Handle time innacuracy by warning owner (#2036)

* handle time innacuracy by warning owner

* Fix typo and add space

redbot/core/bot.py

@@ -106,6 +106,7 @@ class RedBase(BotBase, RPCMixin):
 
         self.counter = Counter()
         self.uptime = None
+        self.checked_time_accuracy = None
         self.color = discord.Embed.Empty  # This is needed or color ends up 0x000000
 
         self.main_dir = bot_dir

redbot/core/events.py

@@ -256,6 +256,20 @@ def init_events(bot, cli_flags):
     async def on_message(message):
         bot.counter["messages_read"] += 1
         await bot.process_commands(message)
+        discord_now = message.created_at
+        if (
+            not bot.checked_time_accuracy
+            or (discord_now - timedelta(minutes=60)) > bot.checked_time_accuracy
+        ):
+            system_now = datetime.datetime.utcnow()
+            diff = abs((discord_now - system_now).total_seconds)
+            if diff > 60:
+                log.warn(
+                    "Detected significant difference (%d seconds) in system clock to discord's clock."
+                    " Any time sensitive code may fail.",
+                    diff,
+                )
+            bot.checked_time_accuracy = discord_now
 
     @bot.event
     async def on_resumed():