use a guild member list for the member cache if possible

youmubot-prelude/src/member_cache.rs

@@ -5,13 +5,40 @@ use serenity::model::{
     id::{GuildId, UserId},
 };
 use serenity::{http::CacheHttp, prelude::*};
+use std::collections::HashMap as Map;
 use std::sync::Arc;
 
+use crate::OkPrint;
+
 const VALID_CACHE_SECONDS: i64 = 15 * 60; // 15 minutes
 
 /// MemberCache resolves `does User belong to Guild` requests, and store them in a cache.
 #[derive(Debug, Default)]
-pub struct MemberCache(DashMap<(UserId, GuildId), (Option<Member>, DateTime<Utc>)>);
+pub struct MemberCache {
+    per_user: DashMap<(UserId, GuildId), Expiring<Option<Member>>>,
+    per_guild: DashMap<GuildId, Expiring<Map<UserId, Member>>>,
+    guild_counts: DashMap<GuildId, Option<u64>>,
+}
+
+#[derive(Debug)]
+struct Expiring<T> {
+    pub value: T,
+    pub timeout: DateTime<Utc>,
+}
+
+impl<T> Expiring<T> {
+    fn new(value: T, timeout: DateTime<Utc>) -> Self {
+        Self { value, timeout }
+    }
+}
+
+impl<T> std::ops::Deref for Expiring<T> {
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        &self.value
+    }
+}
 
 impl TypeMapKey for MemberCache {
     type Value = Arc<MemberCache>;
@@ -23,19 +50,75 @@ impl MemberCache {
         cache_http: impl CacheHttp,
         user_id: UserId,
         guild_id: GuildId,
+    ) -> Option<Member> {
+        let members_count = match self.guild_counts.get(&guild_id) {
+            Some(v) => v.clone(),
+            None => {
+                let res = guild_id
+                    .to_partial_guild_with_counts(cache_http.http())
+                    .await
+                    .ok()
+                    .and_then(|v| v.approximate_member_count);
+                self.guild_counts.insert(guild_id, res);
+                res
+            }
+        };
+        match members_count {
+            Some(g) if g <= 1000 => self.query_per_guild(cache_http, user_id, guild_id).await,
+            _ => self.query_per_user(cache_http, user_id, guild_id).await,
+        }
+    }
+
+    async fn query_per_guild(
+        &self,
+        cache_http: impl CacheHttp,
+        user_id: UserId,
+        guild_id: GuildId,
     ) -> Option<Member> {
         let now = Utc::now();
         // Check cache
-        if let Some(r) = self.0.get(&(user_id, guild_id)) {
-            if r.1 > now {
-                return r.0.clone();
+        if let Some(r) = self.per_guild.get(&guild_id) {
+            if r.timeout > now {
+                return r.get(&user_id).cloned();
+            }
+        }
+        // query
+        let members = guild_id
+            .members(cache_http.http(), None, None)
+            .await
+            .pls_ok()?
+            .into_iter()
+            .map(|m| (m.user.id, m))
+            .collect::<Map<_, _>>();
+        let result = members.get(&user_id).cloned();
+        self.per_guild.insert(
+            guild_id,
+            Expiring::new(
+                members,
+                now + chrono::Duration::seconds(VALID_CACHE_SECONDS),
+            ),
+        );
+        result
+    }
+
+    async fn query_per_user(
+        &self,
+        cache_http: impl CacheHttp,
+        user_id: UserId,
+        guild_id: GuildId,
+    ) -> Option<Member> {
+        let now = Utc::now();
+        // Check cache
+        if let Some(r) = self.per_user.get(&(user_id, guild_id)) {
+            if r.timeout > now {
+                return r.clone();
             }
         }
         // Query
         let t = guild_id.member(&cache_http, user_id).await.ok();
-        self.0.insert(
+        self.per_user.insert(
             (user_id, guild_id),
-            (
+            Expiring::new(
                 t.clone(),
                 now + chrono::Duration::seconds(VALID_CACHE_SECONDS),
             ),