extends SceneTree

## Regression for natural authored locomotion transitions.
## Gameplay velocity remains responsive, but the visual BlendSpace must ease
## into acceleration, direction changes and idle instead of teleporting the
## skeleton between unrelated poses on one frame.

const RESPONSE := 60.0
const TOP := 11.0
const DT := 1.0 / 60.0
const RUN_FRAMES := 48
const STOP_FRAMES := 60

var _frames := 0
var _model: SkinnedPlayerModel
var _speed := 0.0
var _first_speed := 0.0
var _first_stride := 0.0
var _settled_run_stride := 0.0
var _first_stop_stride := 0.0
var _mid_stop_stride := 0.0
var _settled_stop_stride := 0.0
var _largest_stride_step := 0.0
var _previous_stride := 0.0
var _foot_bone := -1
var _foot_rotation_start := Quaternion.IDENTITY
var _foot_rotation_delta := 0.0


func _initialize() -> void:
	var args := OS.get_cmdline_user_args()
	var path: String = args[0] if not args.is_empty() \
		else "res://assets/characters/skins/kiyoko.glb"
	var scene := Node3D.new()
	root.add_child(scene)
	current_scene = scene
	_model = SkinnedPlayerModel.new()
	_model.model_path = path
	scene.add_child(_model)


func _process(_delta: float) -> bool:
	_frames += 1
	if _frames < 8 or not _model.loaded:
		return false
	if _frames == 8:
		_model.set_process(false)
		if _model._spring_mod:
			_model._spring_mod.lod = 3
			_model._spring_mod = null
		_foot_bone = _model._role_bone("foot.L",
			["foot.L", "LeftFoot", "Left ankle"])

	var sample := _frames - 8
	if sample < RUN_FRAMES:
		_speed = lerpf(_speed, TOP, 1.0 - exp(-RESPONSE * DT))
	else:
		_speed = 0.0
	_model.set_locomotion(0.0, 1.0 if _speed > 0.01 else 0.0, 0.0)
	_model.update_state("ground", _speed, false)
	_model._process(DT)
	var stride := _model.locomotion_effective_speed_debug()
	_largest_stride_step = maxf(_largest_stride_step, absf(stride - _previous_stride))
	_previous_stride = stride

	if _foot_bone >= 0:
		var foot_rotation := _model.skeleton.get_bone_pose_rotation(_foot_bone)
		if sample == 1:
			_foot_rotation_start = foot_rotation
		elif sample > 1 and sample < RUN_FRAMES:
			_foot_rotation_delta = maxf(_foot_rotation_delta,
				_foot_rotation_start.angle_to(foot_rotation))

	if sample == 0:
		_first_speed = _speed
		_first_stride = stride
	elif sample == RUN_FRAMES - 1:
		_settled_run_stride = stride
	elif sample == RUN_FRAMES:
		_first_stop_stride = stride
	elif sample == RUN_FRAMES + 12:
		_mid_stop_stride = stride
	elif sample == RUN_FRAMES + STOP_FRAMES:
		_settled_stop_stride = stride
		_finish()
		return true
	return false


func _finish() -> void:
	_model.update_state("dash", 13.0, false)
	var dash_crossfade := _model._state_trans.xfade_time
	_model.update_state("ground", 0.0, false)
	var ground_crossfade := _model._state_trans.xfade_time
	print("\n=== NATURAL LOCOMOTION TRANSITIONS ===")
	print("  first frame body %.3f, visual stride %.3f" % [_first_speed, _first_stride])
	print("  settled run %.3f, stop %.3f -> %.3f -> %.3f" % [
		_settled_run_stride, _first_stop_stride, _mid_stop_stride,
		_settled_stop_stride])
	print("  largest visual stride step %.3f m/s" % _largest_stride_step)
	print("  traversal/ground crossfades %.3f / %.3f s" % [
		dash_crossfade, ground_crossfade])

	var failures: Array[String] = []
	if _first_speed < 6.0:
		failures.append("test did not reproduce high gameplay acceleration")
	if _first_stride <= 0.15 or _first_stride >= _first_speed * 0.65:
		failures.append("acceleration visual either froze or snapped on frame one")
	if absf(_settled_run_stride - TOP) > 0.30:
		failures.append("visual stride did not converge to physical run speed")
	if _first_stop_stride < _settled_run_stride * 0.65:
		failures.append("run pose snapped too close to idle on the stop frame")
	if _mid_stop_stride >= _first_stop_stride or _mid_stop_stride < 0.5:
		failures.append("run-to-idle recovery is not a progressive ease")
	if _settled_stop_stride > 0.30:
		failures.append("run-to-idle recovery did not settle")
	if _largest_stride_step > 2.5:
		failures.append("a rendered frame contains an excessive gait jump")
	if dash_crossfade < 0.19 or ground_crossfade < 0.28:
		failures.append("full-body state crossfades are still too abrupt")
	if _foot_bone < 0 or _foot_rotation_delta < 0.03:
		failures.append("authored foot animation did not move")
	if failures.is_empty():
		print("TRANSITION_CHECK PASS: responsive gameplay, eased animation\n")
		quit(0)
	else:
		for failure in failures:
			push_error("TRANSITION_CHECK FAIL: " + failure)
		quit(1)