Initial commit.

README.txt

+JSON:API image styles
+=======
+
+Adds image styles of a drupal image to jsonapi

jsonapi_image_styles.info.yml

+name: 'JSON:API image styles'
+type: module
+description: 'Expose image styles to JSON:API'
+core: 8.x
+package: 'Web services'
+dependencies:
+  - drupal:jsonapi

jsonapi_image_styles.module

+<?php
+
+/**
+ * @file
+ * Contains jsonapi_image_styles.module.
+ */
+
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Field\BaseFieldDefinition;
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+
+/**
+ * Implements hook_help().
+ */
+function jsonapi_image_styles_help($route_name, RouteMatchInterface $route_match) {
+  switch ($route_name) {
+    // Main module help for the jsonapi_image_styles module.
+    case 'help.page.jsonapi_image_styles':
+      $output = '';
+      $output .= '<h3>' . t('About') . '</h3>';
+      $output .= '<p>' . t('Expose image styles to JSON:API') . '</p>';
+      return $output;
+
+    default:
+  }
+}
+
+/**
+ * Implements hook_entity_base_field_info().
+ */
+function jsonapi_image_styles_entity_base_field_info(EntityTypeInterface $entity_type) {
+  $fields = [];
+  $base_table = $entity_type->getBaseTable();
+
+  // Certain classes are just not supported.
+  $original_class = $entity_type->getOriginalClass();
+
+  if (!empty($base_table) && $original_class == 'Drupal\file\Entity\File') {
+    $fields['image_style_uri'] = BaseFieldDefinition::create('image_style_uri')
+      ->setLabel(t('Entity image styles'))
+      ->setDescription(t('Image styles of the file entity'))
+      ->setComputed(TRUE)
+      ->setCardinality(FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED)
+      ->setTranslatable(TRUE);
+  }
+
+  return $fields;
+}

src/Plugin/Field/FieldType/ImageStyleNormalizedFieldItem.php

+<?php
+
+namespace Drupal\jsonapi_image_styles\Plugin\Field\FieldType;
+
+use Drupal\Core\Field\FieldItemBase;
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+use Drupal\Core\TypedData\DataDefinition;
+
+/**
+ * Plugin implementation of the 'image_style_uri' field type.
+ *
+ * @FieldType(
+ *   id = "image_style_uri",
+ *   label = @Translation("Image style uri"),
+ *   description = @Translation("Normalized image style paths"),
+ *   no_ui = TRUE,
+ *   list_class = "\Drupal\jsonapi_image_styles\Plugin\Field\FieldType\ImageStyleNormalizedFieldItemList",
+ * )
+ */
+class ImageStyleNormalizedFieldItem extends FieldItemBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function schema(FieldStorageDefinitionInterface $field_definition) {
+    return [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function propertyDefinitions(FieldStorageDefinitionInterface $field_definition) {
+    $properties['url'] = DataDefinition::create('any')
+      ->setLabel(t('URI'))
+      ->setRequired(TRUE);
+    return $properties;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function isEmpty() {
+    $value = $this->get('url')->getValue();
+    return $value === serialize([]);
+  }
+
+}

src/Plugin/Field/FieldType/ImageStyleNormalizedFieldItemList.php

+<?php
+
+namespace Drupal\jsonapi_image_styles\Plugin\Field\FieldType;
+
+use Drupal\Core\Field\FieldItemList;
+use Drupal\Core\TypedData\ComputedItemListTrait;
+use Drupal\file\Entity\File;
+use Drupal\image\Entity\ImageStyle;
+
+/**
+ * Represents the computed image styles for a file entity.
+ */
+class ImageStyleNormalizedFieldItemList extends FieldItemList {
+
+  use ComputedItemListTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function computeValue() {
+    $entity = $this->getEntity();
+    $uri = ($entity instanceof File) ? $entity->getFileUri() : FALSE;
+    if (!$entity->id() || !$uri) {
+      return;
+    }
+
+    $offset = 0;
+    // @TODO: Make it a configuration option to define image styles to expose.
+    $styles = [
+      'large',
+      'thumbnail',
+    ];
+
+    foreach ($styles as $style) {
+
+      $image_style = ImageStyle::load($style);
+      $url = ($image_style instanceof ImageStyle) ? $image_style->buildUrl($uri) : $url = file_create_url($uri);
+
+      $this->list[] = $this->createItem(
+        $offset,
+        [
+          'url' => [$style => $url],
+        ]
+      );
+      $offset++;
+    }
+  }
+
+}