defmodule Clacks.ActivityPub do
  @context ["https://www.w3.org/ns/activitystreams"]
  @public "https://www.w3.org/ns/activitystreams#Public"

  @spec note(
          actor :: String.t(),
          html :: String.t(),
          context :: String.t(),
          id :: String.t() | nil,
          published :: DateTime.t(),
          to :: [String.t()],
          cc :: [String.t()]
        ) :: map()
  def note(
        actor,
        html,
        context,
        id \\ nil,
        published \\ DateTime.utc_now(),
        to \\ [@public],
        cc \\ []
      ) do
    id = id || object_id(Ecto.UUID.generate())

    %{
      "@context" => @context,
      "id" => id,
      "url" => id,
      "type" => "Note",
      "actor" => actor,
      "attributedTo" => actor,
      "to" => to,
      "cc" => cc,
      "content" => html,
      "conversation" => context,
      "context" => context,
      "published" => published |> DateTime.to_iso8601()
    }
  end

  @spec create(
          object :: map(),
          id :: String.t() | nil,
          actor :: String.t() | nil,
          to :: [String.t()] | nil,
          cc :: [String.t()] | nil
        ) :: map()
  def create(object, id \\ nil, actor \\ nil, to \\ nil, cc \\ nil) do
    %{
      "@context" => @context,
      "id" => id || activity_id(Ecto.UUID.generate()),
      "actor" => actor || object["actor"],
      "type" => "Create",
      "object" => object,
      "to" => to || object["to"],
      "cc" => cc || object["cc"]
    }
  end

  @spec synthesized_create(object :: map()) :: map()
  def synthesized_create(object) do
    %{
      "@context" => @context,
      "type" => "Create",
      "object" => object,
      # Mastodon doesn't include 'actor' in notes
      "actor" => object["actor"] || object["attributedTo"],
      "to" => object["to"],
      "cc" => object["cc"]
    }
  end

  @spec object_id(id :: String.t()) :: String.t()
  def object_id(id) do
    url = Application.get_env(:clacks, ClacksWeb.Endpoint)[:url]

    %URI{
      scheme: url[:scheme],
      host: url[:host],
      port: url[:port],
      path: Path.join("/objects", id)
    }
    |> URI.to_string()
  end

  @spec activity_id(id :: String.t()) :: String.t()
  def activity_id(id) do
    url = Application.get_env(:clacks, ClacksWeb.Endpoint)[:url]

    %URI{
      scheme: url[:scheme],
      host: url[:host],
      port: url[:port],
      path: Path.join("/activities", id)
    }
    |> URI.to_string()
  end
end