using System.Security.Claims;
using System.Security.Cryptography;
using System.Text;
using System.Text.Json;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Storage;
using RadicadeServer;
using RadicadeServer.DB;
using RadicadeServer.API.Studio;
using RadicadeServer.RecNet.Accounts;
using RadicadeServer.RecNet.Enums;
using RadicadeServer.RecNet.Enums.Rooms;
using RadicadeServer.RecNet.Rooms;
using RadicadeServer.RoomServer;
using RadicadeServer.Utils;
using Xunit;

namespace RadicadeServer.Tests;

/// <summary>
/// Room saves are the one path where losing a request loses a creator's work, and the
/// failure is silent: the client reports a successful save to the player, and the room
/// reopens with nothing in it. These pin the two things that caused exactly that - the
/// save body not binding, and a save with no uploaded blob being recorded anyway - plus
/// the history fallback that keeps a room loadable when one blob goes missing.
/// </summary>
[Collection(DbFactoryCollection.Name)]
public class RoomSaveTests
{
    private const long CreatorId = 7;
    private const long RoomId = 1;

    private static readonly JsonSerializerOptions ServerJson = new()
    {
        PropertyNamingPolicy = null,
        WriteIndented = true,
    };

    private static string Serialize(object? value) => JsonSerializer.Serialize(value, ServerJson);

    private sealed class TestDbContextFactory : IDbContextFactory<RecDBContext>
    {
        private readonly DbContextOptions<RecDBContext> options;

        public TestDbContextFactory()
        {
            // A unique database name isolates each test; the store is NOT given its own
            // InMemoryDatabaseRoot, because a distinct root makes Entity Framework build a
            // distinct internal service provider every time and it throws once the process
            // has more than twenty of them.
            options = TestDbOptions.Create()
                .UseInMemoryDatabase(Guid.NewGuid().ToString())
                .Options;
        }

        public RecDBContext CreateDbContext() => new(options);
    }

    private static void SetUser(Controller controller, long accountId)
    {
        var identity = new ClaimsIdentity("TestAuth");
        identity.AddClaim(new Claim(ClaimTypes.NameIdentifier, accountId.ToString()));
        controller.ControllerContext = new ControllerContext
        {
            HttpContext = new DefaultHttpContext { User = new ClaimsPrincipal(identity) }
        };
    }

    private static void SetJsonBody(Controller controller, string json)
    {
        var request = controller.ControllerContext.HttpContext.Request;
        request.ContentType = "application/json";
        request.Body = new MemoryStream(Encoding.UTF8.GetBytes(json));
    }

    private static void SetFormBody(Controller controller, string body)
    {
        var request = controller.ControllerContext.HttpContext.Request;
        request.ContentType = "application/x-www-form-urlencoded";
        request.Body = new MemoryStream(Encoding.UTF8.GetBytes(body));
    }

    /// <summary>Puts a blob in CDN storage, the way a completed upload would.</summary>
    private static string WriteBlob(string name)
    {
        Directory.CreateDirectory(DBConfig.CDNStorage);
        var path = Path.Join(DBConfig.CDNStorage, name);
        File.WriteAllBytes(path, new byte[] { 1, 2, 3 });
        return path;
    }

    private static void DeleteBlob(string name)
    {
        var path = Path.Join(DBConfig.CDNStorage, name);
        if (File.Exists(path)) File.Delete(path);
    }

