defmodule Resin do
  @moduledoc """
  Introduce a configurable delay to all requests in a plug pipeline.

  Usage

      use Resin

  This will introduce a delay to all incoming requests. This delay defaults to
  3000 ms, but can be configured by the `enterpriseyness` option, like so:

      use Resin, enterpriseyness: 4711

  It can also be configured with a range of integers, to allow some
  variation in how long the delay will be:

      use Resin, enterpriseyness: 1_000 .. 3_000

  When running with `MIX_ENV=prod`, Resin will do nothing, but instead just edit
  itself out of your AST. See docs on `Resin.__using__/1` for more info on that.
  """
  @behaviour Plug
  @default_options [enterpriseyness: 3_000]

  def init(options \\ []) do
    Keyword.merge(@default_options, options)
  end

  def call(conn, options) do
    :timer.sleep(enterpriseyness Keyword.get(options, :enterpriseyness))
    conn
  end

  defp enterpriseyness(min .. max) when max < min,
    do: enterpriseyness(max .. min)
  defp enterpriseyness(min .. max),
    do: min + :random.uniform(max - min)
  defp enterpriseyness(level),
    do: level

  @doc """
  Pour some resin in your plug pipeline, by `use`ing this module.

      use Resin

  Resin will insert itself into your pipeline, unless you compiled your project
  with `MIX_ENV=prod`, and add a configurable delay to every request.

  The default delay is set to 3000 ms.

  If you want a shorter (or longer (really?)) delay, you can use the
  `enterpriseyness` option to set the configured delay in milliseconds, like so:

      use Resin, enterpriseyness: 4711

  When compiling with `MIX_ENV=prod`, this macro will do nothing. You only want
  to display the enterpriseyness during your demo, right?
  """
  defmacro __using__(opts \\ []) do
    unless Mix.env == :prod do
      quote bind_quoted: [opts: opts] do
        plug Resin, opts
      end
    end
  end
end