class_name TransitionSingleton extends Control

enum FadeType {
	NONE,
	FADE_IN,
	FADE_OUT
}

signal fadeOutStart
signal fadeOutEnd
signal fadeInStart
signal fadeInEnd
signal fadeUpdate(t:float)

var fadeType:FadeType = FadeType.NONE
var fadeDuration:float = 0.4
var fadeTime:float = 0.0
var inFade = false

func _enter_tree() -> void:
	$Overlay.visible = false

func _process(delta: float) -> void:
	if fadeType == FadeType.NONE:
		return

	fadeTime += delta
	var t:float = fadeTime / fadeDuration

	# Get destination alpha type.
	var destAlpha:float = 0.0
	var srcAlpha:float
	if fadeType == FadeType.FADE_IN:
		srcAlpha = 1.0
		destAlpha = 0.0
	elif fadeType == FadeType.FADE_OUT:
		srcAlpha = 0.0
		destAlpha = 1.0

	# End?
	if t >= 1.0:
		fadeUpdate.emit(1.0)
		var cFade = fadeType
		fadeType = FadeType.NONE
		$Overlay.color.a = destAlpha
		inFade = false

		if cFade == FadeType.FADE_OUT:
			fadeOutEnd.emit()
		elif cFade == FadeType.FADE_IN:
			fadeInEnd.emit()
		
		return

	# TODO: Use curves
	$Overlay.color.a = srcAlpha + (destAlpha - srcAlpha) * t
	fadeUpdate.emit(t)
	pass

func fade(
	fade:FadeType = FadeType.FADE_IN,
	duration:float = 0.4,
	color:Color = Color(0, 0, 0, 1),
):
	if inFade:
		push_error("Transition: Cannot start a new fade while another is in progress.")
		return

	$Overlay.visible = true
	$Overlay.color = color
	fadeDuration = duration
	fadeTime = 0
	fadeType = fade
	inFade = true

	if fade == FadeType.FADE_IN:
		fadeInStart.emit()
		$Overlay.color.a = 0
	elif fade == FadeType.FADE_OUT:
		fadeOutStart.emit()
		$Overlay.color.a = 1