class_name ButtonBounce
extends RefCounted
## Small animations that make buttons feel alive: a button grows a little under the mouse,
## shrinks while it is held down, and can pop when its icon changes.
##
## The button is scaled around its middle, so its place in a container does not change.
## With [member Settings.reduce_animations] on, buttons keep their size.

## How big a button is under the mouse.
const HOVER_SCALE: Vector2 = Vector2(1.08, 1.08)
## How big a button is while it is held down.
const PRESSED_SCALE: Vector2 = Vector2(0.92, 0.92)
## How small a button starts when it pops.
const POP_SCALE: Vector2 = Vector2(0.8, 0.8)
## How long growing or shrinking takes, in seconds.
const DURATION: float = 0.08
## How long a pop takes, in seconds.
const POP_DURATION: float = 0.18

const _TWEEN_META: StringName = &"button_bounce_tween"
const _PIVOT_META: StringName = &"button_bounce_pivot"
const _ADDED_META: StringName = &"button_bounce_added"


## Gives every button in [param tree] the bounce, also buttons added later, e.g. rows
## of the player list. Check buttons are left out: they span a whole settings row.
static func add_to_every_button(tree: SceneTree) -> void:
	if !tree.node_added.is_connected(_on_node_added):
		tree.node_added.connect(_on_node_added)
	var nodes: Array[Node] = [tree.root]
	while !nodes.is_empty():
		var node: Node = nodes.pop_back()
		_on_node_added(node)
		nodes.append_array(node.get_children())


static func _on_node_added(node: Node) -> void:
	if node is BaseButton && !(node is CheckButton) && !(node is CheckBox):
		add_to(node)


## Makes [param button] grow under the mouse and shrink while held down. Adding it to
## the same button twice does nothing.
static func add_to(button: BaseButton) -> void:
	if button.has_meta(_ADDED_META):
		return
	button.set_meta(_ADDED_META, true)
	_keep_pivot_centred(button)
	button.mouse_entered.connect(func() -> void:
		if !button.disabled:
			_scale_to(button, HOVER_SCALE))
	button.mouse_exited.connect(func() -> void: _scale_to(button, Vector2.ONE))
	button.button_down.connect(func() -> void: _scale_to(button, PRESSED_SCALE))
	button.button_up.connect(func() -> void: _scale_to(button, resting_scale(button)))


## The size [param button] goes back to when it is not held down: bigger under the mouse.
static func resting_scale(button: BaseButton) -> Vector2:
	return HOVER_SCALE if button.is_hovered() && !button.disabled else Vector2.ONE


## Shrinks [param button] and lets it spring back, e.g. when its icon changes.
static func pop(button: BaseButton) -> void:
	if !Anim.enabled():
		return
	_keep_pivot_centred(button)
	button.scale = POP_SCALE
	var tween: Tween = _new_tween(button)
	tween.set_trans(Tween.TRANS_BACK).set_ease(Tween.EASE_OUT)
	tween.tween_property(button, ^"scale", resting_scale(button), POP_DURATION)


static func _scale_to(button: BaseButton, target: Vector2) -> void:
	if !Anim.enabled():
		button.scale = Vector2.ONE
		return
	var tween: Tween = _new_tween(button)
	tween.set_trans(Tween.TRANS_QUAD).set_ease(Tween.EASE_OUT)
	tween.tween_property(button, ^"scale", target, DURATION)


# A new tween for [param button], stopping the one before so they never fight
static func _new_tween(button: BaseButton) -> Tween:
	if button.has_meta(_TWEEN_META):
		var running: Tween = button.get_meta(_TWEEN_META)
		if running.is_valid():
			running.kill()
	var tween: Tween = button.create_tween()
	button.set_meta(_TWEEN_META, tween)
	return tween


static func _keep_pivot_centred(button: BaseButton) -> void:
	button.pivot_offset = button.size / 2
	if !button.has_meta(_PIVOT_META):
		button.set_meta(_PIVOT_META, true)
		button.resized.connect(func() -> void: button.pivot_offset = button.size / 2)