defmodule Gulib.LinkerUtil do

  alias Gulib.HTMLParse

  @auto_link_schemas ~w(mailto http https thunder ftp sftp svn)

  def auto_link_schemas, do: @auto_link_schemas

  @doc """
  返回html中链接的个数
  """
  def links_amount(html) do
    html |> HTMLParse.parse |> HTMLParse.find("a") |> length
  end

  def append_rest(rest, extend_rest) do
    rest |> List.insert_at(-1, extend_rest)
  end

  @doc """
  自动生成链接

  ## Params

  ```
  # opts
    * html: 生成链接相关参数
      * target # _blank or nil (nil)
    * sanitize：是否过滤标签 true/false 默认为false
    * sanitize_options: 过滤标签的参数
    * jump_to # 用于跳转的基础url
    * jump_fn # 调用的时候可以用此回调
    * raw_html # true/false  # 默认为true
    * html_escape # true/false # 默认为false
    * normalize_rest_fn   # 格式化链接内容的方法
    * normalize_href_fn   # 格式化链接链接的方法
    * normalize_linker_fn # 格式化链接, 可以灵活的转换链接！
  ```
  """
  def auto_link(html_or_tree, opts \\ []) do
    html_opts = opts |> Gulib.get(:html, %{})
    html_escape = opts |> Gulib.get(:html_escape, false)

    opts =
      opts
      |> Keyword.take([
        :raw_html, :jump_to, :jump_fn,
        :normalize_rest_fn, :normalize_href_fn, :html_safe,
        :normalize_linker_fn
      ])
      |> Keyword.merge(
        html_escape: html_escape,
        html: html_opts
      )

    rebuild_html_tree =
      html_or_tree
      |> HTMLParse.parse
      |> HTMLParse.transform(fn(html_node, extends) ->
        impl_transform(html_node, extends, opts)
      end)

    raw_html = rebuild_html_tree |> HTMLParse.raw_html

    cond do
      Keyword.get(opts, :html_safe, false) ->
        {:safe, raw_html}
      Keyword.get(opts, :raw_html, true) ->
        raw_html
      true ->
        raw_html |> HTMLParse.parse
    end
  end

  defp impl_transform_linker({"a", attrs, rest}, extends, opts) do
    if is_function(normalize_linker_fn = Gulib.get(opts, :normalize_linker_fn, nil)) do
      normalize_linker_fn.(
        [
          attrs: attrs,
          rest: rest,
          extends: extends,
          opts: opts
        ]
      )
    else
      {"a", attrs, rest}
    end
  end

  # 对A标签的处理
  defp impl_transform({"a", attrs, rest}, extends, opts) do
    {"a", impl_normalize_linker_attrs(attrs, opts), impl_normalize_linker_rest(rest, opts)}
    |> impl_transform_linker(extends, opts)
  end
  defp impl_transform(plain_text, extends, opts) when is_binary(plain_text) do
    impl_transform_plain_text(plain_text, extends, opts)
  end
  defp impl_transform(html_tree, _extends, _opts), do: html_tree

  defp impl_transform_plain_text(plain_text, extends, opts) do
    %{
      ancestors: ancestors
    } = extends

    plain_text =
      if Gulib.get(opts, :html_escape, false) do
        Gulib.html_escape(plain_text)
      else
        plain_text
      end

    if Enum.member?(ancestors, "a") do
      plain_text
    else
      Gulib.Const.scan_url_regex
      |> Regex.replace(plain_text, fn(link_url, _) ->
        {
          "a",
          impl_normalize_linker_attrs([{"href", impl_normalize_href(link_url, opts)}], opts),
          impl_normalize_linker_rest([link_url], opts)
        }
        |> impl_transform_linker(extends, opts)
        |> HTMLParse.raw_html
      end)
    end
  end

  # 对标签属性的处理
  # opts:
  #   * target
  defp impl_normalize_linker_attrs(attrs, opts) do
    parsed_attrs = HTMLParse.parse_attrs(attrs)
    html_opts = opts |> Keyword.get(:html, %{})
    target = html_opts |> Map.get(:target, nil)

    parsed_attrs =
      if Enum.member?(["_blank", "_parent", "_self"], target) do
        parsed_attrs |> Keyword.put(:target, target)
      else
        parsed_attrs |> Keyword.drop([:target])
      end

    parsed_attrs |> HTMLParse.flatten_attrs
  end

  # 实现格式化rest
  defp impl_normalize_linker_rest(rest, opts) do
    normalize_rest_fn = opts |> Keyword.get(:normalize_rest_fn, nil)

    if is_function(normalize_rest_fn) do
      normalize_rest_fn.(rest)
    else
      rest
    end
  end

  def normalize_url(url) do
    url =
      cond do
        Gulib.blank?(url) -> ""
        String.starts_with?(url, ["/"]) -> url
        true ->
          header_str = url |> String.trim |> String.split([":"]) |> List.first |> String.downcase

          cond do
            Enum.member?(auto_link_schemas(), header_str) -> url
            Regex.match?(Gulib.Const.match_url_regex, url) -> "http://" <> url
            true -> "/#{url}"
          end
      end

    url |> Gulib.html_unescape
  end

  # 实现格式化href
  defp impl_normalize_href(url, opts) do
    normalize_href_fn = opts |> Keyword.get(:normalize_href_fn, nil)

    if is_function(normalize_href_fn) do
      url
      |> normalize_href_fn.()
      |> normalize_url
    else
      url = normalize_url(url)

      jump_to_base_uri = Keyword.get(opts, :jump_to, nil)
      jump_fn = Keyword.get(opts, :jump_fn, nil)

      cond do
        is_function(jump_fn) ->
          jump_fn.(url)
        Gulib.present?(jump_to_base_uri) ->
          jump_to_base_uri <> URI.encode_www_form(url)
        true -> url
      end
    end
  end

end