neiam /gitgud

defmodule GitGudWeb.Plugs.Twirp do
  @moduledoc """
  Tiny helpers for emitting Twirp-compliant responses.

  Twirp methods accept POST with `Content-Type: application/json` or
  `application/protobuf`. We currently only do JSON; protobuf framing
  for runner.v1 messages is a TODO — see `lib/git_gud_web/controllers/runner_controller.ex`.
  """

  import Plug.Conn

  @doc "Encode a successful Twirp JSON response."
  def ok(conn, payload) do
    conn
    |> put_resp_content_type("application/json", nil)
    |> send_resp(200, Jason.encode!(payload))
  end

  @doc """
  Emit a Twirp error. `code` is one of the Twirp canonical codes
  (canceled, unknown, invalid_argument, deadline_exceeded, not_found,
  already_exists, permission_denied, unauthenticated, resource_exhausted,
  failed_precondition, aborted, out_of_range, unimplemented, internal,
  unavailable, dataloss).
  """
  def error(conn, code, msg, meta \\ %{}) do
    status = code_to_status(code)

    body =
      %{
        "code" => Atom.to_string(code),
        "msg" => msg,
        "meta" => meta
      }
      |> Jason.encode!()

    conn
    |> put_resp_content_type("application/json", nil)
    # Match the runner-protocol success path: force `Connection:
    # close` so the runner opens a fresh TCP connection for its
    # next request. Eliminates the HTTP/1.1 keep-alive framing-
    # cascade where one mis-sized response corrupts the parse of
    # the next request line.
    |> put_resp_header("connection", "close")
    |> send_resp(status, body)
  end

  defp code_to_status(:invalid_argument), do: 400
  defp code_to_status(:unauthenticated), do: 401
  defp code_to_status(:permission_denied), do: 403
  defp code_to_status(:not_found), do: 404
  defp code_to_status(:already_exists), do: 409
  defp code_to_status(:failed_precondition), do: 412
  defp code_to_status(:resource_exhausted), do: 429
  defp code_to_status(:unimplemented), do: 501
  defp code_to_status(:unavailable), do: 503
  defp code_to_status(_), do: 500
end