Precentage instead of remaining time text

[mystic lodge]

i have a simple spell cooldown text aura, but instead of showing the remaining cooldown, i want to show a 0% to 100% (100% when its ready to use) what should i write for the custom function inside %c. thanks

[drowsy pagoda]

function()
  if aura_env.state.show and aura_env.state.expirationTime then
    local remaining = aura_env.state.expirationTime - GetTime()
    local percent = remaining / aura_env.state.duration * 100
  end
end