Conveyor belt

extends Node

const BELT_SIZE: Vector2 = Vector2(520, 34)
const BOX_SIZE: Vector2 = Vector2(46, 46)


func _ready() -> void:
	_add_background()

	var view: Vector2 = get_viewport().get_visible_rect().size

	_add_belt(Vector2(view.x * 0.35, view.y * 0.4), 260.0)
	_add_belt(Vector2(view.x * 0.65, view.y * 0.65), -260.0)
	_add_wall(Vector2(view.x * 0.5, view.y - 30), Vector2(view.x, 60))

	_spawn_loop(view)

	print('the belts never move, constant_linear_velocity drags whatever touches them')


func _spawn_loop(view: Vector2) -> void:
	while is_inside_tree():
		_add_box(Vector2(view.x * 0.2, view.y * 0.2))
		await get_tree().create_timer(1.1).timeout


func _add_belt(center: Vector2, speed: float) -> void:
	var shape: RectangleShape2D = RectangleShape2D.new()
	shape.size = BELT_SIZE

	var collision: CollisionShape2D = CollisionShape2D.new()
	collision.shape = shape

	var belt: StaticBody2D = StaticBody2D.new()
	belt.position = center
	belt.constant_linear_velocity = Vector2(speed, 0)
	belt.add_child(_make_rect(BELT_SIZE, Color('#8da5f3')))
	belt.add_child(collision)
	add_child(belt)

	var arrow: Label = Label.new()
	arrow.text = '>>>' if speed > 0 else '<<<'
	arrow.position = center + Vector2(-24, -46)
	arrow.add_theme_color_override('font_color', Color('#999999'))
	add_child(arrow)


func _add_wall(center: Vector2, size: Vector2) -> void:
	var shape: RectangleShape2D = RectangleShape2D.new()
	shape.size = size

	var collision: CollisionShape2D = CollisionShape2D.new()
	collision.shape = shape

	var wall: StaticBody2D = StaticBody2D.new()
	wall.position = center
	wall.add_child(_make_rect(size, Color('#2a2f3d')))
	wall.add_child(collision)
	add_child(wall)


func _add_box(at: Vector2) -> void:
	var shape: RectangleShape2D = RectangleShape2D.new()
	shape.size = BOX_SIZE

	var collision: CollisionShape2D = CollisionShape2D.new()
	collision.shape = shape

	var box: RigidBody2D = RigidBody2D.new()
	box.position = at
	box.add_child(_make_rect(BOX_SIZE, Color.from_hsv(randf(), 0.4, 0.9)))
	box.add_child(collision)
	add_child(box)

	await get_tree().create_timer(9.0).timeout

	if is_instance_valid(box):
		box.queue_free()


func _make_rect(size: Vector2, color: Color) -> Polygon2D:
	var rect: Polygon2D = Polygon2D.new()
	rect.polygon = PackedVector2Array([-size * 0.5, Vector2(size.x, -size.y) * 0.5, size * 0.5, Vector2(-size.x, size.y) * 0.5])
	rect.color = color

	return rect


func _add_background() -> void:
	var background: ColorRect = ColorRect.new()
	background.color = Color('#12141a')
	add_child(background)
	background.set_anchors_and_offsets_preset(Control.PRESET_FULL_RECT)