rewrites for all taxonomy combinations

rewrites.php

<?php


function eg_add_rewrite_rules() {

	global $wp_rewrite;
	$post_type = 'post';
	if ( ! is_object( $post_type ) ) {
		$post_type = get_post_type_object( $post_type );
	}

	$new_rewrite_rules = array();

	$taxonomies = get_object_taxonomies( $post_type->name, 'objects' );

	unset( $taxonomies['post_format'] );

	$all_combinations = get_permutations( array_keys( $taxonomies ) );
	foreach ( $all_combinations as $tmp ) {
		if ( count( $tmp ) > 1 ) {
			$new_all_combinations[] = $tmp;
		}
	}


	foreach ( $new_all_combinations as $combination ) {
		$counter = 0;
		$rule    = $rewrite = '';
		foreach ( $combination as $item ) {
			$query_var = $taxonomies[ $item ]->query_var;
			$counter ++;
			$rule .= $item . '/(.+?)/';
			$prefix = 'index.php?';
			if ( $rewrite ) {
				$prefix = '&';
			}
			$rewrite .= $prefix . $query_var . '=matches[' . $counter . ']';
		}
		if ( $rule ) {
			$new_rewrite_rules = array_merge( array( $rule . '?$' => $rewrite ), $new_rewrite_rules );
		}
	}


	$wp_rewrite->rules = $new_rewrite_rules + $wp_rewrite->rules;
}

add_action( 'generate_rewrite_rules', 'eg_add_rewrite_rules' );

function get_permutations( array $values ) {
	$n   = count( $values );
	$rec = function ( array $values, &$ret, $n, array $cur = array() ) use ( &$rec ) {
		if ( $n > 0 ) {
			foreach ( $values as $v ) {
				$newCur = $cur;
				if ( ! in_array( $v, $newCur ) ) {
					$newCur[] = $v;
				}
				$rec( $values, $ret, $n - 1, $newCur );
			}
		} else {
			$ret[] = $cur;
		}
	};
	$ret = array();
	$rec( $values, $ret, $n );
	$combination_permutation = array_filter( array_unique( $ret, SORT_REGULAR ) );


	//sort array by number of elements

	usort( $combination_permutation, function ( $a, $b ) {
		if ( $a == $b ) {
			return 0;
		}

		return ( count( $a ) > count( $b ) ) ? - 1 : 1;
	} );

	return $combination_permutation;


}