Add next/previous navigation

config/install/field.field.node.localgov_blog_channel.localgov_blog_posts.yml

@@ -0,0 +1,28 @@
+langcode: en
+status: true
+dependencies:
+  config:
+    - field.storage.node.localgov_blog_posts
+    - node.type.localgov_blog_channel
+    - node.type.localgov_blog_post
+id: node.localgov_blog_channel.localgov_blog_posts
+field_name: localgov_blog_posts
+entity_type: node
+bundle: localgov_blog_channel
+label: localgov_blog_posts
+description: ''
+required: false
+translatable: false
+default_value: {  }
+default_value_callback: ''
+settings:
+  handler: 'default:node'
+  handler_settings:
+    target_bundles:
+      localgov_blog_post: localgov_blog_post
+    sort:
+      field: _none
+      direction: ASC
+    auto_create: false
+    auto_create_bundle: ''
+field_type: entity_reference

config/install/field.storage.node.localgov_blog_posts.yml

@@ -0,0 +1,18 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - node
+id: node.localgov_blog_posts
+field_name: localgov_blog_posts
+entity_type: node
+type: entity_reference
+settings:
+  target_type: node
+module: core
+locked: false
+cardinality: -1
+translatable: true
+indexes: {  }
+persist_with_no_fields: false
+custom_storage: false

config/optional/block.block.localgov_blogs_prev_next_block_base.yml

@@ -0,0 +1,19 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - localgov_blogs
+  theme:
+    - localgov_base
+id: localgov_blogs_prev_next_block_base
+theme: localgov_base
+region: content_bottom
+weight: -6
+provider: null
+plugin: localgov_blogs_prev_next_block
+settings:
+  id: localgov_blogs_prev_next_block
+  label: 'Blogs prev next block'
+  provider: localgov_blogs
+  label_display: '0'
+visibility: {  }

config/schema/localgov_blogs_prev_next_block_base.schema.yml

@@ -0,0 +1,7 @@
+block.settings.localgov_blogs_prev_next_block:
+  type: block_settings
+  label: 'Previous Next button block settings'
+  mapping:
+    show_title:
+      type: boolean
+      label: 'Show title'

localgov_blogs.module

@@ -12,6 +12,23 @@ use Drupal\node\NodeForm;
 use Drupal\node\NodeInterface;
 use Drupal\views\Views;
 
+/**
+ * Implements hook_theme().
+ */
+function localgov_blogs_theme($existing, $type, $theme, $path) {
+  return [
+    'localgov_blogs_prev_next_block' => [
+      'variables' => [
+        'previous_url' => NULL,
+        'previous_title' => NULL,
+        'next_url' => NULL,
+        'next_title' => NULL,
+        'show_title' => NULL,
+      ],
+    ],
+  ];
+}
+
 /**
  * Implements hook_entity_extra_field_info().
  */

