WP_Query

<?php
function product_filter_ajax() {
        global $wpdb, $product, $post;
        if (!isset($_REQUEST['filters'])) die('none');
        $filters = array();
        $filtersAA = array();
        $possibleTaxonomies = array('price', 'product_brand', 'pa_colour', 'pa_size', 'pa_strap', 'pa_function', 'pa_movement');
        $postCount = 0;

        // Just placing into an easier data structure
        foreach($_REQUEST['filters'] AS $filter) {
                $filters[] = parse_filter_option($filter);
        }

        foreach($filters AS $selectedFilter) {
                $filtersAA[$selectedFilter[0]] = $selectedFilter[1];
        }

        // Set variable variable so each taxonomy can be accessed via $price, $product_brand, $pa_colour etc from $possibleTaxonomies list
        foreach($filtersAA AS $key => $val) {
                $$key = array(
                                'taxonomy' => $key,
                                'field' => 'slug',
                                'terms' => $val
                        );
        }

        // Add all additional filters
        foreach($possibleTaxonomies AS $taxonomy) {
                if (!isset($$taxonomy)) {
                        $$taxonomy = array();
                }
        }

        if (isset($price) && !empty($price)) {
                $priceRange = parse_filter_option($price['terms'], '-');
        }

        // WP_Query thing goes here to actually make use of filter...
        // Base query arguments go here
        $queryArgs = array(
                                'post_type' => 'product',
                                'posts_per_page' => -1,
                                'post_status' => 'publish',
                                'meta_query' => array(
                                        array(
                                                'key'                   => '_visibility',
                                                'value'                 => array('catalog', 'visible'),
                                                'compare'               => 'IN'
                                        )
                                ),
                                'tax_query' => array(

                                )
                        );

        if (count($filtersAA) > 1) {
                $queryArgs['tax_query']['relation'] = 'AND';
        };

        foreach($possibleTaxonomies AS $taxonomy) {
                // Price is different
                if ($taxonomy == 'price') continue;

                if (isset($$taxonomy) && !empty($$taxonomy)) {
                        $queryArgs['tax_query'][] = $$taxonomy;
                }
        }

        if (isset($priceRange) && !empty($priceRange)) {
                $queryArgs['meta_key'] = '_price';
                $queryArgs['meta_query'] = array(
                        array(
                                'key' => '_price',
                                'type' => 'NUMERIC',
                                'value' => $priceRange,
                                'compare' => 'BETWEEN'
                                )
                        );
        }

        if (isset($sortBy) && !empty($sortBy)) {
                $queryArgs['meta_key'] = '_price';
                $queryArgs['orderby'] = array('meta_value_num' => $sortBy['terms']);
        }

        // Add any extra modifications required by the specific page this is called on
        $queryArgs = get_page_category($_REQUEST['page'], $queryArgs);
        var_dump($queryArgs);

        $filteredQuery = new WP_Query($queryArgs);

        // Bestsellers may have applied a filter to ordering...try to check and remove it if so
        if (array_key_exists('edit_bestsellers_orderby', $GLOBALS['wp_filter'])) {
                remove_filter('posts_orderby', 'edit_bestsellers_orderby');
        }
        if (array_key_exists('edit_bestsellers_join', $GLOBALS['wp_filter'])) {
                remove_filter('posts_join', 'edit_bestsellers_join');
        }
        if (array_key_exists('edit_bestsellers_where', $GLOBALS['wp_filter'])) {
                remove_filter('posts_where', 'edit_bestsellers_where');
        }

        if ($filteredQuery->have_posts()) {
                do_action( 'woocommerce_before_shop_loop' );
                while ($filteredQuery->have_posts()) {
                        $filteredQuery->the_post();
                        ?>
                        <?php wc_get_template_part( 'content', 'product' ); ?>
                        <?php
                }
        }

        die();
}

function parse_filter_option($option, $character = '=') {
        $option = explode($character, $option);

        return array($option[0], $option[1]);
}

function get_page_category($href, $queryArgs) {
        $url = parse_url($href);

