namespace ZB.MOM.WW.LocalDb.Tests.Convergence;

/// <summary>
/// Randomized property test: a large stream of mixed insert/update/delete operations on both nodes
/// over a small shared key space, interleaved with genuine transport disconnect/reconnect cycles,
/// must always converge to byte-identical state. Seeded Random only (no time-based seeds) so every
/// failure is reproducible from the logged seed.
/// </summary>
public sealed class RandomOpsConvergenceTests
{
    private const int OpsPerNode = 500;
    private const int KeySpace = 40;

    [Theory]
    [InlineData(1701)]
    [InlineData(42)]
    [InlineData(7)]
    public async Task RandomInterleavedOps_Converge(int seed)
    {
        var rng = new Random(seed);

        // Segment plan derived up front from the seeded RNG (so the whole run is deterministic):
        // steady, OUTAGE-1, steady, OUTAGE-2, steady — summing to OpsPerNode ops on each node.
        var seg1 = rng.Next(80, 150);
        var outage1 = rng.Next(20, 50);
        var seg2 = rng.Next(80, 150);
        var outage2 = rng.Next(20, 50);
        var tail = OpsPerNode - (seg1 + outage1 + seg2 + outage2);

        await using var fx = new ConvergenceFixture();
        await fx.StartAsync();

        try
        {
            await RunOpsAsync(fx, rng, seg1);
            await OutageAsync(fx, rng, outage1);
            await RunOpsAsync(fx, rng, seg2);
            await OutageAsync(fx, rng, outage2);
            await RunOpsAsync(fx, rng, tail);

            await fx.AssertConvergedAsync();
        }
        catch (Exception ex) when (ex is not Xunit.Sdk.XunitException)
        {
            throw new Xunit.Sdk.XunitException($"seed {seed}: run faulted.\n{ex}");
        }
        catch (Xunit.Sdk.XunitException ex)
        {
            throw new Xunit.Sdk.XunitException($"seed {seed}: convergence failed.\n{ex.Message}");
        }

        // Both outage windows actually severed and re-dialed the transport (initial dial + 2
        // reconnects) — proof the run exercised real offline accumulation + resync.
        Assert.True(fx.InitiatorConnectionAttempts >= 3,
            $"seed {seed}: expected >=3 connection attempts (2 reconnects), got {fx.InitiatorConnectionAttempts}");
    }

    // Severs the transport, accumulates offline writes on BOTH nodes, waits until the initiator has
    // actually observed the loss (a reconnect attempt started), then restores the transport.
    private static async Task OutageAsync(ConvergenceFixture fx, Random rng, int ops)
    {
        var baseline = fx.InitiatorConnectionAttempts;
        await fx.KillTransportAsync();
        await RunOpsAsync(fx, rng, ops);
        await WaitForAsync(() => Task.FromResult(fx.InitiatorConnectionAttempts > baseline),
            TimeSpan.FromSeconds(10));
        await fx.RestartTransportAsync();
    }

    private static async Task RunOpsAsync(ConvergenceFixture fx, Random rng, int count)
    {
        // One op per node per iteration; no sleeps — the sessions' pumps drain concurrently.
        for (var i = 0; i < count; i++)
        {
            await ApplyRandomOpAsync(fx.A, rng);
            await ApplyRandomOpAsync(fx.B, rng);
        }
    }

    private static Task ApplyRandomOpAsync(ILocalDb db, Random rng)
    {
        var id = rng.Next(1, KeySpace + 1);
        return rng.Next(3) switch
        {
            // insert / update both resolve through the supported upsert helper (plain UPDATE-else-INSERT).
            0 or 1 => ConvergenceFixture.UpsertAsync(db, id, "v" + rng.Next(1000), rng.Next(10_000)),
            _ => ConvergenceFixture.DeleteAsync(db, id),
        };
    }

    private static async Task WaitForAsync(Func<Task<bool>> predicate, TimeSpan timeout)
    {
        var deadline = DateTime.UtcNow + timeout;
        while (DateTime.UtcNow < deadline)
        {
            if (await predicate())
                return;
            await Task.Delay(20);
        }
        throw new TimeoutException("Condition not reached within " + timeout);
    }
}