defmodule MobilizonWeb.Resolvers.Event do
  @moduledoc """
  Handles the event-related GraphQL calls
  """
  alias Mobilizon.Activity
  alias Mobilizon.Events
  alias Mobilizon.Events.{Event, Participant}
  alias Mobilizon.Actors.Actor
  alias Mobilizon.Users.User

  # We limit the max number of events that can be retrieved
  @event_max_limit 100
  @number_of_related_events 3

  def list_events(_parent, %{page: page, limit: limit}, _resolution)
      when limit < @event_max_limit do
    {:ok, Mobilizon.Events.list_events(page, limit)}
  end

  def list_events(_parent, %{page: _page, limit: _limit}, _resolution) do
    {:error, :events_max_limit_reached}
  end

  def find_event(_parent, %{uuid: uuid}, _resolution) do
    case Mobilizon.Events.get_event_full_by_uuid(uuid) do
      nil ->
        {:error, "Event with UUID #{uuid} not found"}

      event ->
        {:ok, event}
    end
  end

  @doc """
  List participant for event (separate request)
  """
  def list_participants_for_event(_parent, %{uuid: uuid, page: page, limit: limit}, _resolution) do
    {:ok, Mobilizon.Events.list_participants_for_event(uuid, page, limit)}
  end

  @doc """
  List participants for event (through an event request)
  """
  def list_participants_for_event(%Event{uuid: uuid}, _args, _resolution) do
    {:ok, Mobilizon.Events.list_participants_for_event(uuid, 1, 10)}
  end

  @doc """
  List related events
  """
  def list_related_events(
        %Event{tags: tags, organizer_actor: organizer_actor},
        _args,
        _resolution
      ) do
    # We get the organizer's next public event
    events =
      [Events.get_actor_upcoming_public_event(organizer_actor, uuid)] |> Enum.filter(&is_map/1)

    # uniq_by : It's possible event_from_same_actor is inside events_from_tags
    events =
      (events ++
         Events.find_similar_events_by_common_tags(
           tags,
           @number_of_related_events - length(events)
         ))
      |> uniq_events()

    # TODO: We should use tag_relations to find more appropriate events

    # We've considered all recommended events, so we fetch the latest events
    events =
      if @number_of_related_events - length(events) > 0 do
        (events ++
           Events.list_events(1, @number_of_related_events, :begins_on, :asc, true, true))
        |> uniq_events()
      else
        events
      end

    events =
      events
      # We remove the same event from the results
      |> Enum.filter(fn event -> event.uuid != uuid end)
      # We return only @number_of_related_events right now
      |> Enum.take(@number_of_related_events)

    # TODO: We should use tag_relations to find more events
    {:ok, events}
  end

  @doc """
  Join an event for an actor
  """
  def actor_join_event(
        _parent,
        %{actor_id: actor_id, event_id: event_id},
        %{
          context: %{
            current_user: user
          }
        }
      ) do
    with {:is_owned, true, actor} <- User.owns_actor(user, actor_id),
         {:ok, %Event{} = event} <- Mobilizon.Events.get_event(event_id),
         {:error, :participant_not_found} <- Mobilizon.Events.get_participant(event_id, actor_id),
         role <- Mobilizon.Events.get_default_participant_role(event),
         {:ok, participant} <-
           Mobilizon.Events.create_participant(%{
             role: role,
             event_id: event.id,
             actor_id: actor.id
           }),
         participant <-
           Map.put(participant, :event, event)
           |> Map.put(:actor, actor) do
      {:ok, participant}
    else
      {:is_owned, false} ->
        {:error, "Actor id is not owned by authenticated user"}

      {:error, :event_not_found} ->
        {:error, "Event id not found"}

      {:ok, %Participant{}} ->
        {:error, "You are already a participant of this event"}
    end
  end

  def actor_join_event(_parent, _args, _resolution) do
    {:error, "You need to be logged-in to join an event"}
  end

  @doc """
  Leave an event for an actor
  """
  def actor_leave_event(
        _parent,
        %{actor_id: actor_id, event_id: event_id},
        %{
          context: %{
            current_user: user
          }
        }
      ) do
    with {:is_owned, true, _} <- User.owns_actor(user, actor_id),
         {:ok, %Participant{} = participant} <-
           Mobilizon.Events.get_participant(event_id, actor_id),
         {:only_organizer, false} <-
           {:only_organizer, check_that_participant_is_not_only_organizer(event_id, actor_id)},
         {:ok, _} <-
           Mobilizon.Events.delete_participant(participant) do
      {:ok, %{event: %{id: event_id}, actor: %{id: actor_id}}}
    else
      {:is_owned, false} ->
        {:error, "Actor id is not owned by authenticated user"}

      {:only_organizer, true} ->
        {:error, "You can't leave event because you're the only event creator participant"}

      {:error, :participant_not_found} ->
        {:error, "Participant not found"}
    end
  end

  def actor_leave_event(_parent, _args, _resolution) do
    {:error, "You need to be logged-in to leave an event"}
  end

  # We check that the actor asking to leave the event is not it's only organizer
  # We start by fetching the list of organizers and if there's only one of them
  # and that it's the actor requesting leaving the event we return true
  @spec check_that_participant_is_not_only_organizer(integer(), integer()) :: boolean()
  defp check_that_participant_is_not_only_organizer(event_id, actor_id) do
    with [%Participant{actor: %Actor{id: participant_actor_id}}] <-
           Mobilizon.Events.list_organizers_participants_for_event(event_id) do
      participant_actor_id == actor_id
    else
      _ -> false
    end
  end

  @doc """
  Create an event
  """
  def create_event(_parent, args, %{context: %{current_user: _user}}) do
    with {:ok, %Activity{data: %{"object" => %{"type" => "Event"} = object}}} <-
           MobilizonWeb.API.Events.create_event(args) do
      {:ok,
       %Event{
         title: object["name"],
         description: object["content"],
         uuid: object["uuid"],
         url: object["id"]
       }}
    end
  end

  def create_event(_parent, _args, _resolution) do
    {:error, "You need to be logged-in to create events"}
  end

  @doc """
  Delete an event
  """
  def delete_event(_parent, %{event_id: event_id, actor_id: actor_id}, %{
        context: %{current_user: user}
      }) do
    with {:ok, %Event{} = event} <- Mobilizon.Events.get_event(event_id),
         {:is_owned, true, _} <- User.owns_actor(user, actor_id),
         {:event_can_be_managed, true} <- Event.can_event_be_managed_by(event, actor_id),
         event <- Mobilizon.Events.delete_event!(event) do
      {:ok, %{id: event.id}}
    else
      {:error, :event_not_found} ->
        {:error, "Event not found"}

      {:is_owned, false} ->
        {:error, "Actor id is not owned by authenticated user"}

      {:event_can_be_managed, false} ->
        {:error, "You cannot delete this event"}
    end
  end

  def delete_event(_parent, _args, _resolution) do
    {:error, "You need to be logged-in to delete an event"}
  end
end