Add automatic database backups

Elwig/App.xaml.cs

@@ -28,6 +28,8 @@ namespace Elwig {
         public static bool ForceShutdown { get; private set; } = false;
 
         private readonly DispatcherTimer _autoUpdateTimer = new() { Interval = TimeSpan.FromHours(1) };
+        private readonly DispatcherTimer _autoBackupTimer = new() { Interval = TimeSpan.FromHours(1) };
+        private DatabaseBackupService? _databaseBackupService;
         public readonly SerialPortWatcher SerialPortWatcher = new();
 
         public static readonly string DataPath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.CommonApplicationData), "Elwig");
@@ -101,6 +103,13 @@ namespace Elwig {
                 return;
             }
 
+            if (Config.DatabaseBackup) {
+                _databaseBackupService = new DatabaseBackupService(Config.DatabaseFile);
+                await _databaseBackupService.RunIfNeededAsync();
+                _autoBackupTimer.Tick += OnAutoBackupTimer;
+                _autoBackupTimer.Start();
+            }
+
             LastChanged = CurrentLastWrite;
             ContextTimer.Start();
 
@@ -191,6 +200,7 @@ namespace Elwig {
         }
 
         private async void Application_Exit(object sender, ExitEventArgs evt) {
+            _autoBackupTimer.Stop();
             SerialPortWatcher.Dispose();
             foreach (var s in EventScales) {
                 s.Dispose();
@@ -198,6 +208,12 @@ namespace Elwig {
             await Pdf.Cleanup();
         }
 
+        private async void OnAutoBackupTimer(object? sender, EventArgs evt) {
+            if (_databaseBackupService != null) {
+                await _databaseBackupService.RunIfNeededAsync();
+            }
+        }
+
         public static void SetBranch(Branch b) {
             SetBranch((b.ZwstId, b.Name, b.PostalDest?.AtPlz?.Plz, b.PostalDest?.AtPlz?.Ort.Name, b.Address, b.PhoneNr, b.FaxNr, b.MobileNr));
         }

Elwig/Helpers/Config.cs

@@ -42,6 +42,7 @@ namespace Elwig.Helpers {
 
         public bool Debug;
         public string DatabaseFile = App.DataPath + "database.sqlite3";
+        public bool DatabaseBackup = true;
         public string? DatabaseLog = null;
         public string? Branch = null;
         public WeighingMode? WeighingMode;
@@ -76,6 +77,8 @@ namespace Elwig.Helpers {
             var config = new ConfigurationBuilder().AddIniFile(FileName).Build();
 
             DatabaseFile = Path.Combine(Path.GetDirectoryName(FileName) ?? App.DataPath, config["database:file"] ?? "database.sqlite3");
+            var backup = config["database:backup"];
+            DatabaseBackup = backup == null || TrueValues.Contains(backup.ToLower());
             var log = config["database:log"];
             DatabaseLog = log != null ? Path.Combine(Path.GetDirectoryName(FileName) ?? App.DataPath, log) : null;
             Branch = config["general:branch"];

