cachex

defmodule Cachex.Actions.Ttl do
  @moduledoc false
  # This module controls TTL retrieval for cache records by calculating the offset

  # between the touch and ttl fields inside a record. The implementation also

  # accounts for expirations in order to ensure consistency in results provided

  # to the developer.


  # we need our imports

  use Cachex.Actions

  # add some aliases

  alias Cachex.Actions
  alias Cachex.State
  alias Cachex.Util

  @doc """

  Retrieves the remaining TTL for a cache item.



  If the cache item has no TTL, a nil value is returned. If the item is missing,

  a nil is returned, tagged with a :missing flag. Otherwise a Tuple of :ok and

  the remaining time to list (in milliseconds) is returned.



  There are currently no recognised options, the argument only exists for future

  proofing.

  """
  defaction ttl(%State{ } = state, key, options) do
    state
    |> Actions.read(key)
    |> handle_record
  end

  # Handles the record coming back from the read. We normalize the TTL value at

  # this point. If there is no TTL, we return a nil value. Otherwise we calculate

  # the time remaining and return that to the user. If the record does not exist,

  # we just return a missing result.

  defp handle_record({ _key, _touched, nil, _value }),
    do: { :ok, nil }
  defp handle_record({ _key, touched, ttl, _value }),
    do: { :ok, touched + ttl - Util.now() }
  defp handle_record(_missing),
    do: { :missing, nil }

end