using System;
using System.Windows.Forms;
using Microsoft.Win32;

namespace TimerApp
{
    public enum MonitorState
    {
        Idle,
        Working,
        Resting
    }

    public sealed class ActivityMonitor : IDisposable
    {
        private CancellationTokenSource? _cts;
        private readonly object _lock = new object();
        private TimeSpan _accumulatedWorkTime;
        private int _restElapsedSeconds;
        private bool _isPaused;
        private bool _disposed;
        
        // 状态检测缓存
        private int _checkTickCounter;
        private const int CheckIntervalTicks = 3; // 每3秒检查一次空闲状态
        private long _cachedIdleMs;

        // 配置 (默认值)
        public TimeSpan WorkDuration { get; set; } = TimeSpan.FromMinutes(20);
        public TimeSpan RestDuration { get; set; } = TimeSpan.FromMinutes(1);
        public TimeSpan IdleThreshold { get; set; } = TimeSpan.FromSeconds(30);

        public MonitorState CurrentState { get; private set; } = MonitorState.Idle;
        public bool IsPaused
        {
            get { lock (_lock) return _isPaused; }
            private set { lock (_lock) _isPaused = value; }
        }

        // 事件
        public event EventHandler<TimeSpan>? WorkProgressChanged; // 剩余工作时间
        public event EventHandler<TimeSpan>? RestProgressChanged; // 剩余休息时间
        public event EventHandler? RestStarted;
        public event EventHandler? RestEnded;
        public event EventHandler? StateChanged;

        public ActivityMonitor()
        {
        }

        public void Start()
        {
            lock (_lock)
            {
                StopInternal();
                
                _cts = new CancellationTokenSource();
                var token = _cts.Token;
                
                // 启动时立即触发一次检测
                _checkTickCounter = CheckIntervalTicks;
                ResetWork();
                
                Task.Run(() => MonitorLoop(token), token);
            }
        }

        public void Stop()
        {
            lock (_lock)
            {
                StopInternal();
            }
        }

        private void StopInternal()
        {
            if (_cts != null)
            {
                _cts.Cancel();
                _cts.Dispose();
                _cts = null;
            }
        }

        private void ResetWork()
        {
            // Must be called within lock
            _accumulatedWorkTime = TimeSpan.Zero;
            ChangeState(MonitorState.Idle);
        }

        private void ChangeState(MonitorState newState)
        {
            // Must be called within lock
            if (CurrentState != newState)
            {
                CurrentState = newState;
                StateChanged?.Invoke(this, EventArgs.Empty);
            }
        }

        private async Task MonitorLoop(CancellationToken token)
        {
            while (!token.IsCancellationRequested)
            {
                try
                {
                    await Task.Delay(1000, token);
                    OnTick();
                }
                catch (OperationCanceledException)
                {
                    break;
                }
                catch (Exception ex)
                {
                    Logger.LogError("Error in ActivityMonitor MonitorLoop", ex);
                }
            }
        }

        private void OnTick()
        {
            // 在锁外执行耗时的系统检测
            long idleMs = 0;
            bool shouldUpdate = false;

            lock (_lock)
            {
                // 如果处于暂停状态，不处理计时逻辑
                if (_isPaused) return;

                // 检查是否需要更新状态
                _checkTickCounter++;
                if (_checkTickCounter >= CheckIntervalTicks)
                {
                    _checkTickCounter = 0;
                    // 需要更新，但在锁外进行
                    shouldUpdate = true; 
                }
                
                // 如果不需要更新，直接使用缓存值
                if (!shouldUpdate)
                {
                     idleMs = _cachedIdleMs;
                }
            }

            // 在锁外执行实际的检测
            if (shouldUpdate)
            {
                idleMs = NativeMethods.GetIdleTime();
                
                // 更新缓存
                lock (_lock)
                {
                    _cachedIdleMs = idleMs;
                }
            }

            lock (_lock)
            {
                // 再次检查暂停状态
                if (_isPaused) return;

