process_hub

defmodule ProcessHub.Strategy.Redundancy.Singularity do
  @moduledoc """
  The Singularity strategy starts a single instance of a process and creates no replicas on
  other nodes. This is the default strategy.
  """

  alias ProcessHub.Strategy.Redundancy.Base, as: RedundancyStrategy
  alias ProcessHub.Service.Ring

  @typedoc """
  No options are available.
  """
  @type t() :: %__MODULE__{}
  defstruct []

  defimpl RedundancyStrategy, for: ProcessHub.Strategy.Redundancy.Singularity do
    @impl true
    @spec replication_factor(ProcessHub.Strategy.Redundancy.Singularity.t(), :hash_ring.ring()) ::
            1
    def replication_factor(_struct, _hash_ring), do: 1

    @impl true
    @spec belongs_to(
            ProcessHub.Strategy.Redundancy.Singularity.t(),
            :hash_ring.ring(),
            atom() | binary()
          ) :: [atom]
    def belongs_to(_struct, hash_ring, child_id) do
      Ring.key_to_nodes(hash_ring, child_id, 1)
    end

    @impl true
    @spec handle_post_start(
            ProcessHub.Strategy.Redundancy.Singularity.t(),
            :hash_ring.ring(),
            atom() | binary(),
            pid()
          ) :: :ok
    def handle_post_start(_struct, _hash_ring, _child_id, _child_pid), do: :ok

    @impl true
    @spec handle_post_update(
            ProcessHub.Strategy.Redundancy.Singularity.t(),
            ProcessHub.hub_id(),
            atom() | binary(),
            term()
          ) :: :ok
    def handle_post_update(_struct, _hub_id, _child_id, _data), do: :ok
  end
end