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<?php
//Shows out of stock message when a variable product has all variations out of stock
add_filter('wp_footer', function(){
	if(is_product()){
		global $product;
		if($product->is_type('variable')){
			if(!$product->is_in_stock()){
			?>
			<script>
				jQuery(window).load(function(){
					var variations = jQuery('.variations_form.cart').data('product_variations');
					var $form = jQuery('.variations_form.cart');
					var variation = variations[0];
					$form.find( 'input[name="variation_id"], input.variation_id' )
						.val( variation.variation_id )
						.change();
					$form.trigger( 'found_variation', [ variation ] );
				});
			</script>
			<?php
			}
		}
	}
},10);