extends SceneTree

## Does dragging an anchor marker in the rig lab move that anchor where the
## mouse went?
##
## The maths behind a viewport drag has four frames in it — screen, world,
## skeleton, gun — and every one is a chance to transpose an inverse or lose a
## handedness. All of those mistakes still MOVE the marker, so "the number
## changed" proves nothing. What is asserted here is that the number changed by
## the RIGHT AMOUNT, in the frame that knob is written in, derived independently
## from the camera.
##
## Deliberately NOT asserted: that the marker lands exactly under the mouse. It
## does not, and the reason is a real property of the hold rather than a bug in
## the drag — see THE FEEDBACK below. The screen-space check kept here is a
## direction-and-order-of-magnitude one, which is the band the transform
## mistakes above actually live in: a swapped axis or a lost handedness sends
## the marker the wrong way entirely.
##
## THE FEEDBACK. Every anchor hangs off the shoulder — `stock_pos = shoulder +
## pocket`, and the grip and fore anchors are measured out from there. The
## shoulder is driven by the arm, and the arm is chasing the anchor. So moving
## an anchor moves the shoulder, which moves the anchor again. Measured from a
## clean slate it settles at 0.77x-1.13x of the drag depending on which anchor,
## which is small enough to be invisible interactively — you stop dragging when
## it looks right.
##
## It is worth the paragraph because of how it first showed up. Without the
## `_reset` between cases below, each drag started on top of the last one still
## working its way through the arm, and the ratio read 1.5x-1.8x; waiting LONGER
## for the pose to settle made it worse rather than better, which is the
## opposite of how a settling error behaves and is what gave the compounding
## away.
##
##     godot --path . -s res://debug/anchor_drag_check.gd

const LAB := "res://debug/rig_lab.tscn"
const DRAG := Vector2(60, 0)
## Metres. What the knob is checked to — this part is exact maths, so it can be.
const KNOB_TOLERANCE := 0.0005
## The screen-space check is direction and order of magnitude only. See above.
const MIN_TRAVEL := 0.5
const MAX_TRAVEL := 2.2

var _fails := 0


func _init() -> void:
	await process_frame
	var lab: Node = load(LAB).instantiate()
	root.add_child(lab)
	# The pose layer chases its targets exponentially at a rate times DELTA, and
	# a headless run is uncapped, so each frame advances the blend by almost
	# nothing and the hold takes hundreds of frames to stop moving on its own.
	for _i in 300:
		await process_frame

	if lab._model == null or not lab._model.loaded or lab._model._pose_mod == null:
		_expect(false, "the lab built a character with a pose layer")
		_done()
		return
	_expect(true, "the lab built a character with a pose layer")

	# Frame the hands, so a pixel is a small distance in the world — a drag
	# measured at arm's length is mostly noise.
	lab._pivot = lab._model.skeleton.global_transform * lab._model._pose_mod.dbg_grip
	lab._dist = 0.6
	lab._update_camera()
	for _i in 20:
		await process_frame

	for case in [[0, "trigger hand", "grip_shift"], [1, "support hand", "fore_shift"],
			[2, "buttstock", "pocket_hip"]]:
		await _drag_case(lab, case[0], case[1], case[2])
	_done()


func _drag_case(lab: Node, marker: int, label: String, key: String) -> void:
	# From a clean slate each time, or the second case measures the first's
	# shift still working its way through the arm.
	lab._reset("hold")
	for _i in 120:
		await process_frame

	var m: Node3D = lab._markers[marker]
	if not m.visible:
		_expect(false, "the %s marker is visible" % label)
		return
	var before: Vector2 = lab._cam.unproject_position(m.global_position)
	_expect(lab._marker_under(before) == marker,
		"the %s marker is grabbable where it is drawn" % label)

	# What the drag SHOULD write, worked out from the camera here rather than
	# from the lab's own code, so the two have to agree independently.
	var want: Vector3 = _expected(lab, marker, m.global_position, before, before + DRAG)
	var was: Vector3 = _knob(lab, key)

	lab._begin_drag(marker, before)
	# In steps, as a real drag arrives — a single jump would hide an error that
	# accumulates per motion event.
	for step in 6:
		lab._drag_to(before + DRAG * (float(step + 1) / 6.0))
		await process_frame
	lab._drag_marker = -1

	var wrote: Vector3 = _knob(lab, key) - was
	var err: float = (wrote - want).length()
	_expect(err <= KNOB_TOLERANCE,
		"the %s drag wrote %s into '%s' (wanted %s, off by %.2f mm)"
			% [label, _mm(wrote), key, _mm(want), err * 1000.0])

	# ...and the marker really did go that way on screen.
	for _i in 150:
		await process_frame
	var now: Vector2 = lab._cam.unproject_position(m.global_position)
	var moved: Vector2 = now - before
	var along: float = moved.dot(DRAG.normalized()) / DRAG.length()
	_expect(along >= MIN_TRAVEL and along <= MAX_TRAVEL,
		"the %s marker followed the drag (%.2fx of it; the shoulder feedback puts this over 1)"
			% [label, along])


## The knob delta a drag from `a` to `b` ought to produce, in that knob's frame.
func _expected(lab: Node, marker: int, at: Vector3, a: Vector2, b: Vector2) -> Vector3:
	var world := _plane(lab._cam, at, b) - _plane(lab._cam, at, a)
	var v: Vector3 = lab._model.skeleton.global_transform.basis.inverse() * world
	if lab.MARKER_KNOB[marker][1] == "gun":
		v = lab._model._pose_mod.dbg_gun_basis.inverse() * v
	return v


func _plane(cam: Camera3D, at: Vector3, mouse: Vector2) -> Vector3:
	var origin := cam.project_ray_origin(mouse)
	var dir := cam.project_ray_normal(mouse)
	var n := -cam.global_transform.basis.z
	return origin + dir * (((at - origin).dot(n)) / dir.dot(n))


## An absent knob reads as its DEFAULT, not as zero.
##
## Those are the same thing for `grip_shift` and `fore_shift` and not for
## `pocket_hip`, whose default is (30, -70, 60) mm. Reading it as zero made a
## perfectly correct 60 px drag look like a 97 mm error — the difference was
## exactly the default. The lab has a note about this trap in `_reset`; it is
## just as easy to walk into from a test.
func _knob(lab: Node, key: String) -> Vector3:
	var v = lab._knobs["hold"].get(key, WeaponHoldTuning.default_for(key))
	return v if v is Vector3 else Vector3.ZERO


func _mm(v: Vector3) -> String:
	return "(%.0f, %.0f, %.0f) mm" % [v.x * 1000.0, v.y * 1000.0, v.z * 1000.0]


func _expect(ok: bool, what: String) -> void:
	if ok:
		print("  OK: %s" % what)
	else:
		print("  FAIL: %s" % what)
		_fails += 1


func _done() -> void:
	print("\n=== ANCHOR DRAG ===\nFailures: %d" % _fails)
	quit(1 if _fails > 0 else 0)