Tournament Scheduling in Elixir

scheduler.ex

defmodule Scheduler do
  require Integer

  @doc """
  Generate a number of teams (3 or more)
  """

  def generate_teams(number) when number < 3, do: IO.puts "Need to specify at least 3 teams"
  def generate_teams(number) do
    team_names
    |> Enum.shuffle
    |> Enum.take(number)
  end

  @doc """
  Given a list of team names, schedule matches in a round-robin style.
  Returns an array of rounds, which includes several tuples, one per match.
  """

  def schedule(teams) do
    teams
    |> round_out
    |> build_schedule
  end

  defp build_schedule(teams), do: _build_schedule(teams, length(teams))
  defp _build_schedule(team, l), do: __build_schedule(Enum.chunk(team, (l/2 |> float_to_int)), [], number_of_rounds(l))

  defp __build_schedule(_, output, 0), do: output
  defp __build_schedule([t1, t2], output, l) do
    output = [t1, t2]
    |> generate_matches
    |> combine_with(output)

    rotate(t1, t2)
    |> __build_schedule(output, l - 1)
  end

  defp rotate([h1|htail], [a1|atail]) do
    [x|xt] = Enum.reverse(htail)
    
    [
      [h1, a1|Enum.reverse(xt)],
      atail ++ [x]
    ]
  end

  defp combine_with(round, output), do: output ++ [round]

  defp generate_matches([t1, t2]), do: Enum.zip(t1, t2)

  defp number_of_rounds(number_of_teams), do: (number_of_teams - 1) * 2

  defp round_out(teams), do: _round_out(teams, teams |> length |> Integer.is_even)
  defp _round_out(teams, true), do: teams
  defp _round_out(teams, false), do: teams ++ [:bye]

  defp team_names do
    [ "Aardvarks", "Buffalos", "Carrion", "Ducks", "Elephants",
      "Fireants", "Geese", "Hunters", "Impala", "Jokers", "Kings",
      "Lions", "Mice", "Newts", "Orangutans", "Parrots", ]
  end

  defp float_to_int(f) do
    {n, _} = f
      |> to_string
      |> Integer.parse
    n
  end

end