NextPrev.php

<?php
/**
 * Copyright © 2016 Ihor Vansach (ihor@magefan.com). All rights reserved.
 * See LICENSE.txt for license details (http://opensource.org/licenses/osl-3.0.php).
 *
 * Glory to Ukraine! Glory to the heroes!
 */

namespace Magefan\Blog\Block\Post\View;

use Magento\Store\Model\ScopeInterface;

/**
 * Blog post next and prev post links
 */
class NextPrev extends \Magento\Framework\View\Element\Template
{
    /**
     * Previous post
     *
     * @var \Magefan\Blog\Model\Post
     */
    protected $_prevPost;

    /**
     * Next post
     *
     * @var \Magefan\Blog\Model\Post
     */
    protected $_nextPost;

    /**
     * @var \Magefan\Blog\Model\ResourceModel\Post\CollectionFactory
     */
    protected $_postCollectionFactory;

    /**
     * @var Magento\Framework\Registry
     */
    protected $_coreRegistry;

    /**
     * Construct
     *
     * @param \Magento\Framework\View\Element\Context $context
     * @param \Magefan\Blog\Model\ResourceModel\Post\CollectionFactory $_tagCollectionFactory
     * @param \Magento\Framework\Registry $coreRegistry
     * @param array $data
     */
    public function __construct(
        \Magento\Framework\View\Element\Template\Context $context,
        \Magefan\Blog\Model\ResourceModel\Post\CollectionFactory $postCollectionFactory,
        \Magento\Framework\Registry $coreRegistry,
        array $data = []
    ) {
        parent::__construct($context, $data);
        $this->_postCollectionFactory = $postCollectionFactory;
        $this->_coreRegistry = $coreRegistry;
    }

    /**
     * Retrieve true if need to display next-prev links
     *
     * @return boolean
     */
    public function displayLinks()
    {
        return (bool)$this->_scopeConfig->getValue(
            'mfblog/post_view/nextprev/enabled',
            \Magento\Store\Model\ScopeInterface::SCOPE_STORE
        );
    }

    /**
     * Retrieve prev post
     * @return \Magefan\Blog\Model\Post || bool
     */
    public function getPrevPost()
    {
        if ($this->_prevPost === null) {
            $this->_prevPost = false;
            $collection = $this->_getFrontendCollection()->addFieldToFilter(
                'publish_time', [
                    'gteq' => $this->getPost()->getPublishTime()
                ]
            );
            $post = $collection->getFirstItem();

            if ($post->getId()) {
                $this->_prevPost = $post;
            }
        }

        return $this->_prevPost;
    }

    /**
     * Retrieve next post
     * @return \Magefan\Blog\Model\Post || bool
     */
    public function getNextPost()
    {
        if ($this->_nextPost === null) {
            $this->_nextPost = false;
            $collection = $this->_getFrontendCollection()->addFieldToFilter(
                'publish_time', [
                    'lteq' => $this->getPost()->getPublishTime()
                ]
            );
            $post = $collection->getFirstItem();

            if ($post->getId()) {
                $this->_nextPost = $post;
            }
        }

        return $this->_nextPost;
    }

    /**
     * Retrieve post collection with frontend filters and order
     * @return bool
     */
    protected function _getFrontendCollection()
    {
        $collection = $this->_postCollectionFactory->create();
        $collection->addActiveFilter()
            ->addFieldToFilter('post_id', ['neq' => $this->getPost()->getId()])
            ->addStoreFilter($this->_storeManager->getStore()->getId())
            ->setOrder('publish_time', 'DESC')
            ->setPageSize(1);
        return $collection;
    }

    /**
     * Retrieve post instance
     *
     * @return \Magefan\Blog\Model\Post
     */
    public function getPost()
    {
        return $this->_coreRegistry->registry('current_blog_post');
    }

}