        // Sort out path here to get any special WP_Query arguments to pass back
        switch ($url['path']) {
                case '/product-category/mens-watches/':
                        $queryArgs['product_cat'] = 'mens-watches';
                break;

                case '/product-category/womens-watches/':
                        $queryArgs['product_cat'] = 'womens-watches';
                break;

                case '/mens-watches-sale/':
                        $queryArgs['product_cat'] = 'mens-watches';
                        $product_ids_on_sale = wc_get_product_ids_on_sale();
                        $meta_query   = array();
                        $meta_query[] = WC()->query->visibility_meta_query();
                        $meta_query[] = WC()->query->stock_status_meta_query();
                        $meta_query   = array_filter( $meta_query );

                        $queryArgs['meta_query'] = $meta_query;
                        $queryArgs['post__in'] = array_merge( array( 0 ), $product_ids_on_sale );
                break;

                case '/mens-watches-bestsellers/':
                        $queryArgs['posts_per_page'] = 4;
                        $queryArgs['product_cat'] = 'mens-watches';
                        //$queryArgs['meta_key'] = 'total_sales';
                        //$queryArgs['orderby'] = 'meta_value_num';
                        //$queryArgs['meta_query'][] = array('key' => 'total_sales');

                        /*$firstFilteredArg = new WP_Query($queryArgs);
                        $firstFilterPostIDs = array();
                        if ($firstFilteredArg->have_posts()) {
                                while ($firstFilteredArg->have_posts()) {
                                        $firstFilteredArg->the_post();
                                        $firstFilterPostIDs[] = get_the_ID();
                                }
                        }
                        var_dump($firstFilterPostIDs);

                        $queryArgs['meta_key'] = '_price';
                        $queryArgs['post__in'] = $firstFilterPostIDs;
                        add_filter('posts_orderby', 'edit_bestsellers_orderby');
                        add_filter('posts_join', 'edit_bestsellers_join');
                        add_filter('posts_where', 'edit_bestsellers_where');
                        add_filter('posts_clauses', 'edit_bestsellers_clauses');*/
                break;

                case '/womens-watches-sale/':
                        $queryArgs['product_cat'] = 'womens-watches';
                        $product_ids_on_sale = wc_get_product_ids_on_sale();
                        $meta_query   = array();
                        $meta_query[] = WC()->query->visibility_meta_query();
                        $meta_query[] = WC()->query->stock_status_meta_query();
                        $meta_query   = array_filter( $meta_query );

                        $queryArgs['meta_query'] = $meta_query;
                        $queryArgs['post__in'] = array_merge( array( 0 ), $product_ids_on_sale );
                break;

                case '/womens-watches-bestsellers/':
                        $queryArgs['posts_per_page'] = 10;
                        $queryArgs['product_cat'] = 'womens-watches';
                        $queryArgs['meta_key'] = 'total_sales';
                        $queryArgs['orderby'] = 'meta_value_num';
                break;

                case '/newest-products/':
                $queryArgs['posts_per_page'] = 10;
                $queryArgs['tax_query'][] = array(
                                                                                'taxonomy' => 'product_cat',
                                                                                'field' => 'slug',
                                                                                'terms' => 'mens-watches'
                                                                                );
                $queryArgs['tax_query'][] = array(
                                                                                        'taxonomy' => 'product_cat',
                                                                                        'field' => 'slug',
                                                                                        'terms' => 'womens-watches'
                                                                                );
                $queryArgs['orderby'][] = array('date' => 'DESC');
                break;
        }

        return $queryArgs;
}

function orderby_newest_filter($orderby) {
        global $wpdb;
        return " {$wpdb->postmeta}.meta_value, mta.meta_value";
}

add_action('wp_ajax_product_filter_ajax', 'product_filter_ajax');
add_action('wp_ajax_nopriv_product_filter_ajax', 'product_filter_ajax');

/*
 * Test orderby filters
 */
function edit_bestsellers_clauses($clauses) {
        var_dump($clauses);
        return $clauses;
}
function edit_bestsellers_where($where_statement) {
        //$where_statement = substr($where_statement, 0, -1);
        //$where_statement .= " AND (mt99.meta_key='total_sales'))"
        //var_dump($where_statement);
        return $where_statement;
}
function edit_bestsellers_join($join_statement) {
        //$join_statement .= " INNER JOIN wp_postmeta AS mt99 ON (wp_posts.ID = mt99.post_id)"
        //var_dump($join_statement);
        return $join_statement;
}
function edit_bestsellers_orderby($orderby_statement) {
        //$orderby_statement .= " , mt2.meta_value+0 DESC";
        //var_dump($orderby_statement);
        return $orderby_statement;
}