defmodule Plug.CcsAuth do
  import Plug.Conn

  @salt "user"

  # public api

  def sign(conext, params) do
    Phoenix.Token.sign(conext, @salt, extract_payload(params))
  end

  def verify(context, token) do
    case Phoenix.Token.verify(context, @salt, token) do
      {:ok, %{udid: _udid, user_huid: _user_huid} = payload} ->
        {:ok, payload}
      {:ok, _} ->
        {:error, :missing_params}
      {:error, reason} ->
        {:error, reason}
    end
  end

  # Plug callback

  def init(opts), do: opts

  def call(conn, _opts) do
    case verify(conn, parse_bearer_token(conn)) do
      {:ok, %{udid: udid, user_huid: user_huid}} ->
        conn
        |> assign(:udid, udid)
        |> assign(:user_huid, user_huid)
      {:error, _reason} ->
        conn
        |> halt()
        |> put_resp_content_type("application/json")
        |> send_resp(:unauthorized, Poison.encode!(%{error: :unauthorized}))
    end
  end

  # internal functions

  defp parse_bearer_token(conn) do
    case get_req_header(conn, "authorization") do
      ["Bearer " <> token] -> token
      _ -> nil
    end
  end

  defp extract_payload(params) when is_list(params) do
    try do
      %{udid: Keyword.fetch!(params, :udid),
        user_huid: Keyword.fetch!(params, :user_huid)}
    rescue
      KeyError -> raise_params_error
    end
  end
  defp extract_payload(%{udid: _, user_huid: _} = params) when is_map(params) do
    params
  end
  defp extract_payload(_params) do
    raise_params_error
  end

  defp raise_params_error do
    raise "Plug.CcsAuth.sign/2 accepts map or keywords with :user_huid and :udid"
  end
end