SNote/Server/Security/PeerCache.cs

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;

namespace SNote.Server.Security;

public class PeerCache
{
    private readonly ConcurrentDictionary<string, byte> _downstreamPeers = new(StringComparer.OrdinalIgnoreCase);
    private readonly ConcurrentDictionary<string, DateTime> _recentBroadcastIds = new(StringComparer.OrdinalIgnoreCase);

    public void RegisterPeer(string peerUrl)
    {
        if (string.IsNullOrWhiteSpace(peerUrl)) return;
        
        var cleanUrl = peerUrl.Trim().TrimEnd('/');
        _downstreamPeers.TryAdd(cleanUrl, 0);
        Console.WriteLine($"[PeerCache] Registered downstream peer node: {cleanUrl}");
    }

    public void RemovePeer(string peerUrl)
    {
        if (string.IsNullOrWhiteSpace(peerUrl)) return;
        
        var cleanUrl = peerUrl.Trim().TrimEnd('/');
        if (_downstreamPeers.TryRemove(cleanUrl, out _))
        {
            Console.WriteLine($"[PeerCache] Evicted offline peer node: {cleanUrl}");
        }
    }

    public List<string> GetPeers()
    {
        return new List<string>(_downstreamPeers.Keys);
    }

    public bool TryProcessBroadcast(string broadcastId)
    {
        if (string.IsNullOrWhiteSpace(broadcastId)) return false;

        // Clean up old entries to prevent infinite memory growth (older than 10 minutes)
        var cutoff = DateTime.UtcNow.AddMinutes(-10);
        foreach (var kvp in _recentBroadcastIds)
        {
            if (kvp.Value < cutoff)
            {
                _recentBroadcastIds.TryRemove(kvp.Key, out _);
            }
        }

        return _recentBroadcastIds.TryAdd(broadcastId, DateTime.UtcNow);
    }
}