I have been working on an online newspaper/blogging application with CodeIgniter 3.1.8 and Twitter Bootstrap 4.

The latest feature added is lazy loading of posts.

From the Static_model (application\models\Static_model.php), which is responsible with the general settings, I can set $data['is_ajax_loading'] to true and enable loading posts via AJAX.

In the Posts controller, I have:

class Posts extends CI_Controller
{
  public function __construct()
  {
    parent::__construct();
  }

  private function _initPagination($path, $totalRows, $query_string_segment = 'page')
  {
    // load and configure pagination 
    $this->load->library('pagination');
    $config['base_url']             = base_url($path);
    $config['query_string_segment'] = $query_string_segment;
    $config['enable_query_strings'] = TRUE;
    $config['reuse_query_string']   = TRUE;
    $config['total_rows']           = $totalRows;
    $config['per_page']             = 12;

    if ($this->Static_model->get_static_data()['has_pager']) {
      $config['display_pages'] = FALSE;
      $config['first_link'] = FALSE;
      $config['last_link'] = FALSE;
      $config['prev_tag_open'] = '<li class="prev">';
      $config['prev_tag_close'] = '</li>';
      $config['next_tag_open'] = '<li class="next">';
      $config['next_tag_close'] = '</li>';
    }

    if (!isset($_GET[$config['query_string_segment']]) || $_GET[$config['query_string_segment']] < 1) {
      $_GET[$config['query_string_segment']] = 1;
    }
    $this->pagination->initialize($config);

    $limit  = $config['per_page'];
    $offset = ($this->input->get($config['query_string_segment']) - 1) * $limit;

    return array(
      'limit' => $limit,
      'offset' => $offset
    );
  }

  public function index()
  {
    //call initialization method
    $config = $this->_initPagination("/", $this->Posts_model->get_num_rows());
    $data                  = $this->Static_model->get_static_data();
    $data['base_url']      = base_url("/");
    $data['pages']         = $this->Pages_model->get_pages();
    $data['categories']    = $this->Categories_model->get_categories();
    $data['search_errors'] = validation_errors();
    $data['posts'] = $this->Posts_model->get_posts($config['limit'], $config['offset']);
    $data['max_page'] = ceil($this->Posts_model->get_num_rows() / 12);

    $this->twig->addGlobal('pagination', $this->pagination->create_links());

    // Featured posts
    if ($data['is_featured']) {
      $data['featured'] = $this->Posts_model->featured_posts();
      $this->twig->addGlobal('featuredPosts', "themes/{$data['theme_directory']}/partials/hero.twig");
    }

    $this->twig->display("themes/{$data['theme_directory']}/layout", $data);
  }

  public function search()
  {
    // Force validation since the form's method is GET
    $this->form_validation->set_data($this->input->get());
    $this->form_validation->set_rules('search', 'search term', 'required|trim|min_length[3]', array(
      'min_length' => 'The search term must be at least 3 characters long.'
    ));
    $this->form_validation->set_error_delimiters('<p class = "error search-error">', '</p>');
    // If search fails
    if ($this->form_validation->run() === FALSE) {
      $data['search_errors'] = validation_errors();
      return $this->index();
    } else {
      $expression           = $this->input->get('search');
      $posts_count          = $this->Posts_model->search_count($expression);
      $query_string_segment = 'page';
      $config               = $this->_initPagination("/posts/search", $posts_count, $query_string_segment);
      $data                 = $this->Static_model->get_static_data();
      $data['base_url']     = base_url("/");
      $data['pages']        = $this->Pages_model->get_pages();
      $data['categories']   = $this->Categories_model->get_categories();
      //use limit and offset returned by _initPaginator method
      $data['posts']        = $this->Posts_model->search($expression, $config['limit'], $config['offset']);
      $data['expression']   = $expression;
      $data['posts_count']  = $posts_count;
      $data['max_page'] = ceil($posts_count / 12);
      
      $this->twig->addGlobal('pagination', $this->pagination->create_links());
      $this->twig->display("themes/{$data['theme_directory']}/layout", $data);
    }
  }

  public function byauthor($authorid)
  {
    //load and configure pagination 
    $this->load->library('pagination');
    $config['base_url']             = base_url('/posts/byauthor/' . $authorid);
    $config['query_string_segment'] = 'page';
    $config['total_rows']           = $this->Posts_model->posts_by_author_count($authorid);
    $config['per_page']             = 12;

    if ($this->Static_model->get_static_data()['has_pager']) {
      $config['display_pages'] = FALSE;
      $config['first_link'] = FALSE;
      $config['last_link'] = FALSE;
      $config['prev_tag_open'] = '<li class="prev">';
      $config['prev_tag_close'] = '</li>';
      $config['next_tag_open'] = '<li class="next">';
      $config['next_tag_close'] = '</li>';
    }

    if (!isset($_GET[$config['query_string_segment']]) || $_GET[$config['query_string_segment']] < 1) {
      $_GET[$config['query_string_segment']] = 1;
    }

    $limit  = $config['per_page'];
    $offset = ($this->input->get($config['query_string_segment']) - 1) * $limit;
    $this->pagination->initialize($config);

