Place order tracking information onto customer note emails

add_action( 'woocommerce_email_header', function( $email_heading, $email ) {

	// Limit To Specific Email
	if(
		empty( $email->id )
		|| ! in_array( $email->id, [ 'customer_note' ] )
	) {
		return;
	}

	// Get Order
	$order = $email->object;
	if( ! $order ) {
		return;
	}

	// Add Links
	add_filter( 'gettext', function( $text ) use( $order ) {

		// Limit To Specific Copy
		if( $text != 'As a reminder, here are your order details:' ) {
			return $text;
		}

		// Get ShipStation Status
		global $wpdb;
		$sql = "
			SELECT comment_content
			FROM {$wpdb->comments}
			WHERE comment_post_ID = %d
			AND comment_content LIKE '%% shipped via %%'
			ORDER BY comment_ID DESC
			LIMIT 1
		";
		$order_note = $wpdb->get_var(
			$wpdb->prepare( $sql, $order->get_id() )
		);

		// Handle No Results
		if( ! $order_note ) {
			return $text;
		}

		// Get Tracking Number From String
		$words = preg_replace( "/[^A-Za-z0-9 ]/", '', $order_note );
		$words = explode( ' ', $words );
		$last_index = sizeof( $words ) - 1;
		$tracking_num = $words[$last_index];

		// Detect USPS
		if( stristr( $order_note, 'USPS' ) ) {
			$order_note = str_replace( 'USPS', '<strong>USPS</strong>', $order_note );
			$tracking_link = 'https://tools.usps.com/go/TrackConfirmAction?qtc_tLabels1';
		}

		// Detect UPS
		else if( stristr( $order_note, 'UPS' ) ) {
			$order_note = str_replace( 'UPS', '<strong>UPS</strong>', $order_note );
			$tracking_link = 'https://www.ups.com/track?loc=en_US&tracknum';
		}

		// Detect FedEx
		else if( stristr( $order_note, 'FedEx' ) ) {
			$order_note = str_replace( 'FedEx', '<strong>FedEx</strong>', $order_note );
			$tracking_link = 'https://www.fedex.com/fedextrack/?trknbr';
		}

		// Get Tracking Link
		if( empty( $tracking_link ) ) {
			return $text;
		}
		$tracking_link = sprintf(
			'<a target="_blank" href="%s=%s">%s</a>',
			$tracking_link,
			$tracking_num,
			$tracking_num
		);

		// Output Link
		printf(
			'
				<p><strong>Track your package: %s</strong></p>
				<p>%s</p>
			',
			$tracking_link,
			$text
		);

		// Return Text
		return $text;

	} );
	
}, 10, 2 );