Shows how to add an email template tag that shows all the changes made on a Participants Database record update.

pdb-record-edit-log.php

<?php
/**
 * Plugin Name: PDB Record Edit Log Tag
 * Description: provides a custom email tag that shows which fields were updated
 * Version: 1.0
 * 
 */

class PDb_Record_Edit_Log_Tag {
  
  /**
   * @var array the pre-edit record
   */
  private $current_record;
  
  /**
   * @var array the change log  
   * 
   * as 'fieldname' => array( 
   *  'title' => $field_title, 
   *  'old_value' => $current_value, 
   *  'new_value' => $updated_value 
   * )
   */
  private $change_log = array();
  
  /**
   * sets up the filters/actions
   */
  public function __construct()
  {
    add_filter( 'pdb-before_submit_update', array( $this, 'capture_stored_record' ), 1 );
    
    add_action( 'pdb-after_submit_update', array( $this, 'build_log_data' ), 1 );
    
    add_filter( 'pdb-template_email_tag_map', array( $this, 'add_edit_log_tag' ), 20, 2 );
  }
  
  /**
   * captures the stored record before updating
   * 
   * @param array $post the posted data
   * @return array
   */
  public function capture_stored_record( $post )
  {
    $this->current_record = Participants_Db::get_participant( filter_var( $post['id'], FILTER_SANITIZE_NUMBER_INT ) );
    
    return $post;
  }
  
  /**
   * builds the change log data
   * 
   * @param array $submission the submitted data
   */
  public function build_log_data( $submission )
  {
    $this->log_data($submission);
  }
  
  /**
   * adds the change log tag to the tag list
   * 
   * @param array $tag_list
   * @param string $context
   * @return array
   */
  public function add_edit_log_tag( $tag_list, $context ) {
    
    $tag_list['change_log'] = $this->printable_log();
    
    return $tag_list;
  }
  
  /**
   * provides the log data
   * 
   * @param array $submission the submitted record data
   */
  private function log_data( $submission )
  {
    foreach ( $submission as $fieldname => $value ) {
      
      if ( isset( $this->current_record[$fieldname] ) && $value != $this->current_record[$fieldname] ) {
        
        $field = new PDb_Form_Field_Def( $fieldname );
        
        $this->change_log[$fieldname] = array( 
            'title' => $field->title(),
            'old_value' => $this->display_string( $this->current_record[$fieldname] ), 
            'new_value' => $this->display_string( $value ), 
                );
      }
    }
  }
  
  /**
   * provides the change log in printable form
   * 
   * @return string HTML
   */
  private function printable_log()
  {
    $print = array();
    
    if ( count( $this->change_log ) > 0 ) {
      
      // set up the table header
      $print[] = '<table>';
      $print[] = '<tr><th>Field</th><th>Old Value</th><th>New Value</th></tr>';
      
      foreach( $this->change_log as $line ) {
      
        $print[] = vsprintf( '<tr><td>%s</td><td>%s</td><td>%s</td></tr>', $line );
      }
      
      $print[] = '</table>';
    }
    
    return implode( PHP_EOL, $print );
  }
  
  /**
   * converts an array to a string if needed
   * 
   * @param array|string $input
   * @return string output
   */
  private function display_string( $input )
  {
    $output = $input;
    
    if ( is_array( maybe_unserialize( $input ) ) ) {
      
      $output = implode( ', ', maybe_unserialize( $input ) );
    }
    
    return $output;
  }
}

new PDb_Record_Edit_Log_Tag();

You can include this tag in your email template with:

[change_log]

It will show a table listing all the changes made to a record when updated.