defmodule Mobilizon.Federation.ActivityStream.Converter.Event do
  @moduledoc """
  Event converter.

  This module allows to convert events from ActivityStream format to our own
  internal one, and back.
  """

  alias Mobilizon.Actors.Actor
  alias Mobilizon.Addresses
  alias Mobilizon.Addresses.Address
  alias Mobilizon.Events.Event, as: EventModel

  alias Mobilizon.Federation.ActivityStream.{Converter, Convertible}
  alias Mobilizon.Federation.ActivityStream.Converter.Address, as: AddressConverter
  alias Mobilizon.Federation.ActivityStream.Converter.Media, as: MediaConverter
  alias Mobilizon.Web.Endpoint

  import Mobilizon.Federation.ActivityStream.Converter.Utils,
    only: [
      fetch_tags: 1,
      fetch_mentions: 1,
      build_tags: 1,
      maybe_fetch_actor_and_attributed_to_id: 1,
      process_pictures: 2
    ]

  require Logger

  @behaviour Converter

  defimpl Convertible, for: EventModel do
    alias Mobilizon.Federation.ActivityStream.Converter.Event, as: EventConverter

    defdelegate model_to_as(event), to: EventConverter
  end

  @online_address_name "Website"
  @banner_picture_name "Banner"
  @ap_public "https://www.w3.org/ns/activitystreams#Public"

  @doc """
  Converts an AP object data to our internal data structure.
  """
  @impl Converter
  @spec as_to_model_data(map) :: {:ok, map()} | {:error, any()}
  def as_to_model_data(object) do
    with {%Actor{id: actor_id}, attributed_to} <-
           maybe_fetch_actor_and_attributed_to_id(object),
         {:address, address_id} <-
           {:address, get_address(object["location"])},
         {:tags, tags} <- {:tags, fetch_tags(object["tag"])},
         {:mentions, mentions} <- {:mentions, fetch_mentions(object["tag"])},
         {:visibility, visibility} <- {:visibility, get_visibility(object)},
         {:options, options} <- {:options, get_options(object)},
         [description: description, picture_id: picture_id, medias: medias] <-
           process_pictures(object, actor_id) do
      %{
        title: object["name"],
        description: description,
        organizer_actor_id: actor_id,
        attributed_to_id: if(is_nil(attributed_to), do: nil, else: attributed_to.id),
        picture_id: picture_id,
        medias: medias,
        begins_on: object["startTime"],
        ends_on: object["endTime"],
        category: object["category"],
        visibility: visibility,
        join_options: Map.get(object, "joinMode", "free"),
        local: is_local(object["id"]),
        options: options,
        status: object |> Map.get("ical:status", "CONFIRMED") |> String.downcase(),
        online_address: object |> Map.get("attachment", []) |> get_online_address(),
        phone_address: object["phoneAddress"],
        draft: object["draft"] == true,
        url: object["id"],
        uuid: object["uuid"],
        tags: tags,
        mentions: mentions,
        physical_address_id: address_id,
        updated_at: object["updated"],
        publish_at: object["published"]
      }
    else
      {:ok, %Actor{suspended: true}} ->
        :error
    end
  end

  @doc """
  Convert an event struct to an ActivityStream representation.
  """
  @impl Converter
  @spec model_to_as(EventModel.t()) :: map
  def model_to_as(%EventModel{} = event) do
    {to, cc} =
      if event.visibility == :public,
        do: {[@ap_public], []},
        else: {[attributed_to_or_default(event).followers_url], [@ap_public]}

    %{
      "type" => "Event",
      "to" => to,
      "cc" => cc,
      "attributedTo" => attributed_to_or_default(event).url,
      "name" => event.title,
      "actor" =>
        if(Ecto.assoc_loaded?(event.organizer_actor), do: event.organizer_actor.url, else: nil),
      "uuid" => event.uuid,
      "category" => event.category,
      "content" => event.description,
      "published" => (event.publish_at || event.inserted_at) |> date_to_string(),
      "updated" => event.updated_at |> date_to_string(),
      "mediaType" => "text/html",
      "startTime" => event.begins_on |> date_to_string(),
      "joinMode" => to_string(event.join_options),
      "endTime" => event.ends_on |> date_to_string(),
      "tag" => event.tags |> build_tags(),
      "maximumAttendeeCapacity" => event.options.maximum_attendee_capacity,
      "repliesModerationOption" => event.options.comment_moderation,
      "commentsEnabled" => event.options.comment_moderation == :allow_all,
      "anonymousParticipationEnabled" => event.options.anonymous_participation,
      "attachment" => [],
      "draft" => event.draft,
      "ical:status" => event.status |> to_string |> String.upcase(),
      "id" => event.url,
      "url" => event.url
    }
    |> maybe_add_physical_address(event)
    |> maybe_add_event_picture(event)
    |> maybe_add_online_address(event)
    |> maybe_add_inline_media(event)
  end