    /// <summary>
    /// Reads a value back from the store through a NEW context. A context that has already
    /// materialized an entity keeps serving its own copy, so reusing the seeding context
    /// would report pre-repair values even after the repair was persisted.
    /// </summary>
    private static async Task<SubRoom> ReadPersistedSubRoomAsync(TestDbContextFactory factory, long subRoomId)
    {
        await using var db = factory.CreateDbContext();
        return await db.SubRooms.AsNoTracking().FirstAsync(x => x.SubRoomId == subRoomId);
    }

    private static async Task<long> SeedRoomAsync(RecDBContext db, long creatorId = CreatorId, string dataBlob = "")
    {
        db.Rooms.Add(new RoomData
        {
            RoomId = RoomId,
            Name = "Build Room",
            CreatorAccountId = creatorId,
            Accessibility = Accessibility.Public,
            MaxPlayers = 8,
            CreatedAt = DateTime.UtcNow,
        });

        var subRoom = new SubRoom
        {
            RoomId = RoomId,
            Name = "Build Room",
            UnitySceneId = "BuildRoomScene",
            MaxPlayers = 8,
            Accessibility = Accessibility.Public,
            DataBlob = dataBlob,
        };

        db.SubRooms.Add(subRoom);
        await db.SaveChangesAsync();

        return subRoom.SubRoomId;
    }

    private static (TestDbContextFactory Factory, RecDBContext Db) CreateContext()
    {
        var factory = new TestDbContextFactory();
        RoomUtils.DbFactory = factory;
        MatchmakingUtils.DbFactory = factory;
        return (factory, factory.CreateDbContext());
    }

    [Fact]
    public async Task SaveAcceptsTheJsonEnvelopeThe2023ClientPosts()
    {
        var (factory, db) = CreateContext();
        await using var _db = db;

        var subRoomId = await SeedRoomAsync(db);
        var api = new RoomServerAPI(db);
        SetUser(api, CreatorId);
        SetJsonBody(api, """
            {
              "RoomData": { "Filename": "meta-1.bin" },
              "SubRoomData": { "Filename": "scene-1.bin", "Hash": null },
              "UnityAssetId": null,
              "PersistenceVersion": 4,
              "InventionUsage": "",
              "AutoPublish": true
            }
            """);

        WriteBlob("scene-1.bin");
        try
        {
            var result = await api.UploadRoomData(RoomId, subRoomId);
            using var doc = JsonDocument.Parse(Serialize(result));

            Assert.True(doc.RootElement.GetProperty("success").GetBoolean());

            // Studio's Result.EEKDNHEOFFD requires Success == (Error == null), so unlike the
            // shared RecNet envelope this save endpoint must return a null error on success.
            Assert.Equal(JsonValueKind.Null, doc.RootElement.GetProperty("error").ValueKind);

            // The loader downloads the room's `CurrentSave.DataBlob`; a save that records
            // anything else opens empty.
            var saved = doc.RootElement.GetProperty("value").GetProperty("room").GetProperty("SubRooms")[0];
            Assert.Equal("scene-1.bin", saved.GetProperty("CurrentSave").GetProperty("DataBlob").GetString());

            // The save the response hands back is the client's OWN projection: camelCase, and
            // a different field set from that CurrentSave. Serving the room's save here leaves
            // every field the client reads back null, and its save handling NREs on them.
            var save = doc.RootElement.GetProperty("value").GetProperty("subRoomDataSave");
            Assert.Equal("scene-1.bin", save.GetProperty("dataBlob").GetString());
            Assert.Equal(subRoomId, save.GetProperty("subRoomId").GetInt64());
            Assert.Equal(save.GetProperty("subRoomDataSaveId").GetInt64(), saved.GetProperty("CurrentSave").GetProperty("SubRoomDataSaveId").GetInt64());
            Assert.Equal(JsonValueKind.Null, save.GetProperty("dataBlobHash").ValueKind);
            Assert.Equal(JsonValueKind.Null, save.GetProperty("unityAsset").ValueKind);
            Assert.False(save.TryGetProperty("DataBlob", out _));

            // A subroom the client is shown has to name a creator: it NREs on a null one, so
            // the account that saved it is reported from here on.
            Assert.Equal(CreatorId, saved.GetProperty("CreatorAccountId").GetInt64());

            // ...and both room spellings are present for the client's saver to read back.
            Assert.Equal(RoomId, doc.RootElement.GetProperty("value").GetProperty("room").GetProperty("RoomId").GetInt64());
            Assert.Equal(RoomId, doc.RootElement.GetProperty("value").GetProperty("RoomId").GetInt64());

