defmodule Klotho do
  @moduledoc """
  A module that provides a interface to Erlang's time functions.

  In production, all functions are proxied to the `:erlang` module directly.

  In tests, the functions are proxied to `Klotho.Mock`, and the time "flow"
  can be controlled by calling `Klotho.Mock` functions.
  """

  if Mix.env() == :test do
    @backend Klotho.Mock
  else
    @backend Klotho.Real
  end

  def monotonic_time(unit) do
    backend().monotonic_time(unit)
  end

  def monotonic_time() do
    backend().monotonic_time()
  end

  def send_after(time, pid, message) do
    backend().send_after(time, pid, message)
  end

  def send_after(time, pid, message, opts) do
    backend().send_after(time, pid, message, opts)
  end

  def start_timer(time, pid, message) do
    backend().start_timer(time, pid, message)
  end

  def start_timer(time, pid, message, opts) do
    backend().start_timer(time, pid, message, opts)
  end

  def read_timer(ref) do
    backend().read_timer(ref)
  end

  def cancel_timer(ref) do
    backend().cancel_timer(ref)
  end

  def cancel_timer(ref, opts) do
    backend().cancel_timer(ref, opts)
  end

  def system_time(unit) do
    backend().system_time(unit)
  end

  def system_time() do
    backend().system_time()
  end

  def time_offset(unit) do
    backend().time_offset(unit)
  end

  def time_offset() do
    backend().time_offset()
  end

  def set_backend(backend) when backend == Klotho.Mock or backend == Klotho.Real do
    :persistent_term.put(:klotho_backend, backend)
  end

  defp backend() do
    :persistent_term.get(:klotho_backend, @backend)
  end
end