defmodule Readability do
  @moduledoc """
  Readability library for extracting & curating articles.

  ## Example

  ```elixir
  @type html :: binary

  # Extract title
  Readability.title(html)

  # Extract only text from article
  article = html
            |> Readability.article
            |> Readability.readable_text

  # Extract article with transformed html
  article = html
            |> Readability.article
            |> Readability.raw_html
  ```
  """

  alias Readability.TitleFinder
  alias Readability.ArticleBuilder

  @default_options [retry_length: 250,
                    min_text_length: 25,
                    remove_unlikely_candidates: true,
                    weight_classes: true,
                    clean_conditionally: true,
                    remove_empty_nodes: true,
                    min_image_width: 130,
                    min_image_height: 80,
                    ignore_image_format: [],
                    blacklist: nil,
                    whitelist: nil
                   ]

  @regexes [unlikely_candidate: ~r/combx|comment|community|disqus|extra|foot|header|hidden|lightbox|modal|menu|meta|nav|remark|rss|shoutbox|sidebar|sponsor|ad-break|agegate|pagination|pager|popup/i,
            ok_maybe_its_a_candidate: ~r/and|article|body|column|main|shadow/i,
            positive: ~r/article|body|content|entry|hentry|main|page|pagination|post|text|blog|story/i,
            negative: ~r/hidden|^hid|combx|comment|com-|contact|foot|footer|footnote|link|masthead|media|meta|outbrain|promo|related|scroll|shoutbox|sidebar|sponsor|shopping|tags|tool|utility|widget/i,
            div_to_p_elements: ~r/<(a|blockquote|dl|div|img|ol|p|pre|table|ul)/i,
            replace_brs: ~r/(<br[^>]*>[ \n\r\t]*){2,}/i,
            replace_fonts: ~r/<(\/?)font[^>]*>/i,
            normalize: ~r/\s{2,}/,
            video: ~r/\/\/(www\.)?(dailymotion|youtube|youtube-nocookie|player\.vimeo)\.com/i
           ]

  @type html_tree :: tuple | list
  @type options :: list

  @doc """
  Extract title

  ## Example

      iex> title = Readability.title(html_str)
      "Some title in html"
  """
  @spec title(binary) :: binary
  def title(html) when is_binary(html), do: html |> parse |> title
  def title(html_tree), do: TitleFinder.title(html_tree)

  @doc """
  Using a variety of metrics (content score, classname, element types), find the content that is
  most likely to be the stuff a user wants to read

  ## Example

      iex> article_tree = Redability(html_str)
      # returns article that is tuple

  """
  @spec article(binary, options) :: html_tree
  def article(raw_html, opts \\ []) do
    opts = Keyword.merge(@default_options, opts)
    raw_html
    |> parse
    |> ArticleBuilder.build(opts)
  end


  @doc """
  return raw html binary from html_tree
  """
  @spec raw_html(html_tree) :: binary
  def raw_html(html_tree) do
    html_tree |> Floki.raw_html
  end

  @doc """
  return only text binary from html_tree
  """
  @spec raw_html(html_tree) :: binary
  def readable_text(html_tree) do
    # TODO: Remove image caption when extract only text
    tags_to_br = ~r/<\/(p|div|article|h\d)/i
    html_str = html_tree |> raw_html
    Regex.replace(tags_to_br, html_str, &("\n#{&1}"))
    |> Floki.parse
    |> Floki.text
    |> String.strip
  end

  @doc """
  Normalize and Parse to html tree(tuple or list)) from binary html
  """
  @spec parse(binary) :: html_tree
  def parse(raw_html) do
    raw_html
    |> String.replace(Readability.regexes[:replace_brs], "</p><p>")
    |> String.replace(Readability.regexes[:replace_fonts], "<\1span>")
    |> String.replace(Readability.regexes[:normalize], " ")
    |> Floki.parse
    |> Floki.filter_out(:comment)
  end

  def regexes, do: @regexes

  def default_options, do: @default_options
end