defmodule Pleroma.Web.ActivityPub.Builder do
  @moduledoc """
  This module builds the objects. Meant to be used for creating local objects.

  This module encodes our addressing policies and general shape of our objects.
  """

  alias Pleroma.Object
  alias Pleroma.User
  alias Pleroma.Web.ActivityPub.Utils
  alias Pleroma.Web.ActivityPub.Visibility

  @spec undo(User.t(), Activity.t()) :: {:ok, map(), keyword()}
  def undo(actor, object) do
    {:ok,
     %{
       "id" => Utils.generate_activity_id(),
       "actor" => actor.ap_id,
       "type" => "Undo",
       "object" => object.data["id"],
       "to" => object.data["to"] || [],
       "cc" => object.data["cc"] || []
     }, []}
  end

  @spec delete(User.t(), String.t()) :: {:ok, map(), keyword()}
  def delete(actor, object_id) do
    object = Object.normalize(object_id, false)

    user = !object && User.get_cached_by_ap_id(object_id)

    to =
      case {object, user} do
        {%Object{}, _} ->
          # We are deleting an object, address everyone who was originally mentioned
          (object.data["to"] || []) ++ (object.data["cc"] || [])

        {_, %User{follower_address: follower_address}} ->
          # We are deleting a user, address the followers of that user
          [follower_address]
      end

    {:ok,
     %{
       "id" => Utils.generate_activity_id(),
       "actor" => actor.ap_id,
       "object" => object_id,
       "to" => to,
       "type" => "Delete"
     }, []}
  end

  @spec like(User.t(), Object.t()) :: {:ok, map(), keyword()}
  def like(actor, object) do
    object_actor = User.get_cached_by_ap_id(object.data["actor"])

    # Address the actor of the object, and our actor's follower collection if the post is public.
    to =
      if Visibility.is_public?(object) do
        [actor.follower_address, object.data["actor"]]
      else
        [object.data["actor"]]
      end

    # CC everyone who's been addressed in the object, except ourself and the object actor's
    # follower collection
    cc =
      (object.data["to"] ++ (object.data["cc"] || []))
      |> List.delete(actor.ap_id)
      |> List.delete(object_actor.follower_address)

    {:ok,
     %{
       "id" => Utils.generate_activity_id(),
       "actor" => actor.ap_id,
       "type" => "Like",
       "object" => object.data["id"],
       "to" => to,
       "cc" => cc,
       "context" => object.data["context"]
     }, []}
  end
end