//go:build linux

/*
 * ============================================================================
 * Projekt.....: rs2322tcp
 * Datei.......: internal/client/virtual_port_number_linux.go
 * Copyright (C) 2026 Dieter Lang
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 * Beschreibung:
 * Linux-spezifische Umwandlung eines konfigurierten virtuellen
 * seriellen Ports in dessen numerische Portnummer.
 * ============================================================================
 */

package client

import (
	"fmt"
	"strconv"
	"strings"
)

///////////////////////////////////////////////////////////////////////////////
// Virtual port number
///////////////////////////////////////////////////////////////////////////////

// virtualPortNumber converts a configured /dev/ttyUSBxxx path into its
// numeric virtual port number.
func virtualPortNumber(path string) (int, error) {
	const prefix = "/dev/ttyUSB"

	if !strings.HasPrefix(path, prefix) {
		return 0, fmt.Errorf(
			"invalid virtual port %q: expected /dev/ttyUSB<number>",
			path,
		)
	}

	value := strings.TrimPrefix(path, prefix)

	if value == "" {
		return 0, fmt.Errorf(
			"invalid virtual port %q: port number is missing",
			path,
		)
	}

	number, err := strconv.Atoi(value)
	if err != nil {
		return 0, fmt.Errorf(
			"invalid virtual port %q: invalid port number",
			path,
		)
	}

	return number, nil
}