defmodule Aprsme.Cluster.Topology do
  @moduledoc """
  Wrapper for Cluster.Supervisor that only starts when clustering is enabled.
  """
  require Logger

  def child_spec(opts) do
    cluster_enabled = Application.get_env(:aprsme, :cluster_enabled, false)
    topologies = Application.get_env(:libcluster, :topologies, [])
    build_spec(cluster_enabled, topologies, opts)
  end

  # Clustering disabled — no-op spec.
  defp build_spec(false, _topologies, opts), do: noop_spec(opts)

  # Clustering enabled but no topologies configured — no-op + warning.
  defp build_spec(true, topologies, opts) when topologies in [nil, []] do
    Logger.warning("No libcluster topologies configured, clustering will not work")
    noop_spec(opts)
  end

  # Clustering enabled with topologies — delegate to libcluster's supervisor.
  defp build_spec(true, topologies, opts) do
    Logger.info("Cluster.Topology starting with topologies: #{inspect(topologies)}")
    supervisor_opts = Keyword.merge([name: Aprsme.ClusterSupervisor], opts)
    {Cluster.Supervisor, [topologies, supervisor_opts]}
  end

  defp noop_spec(opts) do
    %{
      id: __MODULE__,
      start: {__MODULE__, :start_link, [opts]},
      type: :worker
    }
  end

  def start_link(_opts), do: :ignore
end