LehrerApp/LehrerApp.Core/Services/AppLogger.cs

namespace LehrerApp.Core.Services;

public enum LogLevel { Info, Warning, Error }

/// <summary>
/// Schreibt Log-Zeilen in eine tägliche Datei im App-Datenverzeichnis
/// (<c>&lt;AppData&gt;/LehrerApp/logs/lehrerapp-JJJJ-MM-TT.log</c>).
/// Beim Start werden Dateien entfernt, die älter als <see cref="RetentionDays"/> sind.
/// </summary>
public class AppLogger
{
    private const int RetentionDays = 14;
    private readonly object _lock = new();
    private readonly string _logDirectory;

    public string LogDirectory => _logDirectory;

    public AppLogger(string appDataPath)
    {
        _logDirectory = Path.Combine(appDataPath, "logs");
        Directory.CreateDirectory(_logDirectory);
        RotateOldFiles();
    }

    public void Info(string message) => Write(LogLevel.Info, message, null);
    public void Warn(string message) => Write(LogLevel.Warning, message, null);
    public void Error(string message, Exception? exception = null) => Write(LogLevel.Error, message, exception);

    private void Write(LogLevel level, string message, Exception? exception)
    {
        var levelLabel = level switch
        {
            LogLevel.Info    => "INFO ",
            LogLevel.Warning => "WARN ",
            LogLevel.Error   => "ERROR",
            _                => "?    ",
        };
        var line = $"{DateTime.Now:yyyy-MM-dd HH:mm:ss.fff} [{levelLabel}] {message}";
        if (exception is not null)
            line += Environment.NewLine + exception;

        lock (_lock)
        {
            try
            {
                File.AppendAllText(CurrentLogFile(), line + Environment.NewLine);
            }
            catch
            {
                // Logging darf die App nie zum Absturz bringen (z.B. Datenträger voll/gesperrt).
            }
        }
    }

    private string CurrentLogFile() =>
        Path.Combine(_logDirectory, $"lehrerapp-{DateTime.Now:yyyy-MM-dd}.log");

    private void RotateOldFiles()
    {
        var cutoff = DateTime.Now.AddDays(-RetentionDays);
        try
        {
            foreach (var file in Directory.GetFiles(_logDirectory, "lehrerapp-*.log"))
            {
                if (File.GetLastWriteTime(file) < cutoff)
                {
                    try { File.Delete(file); }
                    catch { /* nächster Start versucht es erneut */ }
                }
            }
        }
        catch
        {
            // Verzeichnis nicht lesbar o.ä. — Logging soll trotzdem weiterlaufen können.
        }
    }
}