defmodule Sorcery.PubSub do
  @moduledoc """
  Provides a clean interface for publishing and subscribing to events.

  ## Configuration

  In your config.exs:

      config :sorcery, :pub_sub,
        pub_sub: Sorcery.PubSub.PostgresStore,
        pub_sub_opts: [
          repo: MyApp.Repo,
          table_name: "events"
        ]

  Or for in-memory storage:

      config :sorcery, :pub_sub,
        pub_sub: Sorcery.PubSub.MemoryStore

  ## Usage

      # Publish an event
      event = Sorcery.Event.new(%{
        type: "user_registered",
        data: %{user_id: "123"},
        domain: "users",
        instance_id: "instance_1",
        domain_sequence_number: 1
      })

      Sorcery.PubSub.publish(event)

      # Subscribe to events
      {:ok, events, pagination} = Sorcery.PubSub.subscribe()

      # Query specific events
      {:ok, events, pagination} = Sorcery.PubSub.subscribe_by_domain("users")
      {:ok, events, pagination} = Sorcery.PubSub.subscribe_by_type("user_registered")
  """

  alias Sorcery.Event
  alias Sorcery.PubSub.Behaviour

  @type subscription :: Behaviour.subscription()

  def child_spec(opts) do
    %{
      id: __MODULE__,
      start: {__MODULE__, :start_link, [opts]},
      type: :worker,
      restart: :permanent,
      shutdown: 5000
    }
  end

  @doc """
  Publishes one or more events to the configured store.
  """
  @spec publish(Event.t() | [Event.t()]) :: :ok | {:error, term()}
  def publish(events) do
    pub_sub().publish(events)
  end

  @doc """
  Subscribes to events for a given subscription.

  """
  @spec subscribe() :: :ok | {:error,term()}
  def subscribe() do
    pub_sub().subscribe()
  end

  @spec pub_sub() :: module()
  def pub_sub do
    Application.get_env(:sorcery, :pub_sub, [])
    |> Keyword.get(:pub_sub, Sorcery.PubSub.Registry)
  end

  @doc """
  Returns the configured options for the pub sub.
  """
  @spec pub_sub_opts() :: Keyword.t()
  def pub_sub_opts do
    Application.get_env(:sorcery, :pub_sub, [])
    |> Keyword.get(:pub_sub_opts, [])
  end

  @doc """
  Starts the configured pub sub.
  """
  @spec start_link(Keyword.t()) :: GenServer.on_start()
  def start_link(opts \\ []) do
    pub_sub().start(pub_sub_opts() ++ opts)
  end
end