the-living-world/tests/TheLivingWorld.Tests/WorldSimulationHostTests.cs

using Microsoft.Extensions.Logging.Abstractions;
using Microsoft.Extensions.Options;
using TheLivingWorld.Api.Simulation;
using TheLivingWorld.Api.Storage;
using TheLivingWorld.Core.Contracts;
using TheLivingWorld.Core.Simulation;

namespace TheLivingWorld.Tests;

public sealed class WorldSimulationHostTests : IDisposable
{
    private readonly string _root = Path.Combine(Path.GetTempPath(), $"tlw-sim-{Guid.NewGuid():n}");
    private readonly WorldStore _store;
    private readonly WorldSimulationHost _host;

    public WorldSimulationHostTests()
    {
        _store = new WorldStore(
            Options.Create(new WorldStorageOptions { RootDirectory = _root }),
            NullLogger<WorldStore>.Instance);
        _host = new WorldSimulationHost(
            _store,
            Options.Create(new SimulationOptions()),
            NullLogger<WorldSimulationHost>.Instance);
    }

    [Fact]
    public async Task Startup_seeds_legacy_worlds_without_catching_up_from_created_at()
    {
        var legacy = Summary("legacy-11111111", "Legacy") with
        {
            CreatedAt = DateTimeOffset.UtcNow - TimeSpan.FromDays(30),
            Clock = null,
            LastTickedAt = null,
        };
        await _store.SaveSummaryAsync(legacy);

        await _host.StartAsync(CancellationToken.None);
        try
        {
            var clock = await WaitForClockAsync(legacy.Id);

            // Thirty days of catch-up would be centuries of game time; the seed must start at the default
            // morning and only drift by the handful of real seconds this test takes.
            Assert.InRange(clock.GameTime, GameTime.DefaultStart, GameTime.DefaultStart.AddHours(1));

            var stored = await _store.GetSummaryAsync(legacy.Id);
            Assert.NotNull(stored?.Clock);
            Assert.NotNull(stored.LastTickedAt);
        }
        finally
        {
            await _host.StopAsync(CancellationToken.None);
        }
    }

    [Fact]
    public void Concurrent_attach_registers_exactly_one_simulation()
    {
        var summary = Summary("racy-44444444", "Racy");

        // Every loser of the GetOrAdd race owns an Arch world that must be disposed, not dropped.
        Parallel.For(0, 32, _ => _host.Attach(summary));

        Assert.True(_host.IsAttached(summary.Id));

        var clock = _host.TryGetClock(summary.Id);
        Assert.NotNull(clock);
        Assert.InRange(clock.GameTime, GameTime.DefaultStart, GameTime.DefaultStart.AddMinutes(5));
    }

    [Fact]
    public void Attach_keeps_the_running_clock_when_called_again_with_a_stale_summary()
    {
        var summary = Summary("stale-55555555", "Stale");
        _host.Attach(summary);
        _host.UpdateClock(summary.Id, new UpdateClockRequest { TimeScale = 4, Paused = true });

        _host.Attach(summary);

        var clock = _host.TryGetClock(summary.Id);
        Assert.NotNull(clock);
        Assert.Equal(4, clock.TimeScale);
        Assert.True(clock.Paused);
    }

    [Fact]
    public async Task UpdateClock_changes_pause_and_Detach_stops_simulation()
    {
        var summary = Summary("ready-22222222", "Ready");
        await _store.SaveSummaryAsync(summary);
        _host.Attach(summary);

        var paused = _host.UpdateClock(summary.Id, new UpdateClockRequest { Paused = true });
        Assert.True(paused.Paused);

        var scaled = _host.UpdateClock(summary.Id, new UpdateClockRequest { TimeScale = 3 });
        Assert.Equal(3, scaled.TimeScale);
        Assert.True(scaled.Paused);

        _host.Detach(summary.Id);
        Assert.False(_host.IsAttached(summary.Id));
        Assert.Null(_host.TryGetClock(summary.Id));
    }

    /// <summary>
    /// Storage bookkeeping cannot leak here by construction - <see cref="WorldSummaryDto"/> has no field to
    /// hold it - so what is left to check is that the facts survive the projection and the live values land.
    /// </summary>
    [Fact]
    public void Overlay_carries_the_stored_facts_and_the_live_clock()
    {
        var summary = Summary("ready-33333333", "Ready");
        _host.Attach(summary);

        var overlaid = _host.Overlay(summary);

