// Go reference: consumer.go:4241 (processResetReq)
using NATS.Server.JetStream;
using NATS.Server.JetStream.Consumers;
using NATS.Server.JetStream.Models;
using NATS.Server.JetStream.Storage;
using System.Text;

namespace NATS.Server.JetStream.Tests.JetStream.Consumers;

/// <summary>
/// Tests for consumer reset-to-sequence (Gap 3.12) and AckProcessor.ClearAll / SetAckFloor.
/// Go reference: consumer.go:4241 processResetReq.
/// </summary>
public class ConsumerResetTests
{
    private static ConsumerManager CreateManager() => new();

    private static void CreateConsumer(ConsumerManager mgr, string stream, string name,
        Action<ConsumerConfig>? configure = null)
    {
        var config = new ConsumerConfig { DurableName = name };
        configure?.Invoke(config);
        mgr.CreateOrUpdate(stream, config);
    }

    // -------------------------------------------------------------------------
    // ResetToSequence tests
    // -------------------------------------------------------------------------

    // Go reference: consumer.go:4241 — processResetReq sets consumer.sseq to
    // the requested sequence so the next fetch starts there.
    [Fact]
    public void ResetToSequence_updates_next_sequence()
    {
        var mgr = CreateManager();
        CreateConsumer(mgr, "ORDERS", "oc1");

        // Advance the consumer naturally so NextSequence is not 1
        mgr.TryGet("ORDERS", "oc1", out var before);
        before.NextSequence = 10;

        mgr.ResetToSequence("ORDERS", "oc1", 5);

        mgr.TryGet("ORDERS", "oc1", out var after);
        after.NextSequence.ShouldBe(5UL);
    }

    // Go reference: consumer.go:4241 — reset clears the pending ack map so
    // stale ack tokens from before the reset cannot be accepted.
    [Fact]
    public void ResetToSequence_clears_pending_acks()
    {
        var mgr = CreateManager();
        CreateConsumer(mgr, "ORDERS", "oc2");

        mgr.TryGet("ORDERS", "oc2", out var handle);
        handle.AckProcessor.Register(3, ackWaitMs: 5000);
        handle.AckProcessor.Register(7, ackWaitMs: 5000);
        handle.AckProcessor.PendingCount.ShouldBe(2);

        mgr.ResetToSequence("ORDERS", "oc2", 1);

        handle.AckProcessor.PendingCount.ShouldBe(0);
    }

    // Go reference: consumer.go:4241 — pendingBytes must be zeroed on reset
    // so the idle heartbeat header is correct after the reset.
    [Fact]
    public void ResetToSequence_clears_pending_bytes()
    {
        var mgr = CreateManager();
        CreateConsumer(mgr, "ORDERS", "oc3");

        mgr.TryGet("ORDERS", "oc3", out var handle);
        handle.PendingBytes = 12345;

        mgr.ResetToSequence("ORDERS", "oc3", 1);

        handle.PendingBytes.ShouldBe(0L);
    }

    // Go reference: consumer.go:4241 — returns false when the consumer does
    // not exist (unknown stream or durable name).
    [Fact]
    public void ResetToSequence_returns_false_for_missing_consumer()
    {
        var mgr = CreateManager();

        mgr.ResetToSequence("NO-STREAM", "NO-CONSUMER", 1).ShouldBeFalse();
    }

    // Go reference: consumer.go:4241 — returns true when the consumer exists
    // and the reset is applied.
    [Fact]
    public void ResetToSequence_returns_true_for_existing_consumer()
    {
        var mgr = CreateManager();
        CreateConsumer(mgr, "ORDERS", "oc4");

        mgr.ResetToSequence("ORDERS", "oc4", 42).ShouldBeTrue();
    }

    // Go reference: consumer.go:4241 — consumer config (subject filters, ack
    // policy, etc.) is immutable during reset; only positional / tracking state
    // is cleared.
    [Fact]
    public void ResetToSequence_preserves_config()
    {
        var mgr = CreateManager();
        CreateConsumer(mgr, "ORDERS", "oc5", cfg =>
        {
            cfg.FilterSubject = "orders.>";
            cfg.AckPolicy = AckPolicy.Explicit;
        });

        mgr.ResetToSequence("ORDERS", "oc5", 1);

        mgr.TryGet("ORDERS", "oc5", out var handle);
        handle.Config.FilterSubject.ShouldBe("orders.>");
        handle.Config.AckPolicy.ShouldBe(AckPolicy.Explicit);
    }

