extends Node

const SHADER_INTERACTOR_LIMIT := 8

@export var grass_material: ShaderMaterial
@export_range(1, SHADER_INTERACTOR_LIMIT, 1) var max_interactors := 8
@export_range(0.02, 0.5, 0.01) var update_interval := 0.08

var _elapsed := 0.0


func _ready() -> void:
	_refresh_interactors()


func _process(delta: float) -> void:
	_elapsed += delta
	if _elapsed < update_interval:
		return
	_elapsed = 0.0
	_refresh_interactors()


func _refresh_interactors() -> void:
	if grass_material == null:
		return
	var camera := get_viewport().get_camera_3d()
	var origin := camera.global_position if camera != null else Vector3.ZERO
	var nearest: Array[Node3D] = []
	for value in get_tree().get_nodes_in_group("grass_interactors"):
		var candidate := value as Node3D
		if candidate == null:
			continue
		var insert_at := nearest.size()
		var candidate_distance := origin.distance_squared_to(candidate.global_position)
		for index in nearest.size():
			if candidate_distance < origin.distance_squared_to(nearest[index].global_position):
				insert_at = index
				break
		nearest.insert(insert_at, candidate)
		if nearest.size() > max_interactors:
			nearest.pop_back()

	var positions := PackedVector3Array()
	positions.resize(SHADER_INTERACTOR_LIMIT)
	for index in SHADER_INTERACTOR_LIMIT:
		positions[index] = Vector3(0.0, -1000.0, 0.0)
	for index in nearest.size():
		positions[index] = nearest[index].global_position
	grass_material.set_shader_parameter("interactor_count", nearest.size())
	grass_material.set_shader_parameter("interactor_positions", positions)