Notification Template Variables

the resolver          entity -> the event's variables      (yours)
      ↓
View::notifications   adds template_name and template_type
      ↓
variables_handler     adds the recipient block  (user id > 0 only)
                      adds the installation block  (always)
      ↓                  ^ both OVERWRITE what is already there, with four exceptions
the engine            renders the body with the merged set
      ↓
                      the rendered body becomes notifi_body
      ↓
the engine            renders the shell, then the subject, with the same set

// coremio/helpers/notification.php
// $type is 'system' | 'user'. Anything else returns $variables with the braces
// stripped, which is how the configuration entry's CSV becomes a badge list.
public static function variables(string $type = '', array $variables = []): array;

// The group baseline the editor shows: 'invoice' | 'order' | 'service' | 'domain'
// | 'user-tickets' | 'admin-tickets'. Every other group returns an empty array.
public static function group_variables(string $group = ''): array;

// coremio/classes/View.php
public static function notifications($type = 'mail', $template_name = '', $content = '',
                                     $variables = [], $lang = '', $user = 0): array;

// Merges the two platform layers into $variables, then renders $str IN PLACE.
// $str is by reference: it is both the template source and the result.
public static function variables_handler($type, $user_id = 0, $variables = [], &$str = '', $lang = ''): void;

// coremio/classes/TemplateEngine.php
// $engine is 'smarty' | 'twig' | 'none'. Returns the ORIGINAL string on any
// compile error, so a failure looks like a template that did nothing.
public static function render_notification($engine, $content, $variables = []): string;

{* recipient layer *}
Dear {$user_greeting_name},

{* event layer: already formatted with its currency, so it is printed as-is *}
Invoice {$invoice_idn} for {$invoice_total} is due on {$invoice_date_due}.

{* event layer, a collection: amountF is the formatted string, amount is the number *}
{foreach from=$items item=item}
- {$item.description} {$item.amountF}
  {if $item.service_domain != ""}({$item.service_domain}){/if}
{/foreach}

{* installation layer, guarded because the list can be empty *}
{if $is_enable_support}Questions: {$support_link}{/if}
{$company_name} {$current_year}

// coremio/helpers/notification.php, in the group's resolver.
// Do not reuse a platform name: user_email and website_url are written after
// this runs and would overwrite whatever you put there.
switch ($name) {
    case 'acme-quota-reached':
        $variables['quota_percent'] = (int) ($context['percent'] ?? 0);
        $variables['quota_limit']   = Money::formatter_symbol(
            (float) ($context['limit'] ?? 0),
            (int) ($service['amount_cid'] ?? 0),
        );
        break;
}

// Runs once per recipient, right before that recipient's body is rendered, so it
// can also vary the value per recipient. The first argument is by reference.
Hook::add('filter:notification.render_variables', 1, function (&$variables, $group, $name, $recipient) {
    if ($group !== 'service') return;

    $variables['acme_portal_link'] = 'https://portal.example.com/s/' . (int) ($variables['service_id'] ?? 0);
});

// Editor only: puts the name in the badge list the operator sees while editing.
// It changes nothing at render time, so both listeners are needed for a name that
// is meant to be discoverable as well as printable.
Hook::add('filter:notification.template_merge_fields', 1, function (&$fields, $group, $name) {
    if ($group === 'service') $fields[] = 'acme_portal_link';
});