    $data                 = $this->Static_model->get_static_data();
    $data['base_url']     = base_url("/");
    $data['pages']        = $this->Pages_model->get_pages();
    $data['categories']   = $this->Categories_model->get_categories();
    $data['posts']        = $this->Posts_model->get_posts_by_author($authorid, $limit, $offset);
    $data['posts_count']  = $this->Posts_model->posts_by_author_count($authorid);
    $data['posts_author'] = $this->Posts_model->posts_author($authorid);
    $data['max_page'] = ceil($data['posts_count'] / $limit);
    $data['tagline']      = "Posts by " . $data['posts_author']->first_name . " " . $data['posts_author']->last_name;

    $this->twig->addGlobal('pagination', $this->pagination->create_links());
    $this->twig->display("themes/{$data['theme_directory']}/layout", $data);
  }

  public function post($slug)
  {
    $data                 = $this->Static_model->get_static_data();
    $data['base_url']     = base_url("/");
    $data['pages']        = $this->Pages_model->get_pages();
    $data['categories']   = $this->Categories_model->get_categories();
    $data['authors']      = $this->Usermodel->getAuthors();
    $data['posts']        = $this->Posts_model->sidebar_posts($limit = 5, $offset = 0);
    $data['post']         = $this->Posts_model->get_post($slug);
    $data['next_post']    = $this->Posts_model->get_next_post($slug);
    $data['prev_post']    = $this->Posts_model->get_prev_post($slug);
    $data['author_image'] = isset($data['post']->avatar) && $data['post']->avatar !== '' ? $data['post']->avatar : 'default-avatar.png';

    if ($data['categories']) {
      foreach ($data['categories'] as &$category) {
        $category->posts_count = $this->Posts_model->count_posts_in_category($category->id);
      }
    }

    if (!empty($data['post'])) {
      // Overwrite the default tagline with the post title
      $data['tagline']  = $data['post']->title;
      // Get post comments
      $post_id          = $data['post']->id;
      $data['comments'] = $this->Comments_model->get_comments($post_id);
      $this->twig->addGlobal('singlePost', "themes/{$data['theme_directory']}/templates/singlepost.twig");
    } else {
      $data['tagline'] = "Page not found";
      $this->twig->addGlobal('notFound', "themes/{$data['theme_directory']}/templates/404.twig");
    }
    $this->twig->display("themes/{$data['theme_directory']}/layout", $data);
  }
}

The script that does the loading:

(function($) {

    var currentPage = 2,
        maxPage = $('#postsContainer').data('max-page'),
        posts = null,
        pageUrl = $(location).attr('href'),
        pageBaseUrl = pageUrl.split('?')[0],
        searchStr = pageUrl.split('?')[1];

    $('.pagination').hide();

    $(window).scroll(function() {
        var toBottom = $(window).scrollTop() >= $(document).height() - $(window).height() - 25;

        if (toBottom && currentPage <= maxPage) {
            loadMore();
        }
    });

    function loadMore() {

        $.ajax({
                url: `${pageBaseUrl}?${typeof searchStr === 'string' ? searchStr : ''}&page=${currentPage}`,
                type: 'GET',
                beforeSend: function() {
                    if (typeof posts != 'undefined') {
                        $('.loader').show();
                    }
                }
            })
            .done(function(data) {
                $('.loader').hide();
                posts = $(data).find('#postsContainer').html();

                if (typeof posts != 'undefined') {

                    $('#postsContainer').append(posts);
                    currentPage = currentPage + 1;

                    if (currentPage > maxPage) {
                        $('#postsContainer').append('<p class="text-center text-muted">No more posts to load</p>');
                    }
                }
            });
    }

})(jQuery);

In the posts-lists.twig view:

{% if posts %}
    {% if is_ajax_loading %}
    <div id="postsContainer" data-max-page="{{max_page}}">
    {% endif %}
        {% for post in posts %}
            <div class="post-preview">
                <a href="{{base_url}}{{post.slug}}">
                    <h2 class="post-title">{{post.title}}</h2>
                    <h3 class="post-subtitle">{{post.description}}</h3>
                </a>
                <p class="post-meta">
                    Posted {% if category_name is null %}in <a href="{{base_url}}categories/posts/{{post.cat_id}}" title="All posts in {{post.post_category}}">{{post.post_category}}</a>,{% endif %} on {{post.created_at | date("M d, Y")}}
               </p>
            </div>
      <hr class="posts-separator">
        {% endfor %}

    {% if is_ajax_loading %}
    </div>
    {% endif %} 
{% else %}
    {% if posts_author is not defined and expression is not defined %}
        <p class="mt-0 text-muted text-center">There are no posts {% if category_name is defined %} in this category {% endif %} yet.</p>
    {% endif %}
{% endif %} 

{% if is_ajax_loading %}
    <div class="loader"><span></span></div>
{% endif %}

My main concerns are security and code redundancy.

Questions:

1. Is the code DRY enough?
2. Are there any security risks?
3. Improvement opportunities?