WordPress: Draft idea on how one could simplify the get_the_category_list() to address code duplication - WP 4.4.2

get_the_category_list.php

/**
 * Retrieve category list in either HTML list or custom format.
 *
 * @since 1.5.1
 *
 * @global WP_Rewrite $wp_rewrite
 *
 * @param string $separator Optional, default is empty string. Separator for between the categories.
 * @param string $parents Optional. How to display the parents.
 * @param int $post_id Optional. Post ID to retrieve categories.
 * @return string
 */
function get_the_category_list( $separator = '', $parents='', $post_id = false ) {
	global $wp_rewrite;
	if ( ! is_object_in_taxonomy( get_post_type( $post_id ), 'category' ) ) {
		/** This filter is documented in wp-includes/category-template.php */
		return apply_filters( 'the_category', '', $separator, $parents );
	}
	/**
	 * Filter the categories before building the category list.
	 *
	 * @since 4.4.0
	 *
	 * @param array    $categories An array of the post's categories.
	 * @param int|bool $post_id    ID of the post we're retrieving categories for. When `false`, we assume the
	 *                             current post in the loop.
	 */
	$categories = apply_filters( 'the_category_list', get_the_category( $post_id ), $post_id );
	if ( empty( $categories ) ) {
		/** This filter is documented in wp-includes/category-template.php */
		return apply_filters( 'the_category', __( 'Uncategorized' ), $separator, $parents );
	}
	$rel = ( is_object( $wp_rewrite ) && $wp_rewrite->using_permalinks() ) ? 'rel="category tag"' : 'rel="category"';
	$thelist = '';

	// Seperator - Begin
	if( '' === $seperator )
		$thelist .= '<ul class="post-categories">';
	
	foreach ( $categories as $category ) {
	
		// Seperator - Before
		if( '' === $seperator )
			$thelist .= "\n\t<li>";
		elseif ( ! empty( $thelist ) )
			$thelist .= $separator;

		switch ( strtolower( $parents ) ) {
			case 'multiple':
				if ( $category->parent )
					$thelist .= get_category_parents( $category->parent, true, $separator );
				$thelist .= '<a href="' . esc_url( get_category_link( $category->term_id ) ) . '" ' . $rel . '>' . $category->name.'</a>';
				break;
			case 'single':
				$thelist .= '<a href="' . esc_url( get_category_link( $category->term_id ) ) . '"  ' . $rel . '>';
				if ( $category->parent )
					$thelist .= get_category_parents( $category->parent, false, $separator );
				$thelist .= $category->name.'</a>';
				break;
			case '':
			default:
				$thelist .= '<a href="' . esc_url( get_category_link( $category->term_id ) ) . '" ' . $rel . '>' . $category->name.'</a>';
		}
	
		// Seperator - After
		if( '' === $seperator )
			$thelist .= "\n\t<li>";
		
	}
	
	// Seperator - End	
	if( '' === $seperator )
		$thelist .= '</ul>';

	/**
	 * Filter the category or list of categories.
	 *
	 * @since 1.2.0
	 *
	 * @param array  $thelist   List of categories for the current post.
	 * @param string $separator Separator used between the categories.
	 * @param string $parents   How to display the category parents. Accepts 'multiple',
	 *                          'single', or empty.
	 */
	return apply_filters( 'the_category', $thelist, $separator, $parents );
}