contributors.ex

defmodule Contributors do
  @client %Tentacat.Client{auth: ""}

  def commit(user, repo), do: Tentacat.Commits.list(user, repo, @client)

  def analysis(commits) do
    commits
    |> Enum.filter(&is_map/1)
    |> Enum.reduce(%{}, &users_first_commit/2)
    |> Enum.sort(fn {_, date1}, {_, date2} -> date1 < date2 end)
  end

  def print(commits) do
    commits
    |> analysis()
    |> Enum.each(fn
      {"missing_author", _} -> nil
      {username, first_commit} -> 
        pretty_date = 
          first_commit
          |> DateTime.from_iso8601()
          |> elem(1)
          |> DateTime.to_date()
          |> Date.to_string()
        IO.puts("#{username} on #{pretty_date}")
    end)
  end

  defp users_first_commit(%{"author" => %{"login" => author}, "commit" => %{"author" => %{"date" => date}}}, acc) do
    {_, new_acc} = Map.get_and_update(acc, author, fn current_value ->
      new_value =
        cond do
          not is_nil(current_value) and current_value < date  -> current_value
          true -> date
        end

      {current_value, new_value}
    end)

    new_acc
  end

  defp users_first_commit(%{"commit" => %{"author" => %{"date" => date}, "message" => commit_msg}}, acc) do
    case Regex.run(~r/from ([\w-]+)\//, commit_msg) do
      [_match, username]  -> users_first_commit(%{"author" => %{"login" => username}, "commit" => %{"author" => %{"date" => date}}}, acc)
      nil -> 
        missing_author = Map.get(acc, "missing_author", [])
        Map.put(acc, "missing_author", [{commit_msg, date}|missing_author])
    end
  end
end