namespace ZB.MOM.WW.ScadaBridge.ClusterInfrastructure.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 real-ActorSystem
/// <c>ClusterBootstrapCoordinatorTests</c> in the integration suite.
/// </summary>
public class ClusterBootstrapGuardTests
{
    private const string A = "akka.tcp://scadabridge@scadabridge-site-a-a:8082";
    private const string B = "akka.tcp://scadabridge@scadabridge-site-a-b:8082";

    /// <summary>Verifies that the node with the lower address is the founder and needs no probe.</summary>
    [Fact]
    public void Lower_address_node_is_the_founder_and_needs_no_probe()
    {
        // scadabridge-site-a-a < scadabridge-site-a-b, so on node-a the guard makes it the founder.
        var role = ClusterBootstrapGuard.Analyze(new[] { A, B }, "scadabridge-site-a-a", 8082);

        Assert.True(role.Applies);
        Assert.True(role.IsFounder);
        Assert.Equal(new[] { A, B }, role.SelfFirstOrder);
    }

    /// <summary>Verifies that the node with the higher address is not the founder and probes its partner.</summary>
    [Fact]
    public void Higher_address_node_is_not_the_founder_and_targets_the_partner_for_probing()
    {
        // On node-b the partner is node-a (the lower/founder).
        var role = ClusterBootstrapGuard.Analyze(new[] { B, A }, "scadabridge-site-a-b", 8082);

        Assert.True(role.Applies);
        Assert.False(role.IsFounder);
        Assert.Equal("scadabridge-site-a-a", role.PartnerHost);
        Assert.Equal(8082, role.PartnerPort);
    }

    /// <summary>Verifies that the founder tie-break gives the same result regardless of seed order.</summary>
    [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 }, "scadabridge-site-a-a", 8082);
        var onHigher = ClusterBootstrapGuard.Analyze(new[] { B, A }, "scadabridge-site-a-b", 8082);

        Assert.True(onLower.IsFounder);
        Assert.False(onHigher.IsFounder);
        // Exactly one founder.
        Assert.True(onLower.IsFounder ^ onHigher.IsFounder);
    }

    /// <summary>Verifies that the tie-break ignores case, so a casing mismatch cannot make both nodes founders.</summary>
    [Fact]
    public void Tie_break_is_case_insensitive_so_a_casing_mismatch_cannot_make_both_founders()
    {
        // The two sides' seed config differ only in host casing (review note 1): if the tie-break
        // were case-sensitive, both could conclude they are the founder and re-open the split.
        var lowerSelf = "akka.tcp://scadabridge@SITE-A-A:8082";
        var higherSelf = "akka.tcp://scadabridge@site-a-b:8082";

        var onLower = ClusterBootstrapGuard.Analyze(new[] { lowerSelf, higherSelf }, "SITE-A-A", 8082);
        var onHigher = ClusterBootstrapGuard.Analyze(new[] { higherSelf, lowerSelf }, "site-a-b", 8082);

        Assert.True(onLower.IsFounder ^ onHigher.IsFounder);
        Assert.True(onLower.IsFounder); // "site-a-a" < "site-a-b" ordinal-ignore-case
    }

    /// <summary>Verifies that the higher node joins the founder when the partner is reachable.</summary>
    [Fact]
    public void Higher_node_joins_the_founder_when_partner_is_reachable()
    {
        var role = ClusterBootstrapGuard.Analyze(new[] { B, A }, "scadabridge-site-a-b", 8082);

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

    /// <summary>Verifies that the higher node forms a cluster alone when the partner is unreachable.</summary>
    [Fact]
    public void Higher_node_forms_alone_when_partner_is_unreachable()
    {
        var role = ClusterBootstrapGuard.Analyze(new[] { B, A }, "scadabridge-site-a-b", 8082);

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

    /// <summary>Verifies that the guard does not apply to a single seed node.</summary>
    [Fact]
    public void Guard_does_not_apply_to_a_single_seed_node()
    {
        // A single-node install lists exactly one seed (itself) — not a pair, guard is inert.
        var role = ClusterBootstrapGuard.Analyze(new[] { "akka.tcp://scadabridge@lone:8081" }, "lone", 8081);

        Assert.False(role.Applies);
    }

    /// <summary>Verifies that the guard does not apply when the local node is absent from the two seeds.</summary>
    [Fact]
    public void Guard_does_not_apply_when_self_is_absent_from_the_two_seeds()
    {
        var role = ClusterBootstrapGuard.Analyze(new[] { A, B }, "scadabridge-central-a", 8081);

        Assert.False(role.Applies);
    }

    /// <summary>Verifies that the guard does not apply to three or more seeds.</summary>
    [Fact]
    public void Guard_does_not_apply_to_three_or_more_seeds()
    {
        var role = ClusterBootstrapGuard.Analyze(
            new[] { A, B, "akka.tcp://scadabridge@scadabridge-site-a-c:8082" }, "scadabridge-site-a-a", 8082);

        Assert.False(role.Applies);
    }

    /// <summary>Verifies that the guard does not apply when a seed address is malformed.</summary>
    [Fact]
    public void Guard_does_not_apply_when_a_seed_is_malformed()
    {
        var role = ClusterBootstrapGuard.Analyze(new[] { A, "not-a-seed" }, "scadabridge-site-a-a", 8082);

        Assert.False(role.Applies);
    }

    /// <summary>Verifies that parsing a seed address extracts the host and port.</summary>
    /// <param name="seed">The seed address to parse.</param>
    /// <param name="expectedHost">The expected host.</param>
    /// <param name="expectedPort">The expected port.</param>
    [Theory]
    [InlineData("akka.tcp://scadabridge@scadabridge-site-a-a:8082", "scadabridge-site-a-a", 8082)]
    [InlineData("akka.tcp://scadabridge@10.0.0.5:8082/", "10.0.0.5", 8082)]
    [InlineData("  akka.tcp://scadabridge@host.lan:1234  ", "host.lan", 1234)]
    public void TryParse_extracts_host_and_port(string seed, string expectedHost, int expectedPort)
    {
        Assert.True(ClusterBootstrapGuard.TryParse(seed, out var host, out var port));
        Assert.Equal(expectedHost, host);
        Assert.Equal(expectedPort, port);
    }

    /// <summary>Verifies that parsing rejects malformed seed addresses.</summary>
    /// <param name="seed">The malformed seed address.</param>
    [Theory]
    [InlineData("")]
    [InlineData("garbage")]
    [InlineData("akka.tcp://scadabridge@host")] // no port
    public void TryParse_rejects_malformed_seeds(string seed)
    {
        Assert.False(ClusterBootstrapGuard.TryParse(seed, out _, out _));
    }

    /// <summary>Verifies that the port decides the tie-break when the hosts are equal.</summary>
    [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://scadabridge@127.0.0.1:8081";
        const string high = "akka.tcp://scadabridge@127.0.0.1:8082";

        Assert.True(ClusterBootstrapGuard.Analyze(new[] { low, high }, "127.0.0.1", 8081).IsFounder);
        Assert.False(ClusterBootstrapGuard.Analyze(new[] { high, low }, "127.0.0.1", 8082).IsFounder);
    }
}