defmodule Panty.Collection do
  @moduledoc """
  Collection utilities
  """

  @doc """
  Get index of a substring from a pattern.

  ## Examples
      iex> Collection.string_find_index("abcdef", "cde")
      2
      iex> Collection.string_find_index("{% sections 'header' %}", "{% endschema %}")
      nil

  """

  @spec substring_index(String.t, String.t) :: integer() | nil

  def substring_index(pattern, substring) do
    case String.split(pattern, substring, parts: 2) do
      [left, _] -> String.length(left)
      [_] -> nil
    end
  end

  @doc """
  Get intersection from given lists.

  ## Examples
      iex> Collection.intersection([1, 2, 3, 4], [2, 3])
      [2, 3]
      iex> Collection.intersection(["index", "carousel", "header", "footer"], ["header", "footer"])
      ["header", "footer"]

  """

  @spec intersection([any()], [any()]) :: [any()]

  def intersection(first, second) do
    first |> Enum.filter(&(Enum.member?(second, &1)))
  end

  @doc """
  Returns the list dropping its last element

  ## Examples
      iex> Tools.initial([1, 2, 3, 4])
      [1, 2, 3]

  """

  @spec initial([any(), ...]) :: [any()]

  def initial(collection), do: _initial(collection)

  def _initial([_]), do: []
  def _initial([h|t]), do: [h| _initial(t)]
end