Provides a "return to search results" shortcode for Participants Database

pdb-return-to-results.php

<?php
/**
 * Plugin Name: PDB Return to Results Shortcode
 * Description: adds a shortcode that displays a ling to return to the previous search result
 * Author: xnau webdesign
 * Version: 1.3
 */

class PDb_Search_Return_Link {
  
  /**
   * @var string name of the filter transient
   */
  private $filter_transient = 'pdb-returnlink-filter';
  
  /**
   * @var holds the permalink to the list search page
   */
  private $listpage;
  
  /**
   * 
   */
  public function __construct()
  {
    add_shortcode( 'pdb_search_return_link', [$this,'show_link']);
    
    add_action( 'pdb-list_query_object', [$this,'save_filter']);
  }
  
  /**
   * displays the return to search result link
   * 
   * @param array|null $shortcode_atts
   */
  public function show_link( $shortcode_atts )
  {
    $this->listpage = get_permalink( Participants_Db::get_id_by_slug($shortcode_atts['listpage']) );
    
    ob_start();
    ?>
<div class="pdb-returnlink">
  <p><a href="<?php echo $this->return_url() ?>">Return to Search Results</a></p>
</div>
    <?php
    
    return ob_get_clean();
  }
  
  /**
   * saves the last used search filter
   * 
   * @param PDb_List_Query $list_query
   */
  public function save_filter( $list_query )
  {
    $last_filter = $list_query->current_filter();
    
    if ( method_exists( $list_query, 'current_page' ) )
    {
      $listpage = $list_query->current_page();
    }
    else
    {
      $listpage = filter_input(INPUT_POST, Participants_Db::$list_page, FILTER_SANITIZE_NUMBER_INT ) ? : 1;
    }
    
    $last_filter[Participants_Db::$list_page] = $listpage;
    
    $last_filter['instance_index'] = 1;
    
    if ( method_exists( $list_query, 'instance_index' ) )
    {
      $last_filter['instance_index'] = $list_query->instance_index();
    }
    
    set_transient( $this->filter_transient, $last_filter );
  }
  
  /**
   * builds the return URL
   */
  private function return_url()
  {
    $baseurl = $this->listpage;
    
    $join = strpos( $baseurl, '?' ) === false ? '?' : '&';
    
    return $baseurl . $join . $this->url_params();
  }
  
  /**
   * builds the URL params
   * 
   * @return string
   */
  private function url_params()
  {
    $filter = get_transient( $this->filter_transient );
    
    if ( ! is_array( $filter ) )
    {
      return [];
    }
    
    $operator = Participants_Db::plugin_setting( 'strict_search', 0 ) == 1 ? '=' : 'LIKE';
    
    $params = [];
    
    foreach( $filter['search_fields'] as $i => $search_field )
    {
      $params[] = 'search_field=' . $search_field . '&value=' . urlencode( $filter['search_values'][$i] ) . '&operator=' . urlencode( $operator );
    }
    
    $params[] = 'listpage=' . $filter[ Participants_Db::$list_page ];
    
    $params[] = 'instance=' . $filter['instance_index'];
    
    return implode( '&', $params );
  }
}

new PDb_Search_Return_Link();

This places a "return to search results" link. Place it on the page with the [pdb_single] shortcode.

You must provide the name of the page where your searchable list is displayed in the "listpage" attribute of the shortcode.

For example:

[pdb_search_return_link listpage=participant-list]

Updated to implement the "strict user searching" feature.

Updated to include support for retaining the page number and multiple tragets on the list page using the "instance index" value.