extends Node2D

const PROJECTILE := preload("res://scenes/game/weapon_projectile.tscn")

func _ready() -> void:
	seed(1234)
	# Both stationary and crossing targets should be intercepted on the first pass.
	for target_velocity in [Vector2.ZERO, Vector2(0, 55)]:
		var target := CharacterBody2D.new()
		target.position = Vector2(350, 70)
		target.velocity = target_velocity
		add_child(target)
		var missile := _missile(target, 1200.0)
		var closest := INF
		for step in 240:
			var previous: Vector2 = missile.position
			target.position += target_velocity / 120.0
			missile._physics_process(1.0 / 120.0)
			var near := Geometry2D.get_closest_point_to_segment(target.position, previous, missile.position)
			closest = minf(closest, near.distance_to(target.position))
			assert(absf(missile._turn_velocity) <= missile.homing_max_turn_speed + 0.001)
			if closest < 18.0 or missile.is_queued_for_deletion():
				break
		assert(closest < 18.0, "Missile missed a reachable intercept: %.2f" % closest)
		missile.free()
		target.free()

	# Compare actual flight direction against the previous turn limits.
	var side_target := Node2D.new()
	side_target.position = Vector2(100, 200)
	add_child(side_target)
	var faster := _missile(side_target, 600.0)
	var previous := _missile(side_target, 600.0)
	previous.homing_turn_acceleration = 2.3
	previous.homing_max_turn_speed = 1.7
	previous.missile_steering_acceleration = 520.0
	for step in 48:
		faster._physics_process(1.0 / 120.0)
		previous._physics_process(1.0 / 120.0)
	assert(faster._heading > previous._heading * 1.5)
	assert(faster._flight_velocity.angle() > previous._flight_velocity.angle() * 1.5)
	assert(faster.homing_target == side_target)
	faster.free()
	previous.free()
	side_target.free()

	# Preserve the original pursuit behavior beyond acquisition range.
	var far_target := Node2D.new()
	far_target.position = Vector2(5000, 0)
	far_target.add_to_group("enemies")
	add_child(far_target)
	var limited := _missile(far_target, 200.0)
	limited._has_locked_target = true
	for step in 120:
		limited._physics_process(1.0 / 120.0)
		if limited.is_queued_for_deletion():
			break
	assert(not limited.is_queued_for_deletion() and limited.homing_target == far_target)
	assert(limited._has_locked_target)
	limited.free()
	far_target.free()
	print("MISSILE_GUIDANCE_TEST: PASS (stationary and moving intercepts, faster heading and actual flight turn, original target pursuit)")
	get_tree().quit()

func _missile(target: Node2D, flight_range: float) -> Area2D:
	var missile := PROJECTILE.instantiate() as Area2D
	missile.configure(Vector2.ZERO, Vector2.RIGHT, ItemDefinition.WeaponKind.MISSILE, 400.0, 10.0, flight_range, target)
	missile.collision_mask = 0
	add_child(missile)
	missile.set_physics_process(false)
	missile.set_process(false)
	return missile