defmodule Mix.Tasks.WebPush.Gen.Vapid do
  @moduledoc """
  Generates a VAPID (P-256) keypair for Web Push.

      mix web_push.gen.vapid

  Prints the keys ready to paste into config or to export as environment
  variables. The public key (65-byte uncompressed point, URL-safe base64
  without padding) is also the value the browser passes to
  `pushManager.subscribe({ applicationServerKey })`.
  """

  use Mix.Task

  @shortdoc "Generates a VAPID P-256 keypair for Web Push"

  @impl Mix.Task
  def run(_args) do
    %{public_key: public_b64, private_key: private_b64} = WebPush.Vapid.generate_keypair()

    IO.puts("""

    # VAPID keypair

    ## config (runtime.exs recommended)
    config :web_push, :vapid,
      public_key: "#{public_b64}",
      private_key: "#{private_b64}",
      subject: "mailto:you@example.com"

    ## env vars (production)
    export VAPID_PUBLIC_KEY="#{public_b64}"
    export VAPID_PRIVATE_KEY="#{private_b64}"
    export VAPID_SUBJECT="mailto:you@example.com"
    """)
  end
end