Add trending links (#16917)

* Add trending links

* Add overriding specific links trendability

* Add link type to preview cards and only trend articles

Change trends review notifications from being sent every 5 minutes to being sent every 2 hours

Change threshold from 5 unique accounts to 15 unique accounts

* Fix tests

1 files changed, 67 insertions, 0 deletions

diff --git a/spec/models/trends/tags_spec.rb b/spec/models/trends/tags_spec.rb
new file mode 100644
index 000000000..4f98c6aa4
--- /dev/null
+++ b/spec/models/trends/tags_spec.rb
@@ -0,0 +1,67 @@
+require 'rails_helper'
+
+RSpec.describe Trends::Tags do
+  subject { described_class.new(threshold: 5, review_threshold: 10) }
+
+  let!(:at_time) { DateTime.new(2021, 11, 14, 10, 15, 0) }
+
+  describe '#add' do
+    let(:tag) { Fabricate(:tag) }
+
+    before do
+      subject.add(tag, 1, at_time)
+    end
+
+    it 'records history' do
+      expect(tag.history.get(at_time).accounts).to eq 1
+    end
+
+    it 'records use' do
+      expect(subject.send(:recently_used_ids, at_time)).to eq [tag.id]
+    end
+  end
+
+  describe '#get' do
+    pending
+  end
+
+  describe '#refresh' do
+    let!(:today) { at_time }
+    let!(:yesterday) { today - 1.day }
+
+    let!(:tag1) { Fabricate(:tag, name: 'Catstodon', trendable: true) }
+    let!(:tag2) { Fabricate(:tag, name: 'DogsOfMastodon', trendable: true) }
+    let!(:tag3) { Fabricate(:tag, name: 'OCs', trendable: true) }
+
+    before do
+      2.times  { |i| subject.add(tag1, i, yesterday) }
+      13.times { |i| subject.add(tag3, i, yesterday) }
+      16.times { |i| subject.add(tag1, i, today) }
+      4.times  { |i| subject.add(tag2, i, today) }
+    end
+
+    context do
+      before do
+        subject.refresh(yesterday + 12.hours)
+        subject.refresh(at_time)
+      end
+
+      it 'calculates and re-calculates scores' do
+        expect(subject.get(false, 10)).to eq [tag1, tag3]
+      end
+
+      it 'omits hashtags below threshold' do
+        expect(subject.get(false, 10)).to_not include(tag2)
+      end
+    end
+
+    it 'decays scores' do
+      subject.refresh(yesterday + 12.hours)
+      original_score = subject.score(tag3.id)
+      expect(original_score).to eq 144.0
+      subject.refresh(yesterday + 12.hours + subject.options[:max_score_halflife])
+      decayed_score = subject.score(tag3.id)
+      expect(decayed_score).to be <= original_score / 2
+    end
+  end
+end