using AcDream.App.Streaming;

namespace AcDream.App.Tests.Streaming;

public sealed class TeleportTransitCoordinatorTests
{
    [Fact]
    public void ReplacementRejectsDelayedPriorDestinationAndAcceptsCurrentAdvance()
    {
        var transit = new TeleportTransitCoordinator<int>();
        Assert.True(transit.QueueStart(10));
        Assert.False(transit.Activate(out _));
        transit.EndActive();
        Assert.True(transit.QueueStart(11));
        Assert.False(transit.Activate(out _));

        Assert.False(transit.OfferDestination(10, true, 100, out _));
        Assert.True(transit.OfferDestination(11, true, 110, out int accepted));
        Assert.Equal(110, accepted);
    }

    [Fact]
    public void PositionBeforeF751IsBufferedAndEqualFollowupCannotReplaceIt()
    {
        var transit = new TeleportTransitCoordinator<int>();

        Assert.False(transit.OfferDestination(11, true, 110, out _));
        Assert.True(transit.QueueStart(11));
        Assert.True(transit.Activate(out int buffered));
        Assert.Equal(110, buffered);
        Assert.False(transit.OfferDestination(11, false, 111, out _));
    }

    [Fact]
    public void InactiveOrdinaryPositionIsNeverBuffered()
    {
        var transit = new TeleportTransitCoordinator<int>();

        Assert.False(transit.OfferDestination(11, false, 110, out _));
        Assert.True(transit.QueueStart(11));
        Assert.False(transit.Activate(out _));
    }

    [Fact]
    public void DuplicateStartIsRejectedButSequenceWrapIsFresh()
    {
        var transit = new TeleportTransitCoordinator<int>();
        Assert.True(transit.QueueStart(ushort.MaxValue));
        Assert.False(transit.Activate(out _));
        transit.EndActive();

        Assert.False(transit.CanBegin(ushort.MaxValue));
        Assert.False(transit.QueueStart(ushort.MaxValue));
        Assert.True(transit.CanBegin(0));
        Assert.True(transit.QueueStart(0));
        Assert.True(transit.HasPendingStart);
    }

    [Fact]
    public void ExactHalfRangeUsesRetailLowerStampTieBreak()
    {
        var transit = new TeleportTransitCoordinator<int>();
        Assert.True(transit.QueueStart(0x8000));
        Assert.False(transit.Activate(out _));
        transit.EndActive();

        Assert.True(transit.CanBegin(0x0000));
        Assert.True(transit.QueueStart(0x0000));
    }

    [Fact]
    public void ClearSessionAllowsSameSequenceInNewSession()
    {
        var transit = new TeleportTransitCoordinator<int>();
        Assert.True(transit.QueueStart(7));
        Assert.False(transit.Activate(out _));

        transit.ClearSession();

        Assert.False(transit.IsActive);
        Assert.True(transit.CanBegin(7));
    }

    [Fact]
    public void PendingStartAcceptsEqualPositionUntilPresentationCanActivate()
    {
        var transit = new TeleportTransitCoordinator<int>();
        Assert.True(transit.QueueStart(11));

        Assert.False(transit.OfferDestination(11, false, 110, out _));
        Assert.True(transit.Activate(out int buffered));

        Assert.Equal(110, buffered);
        Assert.True(transit.IsActive);
    }

    [Fact]
    public void AdvancingPositionPrunesSkippedDestination()
    {
        var transit = new TeleportTransitCoordinator<int>();

        Assert.False(transit.OfferDestination(11, true, 110, out _));
        Assert.False(transit.OfferDestination(12, true, 120, out _));
        Assert.True(transit.QueueStart(12));
        Assert.True(transit.Activate(out int buffered));

        Assert.Equal(120, buffered);
    }

    [Fact]
    public void ObsoleteDestinationCannotSurviveSequenceWrap()
    {
        var transit = new TeleportTransitCoordinator<int>();

        Assert.False(transit.OfferDestination(ushort.MaxValue, true, 999, out _));
        Assert.False(transit.OfferDestination(0, true, 0, out _));
        Assert.True(transit.QueueStart(0));
        Assert.True(transit.Activate(out int wrapped));
        Assert.Equal(0, wrapped);
        transit.EndActive();

        // Advance in legal retail-newer hops until 0xFFFF is current again.
        Assert.True(transit.QueueStart(0x7FFF));
        Assert.False(transit.Activate(out _));
        transit.EndActive();
        Assert.True(transit.QueueStart(0xFFFE));
        Assert.False(transit.Activate(out _));
        transit.EndActive();
        Assert.True(transit.QueueStart(ushort.MaxValue));

        Assert.False(transit.Activate(out _));
    }
}