#nullable enable
using SVSim.BattleEngine.Ambient;
using NUnit.Framework;
using System.Threading.Tasks;

namespace SVSim.BattleEngine.Tests;

[TestFixture, Parallelizable(ParallelScope.Self)]
public class BattleAmbientTests
{
    [Test]
    public void Current_IsNull_WhenNoScope()
    {
        Assert.That(BattleAmbient.Current, Is.Null);
    }

    [Test]
    public void Require_Throws_WhenNoScope()
    {
        Assert.Throws<System.InvalidOperationException>(() => BattleAmbient.Require());
    }

    [Test]
    public void Enter_SetsCurrent_RestoresOnDispose()
    {
        var ctx = new BattleAmbientContext { ViewerId = 42 };
        Assert.That(BattleAmbient.Current, Is.Null);
        using (var _ = BattleAmbient.Enter(ctx))
        {
            Assert.That(BattleAmbient.Current, Is.SameAs(ctx));
            Assert.That(BattleAmbient.Require().ViewerId, Is.EqualTo(42));
        }
        Assert.That(BattleAmbient.Current, Is.Null);
    }

    [Test]
    public void Enter_Nested_RestoresPriorOnDispose()
    {
        var outer = new BattleAmbientContext { ViewerId = 1 };
        var inner = new BattleAmbientContext { ViewerId = 2 };
        using (var _o = BattleAmbient.Enter(outer))
        {
            Assert.That(BattleAmbient.Current!.ViewerId, Is.EqualTo(1));
            using (var _i = BattleAmbient.Enter(inner))
            {
                Assert.That(BattleAmbient.Current!.ViewerId, Is.EqualTo(2));
            }
            Assert.That(BattleAmbient.Current!.ViewerId, Is.EqualTo(1));
        }
    }

    [Test]
    public async Task Enter_FlowsAcrossAwait()
    {
        var ctx = new BattleAmbientContext { ViewerId = 99 };
        using (var _ = BattleAmbient.Enter(ctx))
        {
            await Task.Yield();
            Assert.That(BattleAmbient.Current, Is.SameAs(ctx));
        }
    }

    [Test]
    public async Task Enter_IsolatedBetweenConcurrentTasks()
    {
        var ctxA = new BattleAmbientContext { ViewerId = 100 };
        var ctxB = new BattleAmbientContext { ViewerId = 200 };

        var taskA = Task.Run(async () => {
            using var _ = BattleAmbient.Enter(ctxA);
            await Task.Delay(20);
            return BattleAmbient.Current!.ViewerId;
        });
        var taskB = Task.Run(async () => {
            using var _ = BattleAmbient.Enter(ctxB);
            await Task.Delay(20);
            return BattleAmbient.Current!.ViewerId;
        });

        var results = await Task.WhenAll(taskA, taskB);
        Assert.That(results[0], Is.EqualTo(100));
        Assert.That(results[1], Is.EqualTo(200));
    }
}