clever_solution.rb

def format_duration(seconds)
  *init, last = [3600 * 24 * 365, 3600 * 24, 3600, 60, 1]
                .collect {|x| div, seconds = seconds.divmod(x); div}
                .reverse
                .zip([" second", " minute", " hour", " day", " year"])
                .keep_if {|x, y| x != 0}
                .map{|x, y| x.to_s + y + (x > 1 ? "s" : "")}
                .reverse
  last ? "#{init.join(", ")}#{init == [] ? "" : " and "}#{last}" : "now"
end