From ada2ec3a0bfcdc06ba9dbbccba586a64e557bfa2 Mon Sep 17 00:00:00 2001
From: Daniel Wehner <dawehner@googlemail.com>
Date: Sun, 10 Jul 2016 09:26:46 +0200
Subject: [PATCH] Provide a formatter which limits and provides offsets

---
 config/schema/field_formatter.schema.yml      | 16 ++++
 field_formatter.module                        |  1 +
 .../FieldFormatter/FieldFormatterBase.php     |  2 +-
 .../FieldFormatter/FieldFormatterLimiter.php  | 84 +++++++++++++++++++
 .../Field/FieldFormatter/FieldWrapperBase.php |  2 +-
 5 files changed, 103 insertions(+), 2 deletions(-)
 create mode 100644 src/Plugin/Field/FieldFormatter/FieldFormatterLimiter.php

diff --git a/config/schema/field_formatter.schema.yml b/config/schema/field_formatter.schema.yml
index 1b8aee1..65d8f80 100644
--- a/config/schema/field_formatter.schema.yml
+++ b/config/schema/field_formatter.schema.yml
@@ -30,3 +30,19 @@ field.formatter.settings.field_link:
     settings:
       label: 'Formatter settings'
       type: field.formatter.settings.[%parent.type]
+
+field.formatter.settings.field_formatter_limiter:
+  type: mapping
+  mapping:
+    type:
+      label: 'Machine name of the formatter'
+      type: string
+    settings:
+      label: 'Formatter settings'
+      type: field.formatter.settings.[%parent.type]
+    offset:
+      type: integer
+      label: 'Offset'
+    limit:
+      type: integer
+      label: 'Limit'
diff --git a/field_formatter.module b/field_formatter.module
index 71e916a..65724bb 100644
--- a/field_formatter.module
+++ b/field_formatter.module
@@ -14,4 +14,5 @@ function field_formatter_field_formatter_info_alter(array &$info) {
   $field_types = array_keys($field_type_manager->getDefinitions());
 
   $info['field_link']['field_types'] = $field_types;
+  $info['field_formatter_limite']['field_types'] = $field_types;
 }
diff --git a/src/Plugin/Field/FieldFormatter/FieldFormatterBase.php b/src/Plugin/Field/FieldFormatter/FieldFormatterBase.php
index a45e1f3..3dae6d2 100644
--- a/src/Plugin/Field/FieldFormatter/FieldFormatterBase.php
+++ b/src/Plugin/Field/FieldFormatter/FieldFormatterBase.php
@@ -15,7 +15,7 @@ abstract class FieldFormatterBase extends EntityReferenceFormatterBase {
   /**
    * Entity view display.
    *
-   * @var \Drupal\Core\Entity\Display\EntityViewDisplayInterface
+   * @var \Drupal\Core\Entity\Display\EntityViewDisplayInterface[]
    */
   protected $viewDisplay;
 
diff --git a/src/Plugin/Field/FieldFormatter/FieldFormatterLimiter.php b/src/Plugin/Field/FieldFormatter/FieldFormatterLimiter.php
new file mode 100644
index 0000000..8099687
--- /dev/null
+++ b/src/Plugin/Field/FieldFormatter/FieldFormatterLimiter.php
@@ -0,0 +1,84 @@
+<?php
+
+namespace Drupal\field_formatter\Plugin\Field\FieldFormatter;
+
+use Drupal\Core\Field\FieldDefinitionInterface;
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Plugin implementation of the 'field_formatter_limiter' formatter.
+ *
+ * @FieldFormatter(
+ *   id = "field_formatter_limiter",
+ *   label = @Translation("Limit the amount of deltas being output"),
+ *   field_types = {
+ *     "entity_reference"
+ *   }
+ * )
+ */
+class FieldFormatterLimiter extends FieldWrapperBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function defaultSettings() {
+    $settings = parent::defaultSettings();
+    $settings['limit'] = 0;
+    $settings['offset'] = 0;
+    return $settings;
+  }
+
+  /**
+   * Returns the cardinality setting of the field instance.
+   */
+  protected function getCardinality() {
+    if ($this->fieldDefinition instanceof FieldDefinitionInterface) {
+      return $this->fieldDefinition->getFieldStorageDefinition()->getCardinality();
+    }
+    return 0;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function settingsForm(array $form, FormStateInterface $form_state) {
+    if ($this->getCardinality() == 1) {
+      return [];
+    }
+
+    $element['offset'] = [
+      '#type' => 'number',
+      '#title' => $this->t('Skip items'),
+      '#default_value' => $this->getSetting('offset'),
+      '#required' => TRUE,
+      '#min' => 0,
+      '#description' => $this->t('Number of items to skip from the beginning.')
+    ];
+
+    $element['limit'] = [
+      '#type' => 'number',
+      '#title' => $this->t('Display items'),
+      '#default_value' => $this->getSetting('limit'),
+      '#required' => TRUE,
+      '#min' => 0,
+      '#description' => $this->t('Number of items to display. Set to 0 to display all items.')
+    ];
+
+    return $element;
+   }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function viewElements(FieldItemListInterface $items, $langcode) {
+    $field_output = $this->getFieldOutput($items, $langcode);
+
+    $offset = $this->getSetting('offset');
+    // Array_slice needs NULL to show all elements.
+    $limit = $this->getSetting('limit') == 0 ? NULL : $this->getSetting('limit');
+
+    return array_slice($field_output, $offset, $limit);
+  }
+
+}
diff --git a/src/Plugin/Field/FieldFormatter/FieldWrapperBase.php b/src/Plugin/Field/FieldFormatter/FieldWrapperBase.php
index ed375d4..07ee8ab 100644
--- a/src/Plugin/Field/FieldFormatter/FieldWrapperBase.php
+++ b/src/Plugin/Field/FieldFormatter/FieldWrapperBase.php
@@ -22,7 +22,7 @@ abstract class FieldWrapperBase extends FormatterBase implements ContainerFactor
   /**
    * Entity view display.
    *
-   * @var \Drupal\Core\Entity\Display\EntityViewDisplayInterface
+   * @var \Drupal\Core\Entity\Display\EntityViewDisplayInterface[]
    */
   protected $viewDisplay;