feat(callback): client callback

Allow the client to listen for and respond to server requests.
Basically just copy-paste and swap the two.

imports/callback/client.lua

@@ -69,4 +69,15 @@ function callback.await(event, delay, ...)
 	return triggerServerCallback(_, event, delay, false, ...)
 end
 
+---@param name string
+---@param cb function
+--- Registers an event handler and callback function to respond to server requests.
+function callback.register(name, cb)
+	name = ('__cb_%s'):format(name)
+
+	RegisterNetEvent(name, function(key, ...)
+		TriggerServerEvent(cbEvent, key, { cb(...) })
+	end)
+end
+
 return callback

imports/callback/server.lua

@@ -1,13 +1,62 @@
-local callback = {}
+local events = {}
 local cbEvent = ('__cb_%s'):format(cache.resource)
 
+RegisterNetEvent(cbEvent, function(key, ...)
+	local cb = events[key]
+	return cb and cb(...)
+end)
+
+---@param _ any
+---@param event string
+---@param playerId number
+---@param cb function
+---@param ... unknown
+---@return unknown
+local function triggerClientCallback(_, event, playerId, cb, ...)
+	local key
+
+	repeat
+		key = ('%s:%s:%s'):format(event, math.random(0, 100000), playerId)
+	until not events[key]
+
+	TriggerClientEvent(('__cb_%s'):format(event), playerId, key, ...)
+
+	local promise = not cb and promise.new()
+
+	events[key] = function(response)
+		events[key] = nil
+
+		if promise then
+			return promise:resolve(response)
+		end
+
+		cb(table.unpack(response))
+	end
+
+	if promise then
+		return table.unpack(Citizen.Await(promise))
+	end
+end
+
+---@overload fun(event: string, playerId: number, cb: function, ...)
+local callback = setmetatable({}, {
+	__call = triggerClientCallback
+})
+
+---@param event string
+---@param playerId number
+--- Sends an event to a client and halts the current thread until a response is returned.
+function callback.await(event, playerId, ...)
+	return triggerClientCallback(_, event, playerId, false, ...)
+end
+
 ---@param name string
 ---@param cb function
 --- Registers an event handler and callback function to respond to client requests.
 function callback.register(name, cb)
 	name = ('__cb_%s'):format(name)
 
-	RegisterServerEvent(name, function(key, ...)
+	RegisterNetEvent(name, function(key, ...)
 		TriggerClientEvent(cbEvent, source, key, { cb(source, ...) })
 	end)
 end