1 files changed, 78 insertions, 0 deletions
diff --git a/src/client/timer.rs b/src/client/timer.rs
new file mode 100644
index 00000000..bd5c249a
--- /dev/null
+++ b/src/client/timer.rs
@@ -0,0 +1,78 @@
+use std::time::{Duration, Instant};
+
+pub(super) struct ClientLoopTimer {
+    deadline: Option<Instant>,
+}
+
+impl ClientLoopTimer {
+    pub(super) fn new() -> Self {
+        Self { deadline: None }
+    }
+
+    pub(super) fn deadline(&mut self, now: Instant, delay: Duration) -> Instant {
+        let requested = now.checked_add(delay).unwrap_or(now);
+        let deadline = self
+            .deadline
+            .map_or(requested, |current| current.min(requested));
+        self.deadline = Some(deadline);
+        deadline
+    }
+
+    pub(super) fn fired(&mut self) {
+        self.deadline = None;
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn incoming_events_do_not_postpone_timer_deadline() {
+        let start = Instant::now();
+        let delay = Duration::from_millis(100);
+        let mut timer = ClientLoopTimer::new();
+
+        let first_deadline = timer.deadline(start, delay);
+        assert_eq!(
+            timer.deadline(start + Duration::from_millis(25), delay),
+            first_deadline
+        );
+        assert_eq!(
+            timer.deadline(start + Duration::from_millis(50), delay),
+            first_deadline
+        );
+        assert_eq!(
+            timer.deadline(start + Duration::from_millis(75), delay),
+            first_deadline
+        );
+
+        timer.fired();
+        assert_eq!(
+            timer.deadline(first_deadline, delay),
+            first_deadline + delay
+        );
+    }
+
+    #[test]
+    fn earlier_client_work_can_pull_the_timer_deadline_forward() {
+        let start = Instant::now();
+        let mut timer = ClientLoopTimer::new();
+
+        assert_eq!(
+            timer.deadline(start, Duration::from_millis(100)),
+            start + Duration::from_millis(100)
+        );
+        assert_eq!(
+            timer.deadline(start + Duration::from_millis(20), Duration::from_millis(10)),
+            start + Duration::from_millis(30)
+        );
+        assert_eq!(
+            timer.deadline(
+                start + Duration::from_millis(25),
+                Duration::from_millis(100)
+            ),
+            start + Duration::from_millis(30)
+        );
+    }
+}