woocommerce-global-coupon.php

function apply_global_coupon() {
	global $woocommerce;

	$all_coupons = get_all_store_coupons();

	$coupon_code = 'Global';

	if ( in_array( $coupon_code, $all_coupons) ) {
		if ( WC()->cart->has_discount( $coupon_code ) ) return;
		WC()->cart->add_discount( $coupon_code );
		wc_print_notices();
	}
}
add_action( 'woocommerce_before_cart', 'apply_global_coupon' );

function get_all_store_coupons() {
	$args = array(
		'posts_per_page'   => -1,
		'orderby'          => 'title',
		'order'            => 'asc',
		'post_type'        => 'shop_coupon',
		'post_status'      => 'publish',
	);

	$coupons = get_posts( $args );

	$coupon_names = array();
	foreach ( $coupons as $coupon ) {
		// Get the name for each coupon post
		$coupon_name = $coupon->post_title;
		array_push( $coupon_names, $coupon_name );
	}
	
	return $coupon_names;
}