using System.Net;
using System.Net.Sockets;
using Microsoft.Extensions.Logging.Abstractions;
using NATS.Server.Configuration;
using NATS.Server.LeafNodes;

namespace NATS.Server.Tests.LeafNodes;

/// <summary>
/// Unit tests for JetStream migration checks on leaf node connections (Gap 12.4).
/// Verifies <see cref="LeafNodeManager.CheckJetStreamMigrate"/>,
/// <see cref="LeafNodeManager.GetActiveJetStreamDomains"/>,
/// <see cref="LeafNodeManager.IsJetStreamDomainInUse"/>, and
/// <see cref="LeafNodeManager.JetStreamEnabledConnectionCount"/>.
/// Go reference: leafnode.go checkJetStreamMigrate.
/// </summary>
public class LeafJetStreamMigrationTests
{
    private static LeafNodeManager CreateManager(string serverId = "server-A") =>
        new(
            options: new LeafNodeOptions { Host = "127.0.0.1", Port = 0 },
            stats: new ServerStats(),
            serverId: serverId,
            remoteSubSink: _ => { },
            messageSink: _ => { },
            logger: NullLogger<LeafNodeManager>.Instance);

    /// <summary>
    /// Creates a connected socket pair using a loopback TcpListener and returns both sockets.
    /// The caller is responsible for disposing both.
    /// </summary>
    private static async Task<(Socket serverSide, Socket clientSide)> CreateSocketPairAsync()
    {
        var listener = new TcpListener(IPAddress.Loopback, 0);
        listener.Start();
        var port = ((IPEndPoint)listener.LocalEndpoint).Port;
        var clientSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
        await clientSocket.ConnectAsync(IPAddress.Loopback, port);
        var serverSocket = await listener.AcceptSocketAsync();
        listener.Stop();
        return (serverSocket, clientSocket);
    }

    private static async Task<LeafConnection> CreateConnectionAsync(string remoteId, string? jsDomain = null)
    {
        var (serverSide, clientSide) = await CreateSocketPairAsync();
        clientSide.Dispose();
        var conn = new LeafConnection(serverSide)
        {
            RemoteId = remoteId,
            JetStreamDomain = jsDomain,
        };
        return conn;
    }

    // Go: leafnode.go checkJetStreamMigrate — valid migration to a new unused domain
    [Fact]
    public async Task CheckJetStreamMigrate_Valid_NewDomain()
    {
        var manager = CreateManager();
        await using var conn = await CreateConnectionAsync("server-B", jsDomain: "domain-old");
        manager.InjectConnectionForTesting(conn);
        var connectionId = manager.GetConnectionIds().Single();

        var result = manager.CheckJetStreamMigrate(connectionId, "domain-new");

        result.Valid.ShouldBeTrue();
        result.Status.ShouldBe(JetStreamMigrationStatus.Valid);
        result.Error.ShouldBeNull();
    }

    // Go: leafnode.go checkJetStreamMigrate — unknown connection ID
    [Fact]
    public void CheckJetStreamMigrate_ConnectionNotFound()
    {
        var manager = CreateManager();

        var result = manager.CheckJetStreamMigrate("no-such-id", "some-domain");

        result.Valid.ShouldBeFalse();
        result.Status.ShouldBe(JetStreamMigrationStatus.ConnectionNotFound);
        result.Error.ShouldNotBeNull();
    }

    // Go: leafnode.go checkJetStreamMigrate — clearing the domain (null) is always valid
    [Fact]
    public async Task CheckJetStreamMigrate_NullDomain_AlwaysValid()
    {
        var manager = CreateManager();
        await using var conn = await CreateConnectionAsync("server-B", jsDomain: "domain-existing");
        manager.InjectConnectionForTesting(conn);
        var connectionId = manager.GetConnectionIds().Single();

        var result = manager.CheckJetStreamMigrate(connectionId, null);

        result.Valid.ShouldBeTrue();
        result.Status.ShouldBe(JetStreamMigrationStatus.Valid);
        result.Error.ShouldBeNull();
    }

    // Go: leafnode.go checkJetStreamMigrate — proposed domain matches current, no migration needed
    [Fact]
    public async Task CheckJetStreamMigrate_SameDomain_NoChangeNeeded()
    {
        var manager = CreateManager();
        await using var conn = await CreateConnectionAsync("server-B", jsDomain: "domain-hub");
        manager.InjectConnectionForTesting(conn);
        var connectionId = manager.GetConnectionIds().Single();

        var result = manager.CheckJetStreamMigrate(connectionId, "domain-hub");

        result.Valid.ShouldBeTrue();
        result.Status.ShouldBe(JetStreamMigrationStatus.NoChangeNeeded);
        result.Error.ShouldBeNull();
    }

    // Go: leafnode.go checkJetStreamMigrate — another connection already uses the proposed domain
    [Fact]
    public async Task CheckJetStreamMigrate_DomainConflict()
    {
        var manager = CreateManager();

