add project files

src/watch.rs

@@ -0,0 +1,46 @@
+use async_std::fs;
+use async_std::io;
+use async_std::stream;
+use async_std::stream::Stream;
+use async_std::task;
+use std::path::PathBuf;
+use std::time::{Duration, SystemTime};
+
+pub struct Watch {
+    path: PathBuf,
+    interval: u64,
+}
+
+impl Watch {
+    pub fn new(path: PathBuf, interval: u64) -> Watch {
+        Watch { interval, path }
+    }
+
+    async fn modified(&self) -> io::Result<SystemTime> {
+        let file = fs::File::open(&self.path).await?;
+        let modified = file.metadata().await?.modified()?;
+        Ok(modified)
+    }
+
+    pub async fn change(&mut self, func: fn(path: &PathBuf)) {
+        let mut repeat = stream::repeat(0);
+        let mut before = match self.modified().await {
+            Ok(time) => Some(time),
+            Err(_) => None,
+        };
+
+        while let Some(_) = repeat.next().await {
+            task::sleep(Duration::from_millis(self.interval)).await;
+
+            let after = match self.modified().await {
+                Ok(time) => Some(time),
+                Err(_) => None,
+            };
+
+            if before != after {
+                before = after;
+                func(&self.path);
+            }
+        }
+    }
+}