storageUsage

monitor = peripheral.find("monitor")
width, height = monitor.getSize()

function getStorageStatistics()
    local chest = peripheral.find("functionalstorage:storage_controller")

    local capacity = 0
    local size = 0

    for slot, item in pairs(chest.list()) do
        size = size + item.count
        capacity = capacity + chest.getItemLimit(slot)
    end

    return capacity, size
end

function drawStatusBar(x, y, width, height, itemsPercent)
    paintutils.drawBox(x, y, width, y + 3, colors.white)
    paintutils.drawFilledBox(x + 1, y + 1, (width / 100) * itemsPercent, y + 2, colors.red)
    monitor.setBackgroundColor(colors.black)
end

function main()
    term.redirect(monitor)
    monitor.setTextScale(1)

    while 1 do
        monitor.setBackgroundColor(colors.black)
        local capacity, size = getStorageStatistics()
        local itemsPercent = size * 100 / capacity;

        monitor.setCursorPos(1, 1)
        monitor.write(("Storage is %d%% full [%d | %d items]"):format(itemsPercent, size, capacity))
        drawStatusBar(1, 2, width, height, itemsPercent)


    end
end

monitor.clear();
main()