defmodule Frenzy.Pipeline.Extractor.DaringFireball do
  @moduledoc """
  Extractor for https://daringfireball.net
  """

  alias Frenzy.Pipeline.Extractor
  @behaviour Extractor

  @impl Extractor
  def extract(html_tree) do
    case get_article_element(html_tree) || get_link_element(html_tree) do
      nil ->
        {:error, "no matching elements"}

      elem ->
        {:ok, elem}
    end
  end

  defp get_article_element(html_tree) do
    case Floki.find(html_tree, "div.article") do
      [article_elem | _] ->
        # articles include extra information in the div.article element
        Floki.filter_out(article_elem, "h1, .dateline, #PreviousNext")

      _ ->
        nil
    end
  end

  defp get_link_element(html_tree) do
    case Floki.find(html_tree, "dl.linkedlist dd") do
      [{_, _, dd_children} | _] ->
        dd_children

      _ ->
        nil
    end
  end
end