How to make a key cause delay from low bar?

So I'm trying to make a Magic script where when you press E it would make a Fireball/Create a forcefield but I want it to be used when limited so when a player presses the key once/twice, the bar would go down until it reaches lower than the required power for the magic, so it can delay that key or some sort while it refills until it's available. But it doesn't work very well for some reason.

local UIS = game:GetService('UserInputService')

local Bar = script.Parent:WaitForChild('Background'):WaitForChild('Bar')

local player = game.Players.LocalPlayer

local power = 10

local debounce  = false

repeat wait() until game.Players.LocalPlayer.Character

local character = player.Character

-----------------------------------------------------------------

UIS.InputBegan:connect(function(key, gameProcessed)
    if key.KeyCode == Enum.KeyCode.E and gameProcessed == false then
        debounce = true
        while power > 0 and debounce do
            power = power - 0.5
            Bar:TweenSize(UDim2.new(1, 0, power / 10, 0), 'Out', 'Quint', .1, true)
            wait()
            if power <= 0 then
                delay(5,key)
            end
        end
    end
end)

UIS.InputEnded:connect(function(key, gameProcessed)
    if key.KeyCode == Enum.KeyCode.E and gameProcessed == false then
        debounce = false
        while power < 10 and not debounce do
            power = power + .025
            Bar:TweenSize(UDim2.new(1, 0, power / 10, 0), 'Out', 'Quint', .1, true)
            wait()
            if power <= 0 then
                delay(5,key)
            end
        end
    end
end)