            Assert.Equal("scene-1.bin", (await ReadPersistedSubRoomAsync(factory, subRoomId)).DataBlob);

            await using var verify = factory.CreateDbContext();
            Assert.True(await verify.SubRoomHistory.AnyAsync(x => x.SubRoomId == subRoomId));
        }
        finally { DeleteBlob("scene-1.bin"); }
    }

    [Fact]
    public async Task SaveResponseEchoesTheBlobHashItWasGiven()
    {
        var (factory, db) = CreateContext();
        await using var _db = db;

        var subRoomId = await SeedRoomAsync(db);
        var api = new RoomServerAPI(db);
        SetUser(api, CreatorId);
        SetJsonBody(api, """
            {
              "SubRoomData": { "Filename": "hashed.bin", "Hash": "9f2c1a" },
              "RoomData": { "Filename": "meta-2.bin" },
              "AutoPublish": true
            }
            """);

        WriteBlob("hashed.bin");
        try
        {
            var result = await api.UploadRoomData(RoomId, subRoomId);
            using var doc = JsonDocument.Parse(Serialize(result));

            // The hash goes out on the save the response names, not on the room: it is the
            // only digest either side has of the scene blob that save points at.
            var save = doc.RootElement.GetProperty("value").GetProperty("subRoomDataSave");
            Assert.Equal("hashed.bin", save.GetProperty("dataBlob").GetString());
            Assert.Equal("9f2c1a", save.GetProperty("dataBlobHash").GetString());
        }
        finally { DeleteBlob("hashed.bin"); }
    }

    /// <summary>
    /// A subroom that has never been saved has no creator and says so, rather than leaving the
    /// key out: the client reads a missing key and a null the same way.
    /// </summary>
    [Fact]
    public async Task AnUnsavedSubRoomReportsNoCreator()
    {
        var (factory, db) = CreateContext();
        await using var _db = db;

        var subRoomId = await SeedRoomAsync(db);

        var room = await RoomUtils.GetRoom(RoomId);
        Assert.NotNull(room);

        var subRoom = room!.SubRooms.Single(x => x.SubRoomId == subRoomId);
        Assert.Null(subRoom.CreatorAccountId);
    }

    [Fact]
    public async Task SaveAcceptsTheLegacyFormFields()
    {
        var (factory, db) = CreateContext();
        await using var _db = db;

        var subRoomId = await SeedRoomAsync(db);
        var api = new RoomServerAPI(db);
        SetUser(api, CreatorId);
        SetFormBody(api, "filename=legacy.bin&inventionUsage=&savedByAccountId=999");

        WriteBlob("legacy.bin");
        try
        {
            var result = await api.UploadRoomData(RoomId, subRoomId);
            using var doc = JsonDocument.Parse(Serialize(result));

            Assert.True(doc.RootElement.GetProperty("success").GetBoolean());
            Assert.Equal("legacy.bin", (await ReadPersistedSubRoomAsync(factory, subRoomId)).DataBlob);
        }
        finally { DeleteBlob("legacy.bin"); }
    }

    [Fact]
    public async Task SaveTakesTheSaverFromTheTokenNotTheBodyOrAPresenceRow()
    {
        var (factory, db) = CreateContext();
        await using var _db = db;

        var subRoomId = await SeedRoomAsync(db);
        // No presence row at all: editing a room does not require one, and the old required
        // `savedByAccountId` presence lookup turned an otherwise valid save into "Invalid auth".
        var api = new RoomServerAPI(db);
        SetUser(api, CreatorId);
        SetJsonBody(api, """{ "SubRoomData": { "Filename": "scene-2.bin" }, "SavedByAccountId": 999 }""");

        WriteBlob("scene-2.bin");
        try
        {
            var result = await api.UploadRoomData(RoomId, subRoomId);
            using var doc = JsonDocument.Parse(Serialize(result));