                // 使用（可能是新更新的）缓存值
                idleMs = _cachedIdleMs;
                TimeSpan idleTime = TimeSpan.FromMilliseconds(idleMs);

                if (CurrentState == MonitorState.Resting)
                {
                    // 休息模式逻辑
                    // 使用计数器而不是时间差，避免秒数跳变
                    _restElapsedSeconds++;
                    int totalRestSeconds = (int)RestDuration.TotalSeconds;
                    int remainingSeconds = totalRestSeconds - _restElapsedSeconds;

                    if (remainingSeconds <= 0)
                    {
                        // 休息结束
                        RestEnded?.Invoke(this, EventArgs.Empty);
                        ResetWork(); // 重新开始工作周期
                    }
                    else
                    {
                        TimeSpan remainingRest = TimeSpan.FromSeconds(remainingSeconds);
                        RestProgressChanged?.Invoke(this, remainingRest);
                    }
                }
                else
                {
                    // 工作/空闲模式逻辑
                    bool isUserInactive = idleTime > IdleThreshold;

                    if (isUserInactive)
                    {
                        // 用户确实离开了 -> 进入空闲状态
                        if (CurrentState == MonitorState.Working)
                        {
                            ChangeState(MonitorState.Idle);
                        }

                        // 如果在 Idle 状态，且空闲时间非常长（比如超过了休息时间），
                        // 重置工作计时器
                        if (idleTime > RestDuration)
                        {
                            _accumulatedWorkTime = TimeSpan.Zero;
                        }
                    }
                    else
                    {
                        // 用户在活动
                        if (CurrentState == MonitorState.Idle)
                        {
                            // 从空闲变为工作
                            ChangeState(MonitorState.Working);
                        }

                        // 正常工作：累加时间
                        _accumulatedWorkTime += TimeSpan.FromSeconds(1);

                        // 检查是否达到工作时长
                        TimeSpan remainingWork = WorkDuration - _accumulatedWorkTime;

                        if (remainingWork <= TimeSpan.Zero)
                        {
                            // 触发休息
                            _restElapsedSeconds = 0; // 重置休息计数器
                            ChangeState(MonitorState.Resting);
                            RestStarted?.Invoke(this, EventArgs.Empty);
                        }
                        else
                        {
                            WorkProgressChanged?.Invoke(this, remainingWork);
                        }
                    }
                }
            }
        }

        public void RefreshStatus()
        {
            lock (_lock)
            {
                 if (CurrentState == MonitorState.Working)
                 {
                     TimeSpan remaining = WorkDuration - _accumulatedWorkTime;
                     WorkProgressChanged?.Invoke(this, remaining);
                 }
                 else if (CurrentState == MonitorState.Resting)
                 {
                     int totalRestSeconds = (int)RestDuration.TotalSeconds;
                     int remainingSeconds = totalRestSeconds - _restElapsedSeconds;
                     if (remainingSeconds < 0) remainingSeconds = 0;
                     TimeSpan remaining = TimeSpan.FromSeconds(remainingSeconds);
                     RestProgressChanged?.Invoke(this, remaining);
                 }
            }
        }

        public void Restart()
        {
            lock (_lock)
            {
                _accumulatedWorkTime = TimeSpan.Zero;
                _isPaused = false;
                
                // Force state to Working since user manually restarted
                ChangeState(MonitorState.Working);

                // Immediately refresh UI to show full duration
                RefreshStatus();
            }
        }

        public void Pause()
        {
            lock (_lock)
            {
                if (!_isPaused && CurrentState != MonitorState.Idle)
                {
                    _isPaused = true;
                    StateChanged?.Invoke(this, EventArgs.Empty);
                }
            }
        }

        public void Resume()
        {
            lock (_lock)
            {
                if (_isPaused)
                {
                    _isPaused = false;
                    StateChanged?.Invoke(this, EventArgs.Empty);
                    RefreshStatus();
                }
            }
        }

        public void Dispose()
        {
            if (_disposed) return;
            _disposed = true;

            // SystemEvents.PowerModeChanged -= OnPowerModeChanged;
            Stop();
            GC.SuppressFinalize(this);
        }

    }
}