defmodule Logger.Backends.ExRollbar do
  @moduledoc """
  Logger backend that forwards `Logger.Error/2` to Rollbar
  """
  use GenEvent
  import ExRollbar, only: [report: 4]

  def init(_) do
    {:ok, []}
  end

  def handle_event({level, _, {Logger, message, timestamp, metadata}}, state)
      when level in [:error, :warn] do

    if Keyword.get(metadata, :rollbar, true) == false do
      {:ok, state}
    else
      unix_ts = make_unix_ts(timestamp)
      meta = Keyword.put(metadata, :timestamp, unix_ts)

      module = Keyword.get(meta, :module, :no_module) || :no_module
      {function, arity} = Keyword.get(meta, :function, :no_fun) |> parse_fun
      file = Keyword.get(meta, :file, :no_file)
      line = Keyword.get(meta, :line, :no_line)

      synth_stack = [
        {module, function, arity, [file: file, line: line]}
      ]
      report(level, message, synth_stack, meta)
      {:ok, state}
    end
  end

  def handle_event(_, state), do: {:ok, state}

  defp parse_fun(nil), do: {:no_fun, :no_arity}
  defp parse_fun(fun) when is_atom(fun), do: {fun, :no_arity}
  defp parse_fun(str) when is_binary(str) do
    [name, str_int] = String.split(str, "/")
    {String.to_atom(name), String.to_integer(str_int)}
  end

  defp make_unix_ts(_), do: :os.system_time(:seconds)
end