Computer Craft Energy monitoring

local WAIT_DELAY = 5

local RED_LEVEL = 10
local ORANGE_LEVEL = 50
local YELLOW_LEVEL = 70

function PrintOnMonitor(monitor, cell_array)
    monitor_width,_ = monitor.getSize()
    title = "Energy Monitor"
    energy_level = 0
    monitor.setBackgroundColor(colors.black)
    monitor.clear()
    monitor.setCursorPos(math.floor((monitor_width - string.len(title))/2), 1)
    monitor.setBackgroundColor(colors.red)
    monitor.setTextColor(colors.yellow)
    monitor.write(title)
    if (cell_array[1] == nil) then
        monitor.setCursorPos(1, 3)
        monitor.setBackgroundColor(colors.black)
        monitor.setTextColor(colors.red)
        monitor.write("There in no energy cell connected.")
    end

    for i, cell in ipairs(cell_array)do
        if(cell ~=nil) then
            monitor.setBackgroundColor(colors.black)
            monitor.setTextColor(colors.white)
            monitor.setCursorPos(1, i+1)
            monitor.write(peripheral.getName(cell))
            energyCap = cell.getEnergyCapacity()
            energy = cell.getEnergy()
            if(energy == nil or energyCap == nil) then
                error = "Error: energy or energy capacity is nil"
                monitor.setTextColor(colors.red)
                monitor.setCursorPos(monitor_width - string.len(error), i + 1)
                monitor.write(error)
            else
                monitor.setCursorPos(monitor_width-10, i+1)
                monitor.write("|")
                monitor.setCursorPos(monitor_width-7, i+1)
                energy_level = (energy/energyCap)*100
                if(energy_level < RED_LEVEL) then
                    monitor.setTextColor(colors.red)
                else if(energy_level < ORANGE_LEVEL)then
                        monitor.setTextColor(colors.orange)
                    else if(energy_level < YELLOW_LEVEL) then
                            monitor.setTextColor(colors.yellow)
                        else
                            monitor.setTextColor(colors.green)
                        end
                    end
                end
                monitor.write(string.format("%6.2f %%",energy_level))
            end
        end
    end
end

function SearchMonitor()
    return peripheral.find("monitor")
end

function SearchForEnergyCells()
    list_peripherals = peripheral.getNames()
    energy_cell_array = {}
    array_index = 1
    for i, periph in ipairs(list_peripherals) do
        if(peripheral.hasType(periph,"energy_storage")) then
            energy_cell_array[array_index] = peripheral.wrap(periph)
            array_index = array_index + 1
        end
    end
    return energy_cell_array
end

while true do
    local monitor = SearchMonitor()
    local energy_cell_array = SearchForEnergyCells()

    PrintOnMonitor(monitor, energy_cell_array)
    os.sleep(WAIT_DELAY)
end