COOLDOWN_FACTOR = 0.9998
FACTOR = 0.033

num_modules = 20
center_module = 10

-- maximum energy values for each band
maxRedEnergy = 1
maxGreenEnergy = 1
maxBlueEnergy = 1
maxRMS = 1

-- output color buffers
red = {}
green = {}
blue = {}

function periodic()
  local redEnergy = get_energy_in_band(0, 400);
  local greenEnergy = get_energy_in_band(400, 4000);
  local blueEnergy = get_energy_in_band(4000, 22000);
  local rms = get_rms();

  maxRedEnergy = maxRedEnergy * COOLDOWN_FACTOR
  if redEnergy > maxRedEnergy then
    maxRedEnergy = redEnergy
  end

  maxGreenEnergy = maxGreenEnergy * COOLDOWN_FACTOR
  if greenEnergy > maxGreenEnergy then
    maxGreenEnergy = greenEnergy
  end

  maxBlueEnergy = maxBlueEnergy * COOLDOWN_FACTOR
  if blueEnergy > maxBlueEnergy then
    maxBlueEnergy = blueEnergy
  end

  maxRMS = maxRMS * COOLDOWN_FACTOR
  if rms > maxRMS then
    maxRMS = rms
  end

  local brightness = rms / maxRMS

  for i = 1,num_modules do
    if i <= center_module and
         center_module - i < center_module * redEnergy / maxRedEnergy or
       i > center_module and
         i - (center_module + 1) < (num_modules-center_module) * redEnergy / maxRedEnergy
    then
      redTarget = brightness
    else
      redTarget = 0
    end
    red[i] = (1 - FACTOR) * red[i] + FACTOR * redTarget;

    if i <= center_module and
         center_module - i < center_module * greenEnergy / maxGreenEnergy or
       i > center_module and
         i - (center_module + 1) < (num_modules-center_module) * greenEnergy / maxGreenEnergy
    then
      greenTarget = brightness
    else
      greenTarget = 0
    end
    green[i] = (1 - FACTOR) * green[i] + FACTOR * greenTarget;

    if i <= center_module and
         center_module - i < center_module * blueEnergy / maxBlueEnergy or
       i > center_module and
         i - (center_module + 1) < (num_modules-center_module) * blueEnergy / maxBlueEnergy
    then
      blueTarget = brightness
    else
      blueTarget = 0
    end
    blue[i] = (1 - FACTOR) * blue[i] + FACTOR * blueTarget;
  end

  -- return the 3 color arrays
  return red, green, blue
end

function init(nmod, cmod)
  num_modules = nmod
  center_module = cmod

  for i = 1,nmod do
    red[i] = 0
    green[i] = 0
    blue[i] = 0
  end

  -- fadestep (0 = no fading)
  return 0
end