            Assert.True(doc.RootElement.GetProperty("success").GetBoolean());
            Assert.Equal(CreatorId, (await ReadPersistedSubRoomAsync(factory, subRoomId)).SavedByAccountId);
        }
        finally { DeleteBlob("scene-2.bin"); }
    }

    [Fact]
    public async Task StudioSourceManifestRouteReturnsHashAndHidesPrivateRoomSource()
    {
        var previousStorage = DBConfig.CDNStorage;
        var isolatedStorage = Path.Combine(Path.GetTempPath(), "studio-source-route-" + Guid.NewGuid());
        DBConfig.CDNStorage = isolatedStorage;
        Directory.CreateDirectory(isolatedStorage);
        var (_, db) = CreateContext();
        await using var _db = db;
        var subRoomId = await SeedRoomAsync(db);
        const string manifestId = "0123456789abcdef0123456789abcdef01234567";
        var manifestBytes = Encoding.UTF8.GetBytes("{\"Version\":2,\"Files\":[]}");
        await File.WriteAllBytesAsync(Path.Combine(isolatedStorage, manifestId), manifestBytes);
        var subRoom = await db.SubRooms.SingleAsync(x => x.SubRoomId == subRoomId);
        subRoom.UnityAssetId = manifestId;
        await db.SaveChangesAsync();
        try
        {
            var api = new RoomServerAPI(db);
            SetUser(api, CreatorId);
            var result = Assert.IsType<OkObjectResult>(await api.GetStudioUnityAsset(RoomId, subRoomId));
            var asset = Assert.IsType<StudioUnityAsset>(result.Value);
            Assert.Equal(manifestId, asset.UnityAssetId);
            Assert.Equal(manifestId, asset.Filename);
            Assert.Equal(Convert.ToBase64String(SHA256.HashData(manifestBytes)), asset.Hash);
            Assert.Empty(asset.BakedUnityAssets);

            var room = await db.Rooms.SingleAsync(x => x.RoomId == RoomId);
            room.Accessibility = Accessibility.Private;
            await db.SaveChangesAsync();
            SetUser(api, 42);
            Assert.IsType<NotFoundResult>(await api.GetStudioUnityAsset(RoomId, subRoomId));
        }
        finally
        {
            DBConfig.CDNStorage = previousStorage;
            if (Directory.Exists(isolatedStorage)) Directory.Delete(isolatedStorage, true);
        }
    }

    [Fact]
    public async Task SaveWithAMissingStudioManifestIsRejectedWithoutMutatingCurrentSaveOrHistory()
    {
        var previousStorage = DBConfig.CDNStorage;
        var isolatedStorage = Path.Combine(Path.GetTempPath(), "studio-manifest-test-" + Guid.NewGuid());
        DBConfig.CDNStorage = isolatedStorage;
        Directory.CreateDirectory(isolatedStorage);
        var (factory, db) = CreateContext();
        await using var _db = db;
        var subRoomId = await SeedRoomAsync(db, dataBlob: "keep-manifest.bin");
        var api = new RoomServerAPI(db);
        SetUser(api, CreatorId);
        SetJsonBody(api, """{ "SubRoomData": { "Filename": "next-manifest.bin" }, "UnityAsset": { "Filename": "0000000000000000000000000000000000000000" } }""");
        WriteBlob("keep-manifest.bin");
        WriteBlob("next-manifest.bin");
        try
        {
            var result = await api.UploadRoomData(RoomId, subRoomId);
            using var doc = JsonDocument.Parse(Serialize(result));
            Assert.False(doc.RootElement.GetProperty("success").GetBoolean());
            Assert.Equal("Unity source manifest has not been uploaded.", doc.RootElement.GetProperty("error").GetString());
            Assert.Equal("keep-manifest.bin", (await ReadPersistedSubRoomAsync(factory, subRoomId)).DataBlob);
            Assert.Equal(string.Empty, (await ReadPersistedSubRoomAsync(factory, subRoomId)).UnityAssetId);
            await using var verify = factory.CreateDbContext();
            Assert.False(await verify.SubRoomHistory.AnyAsync(x => x.SubRoomId == subRoomId));
        }
        finally
        {
            DBConfig.CDNStorage = previousStorage;
            if (Directory.Exists(isolatedStorage)) Directory.Delete(isolatedStorage, true);
        }
    }

