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

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

/// <summary>
/// Unit tests for <see cref="ServiceLevelCalculator"/> — the pure ServiceLevel tiering logic.
/// Moved from ControlPlane.Tests to Cluster.Tests because the type lives in Core.Cluster.
/// See code-reviews/Cluster/findings.md Cluster-005.
/// </summary>
public sealed class ServiceLevelCalculatorTests
{
    /// <summary>Non-Up member statuses produce ServiceLevel 0 regardless of other inputs.</summary>
    [Theory]
    [InlineData(MemberStatus.Down)]
    [InlineData(MemberStatus.Removed)]
    [InlineData(MemberStatus.Exiting)]
    [InlineData(MemberStatus.Leaving)]
    public void NotUp_returns_zero(MemberStatus status)
    {
        var sl = ServiceLevelCalculator.Compute(new(status,
            DbReachable: true, OpcUaProbeOk: true, Stale: false, IsDriverPrimary: true));
        sl.ShouldBe((byte)0);
    }

    /// <summary>Up + DB reachable + probe ok + not stale + not leader = tier 240 (healthy follower).</summary>
    [Fact]
    public void Fully_healthy_non_leader_returns_240()
    {
        var sl = ServiceLevelCalculator.Compute(new(MemberStatus.Up,
            DbReachable: true, OpcUaProbeOk: true, Stale: false, IsDriverPrimary: false));
        sl.ShouldBe((byte)240);
    }

    /// <summary>Up + DB reachable + probe ok + not stale + is leader = tier 250 (healthy leader, +10 bonus).</summary>
    [Fact]
    public void Fully_healthy_role_leader_returns_250()
    {
        var sl = ServiceLevelCalculator.Compute(new(MemberStatus.Up,
            DbReachable: true, OpcUaProbeOk: true, Stale: false, IsDriverPrimary: true));
        sl.ShouldBe((byte)250);
    }

    /// <summary>DB reachable but data stale = tier 200 (stale).</summary>
    [Fact]
    public void Db_reachable_but_stale_returns_200()
    {
        var sl = ServiceLevelCalculator.Compute(new(MemberStatus.Up,
            DbReachable: true, OpcUaProbeOk: true, Stale: true, IsDriverPrimary: false));
        sl.ShouldBe((byte)200);
    }

    /// <summary>DB unreachable AND stale = tier 100 (critically degraded).</summary>
    [Fact]
    public void Db_unreachable_and_stale_returns_100()
    {
        var sl = ServiceLevelCalculator.Compute(new(MemberStatus.Up,
            DbReachable: false, OpcUaProbeOk: false, Stale: true, IsDriverPrimary: false));
        sl.ShouldBe((byte)100);
    }

    /// <summary>OPC UA probe failed while not stale falls through to the catch-all 0.</summary>
    [Fact]
    public void Opcua_probe_fail_when_not_stale_returns_zero()
    {
        var sl = ServiceLevelCalculator.Compute(new(MemberStatus.Up,
            DbReachable: true, OpcUaProbeOk: false, Stale: false, IsDriverPrimary: false));
        sl.ShouldBe((byte)0);
    }

    /// <summary>Joining is treated identically to Up for grading (node is joining the cluster).</summary>
    [Fact]
    public void Joining_member_is_treated_like_Up()
    {
        var sl = ServiceLevelCalculator.Compute(new(MemberStatus.Joining,
            DbReachable: true, OpcUaProbeOk: true, Stale: false, IsDriverPrimary: false));
        sl.ShouldBe((byte)240);
    }

    /// <summary>Leader bonus is clamped to 255 even if a hypothetical basis would overflow.</summary>
    [Fact]
    public void Result_is_clamped_to_255()
    {
        // basis 240 + 10 = 250, already within byte range; confirms Clamp is in path
        var sl = ServiceLevelCalculator.Compute(new(MemberStatus.Up,
            DbReachable: true, OpcUaProbeOk: true, Stale: false, IsDriverPrimary: true));
        ((int)sl).ShouldBeLessThanOrEqualTo(255);
    }
}
