extends Node
## Procedural locomotion for the placeholder blocky avatar.
##
## There are no animation clips yet -- this just swings the upper arm/leg bones
## around their local X by a sine wave whose phase advances with distance
## travelled, bends the knees on the rear half of the stride, and eases the
## whole thing back to the rest pose when the character stops.
##
## The owner sets `speed` (horizontal m/s) every frame; setup() is given the
## avatar's Skeleton3D. Bones are addressed by canonical name, so this works
## for the local player and for snapshot-driven remote players alike.

const STRIDE := 0.42         ## peak hip swing, radians (~24 deg)
const ARM_SWING := 0.32      ## peak shoulder swing, radians
const KNEE := 0.5            ## peak knee bend, radians
const CYCLE := 1.9           ## phase (radians) advanced per metre travelled
const BLEND := 12.0          ## ease rate toward the target pose
const MOVE_EPS := 0.35       ## m/s below which we treat the avatar as idle

var speed: float = 0.0

var _skel: Skeleton3D = null
var _idx := {}               # bone name -> skeleton index
var _phase := 0.0
var _amount := 0.0           # 0 = idle, 1 = full walk

const _BONES := [
	"LeftUpperLeg", "RightUpperLeg", "LeftLowerLeg", "RightLowerLeg",
	"LeftUpperArm", "RightUpperArm",
]


func setup(skeleton: Skeleton3D) -> void:
	_skel = skeleton
	_idx.clear()
	if skeleton == null:
		return
	for b in _BONES:
		var i := skeleton.find_bone(b)
		if i != -1:
			_idx[b] = i


func _process(delta: float) -> void:
	if not is_instance_valid(_skel) or _idx.is_empty():
		return

	var moving := speed > MOVE_EPS
	_amount = lerpf(_amount, 1.0 if moving else 0.0, clampf(BLEND * delta, 0.0, 1.0))
	_phase += maxf(speed, 0.0) * delta * CYCLE
	if _phase > TAU:
		_phase -= TAU

	var s := sin(_phase)
	var swing := s * STRIDE * _amount
	var arm := s * ARM_SWING * _amount

	_pitch("LeftUpperLeg", swing)
	_pitch("RightUpperLeg", -swing)
	_pitch("LeftUpperArm", -arm)
	_pitch("RightUpperArm", arm)
	# Knee folds only while that leg is swinging back (negative pitch phase).
	_pitch("LeftLowerLeg", maxf(0.0, -s) * KNEE * _amount)
	_pitch("RightLowerLeg", maxf(0.0, s) * KNEE * _amount)


func _pitch(bone: String, angle: float) -> void:
	if not _idx.has(bone):
		return
	var i: int = _idx[bone]
	var rest_q := _skel.get_bone_rest(i).basis.get_rotation_quaternion()
	_skel.set_bone_pose_rotation(i, rest_q * Quaternion(Vector3.RIGHT, angle))