DurationFormatter.ex

defmodule DurationFormatter do

  def format_duration(0), do: "now"
  def format_duration(s) do

    year = div(s, 31536000)
    day  = div(s - year * 31536000, 86400)
    hour = div(s - year * 31536000 - day * 86400,3600)
    min  = div(s - year * 31536000 - day * 86400 - hour * 3600,60)
    sec  = rem(s,60)
    
    a = sec [ year, day, hour, min, sec ]
    b = min [ year, day, hour, min, sec ]
    c = hur [ year, day, hour, min, sec ]
    d = day [ year, day, hour, min, sec]
    e = yea [ year, day, hour, min, sec]
    #e <> d <> c <> b <> a
    f = [e,d,c,b,a] |> Enum.filter(fn x->
      x != ""
    end)

    [hd|tl] = Enum.reverse(f) 

    cond do
      tl == [] -> hd
      true -> ( Enum.reverse(tl) |> Enum.join(", ") ) <> " and " <> hd
    end
    
  end

  defp sec([_,_,_,_,s]) when s == 0, do: ""
  defp sec([_,_,_,_,s]) when s == 1, do: "1 second"
  defp sec([_,_,_,_,s]) when s > 1, do: "#{s} seconds"

  defp min([_,_,_,m,_]) when m == 0, do: ""
  defp min([_,_,_,m,_]) when m == 1, do: "1 minute"
  defp min([_,_,_,m,_]) when m > 1, do: "#{m} minutes"

  defp hur([_,_,h,_,_]) when h == 0, do: ""
  defp hur([_,_,h,_,_]) when h == 1, do: "1 hour"
  defp hur([_,_,h,_,_]) when h > 1, do: "#{h} hours"

  defp day([_,d,_,_,_]) when d == 0, do: ""
  defp day([_,d,_,_,_]) when d == 1, do: "1 day"
  defp day([_,d,_,_,_]) when d > 1, do: "#{d} days"

  defp yea([y,_,_,_,_]) when y == 0, do: ""
  defp yea([y,_,_,_,_]) when y == 1, do: "1 year"
  defp yea([y,_,_,_,_]) when y > 1, do: "#{y} years"

end