class_name UIFocusStack extends RefCounted

signal activeLayerChanged(layer:ClosableMenu)

const Z_STEP:int = 10

var _stack:Array[ClosableMenu] = []

func push(layer:ClosableMenu) -> void:
  if not _stack.is_empty():
    _stack.back()._onFocusLost()
  _stack.push_back(layer)
  layer.z_index = _stack.size() * Z_STEP
  layer._onFocusGained()
  activeLayerChanged.emit(layer)

func pop() -> void:
  if _stack.is_empty(): return
  var removed:ClosableMenu = _stack.pop_back()
  removed.z_index = 0
  removed._onFocusLost()
  var next:ClosableMenu = top()
  if next != null:
    next._onFocusGained()
  activeLayerChanged.emit(next)

func top() -> ClosableMenu:
  return _stack.back() if not _stack.is_empty() else null

func isTop(layer:ClosableMenu) -> bool:
  return top() == layer