WIP: Supervisor-based plugin base

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

lib/plugin/plugin.ex

@@ -0,0 +1,77 @@
+defmodule Omnibot.Plugin do
+  @default_opts [include_base: true, opts: [strategy: :one_for_one]]
+
+  defmodule CfgState do
+    use Agent
+
+    def start_link(opts) do
+      {cfg, opts} = Keyword.pop(opts, :cfg)
+      {state, opts} = Keyword.pop(opts, :state, nil)
+      Agent.start_link(fn -> {cfg, state} end, opts)
+    end
+
+    def cfg(pid), do: Agent.get(pid, fn {cfg, _} -> cfg end)
+
+    def state(pid), do: Agent.get(pid, fn {_, state} -> state end)
+
+    def update_state(pid, fun, timeout \\ 5000),
+      do: Agent.update(pid, &{&1, apply(fun, [&1])}, timeout)
+  end
+
+  defmacro __using__(opts) do
+    opts = opts ++ @default_opts
+
+    quote do
+      use Supervisor
+      use Omnibot.Plugin.Base
+
+      ## Client API
+
+      def start_link(opts) do
+        Supervisor.start_link(__MODULE__, {opts[:cfg], opts[:state]}, opts)
+      end
+
+      def cfg() do
+        Omnibot.Plugin.CfgState.cfg(__MODULE__.CfgState)
+      end
+
+      def state() do
+        Omnibot.Plugin.CfgState.state(__MODULE__.CfgState)
+      end
+
+      def update_state(fun) do
+        Omnibot.Plugin.CfgState.update_state(__MODULE__.CfgState, fun)
+      end
+
+      @impl Omnibot.Plugin.Base
+      def handle_msg(irc, msg) do
+        GenServer.cast(__MODULE__, {:handle_msg, irc, msg})
+      end
+
+      @impl Omnibot.Plugin
+      def children(_cfg, _state), do: []
+
+      ## Server callbacks
+
+      @impl Supervisor
+      def init({cfg, state}) do
+        base_children = [
+          {Omnibot.Plugin.CfgState, cfg: cfg, state: state, name: __MODULE__.CfgState},
+        ]
+        children = 
+          (if unquote(opts[:include_base]), do: base_children, else: []) ++ children(cfg, state)
+        Supervisor.init(children, unquote(opts[:opts]))
+      end
+
+      def handle_cast({:handle_msg, irc, msg}, state) do
+        on_msg(irc, msg)
+        {:noreply, state}
+      end
+
+      @behaviour Omnibot.Plugin
+      defoverridable Omnibot.Plugin
+    end
+  end
+
+  @callback children(cfg :: [atom: any], state :: any) :: [atom | {atom, [atom: any]} | {atom, any, [atom: any]}]
+end