feat(init): cache.__call metamethod for caching function results

See #385.
Included formatting changes (tabs->spaces).

init.lua

@@ -1,6 +1,7 @@
--- ox_lib <https://github.com/overextended/ox_lib>
+---@meta
--- Copyright (C) 2021 Linden <https://github.com/thelindat>
+---ox_lib <https://github.com/overextended/ox_lib>
--- LGPL-3.0-or-later <https://www.gnu.org/licenses/lgpl-3.0.en.html>
+---Copyright (C) 2021 Linden <https://github.com/thelindat>
+---LGPL-3.0-or-later <https://www.gnu.org/licenses/lgpl-3.0.en.html>
 
 if not _VERSION:find('5.4') then
     error('^1Lua 5.4 must be enabled in the resource manifest!^0', 2)
@@ -144,25 +145,51 @@ function ClearInterval(id)
     intervals[id] = -1
 end
 
------------------------------------------------------------------------------------------------
+--[[
--- Cache
+    lua language server doesn't support generics when using @overload
------------------------------------------------------------------------------------------------
+    see https://github.com/LuaLS/lua-language-server/issues/723
+    this function stub allows the following to work
     
-cache = { game = GetGameName(), resource = GetCurrentResourceName() }
+    local key = cache('key', function() return 'abc' end) -- fff: 'abc'
-local notify = ('__ox_notify_%s'):format(cache.resource)
+    local game = cache.game -- game: string
+]]
 
-if context == 'client' then
+---@generic T
-	setmetatable(cache, {
+---@param key string
-		__index = function(self, key)
+---@param func fun(...: any): T
+---@param timeout? number
+---@return T
+---Caches the result of a function, optionally clearing it after timeout ms.
+function cache(key, func, timeout) end
+
+cache = setmetatable({ game = GetGameName(), resource = GetCurrentResourceName() }, {
+    __index = context == 'client' and function(self, key)
         AddEventHandler(('ox_lib:cache:%s'):format(key), function(value)
             self[key] = value
         end)
 
         return rawset(self, key, export.cache(nil, key) or false)[key]
+    end or nil,
+
+    __call = function(self, key, func, timeout)
+        local value = rawget(self, key)
+
+        if not value then
+            value = func()
+
+            rawset(self, key, value)
+
+            if timeout then SetTimeout(timeout, function() self[key] = nil end) end
+        end
+
+        return value
     end,
 })
 
-	RegisterNetEvent(notify, function(data)
+local notifyEvent = ('__ox_notify_%s'):format(cache.resource)
+
+if context == 'client' then
+    RegisterNetEvent(notifyEvent, function(data)
         if locale then
             if data.title then
                 data.title = locale(data.title) or data.title
@@ -188,6 +215,6 @@ else
     ---@deprecated
     ---@diagnostic disable-next-line: duplicate-set-field
     function lib.notify(playerId, data)
-		TriggerClientEvent(notify, playerId, data)
+        TriggerClientEvent(notifyEvent, playerId, data)
     end
 end