Add ability to view previous topics with .topic command

After a user invokes the ".topic" command and reacts with the reroll emoji, the embed will now show the previous few messages. It cannot display more than
256 characters, which is usually around 5 prompts.

Implements: python-discord#1145

bot/exts/utilities/conversationstarters.py

@@ -43,7 +43,7 @@ def __init__(self, bot: Bot):
         self.bot = bot
 
     @staticmethod
-    def _build_topic_embed(channel_id: int) -> discord.Embed:
+    def _build_topic_embed(channel_id: int, previous_topic: None | str) -> discord.Embed:
         """
         Build an embed containing a conversation topic.
 
@@ -56,21 +56,46 @@ def _build_topic_embed(channel_id: int) -> discord.Embed:
             color=discord.Colour.og_blurple()
         )
 
-        try:
-            channel_topics = TOPICS[channel_id]
-        except KeyError:
-            # Channel doesn't have any topics.
-            embed.title = f"**{next(TOPICS['default'])}**"
+        if previous_topic is None:
+            # Message first sent
+            try:
+                channel_topics = TOPICS[channel_id]
+            except KeyError:
+                # Channel doesn't have any topics.
+                embed.title = f"**{next(TOPICS['default'])}**"
+            else:
+                embed.title = f"**{next(channel_topics)}**"
         else:
-            embed.title = f"**{next(channel_topics)}**"
+            # Message is being edited
+
+            try:
+                channel_topics = TOPICS[channel_id]
+            except KeyError:
+                # Channel doesn't have any topics.
+                new_topic = f"**{next(TOPICS['default'])}**"
+            else:
+                new_topic = f"\n**{next(channel_topics)}**"
+
+            total_topics = previous_topic.count("\n") + 1
+
+            # Add 1 before first topic
+            if total_topics == 1:
+                previous_topic = f"1. {previous_topic}"
+
+            embed.title = previous_topic + f"\n{total_topics + 1}. {new_topic}"
+
+            # When the embed will be larger than the limit, use the previous embed instead
+            if len(embed.title) > 256:
+                embed.title = previous_topic
+
         return embed
 
     @staticmethod
     def _predicate(
-        command_invoker: Union[discord.User, discord.Member],
-        message: discord.Message,
-        reaction: discord.Reaction,
-        user: discord.User
+            command_invoker: Union[discord.User, discord.Member],
+            message: discord.Message,
+            reaction: discord.Reaction,
+            user: discord.User
     ) -> bool:
         user_is_moderator = any(role.id in MODERATION_ROLES for role in getattr(user, "roles", []))
         user_is_invoker = user.id == command_invoker.id
@@ -83,9 +108,9 @@ def _predicate(
         return is_right_reaction
 
     async def _listen_for_refresh(
-        self,
-        command_invoker: Union[discord.User, discord.Member],
-        message: discord.Message
+            self,
+            command_invoker: Union[discord.User, discord.Member],
+            message: discord.Message
     ) -> None:
         await message.add_reaction("🔄")
         while True:
@@ -101,23 +126,25 @@ async def _listen_for_refresh(
                 break
 
             try:
-                await message.edit(embed=self._build_topic_embed(message.channel.id))
+                # The returned discord.Message object from discord.Message.edit is different than the current
+                # discord.Message object, so it must be reassigned to update properly
+                message = await message.edit(embed=self._build_topic_embed(message.channel.id, message.embeds[0].title))
             except discord.NotFound:
                 break
 
             with suppress(discord.NotFound):
                 await message.remove_reaction(reaction, user)
 
     @commands.command()
-    @commands.cooldown(1, 60*2, commands.BucketType.channel)
+    @commands.cooldown(1, 60 * 2, commands.BucketType.channel)
     @whitelist_override(channels=ALL_ALLOWED_CHANNELS)
     async def topic(self, ctx: commands.Context) -> None:
         """
         Responds with a random topic to start a conversation.
 
         Allows the refresh of a topic by pressing an emoji.
         """
-        message = await ctx.send(embed=self._build_topic_embed(ctx.channel.id))
+        message = await ctx.send(embed=self._build_topic_embed(ctx.channel.id, None))
         self.bot.loop.create_task(self._listen_for_refresh(ctx.author, message))