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

app/models/trends/query.rb

@@ -0,0 +1,106 @@
+# frozen_string_literal: true
+
+class Trends::Query
+  include Redisable
+  include Enumerable
+
+  attr_reader :prefix, :klass, :loaded
+
+  alias loaded? loaded
+
+  def initialize(prefix, klass)
+    @prefix  = prefix
+    @klass   = klass
+    @records = []
+    @loaded  = false
+    @allowed = false
+    @limit   = -1
+    @offset  = 0
+  end
+
+  def allowed!
+    @allowed = true
+    self
+  end
+
+  def allowed
+    clone.allowed!
+  end
+
+  def in_locale!(value)
+    @locale = value
+    self
+  end
+
+  def in_locale(value)
+    clone.in_locale!(value)
+  end
+
+  def offset!(value)
+    @offset = value
+    self
+  end
+
+  def offset(value)
+    clone.offset!(value)
+  end
+
+  def limit!(value)
+    @limit = value
+    self
+  end
+
+  def limit(value)
+    clone.limit!(value)
+  end
+
+  def records
+    load
+    @records
+  end
+
+  delegate :each, :empty?, :first, :last, to: :records
+
+  def to_ary
+    records.dup
+  end
+
+  alias to_a to_ary
+
+  def to_arel
+    tmp_ids = ids
+
+    if tmp_ids.empty?
+      klass.none
+    else
+      klass.joins("join unnest(array[#{tmp_ids.join(',')}]) with ordinality as x (id, ordering) on #{klass.table_name}.id = x.id").reorder('x.ordering')
+    end
+  end
+
+  private
+
+  def key
+    [@prefix, @allowed ? 'allowed' : 'all', @locale].compact.join(':')
+  end
+
+  def load
+    unless loaded?
+      @records = perform_queries
+      @loaded  = true
+    end
+
+    self
+  end
+
+  def ids
+    redis.zrevrange(key, @offset, @limit.positive? ? @limit - 1 : @limit).map(&:to_i)
+  end
+
+  def perform_queries
+    apply_scopes(to_arel).to_a
+  end
+
+  def apply_scopes(scope)
+    scope
+  end
+end