linkify/lib/linkify/parser.ex

defmodule Linkify.Parser do
  @moduledoc """
  Module to handle parsing the the input string.
  """

  alias Linkify.Builder

  @invalid_url ~r/(\.\.+)|(^(\d+\.){1,2}\d+$)/

  @match_url ~r{^(?:\W*)?(?<url>(?:https?:\/\/)?[\w.-]+(?:\.[\w\.-]+)+[\w\-\._~%:\/?#[\]@!\$&'\(\)\*\+,;=.]+$)}u

  @get_scheme_host ~r{^\W*(?<scheme>https?:\/\/)?(?:[^@\n]+\\w@)?(?<host>[^:#~\/\n?]+)}u

  # @user
  # @user@example.com
  # credo:disable-for-next-line

  @match_hashtag ~r/^(?<tag>\#[[:word:]_]*[[:alpha:]_·][[:word:]_·\p{M}]*)/u

  @match_skipped_tag ~r/^(?<tag>(a|code|pre)).*>*/

  @delimiters ~r/[,.;:>]*$/

  @prefix_extra [
    "magnet:?",
    "dweb://",
    "dat://",
    "gopher://",
    "ipfs://",
    "ipns://",
    "irc://",
    "ircs://",
    "irc6://",
    "mumble://",
    "ssb://"
  ]

  @tlds "./priv/tlds.txt"
        |> File.read!()
        |> String.split("\n", trim: true)
        |> Enum.concat(["onion"])
        |> MapSet.new()

  @default_opts %{
    url: true,
    validate_tld: true
  }

  @doc """
  Parse the given string, identifying items to link.

  Parses the string, replacing the matching urls with an html link.

  ## Examples

      iex> Linkify.Parser.parse("Check out google.com")
      ~s{Check out <a href="http://google.com">google.com</a>}
  """

  @types [:url, :hashtag, :extra, :mention, :email]

  def parse(input, opts \\ %{})
  def parse(input, opts) when is_binary(input), do: {input, %{}} |> parse(opts) |> elem(0)
  def parse(input, list) when is_list(list), do: parse(input, Enum.into(list, %{}))

  def parse(input, opts) do
    opts = Map.merge(@default_opts, opts)

    {buffer, user_acc} = do_parse(input, opts, {"", [], :parsing})

    if opts[:iodata] do
      {buffer, user_acc}
    else
      {IO.iodata_to_binary(buffer), user_acc}
    end
  end

  defp accumulate(acc, buffer),
    do: [buffer | acc]

  defp accumulate(acc, buffer, trailing),
    do: [trailing, buffer | acc]

  defp do_parse({"", user_acc}, _opts, {"", acc, _}),
    do: {Enum.reverse(acc), user_acc}

  defp do_parse(
         {"<" <> text, user_acc},
         %{hashtag: true} = opts,
         {"#" <> _ = buffer, acc, :parsing}
       ) do
    {buffer, user_acc} = link(buffer, opts, user_acc)

    case Regex.run(@match_skipped_tag, text, capture: [:tag]) do
      [tag] ->
        text = String.trim_leading(text, tag)
        do_parse({text, user_acc}, opts, {"", accumulate(acc, buffer, "<#{tag}"), :skip})

      nil ->
        do_parse({text, user_acc}, opts, {"<", acc, {:open, 1}})
    end
  end

  defp do_parse({"<br" <> text, user_acc}, opts, {buffer, acc, :parsing}) do
    {buffer, user_acc} = link(buffer, opts, user_acc)
    do_parse({text, user_acc}, opts, {"", accumulate(acc, buffer, "<br"), {:open, 1}})
  end

  defp do_parse({"<a" <> text, user_acc}, opts, {buffer, acc, :parsing}),
    do: do_parse({text, user_acc}, opts, {"", accumulate(acc, buffer, "<a"), :skip})

  defp do_parse({"<pre" <> text, user_acc}, opts, {buffer, acc, :parsing}),
    do: do_parse({text, user_acc}, opts, {"", accumulate(acc, buffer, "<pre"), :skip})

  defp do_parse({"<code" <> text, user_acc}, opts, {buffer, acc, :parsing}),
    do: do_parse({text, user_acc}, opts, {"", accumulate(acc, buffer, "<code"), :skip})

  defp do_parse({"</a>" <> text, user_acc}, opts, {buffer, acc, :skip}),
    do: do_parse({text, user_acc}, opts, {"", accumulate(acc, buffer, "</a>"), :parsing})

  defp do_parse({"</pre>" <> text, user_acc}, opts, {buffer, acc, :skip}),
    do: do_parse({text, user_acc}, opts, {"", accumulate(acc, buffer, "</pre>"), :parsing})