    // Go reference: consumer.go:4241 — after reset the push engine can
    // re-enqueue messages starting at the reset sequence.
    [Fact]
    public void ResetToSequence_allows_re_delivery_from_sequence()
    {
        var mgr = CreateManager();
        CreateConsumer(mgr, "ORDERS", "oc6", cfg =>
        {
            cfg.Push = true;
            cfg.DeliverSubject = "deliver.test";
        });

        mgr.TryGet("ORDERS", "oc6", out var handle);
        handle.NextSequence = 50;

        mgr.ResetToSequence("ORDERS", "oc6", 10);

        // After reset the consumer reads from sequence 10
        handle.NextSequence.ShouldBe(10UL);

        // Simulate re-enqueueing a message at that sequence via OnPublished
        var msg = new StoredMessage
        {
            Sequence = 10,
            Subject = "orders.new",
            Payload = Encoding.UTF8.GetBytes("data"),
            TimestampUtc = DateTime.UtcNow,
        };
        mgr.OnPublished("ORDERS", msg);

        // Message should be in the push frame queue
        handle.PushFrames.Count.ShouldBeGreaterThan(0);
    }

    // -------------------------------------------------------------------------
    // AckProcessor.ClearAll tests
    // -------------------------------------------------------------------------

    // Go reference: consumer.go processResetReq — pending ack map cleared
    [Fact]
    public void ClearAll_clears_pending()
    {
        var processor = new AckProcessor();
        processor.Register(1, ackWaitMs: 5000);
        processor.Register(2, ackWaitMs: 5000);
        processor.Register(3, ackWaitMs: 5000);
        processor.PendingCount.ShouldBe(3);

        processor.ClearAll();

        processor.PendingCount.ShouldBe(0);
    }

    // Go reference: consumer.go processResetReq — terminated set cleared
    [Fact]
    public void ClearAll_clears_terminated()
    {
        var processor = new AckProcessor();
        processor.Register(1, ackWaitMs: 5000);
        processor.Register(2, ackWaitMs: 5000);
        processor.ProcessTerm(1);
        processor.ProcessTerm(2);
        processor.TerminatedCount.ShouldBe(2);

        processor.ClearAll();

        processor.TerminatedCount.ShouldBe(0);
    }

    // Go reference: consumer.go processResetReq — ack floor reset to 0
    [Fact]
    public void ClearAll_resets_ack_floor()
    {
        var processor = new AckProcessor();
        processor.Register(1, ackWaitMs: 5000);
        processor.Register(2, ackWaitMs: 5000);
        processor.AckSequence(1);
        processor.AckSequence(2);
        processor.AckFloor.ShouldBeGreaterThan(0UL);

        processor.ClearAll();

        processor.AckFloor.ShouldBe(0UL);
    }

    // -------------------------------------------------------------------------
    // AckProcessor.SetAckFloor tests
    // -------------------------------------------------------------------------

    // Go reference: consumer.go processResetReq — ack floor can be set to a
    // specific sequence to reflect the stream state after reset.
    [Fact]
    public void SetAckFloor_updates_floor()
    {
        var processor = new AckProcessor();

        processor.SetAckFloor(99);

        processor.AckFloor.ShouldBe(99UL);
    }

    // Go reference: consumer.go processResetReq — any pending sequences below
    // the new floor are irrelevant (already delivered before the floor) and
    // must be pruned to avoid ghost acks.
    [Fact]
    public void SetAckFloor_removes_entries_below_floor()
    {
        var processor = new AckProcessor();
        processor.Register(1, ackWaitMs: 5000);
        processor.Register(2, ackWaitMs: 5000);
        processor.Register(5, ackWaitMs: 5000);
        processor.Register(10, ackWaitMs: 5000);
        processor.PendingCount.ShouldBe(4);

        processor.SetAckFloor(5);

        // Sequences 1, 2, and 5 (<=5) are below or at the new floor and must be removed
        processor.PendingCount.ShouldBe(1);
        // Sequence 10 is above the floor and must remain
        processor.HasPending.ShouldBeTrue();
    }
}