regex.ex

defmodule Regex do
  @moduledoc ~S"""
  Provides regular expressions for Elixir.
  """

  defstruct re_pattern: nil, source: "", opts: "", re_version: ""

  @type t :: %__MODULE__{re_pattern: term, source: binary, opts: binary}

  defmodule CompileError do
    defexception message: "regex could not be compiled"
  end

  @doc """
  Compiles the regular expression.
  """
  @spec compile(binary, binary | [term]) :: {:ok, t} | {:error, any}
  def compile(source, options \\ "") when is_binary(source) do
    compile(source, options, version())
  end

  defp compile(source, options, version) when is_binary(options) do
    case translate_options(options, []) do
      {:error, rest} ->
        {:error, {:invalid_option, rest}}

      translated_options ->
        compile(source, translated_options, options, version)
    end
  end

  defp compile(source, options, version) when is_list(options) do
    compile(source, options, "", version)
  end

  defp compile(source, opts, doc_opts, version) do
    case :re.compile(source, opts) do
      {:ok, re_pattern} ->
        {:ok, %Regex{re_pattern: re_pattern, re_version: version, source: source, opts: doc_opts}}

      error ->
        error
    end
  end

  @doc """
  Compiles the regular expression and raises `Regex.CompileError` in case of errors.
  """
  @spec compile!(binary, binary | [term]) :: t
  def compile!(source, options \\ "") when is_binary(source) do
    case compile(source, options) do
      {:ok, regex} -> regex
      {:error, {reason, at}} -> raise Regex.CompileError, "#{reason} at position #{at}"
    end
  end

  @doc """
  Recompiles the existing regular expression if necessary.
  """
  @doc since: "1.4.0"
  @spec recompile(t) :: {:ok, t} | {:error, any}
  def recompile(%Regex{} = regex) do
    version = version()

    case regex do
      %{re_version: ^version} ->
        {:ok, regex}

      _ ->
        %{source: source, opts: opts} = regex
        compile(source, opts, version)
    end
  end

  @doc """
  Recompiles the existing regular expression and raises `Regex.CompileError` in case of errors.
  """
  @doc since: "1.4.0"
  @spec recompile!(t) :: t
  def recompile!(regex) do
    case recompile(regex) do
      {:ok, regex} -> regex
      {:error, {reason, at}} -> raise Regex.CompileError, "#{reason} at position #{at}"
    end
  end

  @doc """
  Returns the version of the underlying Regex engine.
  """
  @doc since: "1.4.0"
  @spec version :: term()
  def version do
    {:re.version(), :erlang.system_info(:endian)}
  end

  @doc """
  Returns a boolean indicating whether there was a match or not.
  """
  @spec match?(t, String.t()) :: boolean
  def match?(%Regex{} = regex, string) when is_binary(string) do
    safe_run(regex, string, [{:capture, :none}]) == :match
  end

  @doc """
  Returns `true` if the given `term` is a regex.
  Otherwise returns `false`.
  """
  # TODO: deprecate permanently on Elixir v1.15
  @doc deprecated: "Use Kernel.is_struct/2 or pattern match on %Regex{} instead"
  def regex?(term)
  def regex?(%Regex{}), do: true
  def regex?(_), do: false

  @doc """
  Runs the regular expression against the given string until the first match.
  It returns a list with all captures or `nil` if no match occurred.
  """
  @spec run(t, binary, [term]) :: nil | [binary] | [{integer, integer}]
  def run(regex, string, options \\ [])

  def run(%Regex{} = regex, string, options) when is_binary(string) do
    return = Keyword.get(options, :return, :binary)
    captures = Keyword.get(options, :capture, :all)
    offset = Keyword.get(options, :offset, 0)

    case safe_run(regex, string, [{:capture, captures, return}, {:offset, offset}]) do
      :nomatch -> nil
      :match -> []
      {:match, results} -> results
    end
  end

  @doc """
  Returns the given captures as a map or `nil` if no captures are found.
  """
  @spec named_captures(t, String.t(), [term]) :: map | nil
  def named_captures(regex, string, options \\ []) when is_binary(string) do
    names = names(regex)
    options = Keyword.put(options, :capture, names)
    results = run(regex, string, options)
    if results, do: Enum.zip(names, results) |> Enum.into(%{})
  end

  @doc """
  Returns the underlying `re_pattern` in the regular expression.
  """
  @spec re_pattern(t) :: term
  def re_pattern(%Regex{re_pattern: compiled}) do
    compiled
  end

  @doc """
  Returns the regex source as a binary.
  """
  @spec source(t) :: String.t()
  def source(%Regex{source: source}) do
    source
  end

  @doc """
  Returns the regex options as a string.
  """
  @spec opts(t) :: String.t()
  def opts(%Regex{opts: opts}) do
    opts
  end

  @doc """
  Returns a list of names in the regex.
  """
  @spec names(t) :: [String.t()]
  def names(%Regex{re_pattern: compiled, re_version: version, source: source}) do
    re_pattern =
      case version() do
        ^version ->
          compiled

        _ ->
          {:ok, recompiled} = :re.compile(source)
          recompiled
      end