    [Fact]
    public async Task SaveWithoutABlobNameIsRejectedAndLeavesTheCurrentSave()
    {
        var (factory, db) = CreateContext();
        await using var _db = db;

        var subRoomId = await SeedRoomAsync(db, dataBlob: "keep.bin");
        var api = new RoomServerAPI(db);
        SetUser(api, CreatorId);
        SetJsonBody(api, """{ "AutoPublish": true }""");

        WriteBlob("keep.bin");
        try
        {
            var result = await api.UploadRoomData(RoomId, subRoomId);
            using var doc = JsonDocument.Parse(Serialize(result));

            Assert.False(doc.RootElement.GetProperty("success").GetBoolean());
            Assert.Equal("keep.bin", (await ReadPersistedSubRoomAsync(factory, subRoomId)).DataBlob);

            await using var verify = factory.CreateDbContext();
            Assert.False(await verify.SubRoomHistory.AnyAsync(x => x.SubRoomId == subRoomId));
        }
        finally { DeleteBlob("keep.bin"); }
    }

    [Fact]
    public async Task SaveRequiresCoOwnerRights()
    {
        var (factory, db) = CreateContext();
        await using var _db = db;

        var subRoomId = await SeedRoomAsync(db, creatorId: 999, dataBlob: "keep.bin");
        var api = new RoomServerAPI(db);
        SetUser(api, CreatorId);
        SetJsonBody(api, """{ "SubRoomData": { "Filename": "scene-3.bin" } }""");

        WriteBlob("scene-3.bin");
        try
        {
            var result = await api.UploadRoomData(RoomId, subRoomId);
            using var doc = JsonDocument.Parse(Serialize(result));

            Assert.False(doc.RootElement.GetProperty("success").GetBoolean());
            Assert.Equal("keep.bin", (await ReadPersistedSubRoomAsync(factory, subRoomId)).DataBlob);
        }
        finally { DeleteBlob("scene-3.bin"); }
    }

    [Fact]
    public async Task RoomLoadFallsBackToTheNewestSaveStillOnDisk()
    {
        var (factory, db) = CreateContext();
        await using var _db = db;

        var subRoomId = await SeedRoomAsync(db, dataBlob: "gone.bin");

        var newer = new RestorableSubRoom
        {
            RoomId = RoomId,
            SubRoomId = subRoomId,
            DataBlob = "also-gone.bin",
            SavedByAccountId = CreatorId,
            CreatedAt = DateTime.UtcNow,
        };
        var older = new RestorableSubRoom
        {
            RoomId = RoomId,
            SubRoomId = subRoomId,
            DataBlob = "old-1.bin",
            SavedByAccountId = CreatorId,
            CreatedAt = DateTime.UtcNow.AddHours(-1),
        };
        db.SubRoomHistory.AddRange(newer, older);
        await db.SaveChangesAsync();

        WriteBlob("old-1.bin");
        try
        {
            var room = await RoomUtils.GetRoom(RoomId);

            Assert.NotNull(room);
            Assert.Equal("old-1.bin", room!.SubRooms.Single(x => x.SubRoomId == subRoomId).DataBlob);

            // The repair is persisted: it is a recovery, not a per-read patch-up.
            Assert.Equal("old-1.bin", (await ReadPersistedSubRoomAsync(factory, subRoomId)).DataBlob);
        }
        finally { DeleteBlob("old-1.bin"); }
    }

