<?php
// Get page by slug.
// https://codex.wordpress.org/Function_Reference/get_page_by_path
// http://wordpress.stackexchange.com/questions/102841/how-to-get-page-id-of-a-page-using-page-slug
$page_slug = 'projects';
$slug_type = 'page';
$output_type = ARRAY_A;
$page = get_page_by_path($page_slug, $output_type, $slug_type);

// // Get all pages belong to a parent.
// // http://wordpress.stackexchange.com/questions/74063/getting-only-direct-child-pages-in-wordpress-with-get-pages
// // https://codex.wordpress.org/Function_Reference/get_pages
// // https://developer.wordpress.org/reference/functions/get_pages/
// $args = array(
//     'child_of' => $page['ID'],
//     'parent ' => $page['ID'],
//     'offset' => 0,
//     'post_type' => 'page',
//     'post_status' => 'publish',
//     'sort_column' => 'menu_order',
//     'sort_order' => 'asc',
// );
// $pages = get_pages($args);

// Get all pages belong to a parent.
// https://codex.wordpress.org/Function_Reference/get_children
// http://stackoverflow.com/questions/6137559/wordpress-limit-get-pages-to-show-5-items
// https://wordpress.org/support/topic/sort-children-by-menu-order
$output_type = ARRAY_A;
$output_type = OBJECT;
$max_items = 6;
$args = array(
    'numberposts' => $max_items,
    'order' => 'DESC',
    'orderby' => 'menu_order',
    'post_parent' => $page['ID'],
    'post_status' => 'publish',
    'post_type' => 'page',
);
$pages = get_children($args, $output_type);

// Get all children and count them.
$children = get_pages('child_of=' . $page['ID']);
?>

<!-- side-box -->
<div class="col-md-3 side-box">

    <?php if (count($pages) > 0) { ?>
    <h2>PROJECTS</h2>
    <ul>
        <?php foreach ($pages as $key => $child) { ?>
        <li>
            <div class="col-md-5 col-sm-3 col-xs-3 project-thumbnail-box">
                <a class="pull-left project-thumbnail transparent-onhover" href="<?php echo get_permalink($child->ID); ?>">
                    <?php if (get_the_post_thumbnail($child->ID, 'thumbnail')) { ?>
                        <?php
                        // Get custom featured image size.
                        // http://stackoverflow.com/questions/9500928/wordpress-custom-featured-image-size
                        // echo get_the_post_thumbnail($child->ID, 'post-thumbnails', array('class' => 'img-responsive'));

                        // Get thumbnail size.
                        echo get_the_post_thumbnail($child->ID, 'thumbnail', array('class' => 'img-responsive')); 
                        ?>
                    <?php } else { ?>
                        <img src="http://placehold.it/500x600" class="img-responsive" alt="<?php the_title(); ?>" />
                    <?php } ?>
                </a>
            </div>
            <div class="col-md-7 col-sm-9 col-xs-9 project-title-box">
                <a class="project-title" href="<?php echo get_permalink($child->ID); ?>"><?php echo $child->post_title; ?></a>
            </div>
        </li>
        <?php } ?>
    </ul>

    <?php
    if (count($children) > $max_items) {
        // Get a random page.
        // https://wordpress.org/support/topic/how-to-get-a-single-random-sub-page
        shuffle($children);
        if ($children) {
            $pageids = array();
            foreach ($children as $page) {
                $pageids[]= $page->ID;
            }
        }
    ?>
    <a href="<?php echo get_permalink($page->ID); ?>" class="button-more">More &raquo;</a>
    <?php } ?>
    <?php } ?>

</div>
<!-- side-box -->