    {:namelist, names} = :re.inspect(re_pattern, :namelist)
    names
  end

  @doc ~S"""
  Same as `run/3`, but scans the target several times collecting all
  matches of the regular expression.
  """
  @spec scan(t, String.t(), [term]) :: [[String.t()]]
  def scan(regex, string, options \\ [])

  def scan(%Regex{} = regex, string, options) when is_binary(string) do
    return = Keyword.get(options, :return, :binary)
    captures = Keyword.get(options, :capture, :all)
    offset = Keyword.get(options, :offset, 0)
    options = [{:capture, captures, return}, :global, {:offset, offset}]

    case safe_run(regex, string, options) do
      :match -> []
      :nomatch -> []
      {:match, results} -> results
    end
  end

  defp safe_run(
         %Regex{re_pattern: compiled, source: source, re_version: version, opts: compile_opts},
         string,
         options
       ) do
    case version() do
      ^version -> :re.run(string, compiled, options)
      _ -> :re.run(string, source, translate_options(compile_opts, options))
    end
  end

  @doc """
  Splits the given target based on the given pattern and in the given number of
  parts.
  """
  @spec split(t, String.t(), [term]) :: [String.t()]
  def split(regex, string, options \\ [])

  def split(%Regex{}, "", opts) do
    if Keyword.get(opts, :trim, false) do
      []
    else
      [""]
    end
  end

  def split(%Regex{} = regex, string, opts)
      when is_binary(string) and is_list(opts) do
    on = Keyword.get(opts, :on, :first)

    case safe_run(regex, string, [:global, capture: on]) do
      {:match, matches} ->
        index = parts_to_index(Keyword.get(opts, :parts, :infinity))
        trim = Keyword.get(opts, :trim, false)
        include_captures = Keyword.get(opts, :include_captures, false)
        do_split(matches, string, 0, index, trim, include_captures)

      :match ->
        [string]

      :nomatch ->
        [string]
    end
  end

  defp parts_to_index(:infinity), do: 0
  defp parts_to_index(n) when is_integer(n) and n > 0, do: n

  defp do_split(_, string, offset, _counter, true, _with_captures)
       when byte_size(string) <= offset do
    []
  end

  defp do_split(_, string, offset, 1, _trim, _with_captures),
    do: [binary_part(string, offset, byte_size(string) - offset)]

  defp do_split([], string, offset, _counter, _trim, _with_captures),
    do: [binary_part(string, offset, byte_size(string) - offset)]

  defp do_split([[{pos, _} | h] | t], string, offset, counter, trim, with_captures)
       when pos - offset < 0 do
    do_split([h | t], string, offset, counter, trim, with_captures)
  end

  defp do_split([[] | t], string, offset, counter, trim, with_captures),
    do: do_split(t, string, offset, counter, trim, with_captures)

  defp do_split([[{pos, length} | h] | t], string, offset, counter, trim, true) do
    new_offset = pos + length
    keep = pos - offset

    <<_::binary-size(offset), part::binary-size(keep), match::binary-size(length), _::binary>> =
      string

    if keep == 0 and trim do
      [match | do_split([h | t], string, new_offset, counter - 1, trim, true)]
    else
      [part, match | do_split([h | t], string, new_offset, counter - 1, trim, true)]
    end
  end

  defp do_split([[{pos, length} | h] | t], string, offset, counter, trim, false) do
    new_offset = pos + length
    keep = pos - offset

    if keep == 0 and trim do
      do_split([h | t], string, new_offset, counter, trim, false)
    else
      <<_::binary-size(offset), part::binary-size(keep), _::binary>> = string
      [part | do_split([h | t], string, new_offset, counter - 1, trim, false)]
    end
  end

  @doc ~S"""
  Receives a regex, a binary and a replacement, returns a new
  binary where all matches are replaced by the replacement.
  """
  @spec replace(t, String.t(), String.t() | (... -> String.t()), [term]) :: String.t()
  def replace(%Regex{} = regex, string, replacement, options \\ [])
      when is_binary(string) and is_list(options) do
    opts = if Keyword.get(options, :global) != false, do: [:global], else: []
    opts = [{:capture, :all, :index} | opts]

    case safe_run(regex, string, opts) do
      :nomatch ->
        string

      {:match, [mlist | t]} when is_list(mlist) ->
        apply_list(string, precompile_replacement(replacement), [mlist | t])
        |> IO.iodata_to_binary()

