A smarter way to get post thumbnail

function.php

<?php
function post_thumbdail($full){
	if ( has_post_thumbnail() ) { 
		echo "<aside><a href='".get_permalink()."' title='".get_the_title()."' rel='canonical'>";
		the_post_thumbnail($full);
		echo "</a></aside>";
	}else{ 
		if( $full == 'full' ) return;
		
		$attachments = get_posts( array(
			'post_type' => 'attachment',
			'numberposts'     => 1,
			'post_parent' => get_the_ID(),
			'exclude'     => get_post_thumbnail_id()
		) );

		if ( $attachments ) {
			foreach ( $attachments as $attachment ) {
				$href = wp_get_attachment_image_src( $attachment->ID, $full);
			}
			echo "<aside><a class='default' href='".get_permalink()."' title='".get_the_title()."' rel='canonical'>";
			echo "<img src='".$href[0]."' alt='".get_the_title()."'/>"; 
			echo "</a></aside>";
		}
	
	}
}
?>