Initial

LehrerApp.Api/SnapshotStore.cs

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+using LiteDB;
+using LehrerApp.Sync.Models;
+
+namespace LehrerApp.Api;
+
+/// <summary>
+/// Server-seitiger Snapshot-Speicher.
+/// Speichert:
+///   - EncryptedPayload: mit Sync-Schlüssel verschlüsselte LiteDB
+///   - EncryptedSyncKey: mit Code-Key (PBKDF2) verschlüsselter Sync-Schlüssel
+///
+/// Der Server versteht beides nicht – er reicht es nur weiter.
+/// TTL: 24h, Einmal-Verwendung.
+/// </summary>
+public class SnapshotStore : IDisposable
+{
+    private readonly LiteDatabase _db;
+    private readonly ILiteCollection<SnapshotEntry> _col;
+    private readonly Timer _cleanupTimer;
+
+    private static readonly string[] Animals =
+    [
+        "TIGER", "ADLER", "DACHS", "LUCHS", "FALKE",
+        "IGEL",  "ELCH",  "FUCHS", "RABE",  "WOLF",
+        "BISON", "LAMM",  "EULE",  "BIBER", "STORCH",
+        "HIRSCH","OTTER", "MARDER","KRANICH","LACHS",
+    ];
+
+    private static readonly string[] Colors =
+    [
+        "BLAU", "GRUEN", "ROT",  "GOLD", "GRAU",
+        "CYAN", "ROSA",  "LILA", "SAND", "MINT",
+        "SMARAGD","KORALLE","INDIGO","AMBER","JADE",
+    ];
+
+    public SnapshotStore(string dataPath)
+    {
+        Directory.CreateDirectory(dataPath);
+        _db  = new LiteDatabase(Path.Combine(dataPath, "snapshots.db"));
+        _col = _db.GetCollection<SnapshotEntry>("snapshots");
+        _col.EnsureIndex(x => x.Code);
+        _col.EnsureIndex(x => x.ExpiresAt);
+
+        _cleanupTimer = new Timer(
+            _ => Cleanup(),
+            null,
+            TimeSpan.FromHours(1),
+            TimeSpan.FromHours(1));
+    }
+
+    // ── Upload ────────────────────────────────────────────────────────────────
+
+    /// <summary>
+    /// Speichert Snapshot und verschlüsselten Sync-Schlüssel.
+    /// Wenn für denselben User bereits ein Snapshot existiert, wird er ersetzt.
+    /// </summary>
+    public SnapshotUploadResponse Store(
+        string userId,
+        SnapshotUploadRequest request)
+    {
+        // Alten Snapshot desselben Users überschreiben
+        _col.DeleteMany(e => e.UserId == userId);
+
+        var code  = GenerateCode();
+        var entry = new SnapshotEntry
+        {
+            Code             = code,
+            UserId           = userId,
+            EncryptedPayload = request.EncryptedPayload,
+            EncryptedSyncKey = request.EncryptedSyncKey,
+            SourceDeviceType = request.DeviceType,
+            CreatedAt        = DateTime.UtcNow,
+            ExpiresAt        = DateTime.UtcNow.AddHours(24),
+        };
+
+        _col.Insert(entry);
+
+        return new SnapshotUploadResponse
+        {
+            Code      = code,
+            ExpiresAt = entry.ExpiresAt,
+        };
+    }
+
+    // ── Download (Einmal-Verwendung) ──────────────────────────────────────────
+
+    public SnapshotDownloadResponse? Retrieve(string userId, string code)
+    {
+        var entry = _col.FindOne(e =>
+            e.UserId == userId &&
+            e.Code   == code.ToUpperInvariant());
+
+        if (entry is null) return null;
+
+        if (entry.ExpiresAt < DateTime.UtcNow)
+        {
+            _col.Delete(entry.Id);
+            return null;
+        }
+
+        // Einmal-Verwendung: sofort löschen
+        _col.Delete(entry.Id);
+
+        return new SnapshotDownloadResponse
+        {
+            EncryptedPayload = entry.EncryptedPayload,
+            EncryptedSyncKey = entry.EncryptedSyncKey,
+            CreatedAt        = entry.CreatedAt,
+            SourceDeviceType = entry.SourceDeviceType,
+        };
+    }
+
+    // ── Bereinigung ───────────────────────────────────────────────────────────
+
+    private void Cleanup()
+    {
+        var now = DateTime.UtcNow;
+        _col.DeleteMany(e => e.ExpiresAt < now);
+    }
+
+    // ── Code-Generierung ──────────────────────────────────────────────────────
+
+    private static string GenerateCode()
+    {
+        var rng    = Random.Shared;
+        var animal = Animals[rng.Next(Animals.Length)];
+        var number = rng.Next(10, 99);
+        var color  = Colors[rng.Next(Colors.Length)];
+        return $"{animal}-{number}-{color}";
+    }
+
+    public void Dispose()
+    {
+        _cleanupTimer.Dispose();
+        _db.Dispose();
+    }
+}
+
+internal class SnapshotEntry
+{
+    public ObjectId Id { get; set; } = ObjectId.NewObjectId();
+    public string Code { get; set; } = "";
+    public string UserId { get; set; } = "";
+    public string EncryptedPayload { get; set; } = "";
+
+    /// <summary>
+    /// Sync-Schlüssel verschlüsselt mit PBKDF2(Code).
+    /// Leer wenn noch nicht gesetzt (zweistufiger Upload).
+    /// </summary>
+    public string EncryptedSyncKey { get; set; } = "";
+
+    public DeviceType SourceDeviceType { get; set; }
+    public DateTime CreatedAt { get; set; }
+    public DateTime ExpiresAt { get; set; }
+}