<?php

use Drupal\views\Views;

// Optional, if using filter values passed via URL (see example below).
use Drupal\Component\Utility\Html;

/**
 * Preprocesses variables for node--NODE_TYPE.html.twig.
 *
 * Replace 'mytheme' with the name of your theme, and NODE_TYPE and VIEW_NAME
 * with actual machine names.
 */
function mytheme_preprocess_node__NODE_TYPE(&$variables) {

  $node = $variables['node'];

  // Execute the view that provides the context.
  $view = \Drupal\views\Views::getView('VIEW_NAME');

  // Optionally set a contextual filter value passed in via the URL;
  // e.g. path-to-node?vid=456. You will need to add the parameter to the pager
  // URLs in your Twig template.
  $variables['arg'] = Html::escape(\Drupal::request()->query->get('vid'));
  $view->setArguments([$variables['arg']]);

  $view->execute();

  // Iterate through the results to find the results index for previous,
  // current, and next nodes.
  $match = FALSE;
  foreach ($view->result as $k => $row) {
      // Break out of iterator when we find the next row.
      if ($match !== FALSE) {
        $next = $k;
        break;
      }
      // This result matches our currently loaded node.
      if ($row->nid == $node->id()) {
        $match = $k;
      }
      // As long as we haven't reached a match, let's keep updating $previous.
      if ($match === FALSE) {
        $previous = $k;
      }
  }

  // If a match is found, set up our template variables.
  if ($match !== FALSE) {
    $variables['node_view_pager'] = [];
    $variables['node_view_pager']['num_results'] = count($view->result);
    $variables['node_view_pager']['index'] = $match + 1;
    $controller = \Drupal::entityManager()->getStorage('node');
    if (isset($previous)) {
      $variables['node_view_pager']['previous'] = $controller->load($view->result[$previous]->nid);
    }
    if (isset($next)) {
      $variables['node_view_pager']['next'] = $controller->load($view->result[$next]->nid);
    }
  }
}