histsdk/src/AVEVA.Historian.Client/Redundancy/MemberState.cs

namespace AVEVA.Historian.Client.Redundancy;

/// <summary>
/// Mutable per-member health used by <see cref="HistorianRedundantClient"/> to route reads and
/// fan out writes. Thread-safe: ops update it from multiple call sites and the watchdog loop.
/// </summary>
internal sealed class MemberState
{
    private readonly Lock _lock = new();
    private readonly int _failureThreshold;

    private bool _isHealthy = true;
    private int _consecutiveFailures;
    private string? _lastError;
    private DateTime? _lastSuccessUtc;
    private DateTime? _lastCheckUtc;

    public MemberState(IHistorianMember member, int failureThreshold)
    {
        Member = member;
        _failureThreshold = failureThreshold;
    }

    public IHistorianMember Member { get; }

    public bool IsHealthy
    {
        get
        {
            lock (_lock)
            {
                return _isHealthy;
            }
        }
    }

    public void MarkSuccess(DateTime utc)
    {
        lock (_lock)
        {
            _consecutiveFailures = 0;
            _isHealthy = true;
            _lastError = null;
            _lastSuccessUtc = utc;
            _lastCheckUtc = utc;
        }
    }

    public void MarkFailure(string? error, DateTime utc)
    {
        lock (_lock)
        {
            _consecutiveFailures++;
            _lastError = error;
            _lastCheckUtc = utc;
            if (_consecutiveFailures >= _failureThreshold)
            {
                _isHealthy = false;
            }
        }
    }

    public HistorianMemberStatus Snapshot()
    {
        lock (_lock)
        {
            return new HistorianMemberStatus
            {
                Name = Member.Name,
                IsHealthy = _isHealthy,
                ConsecutiveFailures = _consecutiveFailures,
                LastError = _lastError,
                LastSuccessUtc = _lastSuccessUtc,
                LastCheckUtc = _lastCheckUtc,
            };
        }
    }
}