inital commit, which is clearly not initial

Signed-off-by: Uncle Stretch <uncle.stretch@ghostchain.io>

metrics/src/metronome.rs

@@ -0,0 +1,51 @@
+use futures::prelude::*;
+use futures_timer::Delay;
+use std::{
+    pin::Pin,
+    task::{Context, Poll},
+    time::Duration,
+};
+
+#[derive(Copy, Clone)]
+enum MetronomeState {
+    Snooze,
+    SetAlarm,
+}
+
+pub struct Metronome {
+    delay: Delay,
+    period: Duration,
+    state: MetronomeState,
+}
+
+impl Metronome {
+    /// Create a new metronome source with a defined cycle duration.
+    pub fn new(cycle: Duration) -> Self {
+        let period = cycle.into();
+        Self { period, delay: Delay::new(period), state: MetronomeState::Snooze }
+    }
+}
+
+impl futures::Stream for Metronome {
+    type Item = ();
+
+    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        loop {
+            match self.state {
+                MetronomeState::SetAlarm => {
+                    let val = self.period;
+                    self.delay.reset(val);
+                    self.state = MetronomeState::Snooze;
+                },
+                MetronomeState::Snooze => {
+                    if !Pin::new(&mut self.delay).poll(cx).is_ready() {
+                        break
+                    }
+                    self.state = MetronomeState::SetAlarm;
+                    return Poll::Ready(Some(()))
+                },
+            }
+        }
+        Poll::Pending
+    }
+}