defmodule Tracer.Formatter do
  @moduledoc """
  Tracer format and io functions.
  """
  def start_link(group_leader, formatter) do
    spawn_link(__MODULE__, :init, [group_leader, formatter])
  end

  def init(group_leader, formatter) do
    :erlang.group_leader(self, group_leader)
    loop(formatter)
  end

  defp loop(formatter) do
    receive do
      {:formatter, new_formatter} ->
        loop(new_formatter)
      msg ->
        format(msg, formatter) |> IO.puts
        loop(formatter)
    end
  end

  defp format(msg, nil), do: format_trace(msg)
  defp format(msg, {m, f}), do: apply(m, f, [msg])
  defp format(msg, fun) when is_function(fun, 1), do: fun.(msg)

  @doc """
  Format trace message to a string.
  """
  def format_trace({:trace, pid, :call, mfa}) do
    "#{inspect pid} call #{call_mfa(mfa)}"
  end
  def format_trace({:trace, pid, :call, mfa, dump}) do
    traces = String.split(dump, "\n")
      |> Enum.filter( &Regex.match?(~r/Return addr 0x|CP: 0x/, &1) )
      |> fold_over
      |> Enum.reverse
    "#{inspect pid} call #{call_mfa(mfa)}#{traces}"
  end
  def format_trace({:trace, pid, :return_from, mfa, return}) do
    "#{inspect pid} returned #{return_mfa(mfa)}#{inspect return}"
  end
  def format_trace({:trace, pid, :exception_from, mfa, {class, value}}) do
    "#{inspect pid} exception #{return_mfa(mfa)}#{inspect class}:#{inspect value}"
  end
  def format_trace(msg) do
    "unknown message: #{inspect msg}"
  end

  defp call_mfa({module, function, arguments}) do
    "#{inspect module}.#{function}(" <> Enum.map_join(arguments, ", ", &inspect(&1, limit: 5000)) <> ")"
  end

  defp return_mfa({module, function, argument}) do
    "#{inspect module}.#{function}/#{argument} -> "
  end

  defp fold_over(list, acc \\ [])

  defp fold_over([_last], acc), do: acc
  defp fold_over([one | tail], acc) do
    fold_over(tail, [extract_function(one) | acc])
  end

  defp extract_function(line) do
    case Regex.run(~r"^.+\((.+):(.+)/(\d+).+\)$", line, capture: :all_but_first) do
      [m, f, a_length] ->
        "\n  #{m |> clean_atom_binary}.#{f |> clean_atom_binary}/#{a_length}"
      nil ->
        ""
    end
  end

  defp clean_atom_binary(binatom), do: String.strip(binatom, ?') |> clean_elixir |> String.to_atom

  defp clean_elixir("Elixir." <> binatom), do: binatom
  defp clean_elixir(binatom), do: binatom
end