minor refactoring

backend/src/messenger/cache.rs

@@ -0,0 +1,87 @@
+use redis::AsyncCommands;
+use rocket_db_pools::Connection;
+
+use crate::{
+    db::{Postgres, Redis},
+    messenger::ChatMsg,
+};
+
+// Helper function to cache message in Redis
+pub async fn insert(
+    cache: &mut Connection<Redis>,
+    channel_id: i32,
+    msg: &super::ChatMsg,
+) -> Result<(), redis::RedisError> {
+    let key = format!("messages:{}", channel_id);
+    let msg_json = serde_json::to_string(msg).unwrap();
+
+    redis::pipe()
+        .atomic()
+        .lpush(&key, &msg_json)
+        .ltrim(&key, 0, 99)
+        .expire(&key, 86400) // 24h expiry
+        .query_async(&mut ***cache)
+        .await
+}
+
+// Helper function to get cached messages from Redis
+pub async fn get(
+    redis: &mut Connection<Redis>,
+    channel_id: i32,
+) -> Result<Vec<super::ChatMsg>, redis::RedisError> {
+    let key = format!("messages:{}", channel_id);
+
+    // query last 100 messages
+    let messages: Vec<ChatMsg> = redis
+        .lrange::<_, Vec<String>>(&key, 0, 99)
+        .await?
+        .into_iter()
+        .rev() // Reverse because LPUSH adds to front, so newest is first
+        .filter_map(|msg_str| serde_json::from_str(&msg_str).ok())
+        .collect();
+
+    Ok(messages)
+}
+
+// Helper function to initialize cache from Postgres if empty
+pub async fn initialise(
+    cache: &mut Connection<Redis>,
+    db: &mut Connection<Postgres>,
+    channel_id: i32,
+) -> Result<(), Box<dyn std::error::Error>> {
+    let key = format!("messages:{}", channel_id);
+
+    let length: usize = cache.llen(&key).await?;
+    if length < 100 {
+        // Fetch from Postgres
+        let messages = sqlx::query!(
+            "SELECT u.username, u.display_name, u.id, m.content, m.created_at
+             FROM messages m
+             JOIN users u ON m.user_id = u.id
+             WHERE m.channel_id = $1
+             ORDER BY m.created_at DESC
+             LIMIT 100",
+            channel_id
+        )
+        .fetch_all(&mut ***db)
+        .await?;
+
+        // Populate cache (in reverse order so oldest is at the end)
+        for msg in messages.into_iter().rev() {
+            let chat_msg = ChatMsg {
+                display_name: Some(msg.display_name.unwrap_or(msg.username)),
+                user_id: msg.id as usize,
+                text: msg.content,
+                timestamp: (msg.created_at.unwrap().unix_timestamp_nanos() / 1_000_000) as usize,
+            };
+
+            let msg_json = serde_json::to_string(&chat_msg)?;
+
+            cache.lpush::<_, _, ()>(&key, &msg_json).await?;
+        }
+
+        cache.expire::<_, ()>(&key, 86400).await?;
+    }
+
+    Ok(())
+}