Add simple druid event library

druid/event.lua

@@ -0,0 +1,37 @@
+--- Lua event small library
+
+local class = require("druid.system.middleclass")
+
+local M = class("druid.event")
+
+
+function M.initialize(self)
+	self._callbacks = {}
+end
+
+
+function M.subscribe(self, callback)
+	assert(type(callback) == "function", "Callback should be function")
+
+	table.insert(self._callbacks, callback)
+end
+
+
+function M.unsubscribe(self, callback)
+	for i = 1, #self._callbacks do
+		if self._callbacks[i] == callback then
+			table.remove(self._callbacks, i)
+			return
+		end
+	end
+end
+
+
+function M.trigger(self, ...)
+	for i = 1, #self._callbacks do
+		self._callbacks[i](...)
+	end
+end
+
+
+return M