bracket_push.exs

defmodule BracketPush do
  @doc """
  Checks that all the brackets and braces in the string are matched correctly, and nested correctly
  """

  @matches %{"}"=> "{", ")"=> "(", "]"=> "["}
  @opening ["{", "(", "["]

  @spec check_brackets(String.t) :: boolean
  def check_brackets(""), do: true
  def check_brackets(str) do
    str
    |> String.replace(~r/[^\(|\{\[|\]|\}|\)]/, "")
    |> String.split("", trim: true)
    |> parse_for_balanced_brackets
  end

  @spec parse_for_balanced_brackets(List.t, List.t, boolean) :: boolean
  defp parse_for_balanced_brackets(list, openers \\ [], balanced \\ true)
  defp parse_for_balanced_brackets(_, _, false), do: false
  defp parse_for_balanced_brackets([], [], balanced), do: balanced
  defp parse_for_balanced_brackets([], list, _), do: false

  defp parse_for_balanced_brackets([h_list | t_list], [], balanced) do
    case Enum.member?(@opening, h_list) do
      false ->
        parse_for_balanced_brackets([], [], false)
      true ->
        parse_for_balanced_brackets(t_list, [h_list], balanced)
    end
  end

  defp parse_for_balanced_brackets([h_list | t_list], [h_open | t_open], balanced) do
    case Enum.member?(@opening, h_list) do
      false ->
        parse_for_balanced_brackets(t_list, t_open, is_bracket_match(h_list, h_open))
      true ->
        parse_for_balanced_brackets(t_list, [h_list | [ h_open | t_open ]], balanced)
    end
  end

  @spec is_bracket_match(String.t, String.t) :: boolean
  defp is_bracket_match(a, b) do
    Map.get(@matches, a) == b
  end

end