defmodule Riverside.Session.TransmissionLimitter do
  @type t :: %__MODULE__{count: non_neg_integer, started_at: non_neg_integer}

  defstruct count: 0,
            started_at: 0

  @spec new() :: t
  def new() do
    %__MODULE__{count: 0, started_at: Riverside.IO.Timestamp.milli_seconds()}
  end

  @spec countup(t, non_neg_integer, non_neg_integer) ::
          {:ok, t}
          | {:error, :too_many_messages}

  def countup(limitter, duration, capacity) do
    now = Riverside.IO.Timestamp.milli_seconds()

    if limitter.started_at + duration < now do
      {:ok, %{limitter | count: 1, started_at: now}}
    else
      count = limitter.count + 1

      if count < capacity do
        {:ok, %{limitter | count: count}}
      else
        {:error, :too_many_messages}
      end
    end
  end
end