rewrite-shop-categories.php

<?php
/**
 * Rewrite Shop Categories
 *
 * @wordpress-plugin
 * Plugin Name:       Rewrite Shop Categories
 * Description:       Allows categories and products both to have 'shop' base
 * Author:            Plant Ninja
 */

if ( ! defined( 'WPINC' ) ) { die; }

// Flush rewrite rules on activation and deactivation.
register_deactivation_hook( __FILE__, 'flush_rewrite_rules' );
register_activation_hook( __FILE__, 'flush_rewrite_rules' );

// Priority 20 so filter runs _after_ woocommerce filter.
add_filter( 'rewrite_rules_array', 'rsc_rewrite_shop_categories' , 20 );

/**
 * Simple function to filter wordpress rewrite rules array.
 *
 * @param array $rules Rules array passed by wordpress.
 */
function rsc_rewrite_shop_categories( $rules ) {
	return rsc_get_product_category_rewrite_rules() + $rules;
}


function rsc_get_product_category_rewrite_rules() : array {

	/*
	  Rewrite rules to match Plant Ninja categories and sub-categories.

	  The Plant Ninja product url structure is as follows:
	  - We want Urls to look like this:
	       shop/<base-category>/<optional-sub-category>/<the-product>
	  - Sharing the 'shop' base between categories and products is not supported
	    by WP/woocommerce out of the box (presumably because wordpress would have
	    no way to distinguish between categories and products.
	  - We can get around this by defining a way to distinguish between the two.
	    For Plant Ninja, the deepest category for a product must start with
	    "vegan-". E.g. "vegan-protein", "vegan-creatine".
	  - We will support one or two levels of categories for now.
	 */
	$new_rules = [

		/*
		 * Match arbitrarily named base categories. Products in these categories
		 * must have an additional sub-category with the 'vegan-' prefix, and the
		 * base category must not be prefixed with 'vegan-'.
		 *
		 * Matches:
		 *     shop/some-arbitrary-base-category
		 *     shop/some-arbitrary-base-category/
		 *
		 * Should NOT match:
		 *     shop/vegan-<anything>
		 *     shop/vegan-<anything>/
		 *     shop/base-category/<anything...>
		 */
		'shop/(?!vegan-)([^/]+?)/?$' => 'index.php?product_cat=$matches[1]',

		/*
		 * Matches:
		 *     shop/some-base-category/vegan-sub-category
		 *     shop/some-base-category/vegan-<sub-category>/
		 *
		 * Should NOT match:
		 *     shop/arbitrary-base-category
		 *     shop/arbitrary-base-category/
		 * which should be covered by the previous rule.
		 */
		'shop(?:/.*)*?/(vegan-[^/]+)/?$' => 'index.php?product_cat=$matches[1]',
	];

	return $new_rules;
}