    /// <summary>Seeds a subroom with a live save plus two revisions behind it.</summary>
    private static async Task<long> SeedSaveHistoryAsync(RecDBContext db)
    {
        var subRoomId = await SeedRoomAsync(db, dataBlob: "live.bin");

        db.SubRoomHistory.AddRange(
            new RestorableSubRoom
            {
                RoomId = RoomId,
                SubRoomId = subRoomId,
                DataBlob = "newer.bin",
                SavedByAccountId = CreatorId,
                CreatedAt = DateTime.UtcNow.AddMinutes(-5),
            },
            new RestorableSubRoom
            {
                RoomId = RoomId,
                SubRoomId = subRoomId,
                DataBlob = "older.bin",
                SavedByAccountId = CreatorId,
                CreatedAt = DateTime.UtcNow.AddHours(-2),
            });

        await db.SaveChangesAsync();

        return subRoomId;
    }

    private static List<string?> BlobsIn(JsonElement page) =>
        page.GetProperty("Results").EnumerateArray()
            .Select(x => x.GetProperty("DataBlob").GetString())
            .ToList();

    /// <summary>
    /// The save list the client asks for on entering a room. A 404 here is the whole history
    /// screen broken, and any revision missing from it is a save nobody can restore.
    /// </summary>
    [Fact]
    public async Task SavesPageListsTheLiveRevisionAndItsHistoryNewestFirst()
    {
        var (factory, db) = CreateContext();
        await using var _db = db;

        var subRoomId = await SeedSaveHistoryAsync(db);
        var api = new RoomServerAPI(db);
        SetUser(api, CreatorId);

        var ok = Assert.IsType<OkObjectResult>(await api.GetSubRoomSaves(RoomId, subRoomId));
        using var doc = JsonDocument.Parse(Serialize(ok.Value));

        // The live save is what the room is running, so it leads; the revisions follow,
        // newest first.
        Assert.Equal(new List<string?> { "live.bin", "newer.bin", "older.bin" }, BlobsIn(doc.RootElement));

        // Both spellings of the total, because the client's paged DTO and the reference
        // disagree on the name - and it counts the history, not the page.
        Assert.Equal(3, doc.RootElement.GetProperty("TotalResults").GetInt32());
        Assert.Equal(3, doc.RootElement.GetProperty("TotalCount").GetInt32());

        // Ids are what the client keys the list by: the live save is 1 (the id the room
        // payload's CurrentSave already carries) and every revision is distinct.
        var ids = doc.RootElement.GetProperty("Results").EnumerateArray()
            .Select(x => x.GetProperty("SubRoomDataSaveId").GetInt64()).ToList();
        Assert.Equal(3, ids.Distinct().Count());
        Assert.Equal(1, ids[0]);
        Assert.All(ids, id => Assert.True(id >= 1));

        // A page is a window onto the history, not the whole of it.
        var paged = Assert.IsType<OkObjectResult>(await api.GetSubRoomSaves(RoomId, subRoomId, 1, 1));
        using var pagedDoc = JsonDocument.Parse(Serialize(paged.Value));
        Assert.Equal(new List<string?> { "newer.bin" }, BlobsIn(pagedDoc.RootElement));
        Assert.Equal(3, pagedDoc.RootElement.GetProperty("TotalResults").GetInt32());

        // The lighter twin carries the same rows.
        var light = Assert.IsType<OkObjectResult>(await api.GetSubRoomSavesWithoutUnityAssets(RoomId, subRoomId));
        using var lightDoc = JsonDocument.Parse(Serialize(light.Value));
        Assert.Equal(new List<string?> { "live.bin", "newer.bin", "older.bin" }, BlobsIn(lightDoc.RootElement));
        Assert.False(lightDoc.RootElement.GetProperty("Results")[0].TryGetProperty("UnitySubAssets", out _));
    }

    [Fact]
    public async Task SavesPageIsEmptyRatherThanMissingForAnUnknownSubroom()
    {
        var (factory, db) = CreateContext();
        await using var _db = db;

        await SeedRoomAsync(db);
        var api = new RoomServerAPI(db);
        SetUser(api, CreatorId);

