using Shouldly;
using Xunit;
using ZB.MOM.WW.OtOpcUa.Cluster;

namespace ZB.MOM.WW.OtOpcUa.Cluster.Tests;

/// <summary>
/// Unit tests for <see cref="ClusterBootstrapGuard"/> — the pure decision core of the
/// simultaneous-cold-start split-brain guard. The runtime probe + JoinSeedNodes wiring lives in
/// <c>ClusterBootstrapCoordinator</c> and is covered by the live gate.
/// </summary>
public sealed class ClusterBootstrapGuardTests
{
    private const string A = "akka.tcp://otopcua@site-a-1:4053";
    private const string B = "akka.tcp://otopcua@site-a-2:4053";

    [Fact]
    public void Lower_address_node_is_the_founder_and_needs_no_probe()
    {
        // site-a-1 < site-a-2, so on site-a-1 the guard makes it the founder.
        var role = ClusterBootstrapGuard.Analyze(new[] { A, B }, "site-a-1", 4053);

        role.Applies.ShouldBeTrue();
        role.IsFounder.ShouldBeTrue();
        role.SelfFirstOrder.ShouldBe(new[] { A, B });
    }

    [Fact]
    public void Higher_address_node_is_not_the_founder_and_targets_the_partner_for_probing()
    {
        // On site-a-2, the partner is site-a-1 (the lower/founder).
        var role = ClusterBootstrapGuard.Analyze(new[] { B, A }, "site-a-2", 4053);

        role.Applies.ShouldBeTrue();
        role.IsFounder.ShouldBeFalse();
        role.PartnerHost.ShouldBe("site-a-1");
        role.PartnerPort.ShouldBe(4053);
    }

    [Fact]
    public void Tie_break_is_symmetric_regardless_of_seed_order()
    {
        // Both nodes must agree on who founds no matter how each lists its seeds.
        var onLower = ClusterBootstrapGuard.Analyze(new[] { A, B }, "site-a-1", 4053);
        var onHigher = ClusterBootstrapGuard.Analyze(new[] { B, A }, "site-a-2", 4053);

        onLower.IsFounder.ShouldBeTrue();
        onHigher.IsFounder.ShouldBeFalse();
        // Exactly one founder.
        (onLower.IsFounder ^ onHigher.IsFounder).ShouldBeTrue();
    }

    [Fact]
    public void Higher_node_joins_the_founder_when_partner_is_reachable()
    {
        var role = ClusterBootstrapGuard.Analyze(new[] { B, A }, "site-a-2", 4053);

        // Reachable ⇒ peer-first ⇒ JoinSeedNodeProcess ⇒ joins the founder, never self-forms.
        ClusterBootstrapGuard.HigherNodeOrder(role, partnerReachable: true)
            .ShouldBe(new[] { A, B }); // partner (site-a-1) first
    }

    [Fact]
    public void Higher_node_forms_alone_when_partner_is_unreachable()
    {
        var role = ClusterBootstrapGuard.Analyze(new[] { B, A }, "site-a-2", 4053);

        // Unreachable after the window ⇒ partner is dead ⇒ self-first ⇒ cold-start-alone preserved.
        ClusterBootstrapGuard.HigherNodeOrder(role, partnerReachable: false)
            .ShouldBe(new[] { B, A }); // self (site-a-2) first
    }

    [Fact]
    public void Guard_does_not_apply_to_a_single_seed_node()
    {
        // A driver-only site node seeded solely by central-1 is not a pair seed — guard is inert.
        var role = ClusterBootstrapGuard.Analyze(new[] { "akka.tcp://otopcua@central-1:4053" }, "site-x", 4053);

        role.Applies.ShouldBeFalse();
    }

    [Fact]
    public void Guard_does_not_apply_when_self_is_absent_from_the_two_seeds()
    {
        var role = ClusterBootstrapGuard.Analyze(new[] { A, B }, "central-1", 4053);

        role.Applies.ShouldBeFalse();
    }

    [Fact]
    public void Guard_does_not_apply_to_three_or_more_seeds()
    {
        var role = ClusterBootstrapGuard.Analyze(
            new[] { A, B, "akka.tcp://otopcua@site-a-3:4053" }, "site-a-1", 4053);

        role.Applies.ShouldBeFalse();
    }

    [Fact]
    public void Guard_does_not_apply_when_a_seed_is_malformed()
    {
        var role = ClusterBootstrapGuard.Analyze(new[] { A, "not-a-seed" }, "site-a-1", 4053);

        role.Applies.ShouldBeFalse();
    }

    [Theory]
    [InlineData("akka.tcp://otopcua@site-a-1:4053", "site-a-1", 4053)]
    [InlineData("akka.tcp://otopcua@10.0.0.5:4053/", "10.0.0.5", 4053)]
    [InlineData("  akka.tcp://otopcua@host.lan:1234  ", "host.lan", 1234)]
    public void TryParse_extracts_host_and_port(string seed, string expectedHost, int expectedPort)
    {
        ClusterBootstrapGuard.TryParse(seed, out var host, out var port).ShouldBeTrue();
        host.ShouldBe(expectedHost);
        port.ShouldBe(expectedPort);
    }

    [Theory]
    [InlineData("")]
    [InlineData("garbage")]
    [InlineData("akka.tcp://otopcua@host")] // no port
    public void TryParse_rejects_malformed_seeds(string seed)
    {
        ClusterBootstrapGuard.TryParse(seed, out _, out _).ShouldBeFalse();
    }

    [Fact]
    public void Port_participates_in_the_tie_break_when_hosts_are_equal()
    {
        // Shared-host loopback pair (test rig): same host, different ports — port breaks the tie.
        const string low = "akka.tcp://otopcua@127.0.0.1:4053";
        const string high = "akka.tcp://otopcua@127.0.0.1:4054";

        ClusterBootstrapGuard.Analyze(new[] { low, high }, "127.0.0.1", 4053).IsFounder.ShouldBeTrue();
        ClusterBootstrapGuard.Analyze(new[] { high, low }, "127.0.0.1", 4054).IsFounder.ShouldBeFalse();
    }
}