Product Collection and Blocks

<?php
/**
 * Plugin Name:       Pocket Coffee Collections
 * Description:       Registers the "Coffee Club picks" collection for the Product Collection block.
 * Version:           0.1.0
 * Requires at least: 7.0
 * Requires PHP:      7.4
 * Requires Plugins:  woocommerce
 * License:           GPL-2.0-or-later
 * Text Domain:       pocket-coffee-collections
 *
 * @package PocketCoffee
 */

defined( 'ABSPATH' ) || exit;

const POCKET_COFFEE_CLUB_COLLECTION = 'pocket-coffee/product-collection/club-picks';

// 1. The editor script registers the collection (it only runs in the block editor).
add_action(
	'enqueue_block_editor_assets',
	function () {
		wp_enqueue_script(
			'pocket-coffee-collections',
			plugins_url( 'assets/collections.js', __FILE__ ),
			array( 'wc-blocks-registry', 'wp-i18n' ),
			filemtime( plugin_dir_path( __FILE__ ) . 'assets/collections.js' ),
			true
		);
	}
);

/**
 * The category that holds the coffee beans (slug), filterable for other shops.
 *
 * @return string
 */
function pocket_coffee_club_category_slug() {
	/**
	 * Filters the slug of the product category that the Coffee Club picks collection reads.
	 *
	 * @since 0.1.0
	 *
	 * @param string $slug Category slug, 'beans' by default.
	 */
	return (string) apply_filters( 'pocket_coffee_club_category_slug', 'beans' );
}

// 2. Front end: WooCommerce builds the query first (priority 10); a later callback adjusts it.
add_filter(
	'query_loop_block_query_vars',
	function ( $query, $block ) {
		if ( POCKET_COFFEE_CLUB_COLLECTION !== ( $block->context['collection'] ?? '' ) ) {
			return $query;
		}
		// phpcs:ignore WordPress.DB.SlowDBQuery.slow_db_query_tax_query
		$query['tax_query'][] = array(
			'taxonomy' => 'product_cat',
			'field'    => 'slug',
			'terms'    => array( pocket_coffee_club_category_slug() ),
		);
		return $query;
	},
	20,
	2
);

// 3. Editor preview: the editor fetches products through the REST API, so repeat the rule for /wp/v2/product.
add_filter(
	'rest_product_query',
	function ( $args, $request ) {
		$context = $request->get_param( 'productCollectionQueryContext' );
		if ( POCKET_COFFEE_CLUB_COLLECTION !== ( $context['collection'] ?? '' ) ) {
			return $args;
		}
		// phpcs:ignore WordPress.DB.SlowDBQuery.slow_db_query_tax_query
		$args['tax_query'][] = array(
			'taxonomy' => 'product_cat',
			'field'    => 'slug',
			'terms'    => array( pocket_coffee_club_category_slug() ),
		);
		return $args;
	},
	20,
	2
);

( function () {
	'use strict';

	const { __ } = window.wp.i18n;
	const { __experimentalRegisterProductCollection: registerProductCollection } = window.wc.wcBlocksRegistry;

	registerProductCollection( {
		name: 'pocket-coffee/product-collection/club-picks',
		title: __( 'Coffee Club picks', 'pocket-coffee-collections' ),
		description: __( 'The four cheapest bean bags in stock, for Coffee Club members.', 'pocket-coffee-collections' ),
		icon: 'coffee',
		keywords: [ 'coffee', 'club', 'beans' ],
		attributes: {
			query: {
				perPage: 4,
				orderBy: 'price',
				order: 'asc',
				woocommerceStockStatus: [ 'instock' ],
			},
			displayLayout: { type: 'flex', columns: 4, shrinkColumns: true },
			hideControls: [ 'created', 'featured', 'hand-picked' ],
		},
		innerBlocks: [
			[ 'core/heading', { level: 2, content: __( 'Coffee Club picks', 'pocket-coffee-collections' ) } ],
			[
				'woocommerce/product-template',
				{},
				[
					[ 'woocommerce/product-image' ],
					[ 'core/post-title', { level: 3, isLink: true, __woocommerceNamespace: 'woocommerce/product-collection/product-title' } ],
					[ 'woocommerce/product-price', { textAlign: 'center' } ],
				],
			],
			[ 'woocommerce/product-collection-no-results' ],
		],
	} );
}() );