        // conn-A already owns "domain-hub"
        await using var connA = await CreateConnectionAsync("server-B", jsDomain: "domain-hub");
        manager.InjectConnectionForTesting(connA);

        // conn-B is on a different domain and wants to migrate to "domain-hub"
        await using var connB = await CreateConnectionAsync("server-C", jsDomain: "domain-spoke");
        manager.InjectConnectionForTesting(connB);

        // Retrieve connection ID for server-C (conn-B)
        var connectionIdB = manager.GetConnectionIds()
            .Single(id => manager.GetConnectionByRemoteId("server-C") != null
                       && _connections_ContainsKey(manager, id, "server-C"));

        var result = manager.CheckJetStreamMigrate(connectionIdB, "domain-hub");

        result.Valid.ShouldBeFalse();
        result.Status.ShouldBe(JetStreamMigrationStatus.DomainConflict);
        result.Error.ShouldNotBeNull();
    }

    // Go: leafnode.go — GetActiveJetStreamDomains returns distinct domains
    [Fact]
    public async Task GetActiveJetStreamDomains_ReturnsDistinct()
    {
        var manager = CreateManager();

        await using var connA = await CreateConnectionAsync("server-B", jsDomain: "domain-hub");
        await using var connB = await CreateConnectionAsync("server-C", jsDomain: "domain-hub");
        await using var connC = await CreateConnectionAsync("server-D", jsDomain: "domain-spoke");
        manager.InjectConnectionForTesting(connA);
        manager.InjectConnectionForTesting(connB);
        manager.InjectConnectionForTesting(connC);

        var domains = manager.GetActiveJetStreamDomains();

        domains.Count.ShouldBe(2);
        domains.ShouldContain("domain-hub");
        domains.ShouldContain("domain-spoke");
    }

    // Go: leafnode.go — GetActiveJetStreamDomains excludes connections without a domain
    [Fact]
    public async Task GetActiveJetStreamDomains_SkipsNull()
    {
        var manager = CreateManager();

        await using var connWithDomain = await CreateConnectionAsync("server-B", jsDomain: "domain-hub");
        await using var connWithoutDomain = await CreateConnectionAsync("server-C", jsDomain: null);
        manager.InjectConnectionForTesting(connWithDomain);
        manager.InjectConnectionForTesting(connWithoutDomain);

        var domains = manager.GetActiveJetStreamDomains();

        domains.Count.ShouldBe(1);
        domains.ShouldContain("domain-hub");
    }

    // Go: leafnode.go — IsJetStreamDomainInUse returns true when domain is active
    [Fact]
    public async Task IsJetStreamDomainInUse_True()
    {
        var manager = CreateManager();
        await using var conn = await CreateConnectionAsync("server-B", jsDomain: "domain-hub");
        manager.InjectConnectionForTesting(conn);

        manager.IsJetStreamDomainInUse("domain-hub").ShouldBeTrue();
    }

    // Go: leafnode.go — IsJetStreamDomainInUse returns false when domain is not active
    [Fact]
    public async Task IsJetStreamDomainInUse_False()
    {
        var manager = CreateManager();
        await using var conn = await CreateConnectionAsync("server-B", jsDomain: "domain-hub");
        manager.InjectConnectionForTesting(conn);

        manager.IsJetStreamDomainInUse("domain-unknown").ShouldBeFalse();
    }

    // Go: leafnode.go — JetStreamEnabledConnectionCount counts only connections with a domain
    [Fact]
    public async Task JetStreamEnabledConnectionCount_CountsNonNull()
    {
        var manager = CreateManager();

        await using var connA = await CreateConnectionAsync("server-B", jsDomain: "domain-hub");
        await using var connB = await CreateConnectionAsync("server-C", jsDomain: null);
        await using var connC = await CreateConnectionAsync("server-D", jsDomain: "domain-spoke");
        manager.InjectConnectionForTesting(connA);
        manager.InjectConnectionForTesting(connB);
        manager.InjectConnectionForTesting(connC);

        manager.JetStreamEnabledConnectionCount.ShouldBe(2);
    }

    // ── Internal helper ────────────────────────────────────────────────────────

    /// <summary>
    /// Checks whether the given connection key in the manager corresponds to the connection
    /// with the specified RemoteId. Uses <see cref="LeafNodeManager.GetConnectionByRemoteId"/>
    /// as an indirect lookup since the key is internal.
    /// </summary>
    private static bool _connections_ContainsKey(LeafNodeManager manager, string key, string remoteId)
    {
        // We use GetConnectionIds() and GetConnectionByRemoteId() — both public/internal.
        // The key format is "remoteId:endpoint:guid" so we can prefix-check.
        return key.StartsWith(remoteId + ":", StringComparison.Ordinal);
    }
}