// 2026년 포트폴리오용 재구성 코드. 실제 업무 당시 소스가 아닙니다.
// 2026 portfolio reconstruction. Generic fictional training data only; no device or military protocol.
using System;
using System.Collections.Generic;
namespace PortfolioExamples
{
    public sealed class TrainingRoster
    {
        readonly Dictionary<string,double> seen=new Dictionary<string,double>();
        public void Heartbeat(string device, double monotonicSeconds)
        {
            if(string.IsNullOrWhiteSpace(device)||double.IsNaN(monotonicSeconds)||double.IsInfinity(monotonicSeconds))throw new ArgumentException();
            if(seen.TryGetValue(device,out double previous)&&monotonicSeconds<previous)return;
            seen[device]=monotonicSeconds;
        }
        public bool IsOnline(string device,double now,double timeout)
            => timeout>=0 && seen.TryGetValue(device,out double last) && now>=last && now-last<=timeout;
    }
}