// Copyright(c) 2019-2022 pypy, Natsumi and individual contributors.
// All rights reserved.
//
// This work is licensed under the terms of the MIT license.
// For a copy, see <https://opensource.org/licenses/MIT>.

using System;
using System.Diagnostics;
using System.Threading;
using NLog;

namespace VRCX
{
    public class SystemMonitor
    {
        public static readonly SystemMonitor Instance;
        public float CpuUsage;
        public double UpTime;
        private bool _enabled;
        private PerformanceCounter _performanceCounterCpuUsage;
        private PerformanceCounter _performanceCounterUpTime;
        private Thread _thread;
        private static readonly NLog.Logger logger = NLog.LogManager.GetLogger("VRCX");

        static SystemMonitor()
        {
            Instance = new SystemMonitor();
        }

        public void Start(bool enabled)
        {
            if (enabled == _enabled)
                return;
            
            _enabled = enabled;
            if (enabled)
                StartThread();
            else
                Exit();
        }

        internal void Exit()
        {
            CpuUsage = 0;
            UpTime = 0;
            try
            {
                if (_thread != null)
                {
                    _thread.Interrupt();
                    _thread.Join();
                    _thread = null;
                }
            }
            catch (ThreadInterruptedException)
            {
            }

            _performanceCounterCpuUsage?.Dispose();
            _performanceCounterCpuUsage = null;
            _performanceCounterUpTime?.Dispose();
            _performanceCounterUpTime = null;
        }
        
        private void StartThread()
        {
            Exit();
            
            try
            {
                _performanceCounterCpuUsage = new PerformanceCounter(
                    "Processor Information",
                    "% Processor Utility",
                    "_Total",
                    true
                );
                _performanceCounterCpuUsage?.NextValue();
            }
            catch (Exception ex)
            {
                logger.Warn($"Failed to create \"Processor Utility\" PerformanceCounter ${ex}");
            }

            // fallback
            if (_performanceCounterCpuUsage == null)
            {
                try
                {
                    _performanceCounterCpuUsage = new PerformanceCounter(
                        "Processor",
                        "% Processor Time",
                        "_Total",
                        true
                    );
                    _performanceCounterCpuUsage?.NextValue();
                }
                catch (Exception ex)
                {
                    logger.Warn($"Failed to create \"Processor Time\" PerformanceCounter ${ex}");
                }
            }
            
            try
            {
                _performanceCounterUpTime = new PerformanceCounter("System", "System Up Time");
                _performanceCounterUpTime?.NextValue();
            }
            catch
            {
                logger.Warn("Failed to create \"System Up Time\" PerformanceCounter");
            }

            if (_performanceCounterCpuUsage == null &&
                _performanceCounterUpTime == null)
            {
                logger.Error("Failed to create any PerformanceCounter");
                return;
            }
            logger.Info("SystemMonitor started");
            
            _thread = new Thread(ThreadProc)
            {
                IsBackground = true
            };
            _thread.Start();
        }
        
        private void ThreadProc()
        {
            try
            {
                while (_enabled)
                {
                    if (_performanceCounterCpuUsage != null)
                        CpuUsage = _performanceCounterCpuUsage.NextValue();

                    if (_performanceCounterUpTime != null)
                        UpTime = TimeSpan.FromSeconds(_performanceCounterUpTime.NextValue()).TotalMilliseconds;
                    
                    Thread.Sleep(1000);
                }
            }
            catch (Exception ex)
            {
                logger.Warn($"SystemMonitor thread exception: {ex}");
            }

            Exit();
        }
    }
}