module Pagy::ArelExtra

def pagy_arel(collection, **vars)
  vars[:count] ||= pagy_arel_count(collection)
  pagy(collection, **vars)
end

def pagy_arel_count(collection)
  if collection.group_values.empty?
    # COUNT(*)
    collection.count(:all)
  else
    # COUNT(*) OVER ()
    sql = Arel.star.count.over(Arel::Nodes::Grouping.new([]))
    collection.unscope(:order).pick(sql).to_i
  end
end