Issue #3483142 by _tarik_: Provide a new formatter to allow output only...

Issue #3483142 by _tarik_: Provide a new formatter to allow output only specific levels of taxonomy terms

src/Plugin/Field/FieldFormatter/CshsSpecificTaxonomyLevelFormatter.php

+<?php
+
+namespace Drupal\cshs\Plugin\Field\FieldFormatter;
+
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Defines the field formatter.
+ *
+ * @FieldFormatter(
+ *   id = "cshs_specific_level_taxonomy",
+ *   label = @Translation("Specific level taxonomy"),
+ *   description = @Translation("Shows only specific level of taxonomy terms"),
+ *   field_types = {
+ *     "entity_reference",
+ *   },
+ * )
+ */
+class CshsSpecificTaxonomyLevelFormatter extends CshsFormatterBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function defaultSettings(): array {
+    $settings = parent::defaultSettings();
+    $settings['level'] = 1;
+
+    return $settings;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function settingsForm(array $form, FormStateInterface $form_state): array {
+    $element = parent::settingsForm($form, $form_state);
+    unset($element['reverse']);
+
+    $element['level'] = [
+      '#type' => 'number',
+      '#min' => 1,
+      '#title' => $this->t('level'),
+      '#description' => $this->t('The taxonomy level to show. If the term in the field has a different level it will be hidden. The root level is 1.'),
+      '#default_value' => $this->getSetting('level'),
+    ];
+
+    return $element;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function settingsSummary(): array {
+    $summary = [];
+
+    $summary[] = $this->t('Linked to term page: @linked', [
+      '@linked' => $this->getSetting('linked') ? $this->t('Yes') : $this->t('No'),
+    ]);
+
+    $summary[] = $this->t('Level to show: @level', [
+      '@level' => $this->getSetting('level') ?? $this->t('Root'),
+    ]);
+
+    return $summary;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function viewElements(FieldItemListInterface $items, $langcode): array {
+    $level = (int) $this->getSetting('level');
+    $linked = (bool) $this->getSetting('linked');
+    $elements = [];
+
+    foreach ($this->getEntitiesToView($items, $langcode) as $term) {
+      $tree = $this->getTermParents($term);
+      if (count($tree) !== $level) {
+        continue;
+      }
+
+      $term_id = $term->id();
+      if (!isset($elements[$term_id])) {
+        $elements[$term_id] = [
+          '#theme' => 'cshs_term_group',
+          '#id' => $term_id,
+          '#title' => $this->getTermsLabels([$term], $linked)[0] ?? $term->label(),
+          '#terms' => [],
+        ];
+      }
+    }
+
+    return $elements;
+  }
+
+}