Add Omnibot.Module

Modules can easily be defined with `use Omnibot.Module`.
Omnibot.Contrib.Fortune has been updated to use this.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

lib/module.ex

@@ -0,0 +1,72 @@
+defmodule Omnibot.Module do
+  defmacro __using__([]) do
+    quote do
+      use GenServer
+      alias Omnibot.{Irc, Module}
+      require Logger
+
+      @behaviour Module
+
+      ## Client API
+
+      def start_link(opts) do
+        GenServer.start_link(__MODULE__, opts[:cfg], opts ++ [name: __MODULE__])
+      end
+
+      def msg(msg), do: GenServer.cast(__MODULE__, msg)
+      def msg(module, msg), do: GenServer.cast(module, {:msg, msg})
+
+      ## Server callbacks
+
+      @impl GenServer
+      def init(cfg), do: {:ok, cfg}
+
+      @impl Module
+      def on_msg(msg) do
+        route_msg(msg)
+      end
+
+      def route_msg(msg) do
+        nick = msg.prefix.nick
+        case String.upcase(msg.command) do
+          "PRIVMSG" -> [channel | text] = msg.params
+            on_channel_msg(channel, nick, Enum.join(text, " "))
+          "JOIN" -> [channel | _] = msg.params
+            on_join(channel, nick)
+          "PART" -> [channel | _] = msg.params
+            on_part(channel, nick)
+          "KICK" -> [channel | _] = msg.params
+            on_kick(channel, nick)
+          _ -> nil
+        end
+      end
+
+      @impl Module
+      def on_channel_msg(_channel, _nick, _line), do: nil
+
+      @impl Module
+      def on_join(_channel, _nick), do: nil
+
+      @impl Module
+      def on_part(_channel, _nick), do: nil
+
+      @impl Module
+      def on_kick(_channel, _nick), do: nil
+
+      @impl GenServer
+      def handle_cast({:msg, msg}, cfg) do
+        on_msg(msg)
+        {:noreply, cfg}
+      end
+
+      defoverridable Module
+      defoverridable GenServer
+    end
+  end
+
+  @callback on_msg(msg :: %Omnibot.Irc.Msg{}) :: any
+  @callback on_channel_msg(channel :: String.t, nick :: String.t, line :: String.t) :: any
+  @callback on_join(channel :: String.t, nick :: String.t) :: any
+  @callback on_part(channel :: String.t, nick :: String.t) :: any
+  @callback on_kick(channel :: String.t, nick :: String.t) :: any
+end