extends Node
## Measures the gap between where the client *draws* the local player and where
## the server actually has it -- the number that decides whether bullets appear
## to leave the ship's nose or trail out of its back.
##
##   godot --headless --path . res://tools/diag_prediction.tscn
##
## Runs the real listen-server path (ServerRuntime + ClientRuntime + the actual
## Net loopback), not a mock, so node process order is exactly production's.

## Tick at which to shove the client's input numbering out of sync, simulating
## the clock drift between two independent processes that produced the original
## "ship and bullets separate after a few minutes, permanently" bug. 0 disables.
const DRIFT_AT := 120
const DRIFT_BY := 14

var _ticks: int = 0
var _worst: float = 0.0
var _sum: float = 0.0
var _samples: int = 0
## Measured only after the injected drift, which is the interesting window.
var _worst_after_drift: float = 0.0
var _drifted: bool = false


func _ready() -> void:
	GameOpts.bot_client = true
	GameOpts.player_name = "diag"
	if Net.host(27300) != OK:
		push_error("could not host")
		get_tree().quit(1)
		return
	Net.start_local_client()


func _physics_process(_delta: float) -> void:
	_ticks += 1
	var srv := Net.server
	var cli := Net.client
	if srv == null or cli == null:
		return
	var inst := srv.instance_of(Net.LOCAL_PEER)
	if inst == null or not inst.world.players.has(Net.LOCAL_PEER):
		return
	var sp: SimPlayer = inst.world.players[Net.LOCAL_PEER]
	var delta_px := sp.pos.distance_to(cli.predicted_pos)

	# Skip the first few ticks while the handshake settles.
	if _ticks > 20:
		_worst = maxf(_worst, delta_px)
		_sum += delta_px
		_samples += 1

	if DRIFT_AT > 0 and _ticks == DRIFT_AT:
		# Exactly what two drifting clocks do, only instantly. With the old
		# constants this landed in the gap between "server stops accepting" and
		# "client notices", and the two never re-converged.
		cli.input_tick += DRIFT_BY
		_drifted = true
		print("--- injected +%d tick input drift ---" % DRIFT_BY)
	# Give the client a moment to notice before judging it.
	if _drifted and _ticks > DRIFT_AT + 90:
		_worst_after_drift = maxf(_worst_after_drift, delta_px)

	if _ticks % 20 == 0:
		print("tick=%4d srv_tick=%4d srv_pos=%-22s pred=%-22s gap=%6.2fpx acked=%4d cli_tick=%4d queue=%d" % [
			_ticks, inst.world.tick, str(sp.pos.round()), str(cli.predicted_pos.round()),
			delta_px, sp.last_input_tick, cli.input_tick, sp.input_queue.size()])

	if _ticks >= 300:
		print("---")
		print("GAP worst=%.2fpx  mean=%.2fpx  over %d samples" % [_worst, _sum / maxf(_samples, 1), _samples])
		print("player speed is %.0f u/s = %.2f px per tick" % [
			SimConfig.PLAYER_SPEED, SimConfig.PLAYER_SPEED * SimConfig.TICK_DELTA])
		print("muzzle offset = %.1fpx, drawn ship radius = %.1fpx, hitbox = %.1fpx" % [
			SimConfig.PLAYER_MUZZLE_OFFSET, SimConfig.PLAYER_VISUAL_RADIUS,
			SimConfig.PLAYER_RADIUS])
		var ok := true
		if _drifted:
			print("RECOVERED gap after drift: worst=%.2fpx" % _worst_after_drift)
			# One tick of movement is 4px; anything near that means the client
			# re-synced. Tens of px means it is stuck, which is the bug.
			ok = _worst_after_drift < 12.0
			print("DRIFT_RECOVERY_" + ("PASS" if ok else "FAIL"))
		Net.shutdown()
		get_tree().quit(0 if ok else 1)