chore: refactor VCs to use a watch channel internally (but I'm going to rework this in the next commit anyway)

src/command/join.rs

@@ -50,9 +50,6 @@ enum GetGuildAndVoiceChannelIdError {
     /// there is no user who invoked this command
     NoUser,
 
-    /// there are no voice chats in this guild
-    NoVCsInGuild,
-
     /// the user is not in a voice chat in this guild
     UserNotInVC,
 }
@@ -70,9 +67,11 @@ fn get_guild_and_voice_channel_id(
         .and_then(|member| member.user.as_ref().map(|user| user.id))
         .context(NoUserSnafu)?;
 
-    let guild_vcs = vcs.get(&guild_id).context(NoVCsInGuildSnafu)?;
+    let voice_channel_id = vcs
-
+        .with_guild(guild_id, |guild_vcs| {
-    let &voice_channel_id = guild_vcs.get_left_for(&user_id).context(UserNotInVCSnafu)?;
+            guild_vcs.get_left_for(&user_id).copied()
+        })
+        .context(UserNotInVCSnafu)?;
 
     Ok((guild_id, voice_channel_id))
 }
@@ -85,9 +84,6 @@ fn get_guild_and_vc_error_to_embed(error: GetGuildAndVoiceChannelIdError) -> Emb
         GetGuildAndVoiceChannelIdError::NoUser => {
             EmbedBuilder::new().title("Not invoked by a user").description("This command works by joining the same VC as the user, but this bot didn't receive any user data. So did no user invoke it?! (This error should be impossible!)").validate().unwrap().build()
         },
-        GetGuildAndVoiceChannelIdError::NoVCsInGuild => {
-            EmbedBuilder::new().title("No VCs in this server").description("This bot can't find a VC to join because there aren't any in this server right now.").validate().unwrap().build()
-        },
         GetGuildAndVoiceChannelIdError::UserNotInVC => {
             EmbedBuilder::new().title("You're not in a VC").description("This bot can't follow you into VC if you aren't in one in this server.").validate().unwrap().build()
         },

src/command/leave.rs

@@ -37,9 +37,6 @@ pub enum GetGuildAndVoiceChannelIdError {
     /// there is no user who invoked this command
     NoUser,
 
-    /// there are no voice chats in this guild
-    NoVCsInGuild,
-
     /// the bot is not in a voice chat in this guild
     BotNotInVC,
 }
@@ -58,10 +55,10 @@ pub fn get_user_and_guild_and_voice_channel_id(
 
     let guild_id = interaction.guild_id.context(NotInGuildSnafu)?;
 
-    let guild_vcs = vcs.get(&guild_id).context(NoVCsInGuildSnafu)?;
+    let voice_channel_id = vcs
-
+        .with_guild(guild_id, |guild_vcs| {
-    let &voice_channel_id = guild_vcs
+            guild_vcs.get_left_for(&bot_user_id).copied()
-        .get_left_for(&bot_user_id)
+        })
         .context(BotNotInVCSnafu)?;
 
     Ok((user_id, guild_id, voice_channel_id))
@@ -75,9 +72,6 @@ fn get_guild_and_vc_error_to_embed(error: GetGuildAndVoiceChannelIdError) -> Emb
         GetGuildAndVoiceChannelIdError::NoUser => {
             EmbedBuilder::new().title("Not invoked by a user").description("This command works by joining the same VC as the user, but this bot didn't receive any user data. So did no user invoke it?! (This error should be impossible!)").validate().unwrap().build()
         },
-        GetGuildAndVoiceChannelIdError::NoVCsInGuild => {
-            EmbedBuilder::new().title("No VCs in this server").description("This bot can't leave VC because there aren't any in this server right now (therefore the bot must not be in any).").validate().unwrap().build()
-        },
         GetGuildAndVoiceChannelIdError::BotNotInVC => {
             EmbedBuilder::new().title("Not in a VC").description("This bot can't leave VC if it isn't in one in this server.").validate().unwrap().build()
         },

src/track_vcs.rs

@@ -2,6 +2,7 @@ use std::collections::BTreeMap;
 
 use dashmap::DashMap;
 use futures::{StreamExt, stream::FuturesUnordered};
+use tokio::sync::watch;
 use twilight_model::{
     gateway::payload::incoming::VoiceStateUpdate,
     id::{
@@ -16,7 +17,37 @@ pub type GuildVoiceChannelToTextChannel =
     BTreeMap<Id<GuildMarker>, OneToOneBTreeMap<Id<ChannelMarker>, Id<ChannelMarker>>>;
 
 type VCsInGuild = OneToManyUniqueBTreeMapWithData<Id<ChannelMarker>, Id<UserMarker>, UserInVCData>;
-pub type VCs = DashMap<Id<GuildMarker>, VCsInGuild>;
+
+#[derive(Debug, Default)]
+pub struct VCs(DashMap<Id<GuildMarker>, watch::Sender<VCsInGuild>>);
+
+impl Extend<(Id<GuildMarker>, VCsInGuild)> for VCs {
+    fn extend<T: IntoIterator<Item = (Id<GuildMarker>, VCsInGuild)>>(&mut self, iter: T) {
+        for (id, guild_vcs) in iter {
+            self.0.insert(id, watch::Sender::new(guild_vcs));
+        }
+    }
+}
+
+impl VCs {
+    pub fn with_guild<R>(&self, id: Id<GuildMarker>, f: impl FnOnce(&VCsInGuild) -> R) -> R {
+        f(&*self.0.entry(id).or_default().borrow())
+    }
+
+    pub fn update_guild<R>(&self, id: Id<GuildMarker>, f: impl FnOnce(&mut VCsInGuild) -> R) -> R {
+        let mut ret_opt = None;
+        self.0.entry(id).or_default().send_modify(|guild_vcs| {
+            let ret = f(guild_vcs);
+            _ = ret_opt.insert(ret);
+        });
+        let ret = ret_opt.unwrap();
+        ret
+    }
+
+    pub fn subscribe_to_guild<R>(&self, id: Id<GuildMarker>) -> watch::Receiver<VCsInGuild> {
+        self.0.entry(id).or_default().subscribe()
+    }
+}
 
 #[tracing::instrument(skip(discord_client), ret)]
 async fn initialize_user_in_vc(
@@ -107,9 +138,9 @@ pub fn update_vcs(voice_state_update: &VoiceStateUpdate, vcs: &VCs) {
                     .build();
                 let user_in_vc_data = voice_status.into();
 
-                vcs.entry(guild_id)
+                vcs.update_guild(guild_id, |guild_vcs| {
-                    .or_default()
+                    guild_vcs.insert(channel_id, user_id, user_in_vc_data)
-                    .insert(channel_id, user_id, user_in_vc_data);
+                });
 
                 tracing::info!(
                     ?guild_id,
@@ -120,9 +151,7 @@ pub fn update_vcs(voice_state_update: &VoiceStateUpdate, vcs: &VCs) {
             }
 
             None => {
-                if let Some(mut channel_vcers) = vcs.get_mut(&guild_id) {
+                vcs.update_guild(guild_id, |guild_vcs| guild_vcs.remove_right(&user_id));
-                    channel_vcers.remove_right(&user_id);
-                }
 
                 tracing::info!(?guild_id, ?user_id, "disconnected");
             }