<?php
/**
 * @file
 * CSV formatter.
 */

namespace Drupal\csv_formatter\Plugin\Field\FieldFormatter;

use Drupal\Core\Field\FieldItemListInterface;
use Drupal\file\Plugin\Field\FieldFormatter;
use Drupal\file\Plugin\Field\FieldFormatter\FileFormatterBase;

/**
 * Plugin implementation of the 'csv_table' formatter.
 *
 * @FileFieldFormatter(
 *   id = "csv_table",
 *   label = @Translation("CSV Formatter"),
 *   field_types = {
 *     "file"
 *   }
 * )
 */
class CSVTableFormatter extends FileFormatterBase {

  /**
   * {@inheritdoc}
   */
  public function viewElements(FieldItemListInterface $items, $langcode) {
    $elements = [];
    foreach ($items as $key => $item) {
      $elements[$key] = [
        '#theme' => 'csv_table_formatter',
        '#custom' => 'Hello world',
      ];
    }
    return $elements;
  }

}