svrnty-mcp-gateway/src/Svrnty.MCP.Gateway.Infrastructure/Health/PassiveHealthTracker.cs

using System.Collections.Concurrent;
using OpenHarbor.MCP.Gateway.Core.Models;

namespace OpenHarbor.MCP.Gateway.Infrastructure.Health;

/// <summary>
/// Passive health tracker that monitors server health based on actual request patterns.
/// Tracks success/failure rates and response times without active probing.
/// </summary>
public class PassiveHealthTracker
{
    private readonly ConcurrentDictionary<string, ServerHealthData> _healthData = new();

    /// <summary>
    /// Number of consecutive failures before marking server as unhealthy. Default is 5.
    /// </summary>
    public int UnhealthyThreshold { get; set; } = 5;

    /// <summary>
    /// Number of consecutive successes before marking server as healthy again. Default is 3.
    /// </summary>
    public int HealthyThreshold { get; set; } = 3;

    /// <summary>
    /// Response time threshold for marking requests as slow. Default is 5 seconds.
    /// </summary>
    public TimeSpan SlowResponseThreshold { get; set; } = TimeSpan.FromSeconds(5);

    /// <summary>
    /// Records a successful request to a server.
    /// </summary>
    public void RecordSuccess(string serverId, TimeSpan responseTime)
    {
        var data = _healthData.GetOrAdd(serverId, _ => new ServerHealthData { ServerId = serverId });

        lock (data)
        {
            data.ConsecutiveSuccesses++;
            data.ConsecutiveFailures = 0;
            data.LastResponseTime = responseTime;
            data.LastCheck = DateTime.UtcNow;
            data.LastErrorMessage = null;

            // Add response time to rolling average
            data.ResponseTimes.Enqueue(responseTime);
            if (data.ResponseTimes.Count > 10) // Keep last 10 response times
            {
                data.ResponseTimes.Dequeue();
            }

            // Update health status based on thresholds
            if (data.ConsecutiveSuccesses >= HealthyThreshold)
            {
                data.IsHealthy = true;
            }
        }
    }

    /// <summary>
    /// Records a failed request to a server.
    /// </summary>
    public void RecordFailure(string serverId, string errorMessage)
    {
        var data = _healthData.GetOrAdd(serverId, _ => new ServerHealthData { ServerId = serverId });

        lock (data)
        {
            data.ConsecutiveFailures++;
            data.ConsecutiveSuccesses = 0;
            data.LastCheck = DateTime.UtcNow;
            data.LastErrorMessage = errorMessage;

            // Update health status based on thresholds
            if (data.ConsecutiveFailures >= UnhealthyThreshold)
            {
                data.IsHealthy = false;
            }
        }
    }

    /// <summary>
    /// Gets the current health status for a specific server.
    /// </summary>
    public ServerHealthStatus? GetServerHealth(string serverId)
    {
        if (!_healthData.TryGetValue(serverId, out var data))
        {
            return null;
        }

        lock (data)
        {
            return new ServerHealthStatus
            {
                ServerId = data.ServerId,
                ServerName = serverId, // Default to ID if name not set
                IsHealthy = data.IsHealthy,
                LastCheck = data.LastCheck,
                ResponseTime = data.ResponseTimes.Any()
                    ? TimeSpan.FromMilliseconds(data.ResponseTimes.Average(t => t.TotalMilliseconds))
                    : data.LastResponseTime,
                ErrorMessage = data.LastErrorMessage
            };
        }
    }

    /// <summary>
    /// Gets health status for all tracked servers.
    /// </summary>
    public IEnumerable<ServerHealthStatus> GetAllServerHealth()
    {
        return _healthData.Keys.Select(serverId => GetServerHealth(serverId)).Where(h => h != null).Cast<ServerHealthStatus>();
    }

    /// <summary>
    /// Resets all tracked health data.
    /// </summary>
    public void Reset()
    {
        _healthData.Clear();
    }

    private class ServerHealthData
    {
        public string ServerId { get; set; } = string.Empty;
        public bool IsHealthy { get; set; } = true; // Start as healthy
        public int ConsecutiveSuccesses { get; set; }
        public int ConsecutiveFailures { get; set; }
        public DateTime LastCheck { get; set; }
        public TimeSpan? LastResponseTime { get; set; }
        public string? LastErrorMessage { get; set; }
        public Queue<TimeSpan> ResponseTimes { get; set; } = new Queue<TimeSpan>();
    }
}