consecutix

defmodule Consecutix do
  @moduledoc """
  Documentation for `Consecutix`.
  """

  @doc """
  Returns consecutively grouped elements.
  Returned elements will be sorted.
  Duplicated elements are deleted.

  ## Examples

      iex> Consecutix.consecutive_lists([])
      []

      iex> Consecutix.consecutive_lists([1])
      [[1]]

      iex> Consecutix.consecutive_lists([1, 2])
      [[1, 2]]

      iex> Consecutix.consecutive_lists([1, 3])
      [[1], [3]]

  """

  @spec consecutive_maps(list(map)) :: [list()]
  def consecutive_maps([]) do
    []
  end

  @type input :: list()
  @type output :: [list()]
  @type sorter :: fun()
  @spec consecutive_lists(input, sorter) :: output
  def consecutive_lists(list, sorter \\ &Enum.sort/1)

  def consecutive_lists(list, sorter) when is_function(sorter, 2) do
    list |> Enum.sort(sorter) |> consecutive_lists_helper([], [])
  end

  def consecutive_lists(list, sorter) when is_function(sorter, 1) do
    list |> sorter.() |> consecutive_lists_helper([], [])
  end

  defp consecutive_lists_helper([], [], result), do: Enum.reverse(result)

  defp consecutive_lists_helper([], current_group, result),
    do: Enum.reverse([Enum.reverse(current_group) | result])

  defp consecutive_lists_helper([current | tail], [], result) do
    consecutive_lists_helper(tail, [current], result)
  end

  defp consecutive_lists_helper([current | tail], [prev | _] = current_group, result)
       when current - prev == 1 do
    consecutive_lists_helper(tail, [current | current_group], result)
  end

  defp consecutive_lists_helper([current | tail], current_group, result) do
    consecutive_lists_helper(tail, [current], [Enum.reverse(current_group) | result])
  end
end