defmodule SpaceAge do
  @type planet ::
          :mercury
          | :venus
          | :earth
          | :mars
          | :jupiter
          | :saturn
          | :uranus
          | :neptune

  @earth_yr_in_secs 31_557_600

  @doc """
  Return the number of years a person that has lived for 'seconds' seconds is
  aged on 'planet'.

    - Earth: orbital period 365.25 Earth days, or 31557600 seconds
    - Mercury: orbital period 0.2408467 Earth years
    - Venus: orbital period 0.61519726 Earth years
    - Mars: orbital period 1.8808158 Earth years
    - Jupiter: orbital period 11.862615 Earth years
    - Saturn: orbital period 29.447498 Earth years
    - Uranus: orbital period 84.016846 Earth years
    - Neptune: orbital period 164.79132 Earth years
  """
  @spec age_on(planet, pos_integer) :: float
  def age_on(planet, seconds) do
    seconds / @earth_yr_in_secs /
      case planet do
        :mercury ->
          0.2408467

        :venus ->
          0.61519726

        :earth ->
          1.0

        :mars ->
          1.8808158

        :jupiter ->
          11.862615

        :saturn ->
          29.447498

        :uranus ->
          84.016846

        :neptune ->
          164.79132
      end
  end
end