Normalize trend by overall average

Author: szakarias

app/lib/service/download_counts/package_trends.dart

@@ -5,6 +5,7 @@
 import 'dart:math';
 
 const analysisWindowDays = 30;
+const totalTrendWindowDays = 330;
 const minThirtyDaysDownloadThreshold = 30000;
 
 /// Calculates the relative daily growth rate of a package's downloads.
@@ -38,7 +39,12 @@ double computeRelativeGrowthRate(List<int> totalDownloads) {
       recentDownloads.reduce((prev, element) => prev + element) /
           recentDownloads.length;
 
-  if (averageRecentDownloads == 0) {
+  final m = min(totalDownloads.length, totalTrendWindowDays);
+  final averageTotalDownloads =
+      totalDownloads.sublist(0, m).reduce((prev, element) => prev + element) /
+          m;
+
+  if (averageRecentDownloads == 0 || averageTotalDownloads == 0) {
     return 0;
   }
 
@@ -51,7 +57,7 @@ double computeRelativeGrowthRate(List<int> totalDownloads) {
   // Normalize slope by average downloads to represent relative growth.
   // This measures how much the download count is growing relative to its
   // current volume.
-  return growthRate / averageRecentDownloads;
+  return growthRate / averageTotalDownloads;
 }
 
 /// Computes the slope of the best-fit line for a given list of data points

app/test/service/download_counts/computations_test.dart

@@ -314,10 +314,16 @@ void main() {
                 'fake_download_counts_data_for_trend2.jsonl'));
         await processDownloadCounts(d);
       }
-      final neonTrend = computeTrendScore(
-          [...List.filled(15, 2000), ...List.filled(15, 1000)]);
-      final oxygenTrend = computeTrendScore(
-          [...List.filled(15, 5000), ...List.filled(15, 3000)]);
+      final neonTrend = computeTrendScore([
+        ...List.filled(15, 2000),
+        ...List.filled(15, 1000),
+        ...List.filled(701, -1)
+      ]);
+      final oxygenTrend = computeTrendScore([
+        ...List.filled(15, 5000),
+        ...List.filled(15, 3000),
+        ...List.filled(701, -1)
+      ]);
 
       expect(await computeTrend(),
           {'flutter_titanium': 0.0, 'neon': neonTrend, 'oxygen': oxygenTrend});