module Pagy::ArelExtra

def pagy_arel(collection, vars = {})
  pagy = Pagy.new(pagy_arel_get_vars(collection, vars))
  [pagy, pagy_get_items(collection, pagy)]
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).limit(1).pluck(sql).first.to_i
  end
end

def pagy_arel_get_vars(collection, vars)
  pagy_set_items_from_params(vars) if defined?(ItemsExtra)
  vars[:count] ||= pagy_arel_count(collection)
  vars[:page]  ||= params[vars[:page_param] || DEFAULT[:page_param]]
  vars
end