Add trending statuses (#17431)

* Add trending statuses

* Fix dangling items with stale scores in localized sets

* Various fixes and improvements

- Change approve_all/reject_all to approve_accounts/reject_accounts
- Change Trends::Query methods to not mutate the original query
- Change Trends::Query#skip to offset
- Change follow recommendations to be refreshed in a transaction

* Add tests for trending statuses filtering behaviour

* Fix not applying filtering scope in controller

spec/models/trends/statuses_spec.rb

@@ -0,0 +1,110 @@
+require 'rails_helper'
+
+RSpec.describe Trends::Statuses do
+  subject! { described_class.new(threshold: 5, review_threshold: 10, score_halflife: 8.hours) }
+
+  let!(:at_time) { DateTime.new(2021, 11, 14, 10, 15, 0) }
+
+  describe 'Trends::Statuses::Query' do
+    let!(:query) { subject.query }
+    let!(:today) { at_time }
+
+    let!(:status1) { Fabricate(:status, text: 'Foo', trendable: true, created_at: today) }
+    let!(:status2) { Fabricate(:status, text: 'Bar', trendable: true, created_at: today) }
+
+    before do
+      15.times { reblog(status1, today) }
+      12.times { reblog(status2, today) }
+
+      subject.refresh(today)
+    end
+
+    describe '#filtered_for' do
+      let(:account) { Fabricate(:account) }
+
+      it 'returns a composable query scope' do
+        expect(query.filtered_for(account)).to be_a Trends::Query
+      end
+
+      it 'filters out blocked accounts' do
+        account.block!(status1.account)
+        expect(query.filtered_for(account).to_a).to eq [status2]
+      end
+
+      it 'filters out muted accounts' do
+        account.mute!(status2.account)
+        expect(query.filtered_for(account).to_a).to eq [status1]
+      end
+
+      it 'filters out blocked-by accounts' do
+        status1.account.block!(account)
+        expect(query.filtered_for(account).to_a).to eq [status2]
+      end
+    end
+  end
+
+  describe '#add' do
+    let(:status) { Fabricate(:status) }
+
+    before do
+      subject.add(status, 1, at_time)
+    end
+
+    it 'records use' do
+      expect(subject.send(:recently_used_ids, at_time)).to eq [status.id]
+    end
+  end
+
+  describe '#query' do
+    it 'returns a composable query scope' do
+      expect(subject.query).to be_a Trends::Query
+    end
+
+    it 'responds to filtered_for' do
+      expect(subject.query).to respond_to(:filtered_for)
+    end
+  end
+
+  describe '#refresh' do
+    let!(:today) { at_time }
+    let!(:yesterday) { today - 1.day }
+
+    let!(:status1) { Fabricate(:status, text: 'Foo', trendable: true, created_at: yesterday) }
+    let!(:status2) { Fabricate(:status, text: 'Bar', trendable: true, created_at: today) }
+    let!(:status3) { Fabricate(:status, text: 'Baz', trendable: true, created_at: today) }
+
+    before do
+      13.times { reblog(status1, today) }
+      13.times { reblog(status2, today) }
+       4.times { reblog(status3, today) }
+    end
+
+    context do
+      before do
+        subject.refresh(today)
+      end
+
+      it 'calculates and re-calculates scores' do
+        expect(subject.query.limit(10).to_a).to eq [status2, status1]
+      end
+
+      it 'omits statuses below threshold' do
+        expect(subject.query.limit(10).to_a).to_not include(status3)
+      end
+    end
+
+    it 'decays scores' do
+      subject.refresh(today)
+      original_score = subject.score(status2.id)
+      expect(original_score).to be_a Float
+      subject.refresh(today + subject.options[:score_halflife])
+      decayed_score = subject.score(status2.id)
+      expect(decayed_score).to be <= original_score / 2
+    end
+  end
+
+  def reblog(status, at_time)
+    reblog = Fabricate(:status, reblog: status, created_at: at_time)
+    subject.add(status, reblog.account_id, at_time)
+  end
+end