migrations: add function to see if a thread can be satisfied

priv/repo/migrations/20190324222404_add_thread_visibility_function.exs

+defmodule Pleroma.Repo.Migrations.AddThreadVisibilityFunction do
+  use Ecto.Migration
+  @disable_ddl_transaction true
+
+  def up do
+    statement = """
+    CREATE OR REPLACE FUNCTION thread_visibility(actor varchar, activity_id varchar) RETURNS boolean AS $$
+    DECLARE
+      public varchar := 'https://www.w3.org/ns/activitystreams#Public';
+      child objects%ROWTYPE;
+      activity activities%ROWTYPE;
+      actor_user users%ROWTYPE;
+      author users%ROWTYPE;
+      author_fa varchar;
+    BEGIN
+      --- Fetch our actor.
+      SELECT * INTO actor_user FROM users WHERE users.ap_id = actor;
+
+      --- Fetch our initial activity.
+      SELECT * INTO activity FROM activities WHERE activities.data->>'id' = activity_id;
+
+      LOOP
+        --- Ensure that we have an activity before continuing.
+        IF activity IS NULL THEN
+          RETURN true;
+        END IF;
+
+        --- Normalize the child object into child.
+        SELECT * INTO child FROM objects
+        INNER JOIN activities ON COALESCE(activities.data->'object'->>'id', activities.data->>'object') = objects.data->>'id'
+        WHERE COALESCE(activity.data->'object'->>'id', activity.data->>'object') = objects.data->>'id';
+
+        --- Fetch the author.
+        SELECT * INTO author FROM users WHERE users.ap_id = activity.actor;
+
+        --- Prepare author's AS2 followers collection.
+        SELECT COALESCE(author.follower_address, '') INTO author_fa;
+
+        --- Check visibility.
+        IF activity.actor = actor THEN
+          --- activity visible
+          NULL;
+        ELSIF ARRAY[public] && activity.recipients THEN
+          --- activity visible
+          NULL;
+        ELSIF ARRAY[author_fa] && activity.recipients AND ARRAY[author_fa] && actor_user.following THEN
+          --- activity visible
+          NULL;
+        ELSIF ARRAY[actor] && activity.recipients THEN
+          --- activity visible
+          NULL;
+        ELSE
+          --- activity not visible, break out of the loop
+          RETURN false;
+        END IF;
+
+        --- If there's a parent, load it and do this all over again.
+        IF (child.data->'inReplyTo' IS NOT NULL) AND (child.data->'inReplyTo' != 'null'::jsonb) THEN
+          SELECT * INTO activity FROM activities
+          INNER JOIN objects ON COALESCE(activities.data->'object'->>'id', activities.data->>'object') = objects.data->>'id'
+          WHERE child.data->>'inReplyTo' = objects.data->>'id';
+        ELSE
+          RETURN true;
+        END IF;
+      END LOOP;
+    END;
+    $$ LANGUAGE plpgsql IMMUTABLE;
+    """
+
+    execute(statement)
+  end
+
+  def down do
+    execute("drop function thread_visibility(actor varchar, activity_id varchar)")
+  end
+end