        Assert.Equal(summary.Id, overlaid.Id);
        Assert.Equal(summary.Name, overlaid.Name);
        Assert.Equal(summary.SizeMeters, overlaid.SizeMeters);
        Assert.Equal(summary.CreatedAt, overlaid.CreatedAt);
        Assert.NotNull(overlaid.Clock);
        Assert.NotNull(overlaid.Weather);
    }

    [Fact]
    public void Overlay_falls_back_to_the_stored_facts_for_a_world_that_is_not_running()
    {
        var pending = Summary("pending-66666666", "Pending") with { Status = WorldStatus.Pending };

        var overlaid = _host.Overlay(pending);

        Assert.Equal(WorldStatus.Pending, overlaid.Status);
        Assert.Equal(pending.Name, overlaid.Name);
        // No simulation is running, so there is no live weather to lay over it.
        Assert.Null(overlaid.Weather);
    }

    [Fact]
    public async Task Reading_a_lazily_ticked_world_reports_the_current_time_not_a_stale_one()
    {
        var summary = Summary("lazy-88888888", "Lazy");
        await _store.SaveSummaryAsync(summary);
        _host.Attach(summary);

        var before = _host.TryGetClock(summary.Id);
        Assert.NotNull(before);

        // Nothing ticks it in between; the read itself has to do the skipped work.
        await Task.Delay(400);

        var after = _host.TryGetClock(summary.Id);
        Assert.NotNull(after);
        Assert.True(
            after.GameTime > before.GameTime,
            "A read must bring the world current rather than answering from the last lazy tick.");

        // 400 ms at x1 is 2 game minutes; allow for scheduling slop either side.
        var advanced = after.GameTime - before.GameTime;
        Assert.InRange(advanced, TimeSpan.FromMinutes(1.5), TimeSpan.FromMinutes(6));
    }

    /// <summary>
    /// The tick loop must not recreate the folder of a world deleted underneath it - that would leave a
    /// state-only husk that lists as Ready but has no map behind it.
    /// </summary>
    [Fact]
    public async Task Persisting_a_deleted_world_does_not_resurrect_it()
    {
        var summary = Summary("doomed-77777777", "Doomed");
        await _store.SaveSummaryAsync(summary);
        _host.Attach(summary);

        // Dirty the clock, then delete the world the way the endpoint does not: storage only, still attached.
        _host.UpdateClock(summary.Id, new UpdateClockRequest { TimeScale = 2 });
        Assert.True(_store.Delete(summary.Id));

        await _host.StartAsync(CancellationToken.None);
        await _host.StopAsync(CancellationToken.None);

        Assert.Null(await _store.GetSummaryAsync(summary.Id));
        Assert.False(Directory.Exists(Path.Combine(_root, summary.Id)));
        Assert.False(_host.IsAttached(summary.Id));
    }

    private async Task<WorldClockDto> WaitForClockAsync(string id)
    {
        for (var attempt = 0; attempt < 100; attempt++)
        {
            if (_host.TryGetClock(id) is { } clock) return clock;
            await Task.Delay(50);
        }

        throw new TimeoutException($"Simulation for world '{id}' never attached.");
    }

    private static StoredWorldDto Summary(string id, string name) => new()
    {
        Id = id,
        Name = name,
        Latitude = 31.9,
        Longitude = -100.5,
        SizeMeters = 10_000,
        Status = WorldStatus.Ready,
        CreatedAt = DateTimeOffset.UtcNow,
        Clock = WorldSimulation.DefaultClock(),
        LastTickedAt = DateTimeOffset.UtcNow,
    };

    public void Dispose()
    {
        // Detach is a no-op for ids this test never attached, so one list covers every case.
        string[] ids =
        [
            "legacy-11111111", "ready-22222222", "ready-33333333",
            "racy-44444444", "stale-55555555", "pending-66666666", "doomed-77777777", "lazy-88888888",
        ];

        foreach (var id in ids)
            _host.Detach(id);

        if (Directory.Exists(_root)) Directory.Delete(_root, recursive: true);
        GC.SuppressFinalize(this);
    }
}