# Pleroma: A lightweight social networking server
# Copyright © 2017-2022 Pleroma Authors <https://pleroma.social/>
# SPDX-License-Identifier: AGPL-3.0-only

defmodule Pleroma.Object.Fetcher do
  alias Pleroma.HTTP
  alias Pleroma.Instances
  alias Pleroma.Maps
  alias Pleroma.Object
  alias Pleroma.Object.Containment
  alias Pleroma.Signature
  alias Pleroma.Web.ActivityPub.InternalFetchActor
  alias Pleroma.Web.ActivityPub.MRF
  alias Pleroma.Web.ActivityPub.ObjectValidator
  alias Pleroma.Web.ActivityPub.Pipeline
  alias Pleroma.Web.ActivityPub.Transmogrifier
  alias Pleroma.Web.Federator

  require Logger
  require Pleroma.Constants

  @spec reinject_object(struct(), map()) :: {:ok, Object.t()} | {:error, any()}
  defp reinject_object(%Object{data: %{}} = object, new_data) do
    Logger.debug("Reinjecting object #{new_data["id"]}")

    with {:ok, new_data, _} <- ObjectValidator.validate(new_data, %{}),
         {:ok, new_data} <- MRF.filter(new_data),
         {:ok, new_object, _} <-
           Object.Updater.do_update_and_invalidate_cache(
             object,
             new_data,
             _touch_changeset? = true
           ) do
      {:ok, new_object}
    else
      e ->
        Logger.error("Error while processing object: #{inspect(e)}")
        {:error, e}
    end
  end

  defp reinject_object(_, new_data) do
    with {:ok, object, _} <- Pipeline.common_pipeline(new_data, local: false) do
      {:ok, object}
    else
      e -> e
    end
  end

  def refetch_object(%Object{data: %{"id" => id}} = object) do
    with {:local, false} <- {:local, Object.local?(object)},
         {:ok, new_data} <- fetch_and_contain_remote_object_from_id(id),
         {:ok, object} <- reinject_object(object, new_data) do
      {:ok, object}
    else
      {:local, true} -> {:ok, object}
      e -> {:error, e}
    end
  end

  # Note: will create a Create activity, which we need internally at the moment.
  def fetch_object_from_id(id, options \\ []) do
    with {_, nil} <- {:fetch_object, Object.get_cached_by_ap_id(id)},
         {_, true} <- {:allowed_depth, Federator.allowed_thread_distance?(options[:depth])},
         {_, {:ok, data}} <- {:fetch, fetch_and_contain_remote_object_from_id(id)},
         {_, nil} <- {:normalize, Object.normalize(data, fetch: false)},
         params <- prepare_activity_params(data),
         {_, :ok} <- {:containment, Containment.contain_origin(id, params)},
         {_, {:ok, activity}} <-
           {:transmogrifier, Transmogrifier.handle_incoming(params, options)},
         {_, _data, %Object{} = object} <-
           {:object, data, Object.normalize(activity, fetch: false)} do
      {:ok, object}
    else
      {:allowed_depth, false} = e ->
        log_fetch_error(id, e)
        {:error, "Max thread distance exceeded."}

      {:containment, reason} = e ->
        log_fetch_error(id, e)
        {:error, reason}

      {:transmogrifier, {:error, {:reject, reason}}} = e ->
        log_fetch_error(id, e)
        {:reject, reason}

      {:transmogrifier, {:reject, reason}} = e ->
        log_fetch_error(id, e)
        {:reject, reason}

      {:transmogrifier, reason} = e ->
        log_fetch_error(id, e)
        {:error, reason}

      {:object, data, nil} ->
        reinject_object(%Object{}, data)

      {:normalize, object = %Object{}} ->
        {:ok, object}

      {:fetch_object, %Object{} = object} ->
        {:ok, object}

      {:fetch, {:error, reason}} = e ->
        log_fetch_error(id, e)
        {:error, reason}

      e ->
        log_fetch_error(id, e)
        {:error, e}
    end
  end

  defp log_fetch_error(id, error) do
    Logger.metadata(object: id)
    Logger.error("Object rejected while fetching #{id} #{inspect(error)}")
  end

  defp prepare_activity_params(data) do
    %{
      "type" => "Create",
      # Should we seriously keep this attributedTo thing?
      "actor" => data["actor"] || data["attributedTo"],
      "object" => data
    }
    |> Maps.put_if_present("to", data["to"])
    |> Maps.put_if_present("cc", data["cc"])
    |> Maps.put_if_present("bto", data["bto"])
    |> Maps.put_if_present("bcc", data["bcc"])
  end

  defp make_signature(id, date) do
    uri = URI.parse(id)

    signature =
      InternalFetchActor.get_actor()
      |> Signature.sign(%{
        "(request-target)": "get #{uri.path}",
        host: uri.host,
        date: date
      })

    {"signature", signature}
  end

  defp sign_fetch(headers, id, date) do
    if Pleroma.Config.get([:activitypub, :sign_object_fetches]) do
      [make_signature(id, date) | headers]
    else
      headers
    end
  end

  defp maybe_date_fetch(headers, date) do
    if Pleroma.Config.get([:activitypub, :sign_object_fetches]) do
      [{"date", date} | headers]
    else
      headers
    end
  end

  def fetch_and_contain_remote_object_from_id(id)

  def fetch_and_contain_remote_object_from_id(%{"id" => id}),
    do: fetch_and_contain_remote_object_from_id(id)

  def fetch_and_contain_remote_object_from_id(id) when is_binary(id) do
    Logger.debug("Fetching object #{id} via AP")

    with {:scheme, true} <- {:scheme, String.starts_with?(id, "http")},
         {:ok, body} <- get_object(id),
         {:ok, data} <- safe_json_decode(body),
         :ok <- Containment.contain_origin_from_id(id, data) do
      if not Instances.reachable?(id) do
        Instances.set_reachable(id)
      end

      {:ok, data}
    else
      {:scheme, _} ->
        {:error, "Unsupported URI scheme"}

      {:error, e} ->
        {:error, e}

      e ->
        {:error, e}
    end
  end

  def fetch_and_contain_remote_object_from_id(_id),
    do: {:error, "id must be a string"}

  defp get_object(id) do
    date = Pleroma.Signature.signed_date()

    headers =
      [{"accept", "application/activity+json"}]
      |> maybe_date_fetch(date)
      |> sign_fetch(id, date)

    case HTTP.get(id, headers) do
      {:ok, %{body: body, status: code, headers: headers}} when code in 200..299 ->
        case List.keyfind(headers, "content-type", 0) do
          {_, content_type} ->
            case Plug.Conn.Utils.media_type(content_type) do
              {:ok, "application", "activity+json", _} ->
                {:ok, body}

              {:ok, "application", "ld+json",
               %{"profile" => "https://www.w3.org/ns/activitystreams"}} ->
                {:ok, body}

              _ ->
                {:error, {:content_type, content_type}}
            end

          _ ->
            {:error, {:content_type, nil}}
        end

      {:ok, %{status: 403}} ->
        {:error, :forbidden}

      {:ok, %{status: code}} when code in [404, 410] ->
        {:error, :not_found}

      {:error, e} ->
        {:error, e}

      e ->
        {:error, e}
    end
  end

  defp safe_json_decode(nil), do: {:ok, nil}
  defp safe_json_decode(json), do: Jason.decode(json)
end