Update cache when UUID changes

If the UUID of the mounted filesystem is different than the cached UUID
for that filesystem, the cache needs to be updated with the new value.
Otherwise, the program will continually emit warnings once the cached
entry expires, regardless of whether or not the filesystem has changed
in that time.

src/cache.rs

@@ -23,6 +23,10 @@ impl CacheEntry {
         let now = chrono::Utc::now();
         now > self.changed + ttl
     }
+
+    pub fn uuid(&self) -> &String {
+        return &self.uuid;
+    }
 }
 
 #[derive(Serialize, Deserialize, Debug)]

src/main.rs

@@ -93,7 +93,12 @@ fn check_and_notify(
     match cache {
         Ok(mut cache) => {
             if let Some(entry) = cache.get(&mountpoint) {
-                if entry.expired(ttl) {
+                if entry.uuid() != uuid {
+                    cache.update(&mountpoint, &uuid);
+                    if let Err(e) = cache.save(&cache_path) {
+                        eprintln!("Failed to save cache: {}", e);
+                    }
+                } else if entry.expired(ttl) {
                     notify(mountpoint, uuid, entry.changed(), mailto);
                 }
             } else {