defmodule PlugMinifyHtml do
  @moduledoc """
  The `PlugMinifyHtml` plug takes care of minifying
  the response body when the response content type is text/html.
  """

  @doc false
  def init(opts \\ []), do: opts

  @doc false
  def call(%Plug.Conn{} = conn, _ \\ []) do
    Plug.Conn.register_before_send(conn, &minify_html/1)
  end

  @doc false
  def minify_html(%Plug.Conn{} = conn) do
    case List.keyfind(conn.resp_headers, "content-type", 0) do
      {_, "text/html" <> _} ->
        {:ok, document} = Floki.parse_document(conn.resp_body)

        body =
          document
          |> Floki.raw_html()

        %Plug.Conn{conn | resp_body: body}

      _ ->
        conn
    end
  end
end