omnibot/lib/core.ex

defmodule Omnibot.Core do
  use Omnibot.Plugin
  alias Omnibot.{Config, Irc}

  @default_config channels: :all

  @impl true
  def on_join(irc, channel, nick) do
    cfg = Irc.cfg(irc)
    if nick == cfg.nick do
      add_channel(channel)
      # Sync if we join a channel we shouldn't be in
      if channel in Config.all_channels(cfg),
        do: sync_channels(irc)
    end
  end

  @impl true
  def on_part(irc, channel, nick) do
    cfg = Irc.cfg(irc)
    if nick == cfg.nick do
      remove_channel(channel)
      # Sync if we join a channel we forcibly part a channel we shouldn't leave
      if channel in Config.all_channels(cfg),
        do: sync_channels(irc)
    end
  end

  @impl true
  def on_kick(irc, channel, _nick, target) do
    cfg = Irc.cfg(irc)
    if target == cfg.nick do
      remove_channel(channel)
      # Generally, being kicked is not intentionally leaving a channel, so always sync here
      sync_channels(irc)
    end
  end

  @impl true
  def on_msg(irc, msg) do
    case String.upcase(msg.command) do
      "001" -> sync_channels(irc)
      "PING" -> Irc.send_msg(irc, "PONG", msg.params)
      _ -> route_msg(irc, msg)
    end
  end

  @impl true
  def on_init(_cfg) do
    %{channels: MapSet.new()}
  end

  defp sync_channels(irc) do
    cfg = Irc.cfg(irc)
    desired = MapSet.new(Config.all_channels(cfg))
    present = state().channels

    to_join = MapSet.difference(desired, present)
      |> MapSet.to_list()
    to_part = MapSet.difference(present, desired)
      |> MapSet.to_list()

    Enum.each(to_join, fn channel -> Irc.join(irc, channel) end)
    Enum.each(to_part, fn channel -> Irc.part(irc, channel) end)
  end

  defp add_channel(channel) do
    update_state(fn cfg = %{channels: channels} -> %{cfg | channels: MapSet.put(channels, channel)} end)
  end
  
  defp remove_channel(channel) do
    update_state(fn cfg = %{channels: channels} -> %{cfg | channels: MapSet.delete(channels, channel)} end)
  end
end