require "lib.utils.vec3"
--- Stateful UI element
--- @class Element
--- @field state table
--- @field update fun(self: Element, dt: number) called each logical frame, alters self.state
--- @field draw fun(self: Element) uses self.state to draw, should not alter anything
--- @field origin Vec3
--- @field size Vec3
--- @field parent Element | nil
--- @field child Element | nil
local Element = {}
Element.__index = Element

Element.state = {}
function Element:update(dt)
    local parent = self.parent
    if not parent then return end

    self.origin = self.origin or parent.origin
    self.size = self.size or parent.size
end

function Element:draw() end

--- Recursive depth-first traversal.
--- If `visit` returns false, traversal is stopped early.
--- @param visit fun(el: Element): boolean|nil
--- @return boolean
function Element:traverse(visit)
    local cont = visit(self)
    if not cont then return false end
    if not self.child then return false end
    self.child.parent = self
    return not not self.child:traverse(visit)
end

--- template constructor
--- @param data {state: table, update: fun(dt: number), draw: fun(), [any]: any}
--- @return Element
function Element.new(data)
    return setmetatable(data, Element)
end

return Element