Port over the sleep command from nushell (#371)

* Port over the sleep command from nushell

* Fix clippy warning

* Remove unused variable

crates/nu-command/src/default_context.rs

@@ -116,6 +116,7 @@ pub fn create_default_context() -> EngineState {
             Select,
             Shuffle,
             Size,
+            Sleep,
             Source,
             Split,
             SplitChars,

crates/nu-command/src/platform/mod.rs

@@ -1,3 +1,5 @@
 mod clear;
+mod sleep;
 
 pub use clear::Clear;
+pub use sleep::Sleep;

crates/nu-command/src/platform/sleep.rs

@@ -0,0 +1,108 @@
+use nu_engine::CallExt;
+use nu_protocol::ast::Call;
+use nu_protocol::engine::{Command, EngineState, Stack};
+use nu_protocol::{
+    Category, Example, IntoPipelineData, PipelineData, ShellError, Signature, SyntaxShape, Value,
+};
+use std::{
+    sync::atomic::Ordering,
+    thread,
+    time::{Duration, Instant},
+};
+
+const CTRL_C_CHECK_INTERVAL: Duration = Duration::from_millis(100);
+
+#[derive(Clone)]
+pub struct Sleep;
+
+impl Command for Sleep {
+    fn name(&self) -> &str {
+        "sleep"
+    }
+
+    fn usage(&self) -> &str {
+        "Delay for a specified amount of time."
+    }
+
+    fn signature(&self) -> Signature {
+        Signature::build("sleep")
+            .required("duration", SyntaxShape::Duration, "time to sleep")
+            .rest("rest", SyntaxShape::Duration, "additional time")
+            .category(Category::Platform)
+    }
+
+    fn run(
+        &self,
+        engine_state: &EngineState,
+        stack: &mut Stack,
+        call: &Call,
+        _input: PipelineData,
+    ) -> Result<PipelineData, ShellError> {
+        fn duration_from_i64(val: i64) -> Duration {
+            Duration::from_nanos(if val < 0 { 0 } else { val as u64 })
+        }
+
+        let duration: i64 = call.req(engine_state, stack, 0)?;
+        let rest: Vec<i64> = call.rest(engine_state, stack, 1)?;
+
+        let total_dur =
+            duration_from_i64(duration) + rest.into_iter().map(duration_from_i64).sum::<Duration>();
+
+        let ctrlc_ref = &engine_state.ctrlc.clone();
+        let start = Instant::now();
+        loop {
+            thread::sleep(CTRL_C_CHECK_INTERVAL);
+            if start.elapsed() >= total_dur {
+                break;
+            }
+
+            if let Some(ctrlc) = ctrlc_ref {
+                if ctrlc.load(Ordering::SeqCst) {
+                    break;
+                }
+            }
+        }
+
+        Ok(Value::Nothing { span: call.head }.into_pipeline_data())
+    }
+
+    fn examples(&self) -> Vec<Example> {
+        vec![
+            Example {
+                description: "Sleep for 1sec",
+                example: "sleep 1sec",
+                result: None,
+            },
+            Example {
+                description: "Sleep for 3sec",
+                example: "sleep 1sec 1sec 1sec",
+                result: None,
+            },
+            Example {
+                description: "Send output after 1sec",
+                example: "sleep 1sec; echo done",
+                result: Some(Value::test_string("done")),
+            },
+        ]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Sleep;
+
+    #[test]
+    fn examples_work_as_expected() {
+        use crate::test_examples;
+        use std::time::Instant;
+
+        let start = Instant::now();
+        test_examples(Sleep {});
+
+        let elapsed = start.elapsed();
+
+        // only examples with actual output are run
+        assert!(elapsed >= std::time::Duration::from_secs(1));
+        assert!(elapsed < std::time::Duration::from_secs(2));
+    }
+}