class_name VesselCooldownFillComponent
extends Node2D

# Shared per-vessel cooldown state and hull-fill feedback for abilities that
# grant one independently recharging shot per ship.

var cooldown_duration: float = 1.0
var cooldown_left: float = 0.0

# Two vertices this close together are the same vertex as far as the fill is
# concerned - a hull is tens of units across, so this is well below anything
# that could be a real edge.
const WELD_DISTANCE: float = 0.01
# Below this the fill is a sliver nobody can see, and drawing it is all cost
# and no picture.
const MIN_FILL_AREA: float = 0.5


func setup() -> void:
	show_behind_parent = true
	queue_redraw()


func is_ready() -> bool:
	return cooldown_left <= 0.0


func _begin_cooldown(duration: float) -> bool:
	if not is_ready():
		return false
	cooldown_duration = maxf(duration, 0.001)
	cooldown_left = cooldown_duration
	queue_redraw()
	return true


func tick(delta: float) -> void:
	if cooldown_left <= 0.0:
		return
	cooldown_left = maxf(cooldown_left - delta, 0.0)
	queue_redraw()


func cooldown_progress() -> float:
	return 1.0 - cooldown_left / maxf(cooldown_duration, 0.001)


# The part of the hull that is "filled up" at this progress, as a list of
# polygons - plural, because a hull with a notch in it (the gas bomber's
# tail, the distorder's waist) genuinely fills as two separate puddles
# before the level rises past the notch.
#
# Geometry2D does the clipping. This used to walk the hull itself and cut
# each edge against the fill line, which is Sutherland-Hodgman, and
# Sutherland-Hodgman is only sound for a CONVEX subject: on a notched hull
# it stitches the pieces back together with a zero-width bridge, and a
# polygon with a zero-width bridge is not one Godot's triangulator will
# accept. It said so, once per frame per cooling vessel, for as long as any
# cooldown ran.
func _filled_hull(points: PackedVector2Array, progress: float) -> Array:
	if points.size() < 3 or progress <= 0.001:
		return []
	if progress >= 0.999:
		return [points.duplicate()]
	var top: float = INF
	var bottom: float = -INF
	var left: float = INF
	var right: float = -INF
	for point in points:
		top = minf(top, point.y)
		bottom = maxf(bottom, point.y)
		left = minf(left, point.x)
		right = maxf(right, point.x)
	var fill_y: float = lerpf(bottom, top, clampf(progress, 0.0, 1.0))
	# Deliberately oversized sideways and downwards, so the box's own edges
	# never coincide with the hull's and the only cut is the horizontal one.
	var box := PackedVector2Array([
		Vector2(left - 8.0, fill_y), Vector2(right + 8.0, fill_y),
		Vector2(right + 8.0, bottom + 8.0), Vector2(left - 8.0, bottom + 8.0),
	])
	var pieces: Array = []
	for piece in Geometry2D.intersect_polygons(points, box):
		var drawable: PackedVector2Array = _drawable(piece)
		if not drawable.is_empty():
			pieces.append(drawable)
	return pieces


# Last guard before the renderer. The clipper is sound where the old walk
# was not, but it can still hand back a vertex repeated at a corner, or a
# sliver of a puddle at the very start of a fill - neither is worth drawing
# and both are the shapes triangulation objects to.
func _drawable(points: PackedVector2Array) -> PackedVector2Array:
	var welded := PackedVector2Array()
	for point in points:
		if welded.is_empty() \
				or welded[welded.size() - 1].distance_to(point) > WELD_DISTANCE:
			welded.append(point)
	# The polygon is implicitly closed, so the last point meeting the first is
	# the same duplication seen from the other end.
	while welded.size() >= 2 \
			and welded[0].distance_to(welded[welded.size() - 1]) <= WELD_DISTANCE:
		welded.remove_at(welded.size() - 1)
	if welded.size() < 3 or _area(welded) < MIN_FILL_AREA:
		return PackedVector2Array()
	return welded


# Shoelace, unsigned: the clip preserves the hull's winding, but which way a
# hull winds is the definition's business and not worth depending on here.
func _area(points: PackedVector2Array) -> float:
	var total: float = 0.0
	var previous: Vector2 = points[points.size() - 1]
	for point in points:
		total += previous.x * point.y - point.x * previous.y
		previous = point
	return absf(total) * 0.5


func _draw() -> void:
	var ship: Node = get_parent()
	if ship == null or ship.definition == null:
		return
	var hull: PackedVector2Array = ship.definition.hull_points
	var ready_color: Color = _ready_color()
	if is_ready():
		draw_colored_polygon(hull, Color(ready_color, 0.42))
		NeonDraw.draw_glowing_polygon(self, hull, ready_color, 0.75,
			ship.core_color, 0.75)
		return
	draw_colored_polygon(hull, Color(_cooling_color(), 0.58))
	for piece in _filled_hull(hull, cooldown_progress()):
		draw_colored_polygon(piece, Color(ready_color, 0.68))


func _ready_color() -> Color: return Color.WHITE
func _cooling_color() -> Color: return Color(0.2, 0.2, 0.2)