Fix download speed going negative on retry

frontend/src/lib/utils/progress.ts

@@ -16,19 +16,22 @@ export function progressStats(progress: Readable<utils.Progress | null>, options
   };
 
   const series = timeSeries(finalOptions.statsInterval);
-  
+
   const stats = writable({ speed: 0, eta: 0 as number | undefined });
   const lastStatsUpdate = { speed: 0, eta: 0 };
-  
+
   progress.subscribe(($progress) => {
     if (!$progress) {
       series.clear();
-    } else {    
+    } else {
+      if ((series.getLast() ?? -1) > $progress.current) {
+        series.clear();
+      }
       series.addValue($progress.current);
-  
+
       const speed = series.getDerivative() ?? 0;
       const eta = speed !== 0 ? ($progress.total - $progress.current) / speed : undefined;
-  
+
       if (Date.now() - lastStatsUpdate.speed > finalOptions.updateInterval.speed) {
         stats.set({ speed: speed, eta: get(stats).eta });
         lastStatsUpdate.speed = Date.now();

frontend/src/lib/utils/timeSeries.ts

@@ -2,6 +2,7 @@ export interface TimeSeries {
   addValue: (value: number) => void;
   getAverage: () => number;
   getDerivative: () => number | undefined;
+  getLast: () => number | undefined;
   clear: () => void;
 }
 
@@ -20,6 +21,9 @@ export function timeSeries(millisecondsLifetime: number): TimeSeries {
     getDerivative: () => {
       return (items[items.length - 1].value - items[0].value) / ((items[items.length - 1].timestamp - items[0].timestamp) / 1000); // per second
     },
+    getLast: () => {
+      return items.length > 0 ? items[items.length - 1]?.value : undefined;
+    },
     clear: () => {
       items.length = 0;
     },