3 files changed, 67 insertions, 2 deletions

diff --git a/lib/pleroma/web/activity_pub/activity_pub.ex b/lib/pleroma/web/activity_pub/activity_pub.ex
index d23ec66ac..74663ac97 100644
--- a/lib/pleroma/web/activity_pub/activity_pub.ex
+++ b/lib/pleroma/web/activity_pub/activity_pub.ex
@@ -312,6 +312,17 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
     end
   end
 
+  def react_with_emoji(user, object, emoji, options \\ []) do
+    with local <- Keyword.get(options, :local, true),
+         activity_id <- Keyword.get(options, :activity_id, nil),
+         Pleroma.Emoji.is_unicode_emoji?(emoji),
+         reaction_data <- make_emoji_reaction_data(user, object, emoji, activity_id),
+         {:ok, activity} <- insert(reaction_data, local),
+         {:ok, object} <- add_emoji_reaction_to_object(activity, object) do
+      {:ok, activity, object}
+    end
+  end
+
   # TODO: This is weird, maybe we shouldn't check here if we can make the activity.
   def like(
         %User{ap_id: ap_id} = user,
diff --git a/lib/pleroma/web/activity_pub/transmogrifier.ex b/lib/pleroma/web/activity_pub/transmogrifier.ex
index 350b83abb..cb5755ccc 100644
--- a/lib/pleroma/web/activity_pub/transmogrifier.ex
+++ b/lib/pleroma/web/activity_pub/transmogrifier.ex
@@ -575,6 +575,27 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
   end
 
   def handle_incoming(
+        %{
+          "type" => "EmojiReaction",
+          "object" => object_id,
+          "actor" => _actor,
+          "id" => id,
+          "content" => emoji
+        } = data,
+        _options
+      ) do
+    with actor <- Containment.get_actor(data),
+         {:ok, %User{} = actor} <- User.get_or_fetch_by_ap_id(actor),
+         {:ok, object} <- get_obj_helper(object_id),
+         {:ok, activity, _object} <-
+           ActivityPub.react_with_emoji(actor, object, emoji, activity_id: id, local: false) do
+      {:ok, activity}
+    else
+      _e -> :error
+    end
+  end
+
+  def handle_incoming(
         %{"type" => "Announce", "object" => object_id, "actor" => _actor, "id" => id} = data,
         _options
       ) do
@@ -976,9 +997,11 @@ defmodule Pleroma.Web.ActivityPub.Transmogrifier do
     |> Map.put("attachment", attachments)
   end
 
-  defp strip_internal_fields(object) do
+  def strip_internal_fields(object) do
     object
     |> Map.drop([
+      "reactions",
+      "reaction_count",
       "likes",
       "like_count",
       "announcements",
diff --git a/lib/pleroma/web/activity_pub/utils.ex b/lib/pleroma/web/activity_pub/utils.ex
index c9c0c3763..95e040c6c 100644
--- a/lib/pleroma/web/activity_pub/utils.ex
+++ b/lib/pleroma/web/activity_pub/utils.ex
@@ -277,6 +277,12 @@ defmodule Pleroma.Web.ActivityPub.Utils do
     |> Repo.all()
   end
 
+  def make_emoji_reaction_data(user, object, emoji, activity_id) do
+    make_like_data(user, object, activity_id)
+    |> Map.put("type", "EmojiReaction")
+    |> Map.put("content", emoji)
+  end
+
   @spec make_like_data(User.t(), map(), String.t()) :: map()
   def make_like_data(
         %User{ap_id: ap_id} = actor,
@@ -311,10 +317,21 @@ defmodule Pleroma.Web.ActivityPub.Utils do
   @spec update_element_in_object(String.t(), list(any), Object.t()) ::
           {:ok, Object.t()} | {:error, Ecto.Changeset.t()}
   def update_element_in_object(property, element, object) do
+    length =
+      if is_map(element) do
+        element
+        |> Map.values()
+        |> List.flatten()
+        |> length()
+      else
+        element
+        |> length()
+      end
+
     data =
       Map.merge(
         object.data,
-        %{"#{property}_count" => length(element), "#{property}s" => element}
+        %{"#{property}_count" => length, "#{property}s" => element}
       )
 
     object
@@ -322,6 +339,20 @@ defmodule Pleroma.Web.ActivityPub.Utils do
     |> Object.update_and_set_cache()
   end
 
+  @spec add_emoji_reaction_to_object(Activity.t(), Object.t()) ::
+          {:ok, Object.t()} | {:error, Ecto.Changeset.t()}
+
+  def add_emoji_reaction_to_object(
+        %Activity{data: %{"content" => emoji, "actor" => actor}},
+        object
+      ) do
+    reactions = object.data["reactions"] || %{}
+    emoji_actors = reactions[emoji] || []
+    new_emoji_actors = [actor | emoji_actors] |> Enum.uniq()
+    new_reactions = Map.put(reactions, emoji, new_emoji_actors)
+    update_element_in_object("reaction", new_reactions, object)
+  end
+
   @spec add_like_to_object(Activity.t(), Object.t()) ::
           {:ok, Object.t()} | {:error, Ecto.Changeset.t()}
   def add_like_to_object(%Activity{data: %{"actor" => actor}}, object) do