class_name Block
extends AnimatableBody2D
## One arc-shaped segment of a ring around the core.

const GAP := 4.0 # px between neighbouring tiles
const CORNER := 4.0 # corner rounding radius in px
const BREAK_SECONDS := 0.15 # fade-out time, after a short flash

var indestructible := false
var color := Params.COLOR_BLUE
var _polygon := PackedVector2Array()
## 0 to 1: how far the tile is washed towards white while breaking.
var _flash := 0.0:
	set(value):
		_flash = value
		queue_redraw()


func _init(inner: float, outer: float, begin: float, end: float, is_indestructible: bool) -> void:
	sync_to_physics = false
	collision_layer = Params.LAYER_BLOCKS
	collision_mask = 0
	indestructible = is_indestructible

	# Collision uses the drawn outline, so the ball bounces exactly where it touches.
	_polygon = _round_corners(_sector(inner + GAP / 2.0, outer - GAP / 2.0, begin, end, GAP / 2.0))
	# Very short segments can leave a sliver too thin to split into convex pieces; skip its
	# collision rather than let Godot fail on it.
	if not Geometry2D.decompose_polygon_in_convex(_polygon).is_empty():
		var collision := CollisionPolygon2D.new()
		collision.polygon = _polygon
		add_child(collision)

	if indestructible:
		color = Params.COLOR_ORANGE
	else:
		color = Color8(
			int(102 * (randf() / 5.0 + 0.5)),
			int(217 * (randf() / 5.0 + 0.5)),
			int(239 * (randf() / 5.0 + 0.5)))


## Flashes and fades out, then frees itself. Stops colliding right away.
func destroy() -> void:
	collision_layer = 0
	var tween := create_tween()
	tween.tween_property(self, "_flash", 0.8, BREAK_SECONDS / 3.0)
	tween.tween_property(self, "modulate:a", 0.0, BREAK_SECONDS)
	tween.parallel().tween_property(self, "scale", Vector2.ONE * 1.04, BREAK_SECONDS)
	tween.tween_callback(queue_free)


func _draw() -> void:
	if _polygon.size() < 3:
		return # segment too short to show at all
	var fill := color.lerp(Color.WHITE, _flash)
	draw_colored_polygon(_polygon, fill)
	# Polygons have no antialiasing of their own; a smooth outline softens the edge.
	var outline := _polygon.duplicate()
	outline.append(_polygon[0])
	draw_polyline(outline, fill, 1.0, true)


## Ring segment between two radii. [param gap] trims each side by that many pixels,
## so the space between neighbours has the same width at every radius. An edge too short
## to trim collapses to a point, turning the segment into a wedge.
static func _sector(inner: float, outer: float, begin: float, end: float, gap: float) -> PackedVector2Array:
	var steps := maxi(2, int((end - begin) * sqrt(outer) / 1.5))
	return _trimmed_arc(outer, begin, end, gap, steps) + _trimmed_arc(inner, end, begin, -gap, steps)


static func _trimmed_arc(radius: float, from: float, to: float, gap: float, steps: int) -> PackedVector2Array:
	var trim := gap / radius
	if (to - from - 2.0 * trim) * signf(to - from) <= 0.0:
		var middle := (from + to) / 2.0
		return PackedVector2Array([Vector2(sin(middle), cos(middle)) * radius])
	return _arc(radius, from + trim, to - trim, steps)


## Shrinks then regrows the polygon with round joins, which rounds its corners.
static func _round_corners(polygon: PackedVector2Array) -> PackedVector2Array:
	var shrunk := Geometry2D.offset_polygon(polygon, -CORNER)
	if shrunk.is_empty():
		return polygon
	var rounded := Geometry2D.offset_polygon(shrunk[0], CORNER, Geometry2D.JOIN_ROUND)
	return polygon if rounded.is_empty() else _without_duplicates(rounded[0])


## offset_polygon can emit repeated points; zero-length edges break convex decomposition.
static func _without_duplicates(polygon: PackedVector2Array) -> PackedVector2Array:
	var result := PackedVector2Array()
	for point in polygon:
		if result.is_empty() or not point.is_equal_approx(result[-1]):
			result.append(point)
	if result.size() > 1 and result[0].is_equal_approx(result[-1]):
		result.remove_at(result.size() - 1)
	return result


static func _arc(radius: float, from: float, to: float, steps: int) -> PackedVector2Array:
	var points := PackedVector2Array()
	for i in steps + 1:
		var angle := lerpf(from, to, float(i) / steps)
		points.append(Vector2(sin(angle), cos(angle)) * radius)
	return points