  @spec attributed_to_or_default(Event.t()) :: Actor.t()
  defp attributed_to_or_default(event) do
    if(is_nil(event.attributed_to) or not Ecto.assoc_loaded?(event.attributed_to),
      do: nil,
      else: event.attributed_to
    ) ||
      event.organizer_actor
  end

  # Get only elements that we have in EventOptions
  @spec get_options(map) :: map
  defp get_options(object) do
    %{
      maximum_attendee_capacity: object["maximumAttendeeCapacity"],
      anonymous_participation: object["anonymousParticipationEnabled"],
      comment_moderation:
        Map.get(
          object,
          "repliesModerationOption",
          if(Map.get(object, "commentsEnabled", true), do: :allow_all, else: :closed)
        )
    }
  end

  @spec get_address(map | binary | nil) :: integer | nil
  defp get_address(address_url) when is_binary(address_url) do
    get_address(%{"id" => address_url})
  end

  defp get_address(%{"id" => url} = map) when is_map(map) and is_binary(url) do
    Logger.debug("Address with an URL, let's check against our own database")

    case Addresses.get_address_by_url(url) do
      %Address{id: address_id} ->
        address_id

      _ ->
        Logger.debug("not in our database, let's try to create it")
        map = Map.put(map, "url", map["id"])
        do_get_address(map)
    end
  end

  defp get_address(map) when is_map(map) do
    do_get_address(map)
  end

  defp get_address(nil), do: nil

  @spec do_get_address(map) :: integer | nil
  defp do_get_address(map) do
    map = AddressConverter.as_to_model_data(map)

    case Addresses.create_address(map) do
      {:ok, %Address{id: address_id}} ->
        address_id

      _ ->
        nil
    end
  end

  @ap_public "https://www.w3.org/ns/activitystreams#Public"

  defp get_visibility(object), do: if(@ap_public in object["to"], do: :public, else: :unlisted)

  @spec date_to_string(DateTime.t() | nil) :: String.t()
  defp date_to_string(nil), do: nil
  defp date_to_string(%DateTime{} = date), do: DateTime.to_iso8601(date)

  defp get_online_address(attachments) do
    Enum.find_value(attachments, fn attachment ->
      case attachment do
        %{
          "type" => "Link",
          "href" => url,
          "mediaType" => "text/html",
          "name" => @online_address_name
        } ->
          url

        _ ->
          nil
      end
    end)
  end

  @spec maybe_add_physical_address(map(), Event.t()) :: map()
  defp maybe_add_physical_address(res, event) do
    if is_nil(event.physical_address),
      do: res,
      else: Map.put(res, "location", AddressConverter.model_to_as(event.physical_address))
  end

  @spec maybe_add_event_picture(map(), Event.t()) :: map()
  defp maybe_add_event_picture(res, event) do
    if is_nil(event.picture),
      do: res,
      else:
        Map.update(
          res,
          "attachment",
          [],
          &(&1 ++
              [
                event.picture
                |> MediaConverter.model_to_as()
                |> Map.put("name", @banner_picture_name)
              ])
        )
  end

  @spec maybe_add_online_address(map(), Event.t()) :: map()
  defp maybe_add_online_address(res, event) do
    if is_nil(event.online_address),
      do: res,
      else:
        Map.update(
          res,
          "attachment",
          [],
          &(&1 ++
              [
                %{
                  "type" => "Link",
                  "href" => event.online_address,
                  "mediaType" => "text/html",
                  "name" => @online_address_name
                }
              ])
        )
  end

  @spec maybe_add_inline_media(map(), Event.t()) :: map()
  defp maybe_add_inline_media(res, event) do
    medias = Enum.map(event.media, &MediaConverter.model_to_as/1)

    Map.update(
      res,
      "attachment",
      [],
      &(&1 ++ medias)
    )
  end

  defp is_local(url) do
    %URI{host: url_domain} = URI.parse(url)
    %URI{host: local_domain} = URI.parse(Endpoint.url())
    url_domain == local_domain
  end
end