Shows how to create a custom format tag for a Participants Database calculated field

pdb-age-detail-format-tag.php

<?php

/**
 * Plugin Name: PDB Age Detail Format Tag
 * Description: shows how to add a custom formatting tag for use in a Participants Database calculated field
 * Version: 1.0
 * 
 */

class PDb_age_detail_format_tag
{
  /**
   * sets up the filters
   */
  public function __construct()
  {
    /*
     * this is the name of the tag 
     * to use this in the calculated field, the tag will be: [?years_or_months]
     */
    $tag = 'age_detail';
    
    add_filter( 'pdb-calc_field_format_tag_' . $tag, array( $this, 'age_detail_tag' ), 10, 2 );
      
    // use this if the tag is for display purposes only
    add_filter( 'pdb-display_only_format_tag_' . $tag, function(){ return true; } );
  }
  
  /**
   * provides the age_detail tag value
   * 
   * @param string $value the raw result of the calculation (unix timestamp)
   * @param \PDb_Field_Item $field the current field
   * @return string
   */
  public function age_detail_tag( $value, $field )
  {
    $interval = $this->interval_object( $value );
    
    $format = [];
    
    if ( $interval->format('%y') != 0 )
    {
      $format[] = '%y years';
    }
    
    if ( $interval->format('%m') != 0 )
    {
      $format[] = '%m months';
    }
    
    if ( $interval->format('%d') != 0 )
    {
      $format[] = '%d days';
    }
    
    // note: this won't be accurate to the day because it cannot account 
    // for the actual lengths of the months in the time span
    
    return $interval->format( implode( ' ', $format ) );
  }
  
  /**
   * provides the DateInterval object
   * 
   * @param int $timestamp
   * @return DateInterval object 
   */
  private function interval_object( $timestamp )
  {
    $y = $timestamp / YEAR_IN_SECONDS;
    $years =  intval( $y );
    $m = ( $y - $years ) * 12;
    $months = intval( $m );
    $days = intval( ( $m - $months ) * 30.41 ); // 30.41 is the average month length in a year
    
    $datecode = 'P' . $years . 'Y' . $months . 'M' . $days  . 'D';
    
    return new DateInterval( $datecode );
  }
}

new PDb_age_detail_format_tag();

This article explains how to use this gist:

How to Install a WordPress Plugin from a Gist