WordPress function to get links to adjacent gallery images, bookend images, and parent page

sjf_deh_get_nav_links.php

<?php

/**
 * Returns links to the adjacent images in a gallery, and to the gallery itself.
 * 
 * @return String Links to the adjacent images in a gallery, and to the gallery itself.
 */
function sjf_deh_get_nav_links() {
	
	// Get the current post, make sure it's an attachment.
	$post = get_post();
	if ( empty( $post->post_type ) || empty( $post->post_parent ) || ( $post->post_type != 'attachment' ) ) { return false; }

	// Try to get the link to the previous image.
	$prev = sjf_deh_get_adjacent_image_link( true, '<i class="icon-chevron-left"></i> ' );
	
	// If there is no previous image, get the link to fast-forward to the final image.
	if(!$prev){$prev = sjf_deh_get_bookend_image_link(true, '<i class="icon-chevron-left"></i> ');}
	
	// try to get the link to the next image
	$next = sjf_deh_get_adjacent_image_link(false, ' <i class="icon-chevron-right"></i>');
	
	// If there is no next image, rewind to the first image.
	if(!$next){$next = sjf_deh_get_bookend_image_link(false, '<i class="icon-chevron-left"></i> ');}
	
	// The link to the gallery.
	$parent = sjf_deh_get_parent_link();

	// Wrap the output
	$out = "
		<nav role='navigation' class='nav'>
			<span class='next_prev'>
				$prev
				$next
			</span>
			$parent
		</nav>
	";
	
	return $out;
}