module Pagy::UrlHelpers

def pagy_url_for(pagy, page, absolute: false, html_escaped: false)

For non-rack environments you can use the standalone extra
It supports all Rack-based frameworks (Sinatra, Padrino, Rails, ...).
Return the URL for the page, relying on the params method and Rack by default. 
def pagy_url_for(pagy, page, absolute: false, html_escaped: false)
  vars                = pagy.vars
  request_path        = vars[:request_path].to_s.empty? ? request.path : vars[:request_path]
  page_param          = vars[:page_param].to_s
  items_param         = vars[:items_param].to_s
  params              = pagy.params.is_a?(Hash) ? pagy.params.transform_keys(&:to_s) : {}
  params              = request.GET.merge(params)
  params[page_param]  = page
  params[items_param] = vars[:items] if vars[:items_extra]
  params              = pagy.params.call(params) if pagy.params.is_a?(Proc)
  query_string        = "?#{Rack::Utils.build_nested_query(params)}"
  query_string        = query_string.gsub('&', '&') if html_escaped  # the only unescaped entity
  "#{request.base_url if absolute}#{request_path}#{query_string}#{vars[:fragment]}"
end