parent_url_param.php

<?php
/**
 * This function should be only used in AJAX templates & AJAX callbacks.
 *
 * 
 * Use cases of this function are when you need to get a URL param inside a 
 * PHP template rendered through AJAX or an AJAX callback that needs access 
 * to the parent URL param (From where the ajax call was made). i.e, 
 * calling ajax.php from http://exmple.com/my-page/?param1=v111&param2=v222. 
 * A header of URLPARAMS needsto be added to the request headers. i.e, using 
 * jQuery.ajax add it by doing $.ajaxSetup({headers: {'URLPARAMS': window.location.search}}). 
 * You can modify it to use HTTP_REFERER param. But some browsers block this for security reasons.
 * This will fallback to current URL params if the request header is not present.
 * 
 * The URL params are sanitized to 3 level in depth. 
 * i.e, aaa[q][]=111&aaa[q][]=99&bbb[]=444&bbb[aaa]=555&bbb[aaa][][]=555
 * 
 * @param string Name of the param to get
 * @return mixed
 */
function parent_url_param($name = false) {

  // $referer = isset($_SERVER['HTTP_REFERER']) ? $_SERVER['HTTP_REFERER'] : get_current_url();
  $referer = isset($_SERVER['HTTP_URLPARAMS']) ? $_SERVER['HTTP_URLPARAMS'] : get_current_url();

  $url_params_str = parse_url($referer, PHP_URL_QUERY);

  parse_str($url_params_str, $url_params);

  $sanitize_fn = function($value) {

    // return is_array($value) ? null : sanitize_text_field($value); // If using WordPress
    return is_array($value) ? null : preg_replace('/[^-a-zA-Z0-9_]/', '', $value);

  };

  $url_params_sanitized = array();

  foreach ($url_params as $key => $value) {

    $url_params_sanitized[$key] = $sanitize_fn($value);

    if ( is_null($sanitize_fn($value)) ) {

      foreach ($value as $key2 => $value2) {

        $url_params_sanitized[$key][$key2] = $sanitize_fn($value2);

        if ( is_null($sanitize_fn($value2)) ) {

          foreach ($value2 as $key3 => $value3) {

            $url_params_sanitized[$key][$key2][$key3] = $sanitize_fn($value3);

            if ( is_null($sanitize_fn($value3)) ) {

              foreach ($value3 as $key4 => $value4) {

                $url_params_sanitized[$key][$key2][$key3][$key4] = $sanitize_fn($value4);

              }

            }

          }

        }

      }

    }

  }

  if ( $name ) {

    return isset($url_params_sanitized[$name]) ? $url_params_sanitized[$name] : null;

  }

  return $url_params_sanitized;

}