Added Rust debounce solution (#112)

Author: jxs

problems/debounce/debounce.rs

@@ -0,0 +1,120 @@
+use std::time::{Duration, Instant};
+
+fn debounce<F: FnMut()>(mut f: F, timeout: u64, pass: bool) -> impl FnMut() {
+  let dur = Duration::from_millis(timeout);
+  let mut active: Option<Instant> = None;
+  move || {
+    match active {
+      Some(inst) if (inst.elapsed() <= dur) && !pass => {
+        active = Some(Instant::now());
+      }
+      Some(_) | None => {
+        f();
+        active = Some(Instant::now());
+      }
+    }
+  }
+}
+
+fn main() {
+  let mut debounced = debounce(|| {println!("debounce!");}, 5, false);
+  debounced();
+}
+
+
+mod tests {
+  use super::debounce;
+  use std::time::Duration;
+  use std::thread::sleep;
+
+  #[test]
+  fn function_is_called_first_time() {
+    let mut start = 0;
+    {
+      let mut debounced = debounce(|| {
+      start += 1;
+      }, 10, false);
+      debounced();
+    }
+    assert_eq!(1, start);
+  }
+
+  #[test]
+  fn function_is_not_called_if_timeout_hasnt_elapsed() {
+    let mut start = 0;
+    {
+      let mut debounced = debounce(|| {
+      start += 1;
+      }, 100, false);
+      debounced();
+      debounced();
+    }
+    assert_eq!(1, start);
+  }
+
+  #[test]
+  fn function_iscalled_after_timeout_has_elapsed() {
+    let mut start = 0;
+    let dur = 100;
+    {
+      let mut debounced = debounce(|| {
+      start += 1;
+      }, dur, false);
+      debounced();
+      sleep(Duration::from_millis(dur));
+      debounced();
+    }
+    assert_eq!(2, start);
+  }
+
+  #[test]
+  fn timeout_is_restarted_if_function_is_called_before_timeout_has_elapsed() {
+    let mut start = 0;
+    let dur = 100;
+    {
+      let mut debounced = debounce(|| {
+      start += 1;
+      }, dur, false);
+      debounced();
+      sleep(Duration::from_millis(dur - 20));
+      debounced();
+      sleep(Duration::from_millis(20));
+      debounced();
+    }
+    assert_eq!(1, start);
+  }
+
+  #[test]
+  fn function_is_called_after_timeout_is_restarted() {
+    let mut start = 0;
+    let dur = 100;
+    {
+      let mut debounced = debounce(|| {
+      start += 1;
+      }, dur, false);
+      debounced();
+      sleep(Duration::from_millis(dur - 20));
+      debounced();
+      sleep(Duration::from_millis(20));
+      debounced();
+      sleep(Duration::from_millis(dur));
+      debounced();
+    }
+    assert_eq!(2, start);
+  }
+
+  #[test]
+  fn function_is_called_is_pass() {
+    let mut start = 0;
+    let dur = 100;
+    {
+      let mut debounced = debounce(|| {
+      start += 1;
+      }, dur, true);
+      debounced();
+      debounced();
+      debounced();
+    }
+    assert_eq!(3, start);
+  }
+}