> bool:
	print("old (acceleration %.0f): reversed in %.3fs, overshot %.1f, coasted %.1f" \
		% [fleet.ships[0].acceleration, r.reverse_time, r.overshoot, r.coast])
	var breaches: int = 0
	if r.reverse_time > MAX_REVERSE_TIME:
		breaches += 1
	if r.overshoot > MAX_OVERSHOOT:
		breaches += 1
	if r.coast > MAX_STOP_COAST:
		breaches += 1
	if breaches == 0:
		return _fail("the OLD, sluggish acceleration passed every bound too (reversed %.3fs, overshot %.1f, coasted %.1f) - these thresholds do not discriminate and would not catch a regression" \
			% [r.reverse_time, r.overshoot, r.coast])
	print("bounds discriminate: the old acceleration breaches %d of 3" % breaches)
	print("TEST_FLEET_AGILITY: PASS")
	quit(0)
	return true


func _fail(message: String) -> bool:
	print("TEST_FLEET_AGILITY: FAIL (%s)" % message)
	quit(1)
	return true