frenzy/lib/frenzy_web/plug/fervor_authenticate.ex

defmodule FrenzyWeb.Plug.FervorAuthenticate do
  import Plug.Conn
  alias Frenzy.{Repo, User, ApprovedClient}

  def init(opts), do: opts

  def call(conn, _opts) do
    with {conn, authorization} when authorization != nil <- get_auth_header(conn),
         {conn, access_token} when access_token != nil <- get_access_token(conn, authorization),
         {conn, approved_client} when approved_client != nil <-
           get_approved_client(conn, access_token) do
      assign(conn, :user, Repo.get(User, approved_client.user_id))
    else
      {conn, _} ->
        conn
    end
  end

  defp get_auth_header(conn) do
    case get_req_header(conn, "authorization") do
      [authorization | _] ->
        {conn, authorization}

      _ ->
        conn =
          conn
          |> put_status(401)
          |> Phoenix.Controller.json(%{
            error: "Missing authorization",
            error_description: "No Authorization header was provided"
          })
          |> halt()

        {conn, nil}
    end
  end

  defp get_access_token(conn, "Bearer " <> access_token), do: {conn, access_token}

  defp get_access_token(conn, _authorization) do
    conn =
      conn
      |> put_status(401)
      |> Phoenix.Controller.json(%{
        error: "Invalid authorization",
        error_description: "The provided Authorization header does not match the expected format"
      })
      |> halt()

    {conn, nil}
  end

  defp get_approved_client(conn, access_token) do
    case Repo.get_by(ApprovedClient, access_token: access_token) do
      nil ->
        conn =
          conn
          |> put_status(400)
          |> Phoenix.Controller.json(%{
            error: "Invalid authorization",
            error_description: "The provided access token is not valid"
          })
          |> halt()

        {conn, nil}

      approved_client ->
        {conn, approved_client}
    end
  end
end