how to get participant id on registration thank-you page

Question

How could I get the participant ID and the corresponding contact ID on the event registration thank-you page? E.g. is there a field (or piece of code) I can insert in /templates/CRM/Event/Form/Registration/DisplayProfile.tpl ?

For participant ID I tried the following but to no avail:

<div class="participant-id hidden">{$participant.id}</div>

Thank you for any tips

Answer 1

the following did the trick - works in this situation well enough as we only allow registering one participant:

{$participantIDs.0}

The above grabs the participant ID of the first (and only in our case) participant

Answer 2

The participant_id can be accessed on the event registration thank you page in two different ways -- by using Smarty template variables when the user is logged in or by using session variables when the user is anonymous. Both approaches work when used inside the "civicrmBuildForm" hook.

1) User logged in

add_action( 'civicrm_buildForm', 'getParticipantId' );

function getParticipantId() {
    $template = (array) CRM_Core_Smarty::singleton();
    $event = $template['_tpl_vars']['event'];

    $participant = civicrm_api3('Participant', 'getsingle', [
        'sequential' => 1,
        'contact_id' => "user_contact_id",
        'event_id' => $event['id'],
    ]);

    echo $participant['id'];
}

2) Anonymous user

add_action( 'civicrm_buildForm', 'getParticipantId' );

function getCrmFromSession($session) {
    if (!empty($session)) {
        $seshAry = (array) $session;
        $seshKey = array_keys($seshAry)[1];
        $CiviCRM = json_decode(json_encode($seshAry[$seshKey]), true)['CiviCRM'];

        if ( !empty($CiviCRM['CRM_Utils_Recent']) && isset($CiviCRM['CRM_Utils_Recent'][0]['id']) ) {
            $CiviCRM['participant_id'] = $CiviCRM['CRM_Utils_Recent'][0]['id'];
        }

        return $CiviCRM;
    } else {
        return array();
    }
}

function getParticipantId() {
    $CiviCRM = getCrmFromSession(CRM_Core_Session::singleton());

    echo $CiviCRM['participant_id'];
}

• I appended a template to the Thank You template with the data related to participant_id.
• In my case, the BuildForm hook lives in my theme's functions.php file.