Add activity expirations table

Add a table to store activity expirations. An activity can have zero or
one expirations. The expiration has a scheduled_at field which stores
the time at which the activity should expire and be deleted.

lib/pleroma/activity.ex

@@ -6,6 +6,7 @@ defmodule Pleroma.Activity do
   use Ecto.Schema
 
   alias Pleroma.Activity
+  alias Pleroma.ActivityExpiration
   alias Pleroma.Bookmark
   alias Pleroma.Notification
   alias Pleroma.Object
@@ -59,6 +60,8 @@ defmodule Pleroma.Activity do
     # typical case.
     has_one(:object, Object, on_delete: :nothing, foreign_key: :id)
 
+    has_one(:expiration, ActivityExpiration, on_delete: :delete_all)
+
     timestamps()
   end
 

lib/pleroma/activity_expiration.ex

@@ -0,0 +1,31 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.ActivityExpiration do
+  use Ecto.Schema
+
+  alias Pleroma.Activity
+  alias Pleroma.ActivityExpiration
+  alias Pleroma.FlakeId
+  alias Pleroma.Repo
+
+  import Ecto.Query
+
+  @type t :: %__MODULE__{}
+
+  schema "activity_expirations" do
+    belongs_to(:activity, Activity, type: FlakeId)
+    field(:scheduled_at, :naive_datetime)
+  end
+
+  def due_expirations(offset \\ 0) do
+    naive_datetime =
+      NaiveDateTime.utc_now()
+      |> NaiveDateTime.add(offset, :millisecond)
+
+    ActivityExpiration
+    |> where([exp], exp.scheduled_at < ^naive_datetime)
+    |> Repo.all()
+  end
+end