[Mod] Allow admins to choose amount of repeats for "deleterepeats" (#2437)

* feat(mod): configurable amount of repeats for "deleterepeats"

resolves #2267

* fix(mod): check user input instead of changing it if it's invalid

* fix(mod): only purge cache when argument is valid

* perf(mod): fetch repeats from config only when guild not in cache

redbot/cogs/mod/mod.py

@@ -1,4 +1,4 @@
-from collections import deque, defaultdict
+from collections import defaultdict
 from typing import List, Tuple
 
 import discord
@@ -15,14 +15,18 @@ from .settings import ModSettings
 
 _ = T_ = Translator("Mod", __file__)
 
+__version__ = "1.0.0"
+
 
 @cog_i18n(_)
 class Mod(ModSettings, Events, KickBanMixin, MoveToCore, MuteMixin, ModInfo, commands.Cog):
     """Moderation tools."""
 
+    default_global_settings = {"version": ""}
+
     default_guild_settings = {
         "ban_mention_spam": False,
-        "delete_repeats": False,
+        "delete_repeats": -1,
         "ignored": False,
         "respect_hierarchy": True,
         "delete_delay": -1,
@@ -41,21 +45,39 @@ class Mod(ModSettings, Events, KickBanMixin, MoveToCore, MuteMixin, ModInfo, com
         self.bot = bot
 
         self.settings = Config.get_conf(self, 4961522000, force_registration=True)
+        self.settings.register_global(**self.default_global_settings)
         self.settings.register_guild(**self.default_guild_settings)
         self.settings.register_channel(**self.default_channel_settings)
         self.settings.register_member(**self.default_member_settings)
         self.settings.register_user(**self.default_user_settings)
         self.ban_queue: List[Tuple[int, int]] = []
         self.unban_queue: List[Tuple[int, int]] = []
-        self.cache: dict = defaultdict(lambda: deque(maxlen=3))
+        self.cache: dict = {}
         self.registration_task = self.bot.loop.create_task(self._casetype_registration())
         self.tban_expiry_task = self.bot.loop.create_task(self.check_tempban_expirations())
         self.last_case: dict = defaultdict(dict)
 
+    async def initialize(self):
+        await self._maybe_update_config()
+
     def __unload(self):
         self.registration_task.cancel()
         self.tban_expiry_task.cancel()
 
+    async def _maybe_update_config(self):
+        """Maybe update `delete_delay` value set by Config prior to Mod 1.0.0."""
+        if await self.settings.version():
+            return
+        guild_dict = await self.settings.all_guilds()
+        for guild_id, info in guild_dict.items():
+            delete_repeats = info.get("delete_repeats", False)
+            if delete_repeats:
+                val = 3
+            else:
+                val = -1
+            await self.settings.guild(discord.Object(id=guild_id)).delete_repeats.set(val)
+        await self.settings.version.set(__version__)
+
     @staticmethod
     async def _casetype_registration():
         try: