using NATS.Server.JetStream.Consumers;

namespace NATS.Server.Tests.JetStream.Consumers;

/// <summary>
/// Tests for WaitingRequestQueue FIFO queue with expiry and batch/byte tracking.
/// Go reference: consumer.go processNextMsgRequest.
/// </summary>
public class WaitingRequestQueueTests
{
    [Fact]
    public void Enqueue_and_dequeue_fifo()
    {
        var queue = new WaitingRequestQueue();
        queue.Enqueue(new PullRequest("reply.1", Batch: 10, MaxBytes: 0, Expires: DateTimeOffset.UtcNow.AddMinutes(1), NoWait: false));
        queue.Enqueue(new PullRequest("reply.2", Batch: 5, MaxBytes: 0, Expires: DateTimeOffset.UtcNow.AddMinutes(1), NoWait: false));

        queue.Count.ShouldBe(2);

        var first = queue.TryDequeue();
        first.ShouldNotBeNull();
        first.ReplyTo.ShouldBe("reply.1");
    }

    [Fact]
    public void TryDequeue_returns_null_when_empty()
    {
        var queue = new WaitingRequestQueue();
        queue.TryDequeue().ShouldBeNull();
        queue.IsEmpty.ShouldBeTrue();
    }

    [Fact]
    public void Expired_requests_are_removed()
    {
        var queue = new WaitingRequestQueue();
        queue.Enqueue(new PullRequest("expired", Batch: 10, MaxBytes: 0, Expires: DateTimeOffset.UtcNow.AddMilliseconds(-100), NoWait: false));
        queue.Enqueue(new PullRequest("valid", Batch: 10, MaxBytes: 0, Expires: DateTimeOffset.UtcNow.AddMinutes(1), NoWait: false));

        queue.RemoveExpired(DateTimeOffset.UtcNow);
        queue.Count.ShouldBe(1);

        var next = queue.TryDequeue();
        next!.ReplyTo.ShouldBe("valid");
    }

    [Fact]
    public void NoWait_request_returns_immediately_when_empty()
    {
        var queue = new WaitingRequestQueue();
        queue.Enqueue(new PullRequest("nowait", Batch: 10, MaxBytes: 0, Expires: DateTimeOffset.UtcNow.AddMinutes(1), NoWait: true));

        var req = queue.TryDequeue();
        req.ShouldNotBeNull();
        req.NoWait.ShouldBeTrue();
    }

    [Fact]
    public void MaxBytes_tracks_accumulation()
    {
        var queue = new WaitingRequestQueue();
        var req = new PullRequest("mb", Batch: 100, MaxBytes: 1024, Expires: DateTimeOffset.UtcNow.AddMinutes(1), NoWait: false);
        queue.Enqueue(req);

        var dequeued = queue.TryDequeue()!;
        dequeued.MaxBytes.ShouldBe(1024L);
        dequeued.RemainingBytes.ShouldBe(1024L);

        dequeued.ConsumeBytes(256);
        dequeued.RemainingBytes.ShouldBe(768L);
        dequeued.IsExhausted.ShouldBeFalse();

        dequeued.ConsumeBytes(800);
        dequeued.IsExhausted.ShouldBeTrue();
    }

    [Fact]
    public void Batch_decrements_on_delivery()
    {
        var queue = new WaitingRequestQueue();
        var req = new PullRequest("batch", Batch: 3, MaxBytes: 0, Expires: DateTimeOffset.UtcNow.AddMinutes(1), NoWait: false);
        queue.Enqueue(req);

        var dequeued = queue.TryDequeue()!;
        dequeued.RemainingBatch.ShouldBe(3);

        dequeued.ConsumeBatch();
        dequeued.RemainingBatch.ShouldBe(2);

        dequeued.ConsumeBatch();
        dequeued.ConsumeBatch();
        dequeued.IsExhausted.ShouldBeTrue();
    }

    [Fact]
    public void RemoveExpired_handles_all_expired()
    {
        var queue = new WaitingRequestQueue();
        queue.Enqueue(new PullRequest("a", Batch: 1, MaxBytes: 0, Expires: DateTimeOffset.UtcNow.AddMilliseconds(-100), NoWait: false));
        queue.Enqueue(new PullRequest("b", Batch: 1, MaxBytes: 0, Expires: DateTimeOffset.UtcNow.AddMilliseconds(-50), NoWait: false));

        queue.RemoveExpired(DateTimeOffset.UtcNow);
        queue.Count.ShouldBe(0);
        queue.IsEmpty.ShouldBeTrue();
    }

    [Fact]
    public void PinId_is_stored()
    {
        var queue = new WaitingRequestQueue();
        queue.Enqueue(new PullRequest("pin", Batch: 1, MaxBytes: 0, Expires: DateTimeOffset.UtcNow.AddMinutes(1), NoWait: false, PinId: "pin-123"));

        var dequeued = queue.TryDequeue()!;
        dequeued.PinId.ShouldBe("pin-123");
    }
}