using ZB.MOM.WW.CBDDC.Core;
using ZB.MOM.WW.CBDDC.Core.Network;
using ZB.MOM.WW.CBDDC.Network.Leadership;

namespace ZB.MOM.WW.CBDDC.Network.Tests;

public class BullyLeaderElectionServiceTests
{
    private static IDiscoveryService CreateDiscovery(IList<PeerNode> peers)
    {
        var discovery = Substitute.For<IDiscoveryService>();
        discovery.GetActivePeers().Returns(_ => peers);
        return discovery;
    }

    private static IPeerNodeConfigurationProvider CreateConfig(string nodeId)
    {
        var configProvider = Substitute.For<IPeerNodeConfigurationProvider>();
        configProvider.GetConfiguration().Returns(new PeerNodeConfiguration { NodeId = nodeId });
        return configProvider;
    }

    /// <summary>
    /// Verifies that a single node elects itself as leader.
    /// </summary>
    [Fact]
    public async Task SingleNode_ShouldBecomeLeader()
    {
        var peers = new List<PeerNode>();
        var electionService = new BullyLeaderElectionService(
            CreateDiscovery(peers),
            CreateConfig("node-A"),
            electionInterval: TimeSpan.FromMilliseconds(100));

        LeadershipChangedEventArgs? lastEvent = null;
        electionService.LeadershipChanged += (_, e) => lastEvent = e;

        await electionService.Start();
        await Task.Delay(200);

        electionService.IsCloudGateway.ShouldBeTrue();
        electionService.CurrentGatewayNodeId.ShouldBe("node-A");
        lastEvent.ShouldNotBeNull();
        lastEvent!.IsLocalNodeGateway.ShouldBeTrue();
        lastEvent.CurrentGatewayNodeId.ShouldBe("node-A");

        await electionService.Stop();
    }

    /// <summary>
    /// Verifies that the smallest node ID is elected as leader among LAN peers.
    /// </summary>
    [Fact]
    public async Task MultipleNodes_SmallestNodeIdShouldBeLeader()
    {
        var peers = new List<PeerNode>
        {
            new("node-B", "192.168.1.2:9000", DateTimeOffset.UtcNow, PeerType.LanDiscovered),
            new("node-C", "192.168.1.3:9000", DateTimeOffset.UtcNow, PeerType.LanDiscovered)
        };

        var electionService = new BullyLeaderElectionService(
            CreateDiscovery(peers),
            CreateConfig("node-A"),
            electionInterval: TimeSpan.FromMilliseconds(100));

        await electionService.Start();
        await Task.Delay(200);

        electionService.IsCloudGateway.ShouldBeTrue();
        electionService.CurrentGatewayNodeId.ShouldBe("node-A");

        await electionService.Stop();
    }

    /// <summary>
    /// Verifies that the local node is not elected when it is not the smallest node ID.
    /// </summary>
    [Fact]
    public async Task LocalNodeNotSmallest_ShouldNotBeLeader()
    {
        var peers = new List<PeerNode>
        {
            new("node-A", "192.168.1.1:9000", DateTimeOffset.UtcNow, PeerType.LanDiscovered),
            new("node-B", "192.168.1.2:9000", DateTimeOffset.UtcNow, PeerType.LanDiscovered)
        };

        var electionService = new BullyLeaderElectionService(
            CreateDiscovery(peers),
            CreateConfig("node-C"),
            electionInterval: TimeSpan.FromMilliseconds(100));

        await electionService.Start();
        await Task.Delay(200);

        electionService.IsCloudGateway.ShouldBeFalse();
        electionService.CurrentGatewayNodeId.ShouldBe("node-A");

        await electionService.Stop();
    }

    /// <summary>
    /// Verifies that leadership is re-elected when the current leader fails.
    /// </summary>
    [Fact]
    public async Task LeaderFailure_ShouldReelect()
    {
        var peers = new List<PeerNode>
        {
            new("node-A", "192.168.1.1:9000", DateTimeOffset.UtcNow, PeerType.LanDiscovered)
        };

        var electionService = new BullyLeaderElectionService(
            CreateDiscovery(peers),
            CreateConfig("node-B"),
            electionInterval: TimeSpan.FromMilliseconds(100));

        var leadershipChanges = new List<LeadershipChangedEventArgs>();
        electionService.LeadershipChanged += (_, e) => leadershipChanges.Add(e);

        await electionService.Start();
        await Task.Delay(200);

        electionService.CurrentGatewayNodeId.ShouldBe("node-A");

        peers.Clear();
        await Task.Delay(200);

        electionService.IsCloudGateway.ShouldBeTrue();
        electionService.CurrentGatewayNodeId.ShouldBe("node-B");
        leadershipChanges.ShouldNotBeEmpty();
        leadershipChanges.Last().IsLocalNodeGateway.ShouldBeTrue();
        leadershipChanges.Last().CurrentGatewayNodeId.ShouldBe("node-B");

        await electionService.Stop();
    }

    /// <summary>
    /// Verifies that cloud peers are excluded from LAN gateway election.
    /// </summary>
    [Fact]
    public async Task CloudPeersExcludedFromElection()
    {
        var peers = new List<PeerNode>
        {
            new("node-A", "192.168.1.1:9000", DateTimeOffset.UtcNow, PeerType.LanDiscovered),
            new("cloud-node-Z", "cloud.example.com:9000", DateTimeOffset.UtcNow, PeerType.CloudRemote)
        };

        var electionService = new BullyLeaderElectionService(
            CreateDiscovery(peers),
            CreateConfig("node-B"),
            electionInterval: TimeSpan.FromMilliseconds(100));

        await electionService.Start();
        await Task.Delay(200);

        electionService.CurrentGatewayNodeId.ShouldBe("node-A");

        await electionService.Stop();
    }
}