defmodule Pleroma.Web.ActivityPub.Utils do
  alias Pleroma.{Repo, Web, Object, Activity, User}
  alias Pleroma.Web.Router.Helpers
  alias Pleroma.Web.Endpoint
  alias Ecto.{Changeset, UUID}
  import Ecto.Query

  def make_date do
    DateTime.utc_now() |> DateTime.to_iso8601
  end

  def generate_activity_id do
    generate_id("activities")
  end

  def generate_context_id do
    generate_id("contexts")
  end

  def generate_object_id do
    Helpers.o_status_url(Endpoint, :object, UUID.generate)
  end

  def generate_id(type) do
    "#{Web.base_url()}/#{type}/#{UUID.generate}"
  end

  @doc """
  Enqueues an activity for federation if it's local
  """
  def maybe_federate(%Activity{local: true} = activity) do
    Pleroma.Web.Federator.enqueue(:publish, activity)
    :ok
  end
  def maybe_federate(_), do: :ok

  @doc """
  Adds an id and a published data if they aren't there,
  also adds it to an included object
  """
  def lazy_put_activity_defaults(map) do
    map = map
    |> Map.put_new_lazy("id", &generate_activity_id/0)
    |> Map.put_new_lazy("published", &make_date/0)

    if is_map(map["object"]) do
      object = lazy_put_object_defaults(map["object"])
      %{map | "object" => object}
    else
      map
    end
  end

  @doc """
  Adds an id and published date if they aren't there.
  """
  def lazy_put_object_defaults(map) do
    map
    |> Map.put_new_lazy("id", &generate_object_id/0)
    |> Map.put_new_lazy("published", &make_date/0)
  end

  @doc """
  Inserts a full object if it is contained in an activity.
  """
  def insert_full_object(%{"object" => object_data}) when is_map(object_data) do
    with {:ok, object} <- Object.create(object_data) do
      :ok
    end
  end
  def insert_full_object(_), do: :ok

  def update_object_in_activities(%{data: %{"id" => id}} = object) do
    # TODO
    # Update activities that already had this. Could be done in a seperate process.
    # Alternatively, just don't do this and fetch the current object each time. Most
    # could probably be taken from cache.
    relevant_activities = Activity.all_by_object_ap_id(id)
    Enum.map(relevant_activities, fn (activity) ->
      new_activity_data = activity.data |> Map.put("object", object.data)
      changeset = Changeset.change(activity, data: new_activity_data)
      Repo.update(changeset)
    end)
  end

  #### Like-related helpers

  @doc """
  Returns an existing like if a user already liked an object
  """
  def get_existing_like(actor, %{data: %{"id" => id}} = object) do
    query = from activity in Activity,
      where: fragment("(?)->>'actor' = ?", activity.data, ^actor),
      # this is to use the index
      where: fragment("coalesce((?)->'object'->>'id', (?)->>'object') = ?", activity.data, activity.data, ^id),
      where: fragment("(?)->>'type' = 'Like'", activity.data)

    Repo.one(query)
  end

  def make_like_data(%User{ap_id: ap_id} = actor, %{data: %{"id" => id}} = object, activity_id) do
    data = %{
      "type" => "Like",
      "actor" => ap_id,
      "object" => id,
      "to" => [actor.follower_address, object.data["actor"]],
      "context" => object.data["context"]
    }

    if activity_id, do: Map.put(data, "id", activity_id), else: data
  end

  def update_element_in_object(property, element, object) do
    with new_data <- object.data |> Map.put("#{property}_count", length(element)) |> Map.put("#{property}s", element),
         changeset <- Changeset.change(object, data: new_data),
         {:ok, object} <- Repo.update(changeset),
          _ <- update_object_in_activities(object) do
      {:ok, object}
    end
  end

  def update_likes_in_object(likes, object) do
    update_element_in_object("like", likes, object)
  end

  def add_like_to_object(%Activity{data: %{"actor" => actor}}, object) do
    with likes <- [actor | (object.data["likes"] || [])] |> Enum.uniq do
      update_likes_in_object(likes, object)
    end
  end

  def remove_like_from_object(%Activity{data: %{"actor" => actor}}, object) do
    with likes <- (object.data["likes"] || []) |> List.delete(actor) do
      update_likes_in_object(likes, object)
    end
  end

  #### Follow-related helpers

  @doc """
  Makes a follow activity data for the given follower and followed
  """
  def make_follow_data(%User{ap_id: follower_id}, %User{ap_id: followed_id}, activity_id) do
    data = %{
      "type" => "Follow",
      "actor" => follower_id,
      "to" => [followed_id],
      "object" => followed_id
    }

    if activity_id, do: Map.put(data, "id", activity_id), else: data
  end

  def fetch_latest_follow(%User{ap_id: follower_id},
                          %User{ap_id: followed_id}) do
    query = from activity in Activity,
      where: fragment("? @> ?", activity.data, ^%{type: "Follow", actor: follower_id,
                                                  object: followed_id}),
      order_by: [desc: :id],
      limit: 1
    Repo.one(query)
  end

  #### Announce-related helpers

  @doc """
  Make announce activity data for the given actor and object
  """
  def make_announce_data(%User{ap_id: ap_id} = user, %Object{data: %{"id" => id}} = object, activity_id) do
    data = %{
      "type" => "Announce",
      "actor" => ap_id,
      "object" => id,
      "to" => [user.follower_address, object.data["actor"]],
      "context" => object.data["context"]
    }

    if activity_id, do: Map.put(data, "id", activity_id), else: data
  end

  def add_announce_to_object(%Activity{data: %{"actor" => actor}}, object) do
    with announcements <- [actor | (object.data["announcements"] || [])] |> Enum.uniq do
      update_element_in_object("announcement", announcements, object)
    end
  end

  #### Unfollow-related helpers

  def make_unfollow_data(follower, followed, follow_activity) do
    %{
      "type" => "Undo",
      "actor" => follower.ap_id,
      "to" => [followed.ap_id],
      "object" => follow_activity.data["id"]
    }
  end


  #### Create-related helpers

  def make_create_data(params, additional) do
    published = params.published || make_date()

    activity = %{
      "type" => "Create",
      "to" => params.to |> Enum.uniq,
      "actor" => params.actor.ap_id,
      "object" => params.object,
      "published" => published,
      "context" => params.context
    }
    |> Map.merge(additional)
  end
end