Use download counts in search index and sort control.

app/lib/fake/backend/fake_popularity.dart

@@ -10,6 +10,8 @@ import '../../shared/popularity_storage.dart';
 
 /// Scans the datastore for packages and generates popularity values with a
 /// deterministic random seed.
+///
+/// TODO: generate similar values for download counts.
 Future<void> generateFakePopularityValues() async {
   final values = <String, double>{};
   final query = dbService.query<Package>();

app/lib/frontend/templates/_consts.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:_pub_shared/search/tags.dart';
+import 'package:pub_dev/frontend/request_context.dart';
 
 import '../dom/dom.dart' as d;
 
@@ -124,5 +125,10 @@ List<SortDict> getSortDicts(bool isSearch) {
   final removeId = isSearch ? 'listing_relevance' : 'search_relevance';
   return <SortDict>[
     ..._sortDicts.where((d) => d.id != removeId),
+    if (requestContext.experimentalFlags.showDownloadCounts)
+      SortDict(
+          id: 'downloads',
+          label: 'downloads',
+          tooltip: 'Packages are sorted by their download counts.'),
   ];
 }

app/lib/search/backend.dart

@@ -22,6 +22,7 @@ import 'package:pool/pool.dart';
 import 'package:pub_dev/publisher/backend.dart';
 
 import 'package:pub_dev/search/search_client.dart';
+import 'package:pub_dev/service/download_counts/backend.dart';
 import 'package:pub_dev/shared/popularity_storage.dart';
 import 'package:pub_dev/shared/redis_cache.dart';
 import 'package:pub_dev/shared/utils.dart';
@@ -356,6 +357,7 @@ class SearchBackend {
       created: p.created!,
       updated: p.lastVersionPublished!,
       readme: compactReadme(readmeAsset?.textContent),
+      downloadCount: downloadCountsBackend.lookup30DaysTotalCounts(pv.package),
       likeCount: p.likes,
       popularityScore: popularityStorage.lookup(packageName),
       grantedPoints: scoreCard.grantedPubPoints,

app/lib/search/mem_index.dart

@@ -33,6 +33,7 @@ class InMemoryPackageIndex {
   late final List<PackageHit> _createdOrderedHits;
   late final List<PackageHit> _updatedOrderedHits;
   late final List<PackageHit> _popularityOrderedHits;
+  late final List<PackageHit> _downloadsOrderedHits;
   late final List<PackageHit> _likesOrderedHits;
   late final List<PackageHit> _pointsOrderedHits;
 
@@ -81,6 +82,8 @@ class InMemoryPackageIndex {
     _updatedOrderedHits = _rankWithComparator(_compareUpdated);
     _popularityOrderedHits = _rankWithComparator(_comparePopularity,
         score: (doc) => doc.popularityScore ?? 0);
+    _downloadsOrderedHits = _rankWithComparator(_compareDownloads,
+        score: (doc) => doc.downloadCount.toDouble());
     _likesOrderedHits = _rankWithComparator(_compareLikes,
         score: (doc) => doc.likeCount.toDouble());
     _pointsOrderedHits = _rankWithComparator(_comparePoints,
@@ -195,6 +198,9 @@ class InMemoryPackageIndex {
       case SearchOrder.popularity:
         packageHits = _popularityOrderedHits.whereInSet(packages);
         break;
+      case SearchOrder.downloads:
+        packageHits = _downloadsOrderedHits.whereInSet(packages);
+        break;
       case SearchOrder.like:
         packageHits = _likesOrderedHits.whereInSet(packages);
         break;
@@ -414,6 +420,12 @@ class InMemoryPackageIndex {
     return _compareUpdated(a, b);
   }
 
+  int _compareDownloads(PackageDocument a, PackageDocument b) {
+    final x = -a.downloadCount.compareTo(b.downloadCount);
+    if (x != 0) return x;
+    return _compareUpdated(a, b);
+  }
+
   int _compareLikes(PackageDocument a, PackageDocument b) {
     final x = -a.likeCount.compareTo(b.likeCount);
     if (x != 0) return x;

app/lib/search/search_service.dart

@@ -73,6 +73,7 @@ class PackageDocument {
 
   final List<String> tags;
 
+  final int downloadCount;
   final int likeCount;
 
   /// The normalized score between [0.0-1.0] (1.0 being the most liked package).
@@ -105,6 +106,7 @@ class PackageDocument {
     DateTime? updated,
     this.readme = '',
     List<String>? tags,
+    int? downloadCount,
     int? likeCount,
     this.likeScore,
     this.popularityScore,
@@ -116,6 +118,7 @@ class PackageDocument {
     this.sourceUpdated,
   })  : created = created ?? clock.now(),
         updated = updated ?? clock.now(),
+        downloadCount = downloadCount ?? 0,
         likeCount = likeCount ?? 0,
         grantedPoints = grantedPoints ?? 0,
         maxPoints = maxPoints ?? 0,

pkg/_pub_shared/lib/search/search_form.dart

@@ -52,6 +52,9 @@ enum SearchOrder {
   /// Search order should be in decreasing popularity score.
   popularity,
 
+  /// Search order should be in decreasing download counts.
+  downloads,
+
   /// Search order should be in decreasing like count.
   like,