startup

twerk = peripheral.wrap("left")
monitor = peripheral.wrap("top")
maxEnergy = twerk.getMaxEnergyStored()
width, height = monitor.getSize()

function getColor(percentage)
  if percentage < 0.2 then
    return colors.red
  elseif percentage < 0.4 then
    return colors.orange
  elseif percentage < 0.6 then
    return colors.yellow
  elseif percentage < 0.8 then
    return colors.lime
  else
    return colors.green
  end
end

function fillMonitor(percentage)
  monitor.setBackgroundColor(colors.black)
  monitor.clear()
  amount = math.floor(percentage*height)
  monitor.setCursorPos(0,height-amount)
  monitor.setBackgroundColor(getColor(percentage))
  for i = 1,amount do
    monitor.setCursorPos(0,height-amount+i)
    monitor.clearLine()
  end
end

while true do
  monitor.clear()
  monitor.setCursorPos(1,1)
  energy = twerk.getEnergyStored()/maxEnergy
  fillMonitor(energy)
  sleep(1)
end