plugin: Add simple signal implementation for future work

plugin/src/createSignal.lua

@@ -0,0 +1,53 @@
+--[[
+	Create a new signal that can be connected to, disconnected from, and fired.
+
+	Usage:
+
+		local signal = createSignal()
+		local disconnect = signal:connect(function(...)
+			print("fired:", ...)
+		end)
+
+		signal:fire("a", "b", "c")
+		disconnect()
+
+	Avoids mutating listeners list directly to prevent iterator invalidation if
+	a listener is disconnected while the signal is firing.
+]]
+local function createSignal()
+	local listeners = {}
+
+	local function connect(newListener)
+		local nextListeners = {}
+		for listener in pairs(listeners) do
+			nextListeners[listener] = true
+		end
+
+		nextListeners[newListener] = true
+		listeners = nextListeners
+
+		return function()
+			local nextListeners = {}
+			for listener in pairs(listeners) do
+				if listener ~= newListener then
+					nextListeners[listener] = true
+				end
+			end
+
+			listeners = nextListeners
+		end
+	end
+
+	local function fire(...)
+		for listener in pairs(listeners) do
+			listener(...)
+		end
+	end
+
+	return {
+		connect = connect,
+		fire = fire,
+	}
+end
+
+return createSignal