  defp do_parse({"</code>" <> text, user_acc}, opts, {buffer, acc, :skip}),
    do: do_parse({text, user_acc}, opts, {"", accumulate(acc, buffer, "</code>"), :parsing})

  defp do_parse({"<" <> text, user_acc}, opts, {"", acc, :parsing}),
    do: do_parse({text, user_acc}, opts, {"<", acc, {:open, 1}})

  defp do_parse({">" <> text, user_acc}, opts, {buffer, acc, {:attrs, _level}}),
    do: do_parse({text, user_acc}, opts, {"", accumulate(acc, buffer, ">"), :parsing})

  defp do_parse({<<ch::8>> <> text, user_acc}, opts, {"", acc, {:attrs, level}}) do
    do_parse({text, user_acc}, opts, {"", accumulate(acc, <<ch::8>>), {:attrs, level}})
  end

  defp do_parse({text, user_acc}, opts, {buffer, acc, {:open, level}}) do
    do_parse({text, user_acc}, opts, {"", accumulate(acc, buffer), {:attrs, level}})
  end

  defp do_parse(
         {<<char::bytes-size(1), text::binary>>, user_acc},
         opts,
         {buffer, acc, state}
       )
       when char in [" ", "\r", "\n"] do
    {buffer, user_acc} = link(buffer, opts, user_acc)

    do_parse(
      {text, user_acc},
      opts,
      {"", accumulate(acc, buffer, char), state}
    )
  end

  defp do_parse({<<ch::8>>, user_acc}, opts, {buffer, acc, state}) do
    {buffer, user_acc} = link(buffer <> <<ch::8>>, opts, user_acc)

    do_parse(
      {"", user_acc},
      opts,
      {"", accumulate(acc, buffer), state}
    )
  end

  defp do_parse({<<ch::8>> <> text, user_acc}, opts, {buffer, acc, state}),
    do: do_parse({text, user_acc}, opts, {buffer <> <<ch::8>>, acc, state})

  def check_and_link(:url, buffer, opts, _user_acc) do
    if url?(buffer, opts) do
      case @match_url |> Regex.run(buffer, capture: [:url]) |> hd() do
        ^buffer ->
          link_url(buffer, opts)

        url ->
          link = link_url(url, opts)
          restore_stripped_symbols(buffer, url, link)
      end
    else
      :nomatch
    end
  end

  def check_and_link(:email, buffer, opts, _user_acc) do
    if email?(buffer, opts), do: link_email(buffer, opts), else: :nomatch
  end

  def check_and_link(:mention, buffer, opts, user_acc) do
    buffer
    |> match_mention
    |> link_mention(buffer, opts, user_acc)
  end

  def check_and_link(:hashtag, buffer, opts, user_acc) do
    buffer
    |> match_hashtag
    |> link_hashtag(buffer, opts, user_acc)
  end

  def check_and_link(:extra, "xmpp:" <> handle = buffer, opts, _user_acc) do
    if email?(handle, opts), do: link_extra(buffer, opts), else: :nomatch
  end

  def check_and_link(:extra, buffer, opts, _user_acc) do
    if String.starts_with?(buffer, @prefix_extra), do: link_extra(buffer, opts), else: :nomatch
  end

  defp strip_parens(buffer) do
    buffer
    |> String.trim_leading("(")
    |> String.trim_trailing(")")
  end

  defp strip_punctuation(buffer), do: String.replace(buffer, @delimiters, "")

  def url?(buffer, opts) do
    valid_url?(buffer) && Regex.match?(@match_url, buffer) && valid_tld?(buffer, opts)
  end

  def email?(buffer, opts) do
    # Note: In reality the local part can only be checked by the remote server
    case Regex.run(~r/^(?<user>.*)@(?<host>[^@]+)$/, buffer, capture: [:user, :host]) do
      [_user, hostname] -> valid_hostname?(hostname) && valid_tld?(hostname, opts)
      _ -> false
    end
  end

  defp valid_url?(url), do: !Regex.match?(@invalid_url, url)

  @doc """
  Validates a URL's TLD. Returns a boolean.

  Will return `true` if `:validate_tld` option set to `false`.

