//go:build linux

/*
 * ============================================================================
 * Projekt.....: rs2322tcp
 * Datei.......: internal/client/virtual_port_validation_linux.go
 * Copyright (C) 2026 Dieter Lang
 *
 * SPDX-License-Identifier: GPL-3.0-or-later
 *
 * Beschreibung:
 * Linux-spezifische Ermittlung der lokal vorhandenen virtuellen
 * rs2322tcp-Schnittstellen.
 *
 * Die öffentliche /dev/ttyUSBxxx-Schnittstelle wird ausschließlich gelesen.
 * Der Client verändert diese Schnittstellen hier nicht.
 * ============================================================================
 */
package client

import (
	"fmt"
	"os"
	"path/filepath"

	"git.lang-dieter.de/rs2322tcp/internal/config"
)

///////////////////////////////////////////////////////////////////////////////
// Existing virtual ports
///////////////////////////////////////////////////////////////////////////////

// existingVirtualPortLinks returns all public virtual-port paths that
// currently exist as symbolic links.
//
// Only ports inside the configured virtual-port range are considered.
// The public /dev/ttyUSBxxx links are only inspected; they are never
// created, changed, or removed by this function.
//
// This check only requires read access and therefore does not require
// root privileges.
func existingVirtualPortLinks(
	cfg config.VirtualPortRangeConfig,
) ([]string, error) {
	return existingVirtualPortLinksInDirectory(
		cfg,
		"/dev",
	)
}

///////////////////////////////////////////////////////////////////////////////
// Existing virtual ports in directory
///////////////////////////////////////////////////////////////////////////////

// existingVirtualPortLinksInDirectory returns all virtual-port paths in
// directory that currently exist as symbolic links.
//
// This helper is deliberately separated from existingVirtualPortLinks so
// the filesystem inspection can be tested without modifying /dev.
func existingVirtualPortLinksInDirectory(
	cfg config.VirtualPortRangeConfig,
	directory string,
) ([]string, error) {
	if directory == "" {
		return nil, fmt.Errorf("virtual port directory is empty")
	}

	manager := NewVirtualPortManager(cfg)
	if manager == nil {
		return nil, fmt.Errorf("virtual port manager is nil")
	}

	links := make([]string, 0)

	for number := cfg.First; number <= cfg.Last; number++ {
		portName := filepath.Base(
			manager.PortPath(number),
		)

		portPath := filepath.Join(directory, portName)

		info, err := os.Lstat(portPath)
		if err != nil {
			if os.IsNotExist(err) {
				continue
			}

			return nil, fmt.Errorf(
				"inspect virtual port %q: %w",
				portPath,
				err,
			)
		}

		if info.Mode()&os.ModeSymlink == 0 {
			continue
		}

		links = append(
			links,
			filepath.Join(directory, portName),
		)
	}

	return links, nil
}