src/Plugin/Block/BlogPrevNextBlock.php

@@ -0,0 +1,233 @@
+<?php
+
+namespace Drupal\localgov_blogs\Plugin\Block;
+
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\Routing\RouteMatchInterface;
+use Drupal\node\NodeInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a 'Next Previous' block.
+ *
+ * @Block(
+ *   id = "localgov_blogs_prev_next_block",
+ *   admin_label = @Translation("Blog Previous Next block"),
+ *   category = @Translation("Blocks")
+ * )
+ */
+class BlogPrevNextBlock extends BlockBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * The current route match.
+   *
+   * @var \Drupal\Core\Routing\RouteMatchInterface
+   */
+  protected $routeMatch;
+
+  /**
+   * Node being displayed.
+   *
+   * @var \Drupal\node\NodeInterface
+   */
+  protected $node;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface
+   */
+  protected $entityTypeManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(
+    ContainerInterface $container,
+    array $configuration,
+    $plugin_id,
+    $plugin_definition,
+  ) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('current_route_match'),
+      $container->get('entity_type.manager')
+    );
+  }
+
+  /**
+   * Creates a PrevNextBlock instance.
+   *
+   * @param array $configuration
+   *   A configuration array containing information about the plugin instance.
+   * @param string $plugin_id
+   *   The plugin_id for the plugin instance.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
+   *   The current route match.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entityTypeManager
+   *   The entity type manager.
+   */
+  public function __construct(
+    array $configuration,
+    $plugin_id,
+    $plugin_definition,
+    RouteMatchInterface $route_match,
+    EntityTypeManagerInterface $entityTypeManager,
+  ) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+    $this->routeMatch = $route_match;
+    $this->entityTypeManager = $entityTypeManager;
+    if ($this->routeMatch->getParameter('node')) {
+      $this->node = $this->routeMatch->getParameter('node');
+      if (!$this->node instanceof NodeInterface) {
+        $node_storage = $this->entityTypeManager->getStorage('node');
+        $this->node = $node_storage->load($this->node);
+      }
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+
+    $node = $this->routeMatch->getParameter('node');
+    $previous_url = '';
+    $previous_title = '';
+    $next_url = '';
+    $next_title = '';
+
+    if ($node instanceof NodeInterface && $node->getType() == 'localgov_blog_post') {
+
+      $prev = $this->generatePrevious($node);
+      if (!empty($prev)) {
+        $previous_title = $prev['title'];
+        $previous_url = $prev['url'];
+      }
+
+      $next = $this->generateNext($node);
+      if (!empty($next)) {
+        $next_title = $next['title'];
+        $next_url = $next['url'];
+      }
+    }
+
+    return [
+      '#theme' => 'localgov_blogs_prev_next_block',
+      '#previous_url' => $previous_url,
+      '#previous_title' => $previous_title,
+      '#next_url' => $next_url,
+      '#next_title' => $next_title,
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheTags() {
+    // Get the created time of the current node.
+    $node = $this->routeMatch->getParameter('node');
+    if (!empty($node) && $node instanceof NodeInterface) {
+      // If there is node add its cachetag.
+      return Cache::mergeTags(parent::getCacheTags(), ['node:' . $node->id()]);
+    }
+    else {
+      // Return default tags instead.
+      return parent::getCacheTags();
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheContexts() {
+    return Cache::mergeContexts(parent::getCacheContexts(), ['route']);
+  }
+
+  /**
+   * Lookup the previous node,youngest node which is still older than the node.
+   *
+   * @param string $node
+   *   Show current page node id.
+   *
+   * @return array
+   *   A render array for a previous node.
+   */
+  private function generatePrevious($node) {
+    return $this->generateNextPrevious($node, 'prev');
+  }
+
+  /**
+   * Lookup the next node,oldest node which is still younger than the node.
+   *
+   * @param string $node
+   *   Show current page node id.
+   *
+   * @return array
+   *   A render array for a next node.
+   */
+  private function generateNext($node) {
+    return $this->generateNextPrevious($node, 'next');
+  }
+
+  const DIRECTION__NEXT = 'next';
+
+  /**
+   * Lookup the next or previous node.
+   *
+   * @param string $node
+   *   Get current page node id.
+   * @param string $direction
+   *   Default value is "next" and other value come from
+   *   generatePrevious() and generatePrevious().
+   *
+   * @return array
+   *   Find the alias of the next node.
+   */
+  private function generateNextPrevious($node, $direction = self::DIRECTION__NEXT) {
+    $comparison_opperator = '>';
+    $sort = 'ASC';
+    $current_node_date = $node->get('localgov_blog_date')->value;
+    $current_langcode = $node->get('langcode')->value;
+    $current_blog_channel = $node->get('localgov_blog_channel')->target_id;
+
+    if ($direction === 'prev') {
+      $comparison_opperator = '<';
+      $sort = 'DESC';
+    }
+
+    // Lookup 1 node younger (or older) than the current node
+    // based upon the `localgov_blog_date` field.
+    $query = $this->entityTypeManager->getStorage('node');
+    $query_result = $query->getQuery();
+    $result = $query_result->condition('localgov_blog_date', $current_node_date, $comparison_opperator)
+      ->condition('type', 'localgov_blog_post')
+      ->condition('localgov_blog_channel', $current_blog_channel)
+      ->condition('status', 1)
+      ->condition('langcode', $current_langcode)
+      ->sort('localgov_blog_date', $sort)
+      ->range(0, 1)
+      ->accessCheck(TRUE)
+      ->execute();
+
+    // If this is not the youngest (or oldest) node.
+    if (!empty($result) && is_array($result)) {
+      $result = array_values($result)[0];
+      $node = $query->load($result);
+
+      return [
+        'title' => $node->get('title')->value,
+        'url' => $node->toUrl()->toString(),
+      ];
+    }
+    return '';
+  }
+
+}

templates/localgov-blogs-prev-next-block.html.twig

@@ -0,0 +1,25 @@
+{#
+/**
+* @file
+* Default theme implementation for the localgov_blogs_prev_next_block block.
+*/
+#}
+<nav class="localgov-blog-navigation">
+  {% if previous_url %}
+    <a href="{{ previous_url }}" class="localgov-blog-navigation__previous" rel="prev" aria-label="{{ 'Previous'|t }}: {{ previous_title }}">
+      <span class="localgov-blog-navigation__navigation-wrapper">
+        <span class="localgov-blog-navigation__navigation-nextprev">{{ 'Previous'|t }}<span class="visually-hidden">: </span></span>
+        <span class="localgov-blog-navigation__navigation-title">{{ previous_title }}</span>
+      </span>
+    </a>
+  {% endif %}
+
+  {% if next_url %}
+    <a href="{{ next_url }}" class="localgov-blog-navigation__next" rel="next" aria-label="{{ 'Next'|t }}: {{ next_title }}">
+      <span class="localgov-blog-navigation__navigation-wrapper">
+        <span class="localgov-blog-navigation__navigation-nextprev">{{ 'Next'|t }}<span class="visually-hidden">: </span></span>
+        <span class=" localgov-blog-navigation__navigation-title">{{ next_title }}</span>
+      </span>
+    </a>
+  {% endif %}
+</nav>