Bracket push solution

bracket_push.exs

defmodule BracketPush do
  def check_brackets(""), do: true

  def check_brackets(s) do
    do_check_brackets([],String.codepoints(s))
  end

  defp do_check_brackets(stack,[]) do
    length(stack) === 0
  end

  defp do_check_brackets(stack,["{"|rest]) do
    do_check_brackets(["{"|stack],rest)
  end

  defp do_check_brackets(stack,["["|rest]) do
    do_check_brackets(["["|stack],rest)
  end

  defp do_check_brackets(stack,["("|rest]) do
    do_check_brackets(["("|stack],rest)
  end

  defp do_check_brackets(stack,["}"|rest]) do
    case peek(stack) do
      {:ok, "{"} ->
          [h|t] = stack
          do_check_brackets(t,rest)
      {:ok, _} -> false
      {:error, _} -> false
    end
  end

  defp do_check_brackets(stack,["]"|rest]) do
    case peek(stack) do
      {:ok, "["} ->
          [h|t] = stack
          do_check_brackets(t,rest)
      {:ok, _} -> false
      {:error, _} -> false
    end
  end

  defp do_check_brackets(stack,[")"|rest]) do
      case peek(stack) do
        {:ok, "("} ->
            [h|t] = stack
            do_check_brackets(t,rest)
        {:ok, _} -> false
        {:error, _} -> false
      end
  end

  defp do_check_brackets(stack,[_|rest]) do
    do_check_brackets(stack,rest)
  end

  defp peek([]) do
    {:error, nil}
  end

  defp peek([h|_]) do
    {:ok, h}
  end
end

ExUnit.start

defmodule BracketPushTest do
  use ExUnit.Case, async: true

  test "empty string" do
    assert BracketPush.check_brackets("")
  end

  test "appropriate bracketing in a set of brackets" do
    assert BracketPush.check_brackets("{}")
  end

  test "unclosed brackets" do
    refute BracketPush.check_brackets("{{")
  end

  test "more than one pair of brackets" do
    assert BracketPush.check_brackets("{}[]")
  end

  test "brackets are out of order" do
    refute BracketPush.check_brackets("}{")
  end

  test "nested brackets" do
    assert BracketPush.check_brackets("{[()]}")
  end

  test "unbalanced nested brackets" do
    refute BracketPush.check_brackets("{[}]")
  end

  test "bracket closure with deeper nesting" do
    refute BracketPush.check_brackets("{[)][]}")
  end

  test "bracket closure in a long string of brackets" do
    assert BracketPush.check_brackets("{[]([()])}")
  end

  test "should ignore non-bracket characters" do
    assert BracketPush.check_brackets("{hello[]([a()])b}c")
  end

  test "string with newlines" do
    assert BracketPush.check_brackets("[]\n{()}\n[(({}))]\n")
  end

end