social sharing with Pinterest first image

functions.php

//Get the first image from the post
function get_first_image_url() {
  global $post, $posts;

  $first_img = '';
  ob_start();
  ob_end_clean();
  $output = preg_match_all('/<img.+src=[\'"]([^\'"]+)[\'"].*>/i', $post->post_content, $matches);
  $first_img = $matches[1][0];

  // Defines a default image here
  if(empty($first_img)){
    $first_img = "/images/default.jpg";
  }
  return $first_img;
}

// Social sharing shortcode
/** <?php echo do_shortcode('[social_sharing]') ; ?> */
function social_sharing()
{
		// Get current page URL
		$pageURL = urlencode(get_permalink());

		// Get current page title
		$pageTitle = str_replace( ' ', '%20', get_the_title());
    $postMeta = get_post_meta(get_the_ID(), 'description', true);

		// Get Post Thumbnail for pinterest
    global $post;
		$postThumbnail = get_first_image_url();

		// Facebook URL
		$facebookURL = 'https://www.facebook.com/sharer/sharer.php?u='.$pageURL;

		// Pinterest
		$pinterestURL = 'https://pinterest.com/pin/create/button/?url='.$pageURL.'&amp;media='.$postThumbnail.'&amp;description='.$pageTitle.' - '.$postMeta;

	return'
	<div class="social-sharing-container">
		<a class="btn social-sharing-btn btn-facebook" target="_new" href="'.$facebookURL.'"><i class="fa fa-facebook"></i></a>
    <a class="btn social-sharing-btn btn-pinterest" target="_new" href="'.$pinterestURL.'" data-pin-custom="true" target="_blank"><i class="fa fa-pinterest"></i></a>
<a class="btn social-sharing-btn btn-email" href="mailto:?subject='.$pageTitle.'&body='.$pageURL.'"><i class="fa fa-envelope"></i></a>
	</div>
';
}
add_shortcode("social_sharing", "social_sharing");