      {:match, slist} ->
        apply_list(string, precompile_replacement(replacement), [slist])
        |> IO.iodata_to_binary()
    end
  end

  defp precompile_replacement(replacement) when is_function(replacement) do
    {:arity, arity} = Function.info(replacement, :arity)
    {replacement, arity}
  end

  defp precompile_replacement(""), do: []

  defp precompile_replacement(<<?\\, ?g, ?{, rest::binary>>) when byte_size(rest) > 0 do
    {ns, <<?}, rest::binary>>} = pick_int(rest)
    [List.to_integer(ns) | precompile_replacement(rest)]
  end

  defp precompile_replacement(<<?\\, ?\\, rest::binary>>) do
    [<<?\\>> | precompile_replacement(rest)]
  end

  defp precompile_replacement(<<?\\, x, rest::binary>>) when x in ?0..?9 do
    {ns, rest} = pick_int(rest)
    [List.to_integer([x | ns]) | precompile_replacement(rest)]
  end

  defp precompile_replacement(<<x, rest::binary>>) do
    case precompile_replacement(rest) do
      [head | t] when is_binary(head) ->
        [<<x, head::binary>> | t]

      other ->
        [<<x>> | other]
    end
  end

  defp pick_int(<<x, rest::binary>>) when x in ?0..?9 do
    {found, rest} = pick_int(rest)
    {[x | found], rest}
  end

  defp pick_int(bin) do
    {[], bin}
  end

  defp apply_list(string, replacement, list) do
    apply_list(string, string, 0, replacement, list)
  end

  defp apply_list(_, "", _, _, []) do
    []
  end

  defp apply_list(_, string, _, _, []) do
    string
  end

  defp apply_list(whole, string, pos, replacement, [[{mpos, _} | _] | _] = list)
       when mpos > pos do
    length = mpos - pos
    <<untouched::binary-size(length), rest::binary>> = string
    [untouched | apply_list(whole, rest, mpos, replacement, list)]
  end

  defp apply_list(whole, string, pos, replacement, [[{pos, length} | _] = head | tail]) do
    <<_::size(length)-binary, rest::binary>> = string
    new_data = apply_replace(whole, replacement, head)
    [new_data | apply_list(whole, rest, pos + length, replacement, tail)]
  end

  defp apply_replace(string, {fun, arity}, indexes) do
    apply(fun, get_indexes(string, indexes, arity))
  end

  defp apply_replace(_, [bin], _) when is_binary(bin) do
    bin
  end

  defp apply_replace(string, repl, indexes) do
    indexes = List.to_tuple(indexes)

    for part <- repl do
      cond do
        is_binary(part) ->
          part

        part >= tuple_size(indexes) ->
          ""

        true ->
          get_index(string, elem(indexes, part))
      end
    end
  end

  defp get_index(_string, {pos, _length}) when pos < 0 do
    ""
  end

  defp get_index(string, {pos, length}) do
    <<_::size(pos)-binary, res::size(length)-binary, _::binary>> = string
    res
  end

  defp get_indexes(_string, _, 0) do
    []
  end

  defp get_indexes(string, [], arity) do
    ["" | get_indexes(string, [], arity - 1)]
  end

  defp get_indexes(string, [h | t], arity) do
    [get_index(string, h) | get_indexes(string, t, arity - 1)]
  end

  @doc ~S"""
  Escapes a string to be literally matched in a regex.
  """
  @spec escape(String.t()) :: String.t()
  def escape(string) when is_binary(string) do
    string
    |> escape(_length = 0, string)
    |> IO.iodata_to_binary()
  end

  @escapable '.^$*+?()[]{}|#-\\\t\n\v\f\r\s'

  defp escape(<<char, rest::binary>>, length, original) when char in @escapable do
    escape_char(rest, length, original, char)
  end

  defp escape(<<_, rest::binary>>, length, original) do
    escape(rest, length + 1, original)
  end

  defp escape(<<>>, _length, original) do
    original
  end

  defp escape_char(<<rest::binary>>, 0, _original, char) do
    [?\\, char | escape(rest, 0, rest)]
  end

  defp escape_char(<<rest::binary>>, length, original, char) do
    [binary_part(original, 0, length), ?\\, char | escape(rest, 0, rest)]
  end

  # Helpers

  @doc false
  # Unescape map function used by Macro.unescape_string.
  def unescape_map(?f), do: ?\f
  def unescape_map(?n), do: ?\n
  def unescape_map(?r), do: ?\r
  def unescape_map(?t), do: ?\t
  def unescape_map(?v), do: ?\v
  def unescape_map(?a), do: ?\a
  def unescape_map(_), do: false

  # Private Helpers

  defp translate_options(<<?u, t::binary>>, acc), do: translate_options(t, [:unicode, :ucp | acc])
  defp translate_options(<<?i, t::binary>>, acc), do: translate_options(t, [:caseless | acc])
  defp translate_options(<<?x, t::binary>>, acc), do: translate_options(t, [:extended | acc])
  defp translate_options(<<?f, t::binary>>, acc), do: translate_options(t, [:firstline | acc])
  defp translate_options(<<?U, t::binary>>, acc), do: translate_options(t, [:ungreedy | acc])

  defp translate_options(<<?s, t::binary>>, acc),
    do: translate_options(t, [:dotall, {:newline, :anycrlf} | acc])

  defp translate_options(<<?m, t::binary>>, acc), do: translate_options(t, [:multiline | acc])

  defp translate_options(<<?r, t::binary>>, acc) do
    IO.warn("the /r modifier in regular expressions is deprecated, please use /U instead")
    translate_options(t, [:ungreedy | acc])
  end

  defp translate_options(<<>>, acc), do: acc
  defp translate_options(rest, _acc), do: {:error, rest}
end