only update last_seen every 12 hours

src/users.rs

@@ -1,4 +1,7 @@
-use std::fmt::Display;
+use std::{
+    fmt::Display,
+    time::{SystemTime, UNIX_EPOCH},
+};
 
 use axum::{extract::State, http::Request, middleware::Next, response::IntoResponse};
 use axum_login::{secrecy::SecretVec, AuthUser};
@@ -78,7 +81,18 @@ pub async fn handle_update_last_seen<BodyT>(
     next: Next<BodyT>,
 ) -> impl IntoResponse {
     if let Some(user) = auth.current_user {
-        user.update_last_seen(&pool).await;
+        if let Some(then) = user.last_seen {
+            let now = SystemTime::now()
+                .duration_since(UNIX_EPOCH)
+                .unwrap_or_default()
+                .as_secs() as i64;
+            // The Nyquist frequency for 1-day tracking resolution is 12 hours.
+            if now - then > 12 * 3600 {
+                user.update_last_seen(&pool).await;
+            }
+        } else {
+            user.update_last_seen(&pool).await;
+        }
     }
     next.run(request).await
 }