element = {}

function element:element(name, tags)
   local obj = {}

   obj.name = name
   obj.tags = tags

   for k,v in pairs(element) do
      obj[k] = v
   end

   return obj
end

function element:getName()
   return self.name
end

function element:onClick(callback)
   self.clickCallback = callback
   return self
end

function element:click()
   self.clickCallback()
end

--=======================================

screen = {}

function screen:screen(name)
   local obj = {}

   obj.name = name
   obj.elements = {}

   for k,v in pairs(screen) do
      obj[k] = v
   end
   print("creating screen")
   return obj
end

function screen:addElement(e)
   self.elements[e:getName()] = e
end

function screen:update()
   -- for testing
   self.elements["profile1"]:click()
end

--=======================================

ui = {}
ui.screens = {}

function ui:screen(name)
   if ui.screens[name] == nil then
      ui.screens[name] = screen:screen(name)    --<---- ERROR: index is nil
   end

   return ui.screens[name]
end

function ui:element(name, tags)
   return element:element(name, tags)
end

--local e = ui.element("profile1", "profile_button btnProfile1")
ui.screen("profiles"):addElement(
   ui.element("profile1", "profile_button btnProfile1")
      :onClick(function() print("Profile1 button clicked")
      end)
)

ui.screen("profiles"):update()