class_name WreckActor
extends StaticBody3D

## A wreck resting on a site: two visual levels of detail from one glTF and a
## separate, much lighter trimesh collision. The sonar reads the body's
## metadata, so this node is the one owner of how a wreck echoes.

const LOD0_NODE_NAME := "WreckLOD0"
const LOD1_NODE_NAME := "WreckLOD1"
const COLLISION_NODE_NAME := "WreckCollision"
const COLLISION_SHAPE_NAME := "Collision"
const VISUAL_NAME := "Visual"
## Hysteresis around the LOD handover so a hovering submarine never flickers.
const LOD_MARGIN_M := 4.0

@export var visual_scene: PackedScene
@export var collision_scene: PackedScene
## Beyond this distance the coarse LOD is drawn instead of the detailed one.
@export_range(10.0, 400.0, 1.0) var lod_switch_distance_m := 45.0
@export_range(0.0, 1.0, 0.01) var sonar_reflectivity := 0.9


func _ready() -> void:
	set_meta("sonar_material", SonarMaterial.Value.METAL)
	set_meta("sonar_reflectivity", sonar_reflectivity)
	_build_visual()
	_build_collision()


func _build_visual() -> void:
	if visual_scene == null:
		push_error("WreckActor %s has no visual scene" % name)
		return
	var visual := visual_scene.instantiate() as Node3D
	visual.name = VISUAL_NAME
	add_child(visual)
	var lod0 := visual.find_child(LOD0_NODE_NAME, true, false) as MeshInstance3D
	var lod1 := visual.find_child(LOD1_NODE_NAME, true, false) as MeshInstance3D
	if lod0 == null or lod1 == null:
		push_error("WreckActor %s visual scene lacks %s or %s" % [
			name, LOD0_NODE_NAME, LOD1_NODE_NAME
		])
		return
	lod0.visibility_range_end = lod_switch_distance_m
	lod0.visibility_range_end_margin = LOD_MARGIN_M
	lod1.visibility_range_begin = lod_switch_distance_m
	lod1.visibility_range_begin_margin = LOD_MARGIN_M


func _build_collision() -> void:
	if collision_scene == null:
		push_error("WreckActor %s has no collision scene" % name)
		return
	var source := collision_scene.instantiate() as Node3D
	var collision_mesh := source.find_child(COLLISION_NODE_NAME, true, false) as MeshInstance3D
	if collision_mesh == null or collision_mesh.mesh == null:
		push_error("WreckActor %s collision scene lacks %s" % [name, COLLISION_NODE_NAME])
		source.free()
		return
	var shape := CollisionShape3D.new()
	shape.name = COLLISION_SHAPE_NAME
	shape.shape = collision_mesh.mesh.create_trimesh_shape()
	shape.transform = collision_mesh.transform
	source.free()
	add_child(shape)