AffiliateWP: Block WC Coupon if not referred - enhanced

functions.php

add_action( 'woocommerce_coupon_options', 'affwp_only_referral_coupon_option' );
add_action( 'woocommerce_coupon_options_save', 'affwp_store_only_referral_coupon_option' );
add_filter( 'woocommerce_coupon_is_valid', 'affwp_custom_block_coupon_if_no_referrer', 10, 2 );

/**
 * Add coupon option to enable only referral validity
 */
function affwp_only_referral_coupon_option() {

		global $post;

	    if ( function_exists( 'affiliate_wp' ) ) {
	
		$affwp_only_referral = get_post_meta( $post->ID, 'affwp_discount_only_referral', true );

?>
		<p class="form-field affwp-woo-coupon-field-was-referred">
			<label for="only_referral"><?php _e( 'Only for Referrals?', 'affiliate-wp' ); ?></label>
			<?php
				echo wc_help_tip( __( 'If you would like to have this coupon only valid for referrals.', 'affiliate-wp' ) );
			?>
			<select style="" id="only_referral" name="only_referral" class="select short">
				<option value="">No, anyone can use this coupon</option>
				<option value="specific" <?php echo ($affwp_only_referral == 'specific' ? 'selected="selected"' : ''); ?>>Yes, Specific Affiliate Referrals</option>
				<option value="any" <?php echo ($affwp_only_referral == 'any' ? 'selected="selected"' : ''); ?>>Yes, Any Affiliate Referrals</option>	
			</select>
		</p>
<?php
		}
}

/**
 * Store coupon option to enable only referral validity
 */
function affwp_store_only_referral_coupon_option( $coupon_id = 0 ) {

		if( empty( $_POST['only_referral'] ) ) {

			delete_post_meta( $coupon_id, 'affwp_discount_only_referral' );
			return;

		}

		update_post_meta( $coupon_id, 'affwp_discount_only_referral', $_POST['only_referral'] );
}

/**
 * Make coupon invalid if customer is not currently tracking an affiliate (can be any affiliate)
 */
function affwp_custom_block_coupon_if_no_referrer( $return, $coupon ) {
	
	// make sure AffiliateWP is installed
	if ( ! function_exists( 'affiliate_wp' ) ) {
		return $return;
	}

	// check to see if the coupon is requires refferal
	$is_only_referral_coupon = get_post_meta( $coupon->id, 'affwp_discount_only_referral', true );

	// check to see if the coupon is linked to an affiliate
	$is_tracked_coupon = get_post_meta( $coupon->id, 'affwp_discount_affiliate', true );

	// make sure an affiliate is being tracked 
	if ( ! affiliate_wp()->tracking->was_referred() && $is_tracked_coupon && ( $is_only_referral_coupon == 'specific') ) {
		$return = false; // disallow the coupon
	} elseif ( ! affiliate_wp()->tracking->was_referred() && ( $is_only_referral_coupon == 'any') ) {
		$return = false; // disallow the coupon
	}

	return $return;
}

Adds a new field to the Coupon add / edit screen to select if this coupon if only for referral orders.
Can be for the specific Affiliate linked to the coupon or any affiliate.

Based on this gist:
https://github.com/awesomemotive/affiliatewp-code-snippet-library/blob/master/misc/block-coupon-if-not-referred.php