defmodule Pleroma.Gopher.Server do
  use GenServer
  require Logger
  @gopher Application.get_env(:pleroma, :gopher)

  def start_link() do
    ip = Keyword.get(@gopher, :ip, {0, 0, 0, 0})
    port = Keyword.get(@gopher, :port, 1234)
    GenServer.start_link(__MODULE__, [ip, port], [])
  end

  def init([ip, port]) do
    if Keyword.get(@gopher, :enabled, false) do
      Logger.info("Starting gopher server on #{port}")

      :ranch.start_listener(
        :gopher,
        100,
        :ranch_tcp,
        [port: port],
        __MODULE__.ProtocolHandler,
        []
      )

      {:ok, %{ip: ip, port: port}}
    else
      Logger.info("Gopher server disabled")
      {:ok, nil}
    end
  end
end

defmodule Pleroma.Gopher.Server.ProtocolHandler do
  alias Pleroma.Web.ActivityPub.ActivityPub
  alias Pleroma.User
  alias Pleroma.Activity
  alias Pleroma.Repo

  @instance Application.get_env(:pleroma, :instance)
  @gopher Application.get_env(:pleroma, :gopher)

  def start_link(ref, socket, transport, opts) do
    pid = spawn_link(__MODULE__, :init, [ref, socket, transport, opts])
    {:ok, pid}
  end

  def init(ref, socket, transport, _Opts = []) do
    :ok = :ranch.accept_ack(ref)
    loop(socket, transport)
  end

  def info(text) do
    "#{text}\tfake\(NULL)\t0\r\n"
  end

  def link(name, selector, type \\ 1) do
    address = Pleroma.Web.Endpoint.host()
    port = Keyword.get(@gopher, :port, 1234)
    "#{type}#{name}\t#{selector}\t#{address}\t#{port}\r\n"
  end

  def response("") do
    info("Welcome to #{Keyword.get(@instance, :name, "Pleroma")}!") <>
      link("Public Timeline", "/main/public") <>
      link("Federated Timeline", "/main/all") <> ".\r\n"
  end

  def render_activities(activities) do
    activities
    |> Enum.reverse()
    |> Enum.map(fn activity ->
      user = User.get_cached_by_ap_id(activity.data["actor"])

      link("Post ##{activity.id} by #{user.nickname}", "/notices/#{activity.id}") <>
        info(HtmlSanitizeEx.strip_tags(activity.data["object"]["content"]))
    end)
    |> Enum.join("\r\n")
  end

  def response("/main/public") do
    posts =
      ActivityPub.fetch_public_activities(%{"type" => ["Create"], "local_only" => true})
      |> render_activities

    info("Welcome to the Public Timeline!") <> posts <> ".\r\n"
  end

  def response("/main/all") do
    posts =
      ActivityPub.fetch_public_activities(%{"type" => ["Create"]})
      |> render_activities

    info("Welcome to the Federated Timeline!") <> posts <> ".\r\n"
  end

  def response("/notices/" <> id) do
    with %Activity{} = activity <- Repo.get(Activity, id),
         true <- ActivityPub.is_public?(activity) do
      activities =
        ActivityPub.fetch_activities_for_context(activity.data["context"])
        |> render_activities

      user = User.get_cached_by_ap_id(activity.data["actor"])

      info("Post #{activity.id} by #{user.nickname}") <>
        link("More posts by #{user.nickname}", "/users/#{user.nickname}") <> activities <> ".\r\n"
    else
      _e ->
        info("Not public") <> ".\r\n"
    end
  end

  def response("/users/" <> nickname) do
    with %User{} = user <- User.get_cached_by_nickname(nickname) do
      params = %{
        "type" => ["Create"],
        "actor_id" => user.ap_id
      }

      activities =
        ActivityPub.fetch_public_activities(params)
        |> render_activities

      info("Posts by #{user.nickname}") <> activities <> ".\r\n"
    else
      _e ->
        info("No such user") <> ".\r\n"
    end
  end

  def loop(socket, transport) do
    case transport.recv(socket, 0, 5000) do
      {:ok, data} ->
        data = String.trim_trailing(data, "\r\n")
        transport.send(socket, response(data))
        :ok = transport.close(socket)

      _ ->
        :ok = transport.close(socket)
    end
  end
end