feat: caching

src/dwd.rs

@@ -1,10 +1,15 @@
-use std::collections::{BTreeMap, HashMap};
+use std::{
+    collections::{BTreeMap, HashMap},
+    time::Instant,
+};
 
 use reqwest::Url;
 use serde::Deserialize;
 
 #[derive(Default)]
-pub struct DwdCache {}
+pub struct DwdCache {
+    dwd_responses: HashMap<Vec<String>, (Instant, Result<Forecast, String>)>,
+}
 
 pub type Forecast = HashMap<String, ForecastDatas>;
 #[derive(Deserialize)]
@@ -168,7 +173,40 @@ impl ForecastData {
     }
 }
 
-pub async fn forecast(ids: &[&str], cache: &mut DwdCache) -> Result<Forecast, String> {
+pub async fn forecast<'a>(
+    ids: Vec<String>,
+    cache: &'a mut DwdCache,
+) -> Result<&'a Forecast, &'a String> {
+    let now = Instant::now();
+    let v = if let Some((time, cached)) = cache.dwd_responses.get(&ids) {
+        let age = now.saturating_duration_since(*time).as_secs();
+        if age < if cached.is_ok() { 600 } else { 90 } {
+            // cache is fresh, don't remove it,
+            // don't fetch new data.
+            // or_insert_with will not run.
+            None
+        } else {
+            // cache is outdated, remove it,
+            // and fetch new data.
+            // or_insert_with will run.
+            cache.dwd_responses.remove(&ids);
+            Some(forecast_impl(&ids).await)
+        }
+    } else {
+        // there is no cache,
+        // fetch new data.
+        // or_insert_with will run.
+        Some(forecast_impl(&ids).await)
+    };
+    cache
+        .dwd_responses
+        .entry(ids)
+        // closure will run exactly when `v` is `Some`
+        .or_insert_with(|| (now, v.unwrap()))
+        .1
+        .as_ref()
+}
+async fn forecast_impl(ids: &[String]) -> Result<Forecast, String> {
     dbg!(ids);
     let mut url =
         Url::parse("https://app-prod-ws.warnwetter.de/v30/stationOverviewExtended").unwrap();

src/main.rs

@@ -196,13 +196,13 @@ async fn weather_overview(q: &str, data: &State, accept: &Accept) -> Page {
                 let q = q.to_lowercase();
                 dwd_stations
                     .range((q.clone(), 0)..=(q, usize::MAX))
-                    .map(|(_, station)| station.station.as_str())
+                    .map(|(_, station)| station.station.clone())
                     .take(WEATHER_MAX_STATIONS)
                     .collect()
             }
             LocationString::Station(q) => q
                 .iter()
-                .map(|s| s.as_str())
+                .map(|s| s.clone())
                 .take(WEATHER_MAX_STATIONS)
                 .collect(),
             LocationString::Coords(lat, lon) => vec![
@@ -211,7 +211,7 @@ async fn weather_overview(q: &str, data: &State, accept: &Accept) -> Page {
                     .min_by(|a, b| dist2(a, *lat, *lon).total_cmp(&dist2(b, *lat, *lon)))
                     .unwrap()
                     .station
-                    .as_str(),
+                    .clone(),
             ],
         };
         if stations.is_empty() {
@@ -220,7 +220,7 @@ async fn weather_overview(q: &str, data: &State, accept: &Accept) -> Page {
                 "could not find any such station".to_owned(),
             )));
         }
-        match crate::dwd::forecast(&stations, dwd_cache).await {
+        match crate::dwd::forecast(stations, dwd_cache).await {
             Ok(forecast) => {
                 fn forecasts(
                     forecast: &HashMap<String, ForecastDatas>,