> wp.blocks.getBlockVariations('woocommerce/product-collection').filter( v => v.name.startsWith('pocket-coffee') )
name:       pocket-coffee/product-collection/club-picks
title:      Coffee Club picks
isDefault:  false
attributes: { query: { perPage: 4, pages: 0, offset: 0, postType: "product", order: "asc", orderBy: "price", search: "",
              exclude: [], inherit: false, taxQuery: {}, isProductCollectionBlock: true, featured: false,
              woocommerceOnSale: false, woocommerceStockStatus: ["instock"], woocommerceAttributes: [],
              woocommerceHandPickedProducts: [], filterable: false, relatedBy: { categories: true, tags: true } },
              tagName: "div", displayLayout: { type: "flex", columns: 4, shrinkColumns: true },
              dimensions: { widthType: "fill" }, queryContextIncludes: ["collection"], forcePageReload: false,
              hideControls: ["inherit","created","featured","hand-picked"],
              collection: "pocket-coffee/product-collection/club-picks", inherit: false }

<!-- wp:woocommerce/product-collection {"queryId":1,"query":{"perPage":4,"pages":0,"offset":0,"postType":"product","order":"asc","orderBy":"price","search":"","exclude":[],"inherit":false,"taxQuery":{},"isProductCollectionBlock":true,"featured":false,"woocommerceOnSale":false,"woocommerceStockStatus":["instock"],"woocommerceAttributes":[],"woocommerceHandPickedProducts":[],"filterable":false,"relatedBy":{"categories":true,"tags":true}},"tagName":"div","displayLayout":{"type":"flex","columns":4,"shrinkColumns":true},"collection":"pocket-coffee/product-collection/club-picks","hideControls":["created","featured","hand-picked"],"queryContextIncludes":["collection"]} -->
<div class="wp-block-woocommerce-product-collection"><!-- wp:woocommerce/product-template -->
<!-- wp:post-title {"level":3,"isLink":true,"__woocommerceNamespace":"woocommerce/product-collection/product-title"} /-->
<!-- wp:woocommerce/product-price {"isDescendentOfQueryLoop":true} /-->
<!-- /wp:woocommerce/product-template --></div>
<!-- /wp:woocommerce/product-collection -->

wp post create ./club-picks.html --post_type=page --post_status=publish \
  --post_title='Coffee Club picks' --post_name=club-picks --porcelain

# plugin active
curl -s http://localhost:8081/club-picks/ | grep -oE 'wp-block-post-title[^>]*><a[^>]*>[^<]+' | sed 's/.*>//;s/ (hello)//'
Colombia Huila 250 g
Brazil Cerrado 250 g
Ethiopia Yirgacheffe 250 g

# plugin deactivated: same page, the rule is gone and every in-stock product of the store is eligible (first four shown)
Brewing guide (PDF)
Colombia Huila 250 g
Brazil Cerrado 250 g
Single-origin beans

# the editor's preview request (the editor also sends the stock status of the query)
curl -s -g 'http://localhost:8081/wp-json/wp/v2/product?per_page=10&isProductCollectionBlock=true&productCollectionQueryContext[collection]=pocket-coffee/product-collection/club-picks&woocommerceStockStatus[]=instock&orderby=price&order=asc&_fields=id'
[{"id":77},{"id":78},{"id":76}]

warning: To prevent conflicts with other collections, please use a unique name following the pattern: "<plugin-name>/product-collection/<collection-name>". Ensure "<plugin-name>" is your plugin name and "<collection-name>" is your collection name. Both should consist only of alphanumeric characters and hyphens (e.g., "my-plugin/product-collection/my-collection").
error: Invalid title: title must be a non-empty string.
error: Collection could not be registered due to invalid configuration.

