extends CanvasLayer

# Autoload: toggleable frame-time/bottleneck overlay (F3 by default — see
# toggle_perf_overlay in project.godot's [input]). Read-only against
# Performance monitors; never touches rendering or gameplay state. Exists so
# 0.17/0.17b's graphics presets and resolution scaling are self-diagnosing —
# TIME_PROCESS vs total frame time tells the player whether they're CPU- or
# GPU-bound. See multiplayer-next.md task 0.20.

# ~2s of history at 60 fps; enough to make p50/p99 meaningful without the
# history itself being a rate-dependent quantity.
const HISTORY_SIZE := 120

var _label: Label
var _frame_times_ms: PackedFloat32Array = PackedFloat32Array()
var _history_index := 0
var _history_filled := 0


func _ready() -> void:
	# A headless server never renders and has no input to toggle this with.
	if DisplayServer.get_name() == "headless":
		set_process(false)
		return
	layer = 100
	_label = Label.new()
	_label.add_theme_font_size_override("font_size", 14)
	_label.add_theme_color_override("font_color", Color(0.4, 1.0, 0.5))
	_label.add_theme_color_override("font_shadow_color", Color(0, 0, 0, 0.85))
	_label.add_theme_constant_override("shadow_offset_x", 1)
	_label.add_theme_constant_override("shadow_offset_y", 1)
	_label.position = Vector2(12, 12)
	_label.visible = false
	add_child(_label)
	_frame_times_ms.resize(HISTORY_SIZE)
	_frame_times_ms.fill(0.0)


func _unhandled_input(event: InputEvent) -> void:
	if event.is_action_pressed("toggle_perf_overlay") and _label:
		_label.visible = not _label.visible


func _process(_delta: float) -> void:
	if not _label or not _label.visible:
		return
	var frame_ms := Performance.get_monitor(Performance.TIME_PROCESS) * 1000.0
	var physics_ms := Performance.get_monitor(Performance.TIME_PHYSICS_PROCESS) * 1000.0
	_frame_times_ms[_history_index] = frame_ms
	_history_index = (_history_index + 1) % HISTORY_SIZE
	_history_filled = mini(_history_filled + 1, HISTORY_SIZE)

	var sorted := _frame_times_ms.slice(0, _history_filled)
	sorted.sort()
	var p50 := sorted[sorted.size() / 2]
	var p99 := sorted[int(sorted.size() * 0.99)]

	_label.text = "FPS %d  (p50 %.2fms  p99 %.2fms)\nprocess %.2fms  physics %.2fms\ndraw calls %d" % [
		Performance.get_monitor(Performance.TIME_FPS),
		p50, p99, frame_ms, physics_ms,
		Performance.get_monitor(Performance.RENDER_TOTAL_DRAW_CALLS_IN_FRAME),
	]