  Will skip validation and return `true` if `:validate_tld` set to `:no_scheme` and the url has a scheme.
  """
  def valid_tld?(url, opts) do
    [scheme, host] = Regex.run(@get_scheme_host, url, capture: [:scheme, :host])

    cond do
      opts[:validate_tld] == false ->
        true

      ip?(host) ->
        true

      # don't validate if scheme is present
      opts[:validate_tld] == :no_scheme and scheme != "" ->
        true

      true ->
        tld = host |> String.trim_trailing(".") |> String.split(".") |> List.last()
        MapSet.member?(@tlds, tld)
    end
  end

  def safe_to_integer(string, base \\ 10) do
    String.to_integer(string, base)
  rescue
    _ ->
      nil
  end

  def ip?(buffer) do
    v4 = String.split(buffer, ".")

    v6 =
      buffer
      |> String.trim_leading("[")
      |> String.trim_trailing("]")
      |> String.split(":", trim: true)

    cond do
      length(v4) == 4 ->
        !Enum.any?(v4, fn x -> safe_to_integer(x, 10) not in 0..255 end)

      length(v6) in 1..8 ->
        !Enum.any?(v4, fn x -> safe_to_integer(x, 16) not in 0..0xFFFF end)

      false ->
        false
    end
  end

  # IDN-compatible, ported from musl-libc's is_valid_hostname()
  def valid_hostname?(hostname) do
    hostname
    |> String.to_charlist()
    |> Enum.any?(fn s ->
      !(s >= 0x80 || s in 0x30..0x39 || s in 0x41..0x5A || s in 0x61..0x7A || s in '.-')
    end)
    |> Kernel.!()
  end

  def match_mention(buffer) do
    case Regex.run(~r/^@(?<user>[a-zA-Z\d_-]+)(@(?<host>[^@]+))?$/, buffer,
           capture: [:user, :host]
         ) do
      [user, ""] ->
        "@" <> user

      [user, hostname] ->
        if valid_hostname?(hostname) && valid_tld?(hostname, []),
          do: "@" <> user <> "@" <> hostname,
          else: nil

      _ ->
        nil
    end
  end

  def match_hashtag(buffer) do
    case Regex.run(@match_hashtag, buffer, capture: [:tag]) do
      [hashtag] -> hashtag
      _ -> nil
    end
  end

  def link_hashtag(nil, _buffer, _, _user_acc), do: :nomatch

  def link_hashtag(hashtag, buffer, %{hashtag_handler: hashtag_handler} = opts, user_acc) do
    hashtag
    |> hashtag_handler.(buffer, opts, user_acc)
    |> maybe_update_buffer(hashtag, buffer)
  end

  def link_hashtag(hashtag, buffer, opts, _user_acc) do
    hashtag
    |> Builder.create_hashtag_link(buffer, opts)
    |> maybe_update_buffer(hashtag, buffer)
  end

  def link_mention(nil, _buffer, _, _user_acc), do: :nomatch

  def link_mention(mention, buffer, %{mention_handler: mention_handler} = opts, user_acc) do
    mention
    |> mention_handler.(buffer, opts, user_acc)
    |> maybe_update_buffer(mention, buffer)
  end

  def link_mention(mention, buffer, opts, _user_acc) do
    mention
    |> Builder.create_mention_link(buffer, opts)
    |> maybe_update_buffer(mention, buffer)
  end

  defp maybe_update_buffer(out, match, buffer) when is_binary(out) do
    maybe_update_buffer({out, nil}, match, buffer)
  end

  defp maybe_update_buffer({out, user_acc}, match, buffer)
       when match != buffer and out != buffer do
    out = String.replace(buffer, match, out)
    {out, user_acc}
  end

  defp maybe_update_buffer(out, _match, _buffer), do: out

  @doc false
  def link_url(buffer, opts) do
    Builder.create_link(buffer, opts)
  end

  @doc false
  def link_email(buffer, opts) do
    Builder.create_email_link(buffer, opts)
  end

  def link_extra(buffer, opts) do
    Builder.create_extra_link(buffer, opts)
  end

  defp link(buffer, opts, user_acc) do
    Enum.reduce_while(@types, {buffer, user_acc}, fn type, _ ->
      if opts[type] == true do
        check_and_link_reducer(type, buffer, opts, user_acc)
      else
        {:cont, {buffer, user_acc}}
      end
    end)
  end

  defp check_and_link_reducer(type, buffer, opts, user_acc) do
    str =
      buffer
      |> String.split("<")
      |> List.first()
      |> strip_punctuation()
      |> strip_parens()

    case check_and_link(type, str, opts, user_acc) do
      :nomatch ->
        {:cont, {buffer, user_acc}}

      {link, user_acc} ->
        {:halt, {restore_stripped_symbols(buffer, str, link), user_acc}}

      link ->
        {:halt, {restore_stripped_symbols(buffer, str, link), user_acc}}
    end
  end

  defp restore_stripped_symbols(buffer, buffer, link), do: link

  defp restore_stripped_symbols(buffer, stripped_buffer, link) do
    buffer
    |> String.split(stripped_buffer)
    |> Enum.intersperse(link)
  end
end