        // An unknown id answers an empty page, so a client holding a stale one still renders.
        var ok = Assert.IsType<OkObjectResult>(await api.GetSubRoomSaves(RoomId, 9999));
        using var doc = JsonDocument.Parse(Serialize(ok.Value));

        Assert.Empty(doc.RootElement.GetProperty("Results").EnumerateArray());
        Assert.Equal(0, doc.RootElement.GetProperty("TotalResults").GetInt32());
    }

    [Fact]
    public async Task SavesAreReadableByAStrangerOnlyWhileTheyAreInTheRoom()
    {
        const long visitorId = 42;

        var (factory, db) = CreateContext();
        await using var _db = db;

        var subRoomId = await SeedSaveHistoryAsync(db);
        var api = new RoomServerAPI(db);
        SetUser(api, visitorId);

        // Not the creator and holding no role: the list exposes unpublished work, so from
        // outside the room it is a 403.
        var refused = Assert.IsType<StatusCodeResult>(await api.GetSubRoomSaves(RoomId, subRoomId));
        Assert.Equal(StatusCodes.Status403Forbidden, refused.StatusCode);

        // Standing in the room is its own grant: the client resolves which version to load
        // from this list, so a visitor who cannot read it cannot load the room.
        var instance = new RoomInstance { roomId = RoomId, subRoomId = subRoomId };
        db.RoomInstances.Add(instance);
        await db.SaveChangesAsync();

        db.Presences.Add(new RealPresence { playerId = visitorId, isOnline = true, roomInstance = instance.roomInstanceId });
        await db.SaveChangesAsync();

        var ok = Assert.IsType<OkObjectResult>(await api.GetSubRoomSaves(RoomId, subRoomId));
        using var doc = JsonDocument.Parse(Serialize(ok.Value));
        Assert.Equal(3, doc.RootElement.GetProperty("TotalResults").GetInt32());

        // A visitor in a DIFFERENT room is not in this one.
        instance.roomId = RoomId + 1;
        await db.SaveChangesAsync();

        var elsewhere = Assert.IsType<StatusCodeResult>(await api.GetSubRoomSaves(RoomId, subRoomId));
        Assert.Equal(StatusCodes.Status403Forbidden, elsewhere.StatusCode);
    }

    [Fact]
    public async Task RestoreKeepsTheRevisionItReplaced()
    {
        var (factory, db) = CreateContext();
        await using var _db = db;

        var subRoomId = await SeedRoomAsync(db, dataBlob: "current.bin");
        var api = new RoomServerAPI(db);
        SetUser(api, CreatorId);
        SetJsonBody(api, """{ "Filename": "older.bin" }""");

        WriteBlob("older.bin");
        try
        {
            var result = await api.RestoreRoomData(RoomId, subRoomId);
            using var doc = JsonDocument.Parse(Serialize(result));
            Assert.True(doc.RootElement.GetProperty("success").GetBoolean());

            // Restoring is the one path that can drop a save outright: the revision it
            // replaced has to be in the history afterwards, or it is gone.
            await using var verify = factory.CreateDbContext();
            var history = await verify.SubRoomHistory.Where(x => x.SubRoomId == subRoomId).ToListAsync();
            Assert.Contains(history, x => x.DataBlob == "current.bin");
            Assert.Equal("older.bin", (await ReadPersistedSubRoomAsync(factory, subRoomId)).DataBlob);
        }
        finally { DeleteBlob("older.bin"); }
    }

    [Fact]
    public async Task RoomLoadClearsTheSaveOnlyWhenNothingIsRecoverable()
    {
        var (factory, db) = CreateContext();
        await using var _db = db;

        var subRoomId = await SeedRoomAsync(db, dataBlob: "gone.bin");

        var room = await RoomUtils.GetRoom(RoomId);

        Assert.NotNull(room);
        Assert.Equal(string.Empty, room!.SubRooms.Single(x => x.SubRoomId == subRoomId).DataBlob);
    }
}