Truncate cache if max_messages is set to a lower value at runtime

src/cache/mod.rs

@@ -644,6 +644,27 @@ impl Cache {
     ///
     /// By default, no messages will be cached.
     pub fn set_max_messages(&self, max: usize) {
+        let current_max_messages = self.settings.read().max_messages;
+
+        // Check if the cache needs to be truncated
+        if max < current_max_messages {
+            let difference = current_max_messages - max;
+
+            // Iterate over the queues that each correspond to a channel
+            for mut channel_queue in self.message_queue.iter_mut() {
+                let channel_id = *channel_queue.key();
+
+                for _ in 0..difference {
+                    // Get the message ID from the front of the queue and
+                    // remove it from the corresponding channel's message map
+                    if let Some(message_id) = channel_queue.value_mut().pop_front() {
+                        if let Some(mut channel_messages) = self.messages.get_mut(&channel_id) {
+                            channel_messages.remove(&message_id);
+                        }
+                    }
+                }
+            }
+        }
         self.settings.write().max_messages = max;
     }