defmodule GoogleAds.TokenCache do
  @moduledoc """
  Cache instance for Google Ads tokens.
  """

  use GenServer

  @cache_table :google_ads_tokens

  @type prismatic_ref :: String.t()

  @spec start_link(any()) :: {:ok, pid()} | {:error, any()}
  def start_link(_opts) do
    GenServer.start_link(__MODULE__, nil, name: __MODULE__)
  end

  @impl GenServer
  def init(_opts) do
    @cache_table = :ets.new(@cache_table, [:set, :public, :named_table])

    {:ok, %{}}
  end

  @spec insert(prismatic_ref(), GoogleAds.Token.t()) :: :ok
  @spec insert(prismatic_ref(), GoogleAds.Token.t(), DateTime.t()) :: :ok
  def insert(prismatic_ref, %GoogleAds.Token{} = token, now \\ DateTime.utc_now()) do
    GenServer.call(__MODULE__, {:insert, prismatic_ref, token, now})
  end

  @spec get(prismatic_ref()) :: GoogleAds.Token.t() | nil
  def get(prismatic_ref) do
    case :ets.lookup(@cache_table, prismatic_ref) do
      [{^prismatic_ref, %GoogleAds.Token{} = token}] -> token
      _any -> nil
    end
  end

  @doc false
  @spec flush() :: any()
  def flush, do: :ets.delete_all_objects(@cache_table)

  @impl GenServer
  def handle_call({:insert, prismatic_ref, %GoogleAds.Token{} = token, now}, _from, state) do
    {:ok, expires_at, 0} = DateTime.from_iso8601(token.expires_at)
    expires_in_seconds = DateTime.diff(expires_at, now, :second)

    true = :ets.insert(@cache_table, {prismatic_ref, token})

    Process.send_after(self(), {:remove, prismatic_ref}, :timer.seconds(expires_in_seconds))

    {:reply, :ok, state}
  end

  @impl GenServer
  def handle_info({:remove, prismatic_ref}, state) do
    true = :ets.delete(@cache_table, prismatic_ref)

    {:noreply, state}
  end
end