class_name GunkBody extends StaticBody3D
## StaticBody3D with an associated "gunkable" mesh.

signal painted

const CONTINUITY_LIMIT := 16
const BUFFER_LIMIT := 3
const FACE_EPSILON := 0.01
const MASK_COLOR := Color.RED

@export var mask_dim := 256
@export var mesh_instance: MeshInstance3D

var meshtool := MeshDataTool.new()

var _polyline_buffer: Array[Vector2] = []
var _continued_paint_this_frame := false

var _multiline_buffer := PackedVector2Array()
var _multiline_width := 1.0

var _clear_total := 0.0
var _clear_total_dirty := true

@onready var mesh: ArrayMesh = mesh_instance.mesh
@onready var gunk_mat: ShaderMaterial = mesh_instance.mesh.surface_get_material(0).next_pass

@onready var mask_viewport: SubViewport = %MaskViewport
@onready var mask_control: DrawController = %MaskControl

@onready var debug_draw: DebugDraw = $DebugDraw


func _ready() -> void:
	mask_viewport.size = Vector2(mask_dim, mask_dim)
	gunk_mat.set_shader_parameter("gunk_mask", mask_viewport.get_texture())
	meshtool.create_from_surface(mesh, 0)


func clear_all() -> void:
	mask_control.queue_draw(
		func() -> void:
			mask_control.draw_rect(
				Rect2(0, 0, mask_control.size.x, mask_control.size.y), MASK_COLOR
			)
	)


## Get the precise number of gunk pixels cleared from this image.
##
## This will use a cached result unless the mask has been painted since the last calculation.
## Be aware that cache misses are potentially quite expensive.
func get_clear_total() -> float:
	if _clear_total_dirty:
		var mask_img := mask_viewport.get_texture().get_image()
		mask_img.convert(Image.FORMAT_R8)
		var px_data := mask_img.get_data()
		var px_sum := 0
		for px in px_data:
			px_sum += px
		_clear_total = px_sum / 255.0
		_clear_total_dirty = false
	return _clear_total


## Transform cartesian coordinates to barycentric wrt the given triangle.
func _barycentric(p: Vector3, a: Vector3, b: Vector3, c: Vector3) -> Vector3:
	var v0 := b - a
	var v1 := c - a
	var v2 := p - a
	var d00 := v0.dot(v0)
	var d01 := v0.dot(v1)
	var d11 := v1.dot(v1)
	var d20 := v2.dot(v0)
	var d21 := v2.dot(v1)
	var denom := d00 * d11 - d01 * d01
	var v := (d11 * d20 - d01 * d21) / denom
	var w := (d00 * d21 - d01 * d20) / denom
	var u := 1.0 - v - w
	return Vector3(u, v, w)


## Is the given point on the planar triangle defined by v1, v2, and v3?
func _is_in_triangle(point: Vector3, v1: Vector3, v2: Vector3, v3: Vector3) -> bool:
	var bc := _barycentric(point, v1, v2, v3)
	return (bc.x > 0 and bc.x < 1) and (bc.y > 0 and bc.y < 1) and (bc.z > 0 and bc.z < 1)


## Get the index of the mesh face on which the given point+normal lies.
##
## Returns -1 if the given point+normal does not lie on a mesh face within tolerance.
func _get_face(point: Vector3, normal: Vector3) -> int:
	var min_i := -1
	var min_sdist := INF

	for i in range(meshtool.get_face_count()):
		var sdist := meshtool.get_face_normal(i).distance_squared_to(normal)
		if sdist > FACE_EPSILON or sdist > min_sdist:
			continue
		# Normals match, so check if the point is on this face
		var v1 := meshtool.get_vertex(meshtool.get_face_vertex(i, 0))
		var v2 := meshtool.get_vertex(meshtool.get_face_vertex(i, 1))
		var v3 := meshtool.get_vertex(meshtool.get_face_vertex(i, 2))
		if _is_in_triangle(point, v1, v2, v3):
			min_i = i
			min_sdist = sdist
	return min_i


