// Copyright 2012-2026 The NATS Authors
// Licensed under the Apache License, Version 2.0

using Shouldly;

namespace ZB.MOM.NatsNet.Server.Tests.ImplBacklog;

public sealed class RaftNodeTests
{
    [Fact]
    public void NRGAppendEntryEncode_ShouldSucceed()
    {
        var raft = new Raft();
        var ae = raft.NewAppendEntry("N1", 2, 1, 1, 0, [raft.NewEntry(EntryType.EntryNormal, [1])]);
        var enc = ae.Encode();
        enc.Length.ShouldBeGreaterThan(0);
    }

    [Fact]
    public void NRGAppendEntryDecode_ShouldSucceed()
    {
        var raft = new Raft();
        var ae = raft.NewAppendEntry("N1", 2, 1, 1, 0, [raft.NewEntry(EntryType.EntryNormal, [1])]);
        var dec = raft.DecodeAppendEntry(ae.Encode());
        dec.Leader.ShouldBe("N1");
        dec.TermV.ShouldBe(2UL);
    }

    [Fact]
    public void NRGInlineStepdown_ShouldSucceed()
    {
        var raft = new Raft { StateValue = (int)RaftState.Leader };
        raft.StepdownLocked("N2");
        raft.State().ShouldBe(RaftState.Follower);
        raft.LeaderId.ShouldBe("N2");
    }

    [Fact]
    public void NRGAEFromOldLeader_ShouldSucceed()
    {
        var raft = new Raft { Term_ = 4 };
        var ae = raft.NewAppendEntry("L1", 3, 1, 2, 0, []);
        raft.ProcessAppendEntries(ae);
        raft.Term_.ShouldBe(4UL);
    }

    [Fact]
    public void NRGLeaderTransfer_ShouldSucceed()
    {
        var raft = new Raft { StateValue = (int)RaftState.Follower };
        raft.XferCampaign().ShouldBeNull();
        raft.State().ShouldBe(RaftState.Candidate);
    }

    [Fact]
    public void NRGHeartbeatOnLeaderChange_ShouldSucceed()
    {
        var raft = new Raft { StateValue = (int)RaftState.Follower };
        raft.RunAsLeader();
        raft.Leader().ShouldBeTrue();
        raft.LeadChangeC().ShouldNotBeNull();
    }

    [Fact]
    public void NRGElectionTimerAfterObserver_ShouldSucceed()
    {
        var raft = new Raft { StateValue = (int)RaftState.Follower };
        raft.SetObserverInternal(true);
        raft.ResetElectionTimeout();
        raft.Elect.ShouldNotBeNull();
    }

    [Fact]
    public void NRGRemoveLeaderPeerDeadlockBug_ShouldSucceed()
    {
        var raft = new Raft { Id = "N1", StateValue = (int)RaftState.Leader };
        raft.ProposeRemovePeer("N2");
        raft.MembershipChangeInProgress().ShouldBeTrue();
    }

    [Fact]
    public void NRGPendingAppendEntryCacheInvalidation_ShouldSucceed()
    {
        var raft = new Raft { GroupName = "RG" };
        var ae = raft.NewAppendEntry("N1", 1, 1, 0, 0, [raft.NewEntry(EntryType.EntryNormal, [1])]);
        raft.ProcessAppendEntries(ae);
        raft.LoadFirstEntry().ShouldNotBeNull();
    }

    [Fact]
    public void NRGVoteResponseEncoding_ShouldSucceed()
    {
        var raft = new Raft();
        var vr = new VoteResponse { TermV = 2, Peer = "N1", Granted = true };
        var decoded = raft.DecodeVoteResponse(vr.Encode());
        decoded.Peer.ShouldBe("N1");
        decoded.Granted.ShouldBeTrue();
    }

    [Fact]
    public void NRGProposeRemovePeer_ShouldSucceed()
    {
        var raft = new Raft { PIndex = 5 };
        raft.ProposeRemovePeer("N2");
        raft.Removed.ContainsKey("N2").ShouldBeTrue();
    }

    [Fact]
    public void NRGProposeRemovePeerConcurrent_ShouldSucceed()
    {
        var raft = new Raft { PIndex = 10 };
        Parallel.For(0, 4, i => raft.ProposeRemovePeer($"N{i}"));
        raft.Removed.Count.ShouldBeGreaterThan(0);
    }

    [Fact]
    public void NRGProposeRemovePeerQuorum_ShouldSucceed()
    {
        var raft = new Raft { Qn = 2, Csz = 3 };
        raft.ProposeRemovePeer("N2");
        raft.ClusterSize().ShouldBe(1);
    }

    [Fact]
    public void NRGProposeRemovePeerLeader_ShouldSucceed()
    {
        var raft = new Raft { Id = "N1", StateValue = (int)RaftState.Leader };
        raft.ProposeRemovePeer("N2");
        raft.State().ShouldBe(RaftState.Leader);
    }

    [Fact]
    public void NRGProposeRemovePeerAll_ShouldSucceed()
    {
        var raft = new Raft();
        raft.ProposeRemovePeer("N2");
        raft.ProposeRemovePeer("N3");
        raft.Removed.Count.ShouldBe(2);
    }

    [Fact]
    public void NRGLeaderResurrectsRemovedPeers_ShouldSucceed()
    {
        var raft = new Raft();
        raft.ProposeRemovePeer("N2");
        raft.ProposeAddPeer("N2");
        raft.Peers_.ContainsKey("N2").ShouldBeTrue();
    }

    [Fact]
    public void NRGAddPeers_ShouldSucceed()
    {
        var raft = new Raft();
        raft.AddPeer("N2");
        raft.AddPeer("N3");
        raft.Peers_.Count.ShouldBe(2);
    }

    [Fact]
    public void NRGDisjointMajorities_ShouldSucceed()
    {
        var raft = new Raft
        {
            Qn = 3,
            Peers_ = new Dictionary<string, Lps>
            {
                ["N2"] = new() { Ts = DateTime.UtcNow },
                ["N3"] = new() { Ts = DateTime.UtcNow },
            },
        };
        raft.LostQuorum().ShouldBeFalse();
    }

    [Fact]
    public void NRGSingleNodeElection_ShouldSucceed()
    {
        var raft = new Raft { Csz = 1, Qn = 1, StateValue = (int)RaftState.Follower };
        raft.CampaignInternal(TimeSpan.FromMilliseconds(10)).ShouldBeNull();
        raft.State().ShouldBe(RaftState.Candidate);
    }
}