playground_test.exs

defmodule PlaygroundTest do
  use ExUnit.Case, async: true

  test "playground" do
    source = """
    <p><%= bar( 1,  2 ) %></p>
    """

    IO.puts "before:"
    IO.puts source

    IO.puts "after:"
    IO.puts format_eex!(source)
  end

  defp format_eex!(source) do
    source
    |> tokenize!()
    |> format!()
    |> to_source()
  end

  defp tokenize!(source) do
    {:ok, tokens} = EEx.Tokenizer.tokenize(source, 1, 1, %{indentation: 4, trim: false})
    tokens
  end

  defp format!(tokens) do
    Enum.map(tokens, fn
      {:expr, line, column, marker, content} ->
        content = content |> List.to_string() |> Code.format_string!()
        content = [" ", content, " "] |> IO.iodata_to_binary() |> String.to_charlist()
        {:expr, line, column, marker, content}

      other ->
        other
    end)
  end

  defp to_source(tokens) do
    Enum.map(tokens, fn
      {:expr, _line, _column, marker, content} ->
        ["<%", marker, content, "%>"]

      {:text, content} ->
        content

      {:eof, _, _} ->
        ""
    end)
  end
end