2 files changed, 71 insertions, 0 deletions
diff --git a/lib/pleroma/web/activity_pub/utils.ex b/lib/pleroma/web/activity_pub/utils.ex
index d2e457a68..d516818d9 100644
--- a/lib/pleroma/web/activity_pub/utils.ex
+++ b/lib/pleroma/web/activity_pub/utils.ex
@@ -25,6 +25,20 @@ defmodule Pleroma.Web.ActivityPub.Utils do
     Map.put(params, "actor", get_ap_id(params["actor"]))
   end
 
+  def determine_explicit_mentions(%{"tag" => tag} = _object) when is_list(tag) do
+    tag
+    |> Enum.filter(fn x -> is_map(x) end)
+    |> Enum.filter(fn x -> x["type"] == "Mention" end)
+    |> Enum.map(fn x -> x["href"] end)
+  end
+
+  def determine_explicit_mentions(%{"tag" => tag} = object) when is_map(tag) do
+    Map.put(object, "tag", [tag])
+    |> determine_explicit_mentions()
+  end
+
+  def determine_explicit_mentions(_), do: []
+
   defp recipient_in_collection(ap_id, coll) when is_binary(coll), do: ap_id == coll
   defp recipient_in_collection(ap_id, coll) when is_list(coll), do: ap_id in coll
   defp recipient_in_collection(_, _), do: false
diff --git a/test/web/activity_pub/utils_test.exs b/test/web/activity_pub/utils_test.exs
new file mode 100644
index 000000000..aeed0564c
--- /dev/null
+++ b/test/web/activity_pub/utils_test.exs
@@ -0,0 +1,57 @@
+defmodule Pleroma.Web.ActivityPub.UtilsTest do
+  use Pleroma.DataCase
+  alias Pleroma.Web.ActivityPub.Utils
+
+  describe "determine_explicit_mentions()" do
+    test "works with an object that has mentions" do
+      object = %{
+        "tag" => [
+          %{
+            "type" => "Mention",
+            "href" => "https://example.com/~alyssa",
+            "name" => "Alyssa P. Hacker"
+          }
+        ]
+      }
+
+      assert Utils.determine_explicit_mentions(object) == ["https://example.com/~alyssa"]
+    end
+
+    test "works with an object that does not have mentions" do
+      object = %{
+        "tag" => [
+          %{"type" => "Hashtag", "href" => "https://example.com/tag/2hu", "name" => "2hu"}
+        ]
+      }
+
+      assert Utils.determine_explicit_mentions(object) == []
+    end
+
+    test "works with an object that has mentions and other tags" do
+      object = %{
+        "tag" => [
+          %{
+            "type" => "Mention",
+            "href" => "https://example.com/~alyssa",
+            "name" => "Alyssa P. Hacker"
+          },
+          %{"type" => "Hashtag", "href" => "https://example.com/tag/2hu", "name" => "2hu"}
+        ]
+      }
+
+      assert Utils.determine_explicit_mentions(object) == ["https://example.com/~alyssa"]
+    end
+
+    test "works with an object that has no tags" do
+      object = %{}
+
+      assert Utils.determine_explicit_mentions(object) == []
+    end
+
+    test "works with an object that has only IR tags" do
+      object = %{"tag" => ["2hu"]}
+
+      assert Utils.determine_explicit_mentions(object) == []
+    end
+  end
+end