Elwig/Helpers/DatabaseBackupService.cs

@@ -0,0 +1,201 @@
+using Microsoft.Data.Sqlite;
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+using System.IO.Compression;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace Elwig.Helpers {
+    internal sealed class DatabaseBackupService {
+
+        private const int DailyBackupCount = 7;
+        private const int WeeklyBackupCount = 5;
+
+        private readonly string DatabaseFile;
+        private readonly string BackupDirectory;
+        private readonly string DatabaseName;
+        private readonly string BackupPrefix;
+        private readonly string LockFile;
+        private readonly Func<DateTime> Now;
+        private readonly SemaphoreSlim Gate = new(1, 1);
+
+        internal DatabaseBackupService(string databaseFile, Func<DateTime>? now = null) {
+            DatabaseFile = Path.GetFullPath(databaseFile);
+            BackupDirectory = Path.Combine(Path.GetDirectoryName(DatabaseFile)!, "backup");
+            DatabaseName = Path.GetFileNameWithoutExtension(DatabaseFile);
+            BackupPrefix = $"{DatabaseName}_";
+            LockFile = Path.Combine(BackupDirectory, $".{DatabaseName}.backup.lock");
+            Now = now ?? (() => DateTime.Now);
+        }
+
+        internal async Task RunIfNeededAsync() {
+            if (!await Gate.WaitAsync(0)) return;
+            try {
+                var slotDate = GetSlotDate(Now());
+                await Task.Run(() => Run(slotDate));
+            } catch {
+                // Automatic backups dont prevent Elwig from starting or running.
+            } finally {
+                Gate.Release();
+            }
+        }
+
+        private void Run(DateOnly slotDate) {
+            Directory.CreateDirectory(BackupDirectory);
+
+            FileStream lockStream;
+            try {
+                lockStream = new FileStream(LockFile, FileMode.OpenOrCreate, FileAccess.ReadWrite, FileShare.None);
+            } catch (IOException) {
+                // Another Elwig instance is currently creating/pruning backups.
+                return;
+            }
+
+            using (lockStream) {
+                CleanupTemporaryFiles();
+
+                var backupFile = GetBackupFile(slotDate);
+                if (!File.Exists(backupFile)) {
+                    CreateBackup(backupFile);
+                }
+
+                if (File.Exists(backupFile)) {
+                    PruneBackups(slotDate);
+                }
+            }
+        }
+
+        private void CreateBackup(string backupFile) {
+            var id = Guid.NewGuid().ToString("N");
+            var temporaryDatabase = Path.Combine(BackupDirectory, $".{DatabaseName}.backup-{id}.sqlite3.tmp");
+            var temporaryArchive = Path.Combine(BackupDirectory, $".{DatabaseName}.backup-{id}.zip.tmp");
+
+            try {
+                var sourceConnectionString = new SqliteConnectionStringBuilder {
+                    DataSource = DatabaseFile,
+                    Mode = SqliteOpenMode.ReadOnly,
+                    Cache = SqliteCacheMode.Default,
+                    Pooling = false,
+                }.ToString();
+                var destinationConnectionString = new SqliteConnectionStringBuilder {
+                    DataSource = temporaryDatabase,
+                    Mode = SqliteOpenMode.ReadWriteCreate,
+                    Cache = SqliteCacheMode.Default,
+                    Pooling = false,
+                }.ToString();
+
+                using (var source = new SqliteConnection(sourceConnectionString))
+                using (var destination = new SqliteConnection(destinationConnectionString)) {
+                    source.Open();
+                    destination.Open();
+                    source.BackupDatabase(destination);
+
+                    using var check = destination.CreateCommand();
+                    check.CommandText = "PRAGMA quick_check";
+                    if (!string.Equals(check.ExecuteScalar()?.ToString(), "ok", StringComparison.OrdinalIgnoreCase)) {
+                        throw new InvalidDataException("The automatic database backup failed its SQLite integrity check.");
+                    }
+                }
+
+                using (var archive = ZipFile.Open(temporaryArchive, ZipArchiveMode.Create)) {
+                    archive.CreateEntryFromFile(temporaryDatabase, "database.sqlite3", CompressionLevel.SmallestSize);
+                }
+
+                try {
+                    File.Move(temporaryArchive, backupFile, false);
+                } catch (IOException) when (File.Exists(backupFile)) {
+                    // A completed backup won a publish race. Its time slot is satisfied.
+                }
+            } finally {
+                DeleteFile(temporaryDatabase);
+                DeleteFile(temporaryArchive);
+            }
+        }
+
+        private void CleanupTemporaryFiles() {
+            foreach (var file in Directory.EnumerateFiles(BackupDirectory, $".{DatabaseName}.backup-*.tmp")) {
+                DeleteFile(file);
+            }
+        }
+
+        internal void PruneBackups(DateOnly slotDate) {
+            var backups = GetManagedBackups().ToArray();
+            var retained = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+
+            var dailyStart = slotDate.AddDays(-(DailyBackupCount - 1));
+            foreach (var backup in backups.Where(b => b.Date >= dailyStart && b.Date <= slotDate)) {
+                retained.Add(backup.File);
+            }
+
+            var daysSinceMonday = ((int)slotDate.DayOfWeek + 6) % 7;
+            var currentWeekStart = slotDate.AddDays(-daysSinceMonday);
+            for (var i = 1; i <= WeeklyBackupCount; i++) {
+                var weekStart = currentWeekStart.AddDays(-7 * i);
+                RetainNewest(backups, retained, weekStart, weekStart.AddDays(7));
+            }
+
+            var currentMonthStart = new DateOnly(slotDate.Year, slotDate.Month, 1);
+            foreach (var month in backups
+                .Where(b => b.Date < currentMonthStart)
+                .GroupBy(b => (b.Date.Year, b.Date.Month))) {
+                retained.Add(month.OrderByDescending(b => b.Date).First().File);
+            }
+
+            // Clock corrections should not cause future-dated backups to be deleted.
+            foreach (var backup in backups.Where(b => b.Date > slotDate)) {
+                retained.Add(backup.File);
+            }
+
+            foreach (var backup in backups.Where(b => !retained.Contains(b.File))) {
+                DeleteFile(backup.File);
+            }
+        }
+
+        private static void RetainNewest(
+            IEnumerable<(string File, DateOnly Date)> backups,
+            ISet<string> retained,
+            DateOnly start,
+            DateOnly end
+        ) {
+            var newest = backups
+                .Where(b => b.Date >= start && b.Date < end)
+                .OrderByDescending(b => b.Date)
+                .FirstOrDefault();
+            if (newest.File != null) retained.Add(newest.File);
+        }
+
+        private IEnumerable<(string File, DateOnly Date)> GetManagedBackups() {
+            foreach (var file in Directory.EnumerateFiles(BackupDirectory, $"{BackupPrefix}*.sqlite3.zip")) {
+                var name = Path.GetFileName(file);
+                if (!name.StartsWith(BackupPrefix, StringComparison.OrdinalIgnoreCase) ||
+                    !name.EndsWith(".sqlite3.zip", StringComparison.OrdinalIgnoreCase)) {
+                    continue;
+                }
+
+                var dateText = name[BackupPrefix.Length..^".sqlite3.zip".Length];
+                if (DateOnly.TryParseExact(dateText, "yyyy-MM-dd", CultureInfo.InvariantCulture, DateTimeStyles.None, out var date)) {
+                    yield return (file, date);
+                }
+            }
+        }
+
+        private string GetBackupFile(DateOnly date) {
+            return Path.Combine(BackupDirectory, $"{BackupPrefix}{date:yyyy-MM-dd}.sqlite3.zip");
+        }
+
+        private static void DeleteFile(string file) {
+            try {
+                File.Delete(file);
+            } catch {
+                // Cleanup and retention are best-effort and will be retried later.
+            }
+        }
+
+        internal static DateOnly GetSlotDate(DateTime timestamp) {
+            return DateOnly.FromDateTime(timestamp.Hour >= 3 ? timestamp : timestamp.AddDays(-1));
+        }
+    }
+}

Installer/Files/config.ini

@@ -7,6 +7,8 @@
 [database]
 ; Relative or absolute path to database file
 file = database.sqlite3
+; Enables automatic compressed database backups
+backup = true
 ; Enables database logging
 ;log = db.log