Working symfony dispatcher for civicrm api wrapper

APIWrapper.php

<?php

/**
 * Implements an API Wrapper to signal the membership creation preHook that
 * we're currently inside of a payment transaction.
 */
class CRM_MembershipApproval_APIWrapper {
  private static $in_approval = [];

  /**
   * Callback to wrap completetransaction API calls.
   */
  public static function PREPARE ($event) {
    $request = $event->getApiRequestSig(); //getApiRequestSig() returns '<api version>.<entity>.<action>', all lower case

    switch($request) {
      // Wrap completetransaction in the v3 API.
      // Doesn't exist yet in the v4 API.
      case '3.contribution.completetransaction':
        $event->wrapApi(['CRM_MembershipApproval_APIWrapper', 'completeTransaction']);
        break;
      default:
        break;
    }
  }

  /**
   * Accessor function to check for approval status.
   */
  public static function isInApproval($id) {
    return (isset(static::$in_approval[$id]) && static::$in_approval[$id]);
  }

  /**
   * API wrapper for completetransaction.
   */
  public static function completeTransaction($apiRequest, $callsame) {
    $approval_status = CRM_Core_ManagedEntities::singleton()->get('au.com.agileware.membershipapproval', 'membership-status:awaiting-approval');

    // Filter line items for this contributions for memberships.
    // Actual request parameters are passed via the 'params' value of the $apiRequest array
    $items = civicrm_api3('LineItem', 'get', [ 'contribution_id' => $apiRequest['params']['id'] ])['values'];

    foreach ($items as &$item) {
      if(($item['entity_table'] == 'civicrm_membership')) {
        // Found a membership, record whether it's in_approval for the pre hook
        $status = civicrm_api3('Membership', 'getvalue', [ 'id' => $item['entity_id'], 'return' => 'status_id' ]);
        static::$in_approval[$item['entity_id']] = ($status == $approval_status['id']);
      }
    }

    // Continue through to the actual API call.
    $callsame($apiRequest);

    foreach ($items as &$item) {
      if(($item['entity_table'] == 'civicrm_membership') && static::isInApproval($item['entity_id'])) {
        unset(static::$in_approval[$item['entity_id']]);
      }
    }
  }

  /**
   * Stub for a createMembership API wrapper.
   */
  public static function createMembership($apiRequest, $callsame) {
    if(!self::isInApproval($apiRequest['params']['id'])) {
      $callsame($apiRequest);
    }
  }
}

config_hook.php

/**
 * Implements hook_civicrm_config().
 * Most of the magic is in the CRM_MembershipApproval_APIWrapper class
 */
function membershipapproval_civicrm_config(&$config){
  // Set up our extension for autoloading
  $extRoot = dirname(__FILE__) . DIRECTORY_SEPARATOR;
  $include_path = $extRoot . PATH_SEPARATOR . get_include_path( );
  set_include_path($include_path);

  // Bind our wrapper for API Events
  Civi::dispatcher()->addListener(\Civi\API\Events::PREPARE, ['CRM_MembershipApproval_APIWrapper', 'PREPARE'], -100);
}