## UV-unwrap a point+normal in 3D space onto the UV space of this mesh.
##
## Returns Vector2.INF if the given point+normal does not lie on this mesh within tolerance.
func _get_uv(point: Vector3, normal: Vector3) -> Vector2:
	var face := _get_face(point, normal)
	if face < 0:
		return Vector2.INF
	var fv0 := meshtool.get_face_vertex(face, 0)
	var fv1 := meshtool.get_face_vertex(face, 1)
	var fv2 := meshtool.get_face_vertex(face, 2)
	var v1 := meshtool.get_vertex(fv0)
	var v2 := meshtool.get_vertex(fv1)
	var v3 := meshtool.get_vertex(fv2)
	var bc := _barycentric(point, v1, v2, v3)  # TODO memoize
	var uv1 := meshtool.get_vertex_uv(fv0)
	var uv2 := meshtool.get_vertex_uv(fv1)
	var uv3 := meshtool.get_vertex_uv(fv2)
	return (uv1 * bc.x) + (uv2 * bc.y) + (uv3 * bc.z)


## UV-unwrap a point+normal in 3D space onto the pixel space of this mesh's texture.
##
## Returns Vector2.INF if the given point+normal does not lie on this mesh within tolerance.
func _get_px(point: Vector3, normal: Vector3) -> Vector2:
	return _get_uv(point * global_transform, normal * global_basis) * mask_control.size


## Paint a dot on the gunk mask.
func paint_dot(point: Vector3, normal: Vector3, radius: float) -> void:
	var px := _get_px(point, normal)
	if px == Vector2.INF:
		return

	mask_control.queue_draw(
		func() -> void: mask_control.draw_circle(px, radius, MASK_COLOR, true, -1, true)
	)


## Paint a continuous line on the gunk mask if called on successive frames.
func paint_continuous(point: Vector3, normal: Vector3, width: float) -> void:
	debug_draw.draw_vector(normal, point)

	var px := _get_px(point, normal)
	if _polyline_buffer and px.distance_to(_polyline_buffer[0]) <= CONTINUITY_LIMIT:
		_polyline_buffer.push_front(px)
		if len(_polyline_buffer) > BUFFER_LIMIT:
			_polyline_buffer.pop_back()
		var polyline := PackedVector2Array(_polyline_buffer)
		mask_control.queue_draw(
			func() -> void: mask_control.draw_polyline(polyline, MASK_COLOR, width * 2, true)
		)
	else:
		_polyline_buffer = [px]

	# Always paint a circle, to round out corners & cap ends
	mask_control.queue_draw(
		func() -> void: mask_control.draw_circle(px, width, MASK_COLOR, true, -1, true)
	)
	_continued_paint_this_frame = true


## Add a segment to the multiline to paint this frame.
func add_to_multiline(
	point_a: Vector3, normal_a: Vector3, point_b: Vector3, normal_b: Vector3, width: float
) -> void:
	var px_a := _get_px(point_a, normal_a)
	var px_b := _get_px(point_b, normal_b)
	if px_a == Vector2.INF or px_b == Vector2.INF or px_a.distance_to(px_b) > CONTINUITY_LIMIT:
		return
	_multiline_buffer.append(px_a)
	_multiline_buffer.append(px_b)
	_multiline_width = width


func _process(_delta: float) -> void:
	# If paint_continuous wasn't called last frame, stop the current polyline.
	if not _continued_paint_this_frame:
		_polyline_buffer = []
	_continued_paint_this_frame = false

	# If we've buffered a multiline in the last frame, draw it & clear the buffer.
	# The width of the multiline will just be the width of the last call.
	if _multiline_buffer:
		var points := _multiline_buffer.duplicate()
		var width := _multiline_width
		mask_control.queue_draw(
			func() -> void: mask_control.draw_multiline(points, MASK_COLOR, width, true)
		)
		_multiline_buffer = PackedVector2Array()


func _on_mask_painted() -> void:
	_clear_total_dirty = true
	painted.emit()