extends Node2D

const SETTLE_TIME := 8.0
var _texture: Texture2D
var _fragments: Array[Dictionary] = []
var _dust: Array[Dictionary] = []
var _elapsed := 0.0
var _rng := RandomNumberGenerator.new()
var _dust_color := Color("b4a99a")

func configure(sprite: Sprite2D) -> void:
	_texture = sprite.texture
	transform = sprite.global_transform
	var sprite_scale := global_scale
	scale = Vector2.ONE
	_rng.randomize()
	var dimensions := _texture.get_size()
	var grid: Array[Vector2] = []
	for y in 5:
		for x in 5:
			var vertex := Vector2(x, y) * dimensions / 4.0
			if x > 0 and x < 4:
				vertex.x += _rng.randf_range(-0.3, 0.3) * dimensions.x / 4.0
			if y > 0 and y < 4:
				vertex.y += _rng.randf_range(-0.3, 0.3) * dimensions.y / 4.0
			grid.append(vertex)
	# Shared jagged cracks keep neighbouring pieces fitted together.
	var horizontal: Array[PackedVector2Array] = []
	var vertical: Array[PackedVector2Array] = []
	for y in 5:
		for x in 4:
			horizontal.append(_fracture_edge(grid[y * 5 + x], grid[y * 5 + x + 1], y > 0 and y < 4))
	for y in 4:
		for x in 5:
			vertical.append(_fracture_edge(grid[y * 5 + x], grid[(y + 1) * 5 + x], x > 0 and x < 4))
	for y in 4:
		for x in 4:
			var outline := PackedVector2Array()
			outline.append_array(_edge_vertices(horizontal[y * 4 + x], false))
			outline.append_array(_edge_vertices(vertical[y * 5 + x + 1], false))
			outline.append_array(_edge_vertices(horizontal[(y + 1) * 4 + x], true))
			outline.append_array(_edge_vertices(vertical[y * 5 + x], true))
			var center := Vector2.ZERO
			for vertex in outline:
				center += vertex
			center /= outline.size()
			var origin := (center - dimensions * 0.5) * sprite_scale
			var points := PackedVector2Array()
			var uv := PackedVector2Array()
			for vertex in outline:
				points.append((vertex - center) * sprite_scale)
				uv.append(vertex / dimensions)
			var direction := origin.normalized() if origin.length_squared() > 0.1 else Vector2.RIGHT
			_fragments.append({"points": points, "uv": uv, "position": origin,
				"velocity": direction.rotated(_rng.randf_range(-0.35, 0.35)) * _rng.randf_range(40.0, 95.0),
				"angle": 0.0, "spin": _rng.randf_range(-4.0, 4.0)})
	_dust_color = Color("a1c7df") if "ice" in _texture.resource_path else Color("b4a99a")
	for index in 28:
		_dust.append({"direction": Vector2.RIGHT.rotated(_rng.randf_range(0.0, TAU)),
			"speed": _rng.randf_range(45.0, 210.0), "size": _rng.randf_range(1.0, 3.0)})
	z_index = 35
	light_mask = 4

func _fracture_edge(start: Vector2, end: Vector2, jagged: bool) -> PackedVector2Array:
	var edge := PackedVector2Array([start])
	if jagged:
		var normal := (end - start).orthogonal().normalized()
		var roughness := start.distance_to(end) * 0.13
		var side := 1.0 if _rng.randf() > 0.5 else -1.0
		for index in 3:
			var along := (index + 1.0) / 4.0 + _rng.randf_range(-0.05, 0.05)
			edge.append(start.lerp(end, along) + normal * roughness * side * _rng.randf_range(0.5, 1.0))
			side *= -1.0
	edge.append(end)
	return edge

func _edge_vertices(edge: PackedVector2Array, backwards: bool) -> PackedVector2Array:
	var vertices := PackedVector2Array()
	# The next edge supplies the end vertex, avoiding duplicate polygon points.
	for index in edge.size() - 1:
		vertices.append(edge[edge.size() - 1 - index] if backwards else edge[index])
	return vertices

func _process(delta: float) -> void:
	_elapsed += delta
	for fragment in _fragments:
		fragment.position += fragment.velocity * delta
		fragment.velocity *= exp(-1.2 * delta)
		fragment.angle += fragment.spin * delta
		fragment.spin *= exp(-0.7 * delta)
	queue_redraw()
	# Leave the settled debris visible without updating it every frame.
	if _elapsed >= SETTLE_TIME:
		_dust.clear()
		set_process(false)

func _draw() -> void:
	for fragment in _fragments:
		draw_set_transform(fragment.position, fragment.angle)
		draw_polygon(fragment.points, PackedColorArray([Color.WHITE]), fragment.uv, _texture)
	draw_set_transform(Vector2.ZERO)
	var dust_fade := maxf(0.0, 1.0 - _elapsed / 0.8)
	for mote in _dust:
		var travel: Vector2 = mote.direction * mote.speed * (1.0 - exp(-2.0 * _elapsed)) / 2.0
		draw_circle(travel, mote.size * (1.0 + _elapsed), Color(_dust_color, dust_fade * 0.65))
	if _elapsed < 0.18:
		draw_circle(Vector2.ZERO, 16.0 * (1.0 - _elapsed / 0.18), Color(0.85, 0.9, 1.0, (1.0 - _elapsed / 0.18) * 0.55))