defmodule Ecto.Adapters.DynamoDB.QueryInfo do
  @moduledoc """
  An Elixir agent to optionally record DynamoDB query information (like LastEvaluatedKey) that's not part of expected Ecto return values.
  """

  def child_spec(_) do
    %{
      id: __MODULE__,
      start: {__MODULE__, :start_link, []}
    }
  end

  def start_link, do: Agent.start_link(fn -> %{} end, name: __MODULE__)

  @doc """
  Provides a random 32 character, base 64 encoded string.
  """
  def get_key, do: :crypto.strong_rand_bytes(32) |> Base.url_encode64()

  @doc """
  Updates the value of a given key in the Agent map.
  """
  def put(key, val), do: Agent.update(__MODULE__, fn map -> Map.put(map, key, val) end)

  @doc """
  Updates the value of a given key in the Agent map according to a specific function.
  """
  def update(key, initial, fun),
    do: Agent.update(__MODULE__, fn map -> Map.update(map, key, initial, fun) end)

  @doc """
  Returns the value (query info) in the QueryInfo agent associated with the provided key.
  """
  def get(key),
    do: Agent.get_and_update(__MODULE__, fn map -> {map[key], Map.delete(map, key)} end)

  @doc """
  Returns the complete current map recorded by the agent.
  """
  def get_map, do: Agent.get(__MODULE__, fn map -> map end)
end