<!-- wp:woocommerce/product-collection {"queryId":0,"query":{"perPage":6,"pages":0,"offset":0,"postType":"product","order":"asc","orderBy":"title","search":"","exclude":[],"inherit":false,"taxQuery":{"product_cat":[19]},"isProductCollectionBlock":true,"featured":false,"woocommerceOnSale":false,"woocommerceStockStatus":["instock","outofstock","onbackorder"],"woocommerceAttributes":[],"woocommerceHandPickedProducts":[],"filterable":true,"relatedBy":{"categories":true,"tags":true}},"tagName":"div","displayLayout":{"type":"flex","columns":3,"shrinkColumns":true},"dimensions":{"widthType":"fill"},"queryContextIncludes":["collection"]} -->
<div class="wp-block-woocommerce-product-collection"><!-- wp:woocommerce/product-filters -->
<div class="wp-block-woocommerce-product-filters"><!-- wp:woocommerce/product-filter-price -->
<div class="wp-block-woocommerce-product-filter-price"><!-- wp:woocommerce/product-filter-price-slider /--></div>
<!-- /wp:woocommerce/product-filter-price -->

<!-- wp:woocommerce/product-filter-attribute {"attributeId":1,"showCounts":true} -->
<div class="wp-block-woocommerce-product-filter-attribute"><!-- wp:woocommerce/product-filter-checkbox-list /--></div>
<!-- /wp:woocommerce/product-filter-attribute -->

<!-- wp:woocommerce/product-filter-status {"showCounts":true} -->
<div class="wp-block-woocommerce-product-filter-status"><!-- wp:woocommerce/product-filter-checkbox-list /--></div>
<!-- /wp:woocommerce/product-filter-status --></div>
<!-- /wp:woocommerce/product-filters -->

<!-- wp:woocommerce/product-template -->
<!-- wp:post-title {"level":3,"isLink":true,"__woocommerceNamespace":"woocommerce/product-collection/product-title"} /-->
<!-- wp:woocommerce/product-price {"isDescendentOfQueryLoop":true} /-->
<!-- /wp:woocommerce/product-template -->

<!-- wp:woocommerce/product-collection-no-results -->
<!-- wp:paragraph --><p>No coffee matches these filters.</p><!-- /wp:paragraph -->
<!-- /wp:woocommerce/product-collection-no-results --></div>
<!-- /wp:woocommerce/product-collection -->

for u in "" "?min_price=9&max_price=10" "?filter_origin=brazil-cerrado" \
         "?filter_origin=brazil-cerrado,colombia-huila&query_type_origin=or" \
         "?filter_origin=brazil-cerrado&filter_stock_status=instock" "?categories=coffee-equipment"; do
  echo "== $u"
  curl -s "http://localhost:8081/product-filters-demo/$u" | grep -oE 'wp-block-post-title[^>]*><a[^>]*>[^<]+' | sed 's/.*>//;s/ (hello)//'
done
==
Brazil Cerrado 1 kg
Brazil Cerrado 250 g
Colombia Huila 250 g
Ethiopia Yirgacheffe 250 g
== ?min_price=9&max_price=10
Ethiopia Yirgacheffe 250 g
== ?filter_origin=brazil-cerrado
Brazil Cerrado 1 kg
Brazil Cerrado 250 g
== ?filter_origin=brazil-cerrado,colombia-huila&query_type_origin=or
Brazil Cerrado 1 kg
Brazil Cerrado 250 g
Colombia Huila 250 g
== ?filter_origin=brazil-cerrado&filter_stock_status=instock
Brazil Cerrado 250 g
== ?categories=coffee-equipment

add_filter(
	'woocommerce_pre_product_filter_data',
	function ( $results, $filter_type ) {
		if ( 'price' === $filter_type ) {
			return array(
				'min_price' => 0,
				'max_price' => 100,
			);
		}
		return $results;
	},
	10,
	2
);