using System;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;

namespace TimerApp
{
    public static class NativeMethods
    {
        [StructLayout(LayoutKind.Sequential)]
        struct LASTINPUTINFO
        {
            public static readonly int SizeOf = Marshal.SizeOf(typeof(LASTINPUTINFO));

            [MarshalAs(UnmanagedType.U4)]
            public UInt32 cbSize;
            [MarshalAs(UnmanagedType.U4)]
            public UInt32 dwTime;
        }

        [DllImport("user32.dll")]
        static extern bool GetLastInputInfo(ref LASTINPUTINFO plii);

        /// <summary>
        /// 获取系统空闲时间（毫秒）
        /// </summary>
        /// <returns></returns>
        public static long GetIdleTime()
        {
            LASTINPUTINFO lastInputInfo = new LASTINPUTINFO
            {
                cbSize = (uint)Marshal.SizeOf<LASTINPUTINFO>(),
                dwTime = 0
            };

            if (GetLastInputInfo(ref lastInputInfo))
            {
                uint tickCount = GetTickCount();
                uint idleMs = unchecked(tickCount - lastInputInfo.dwTime);
                return idleMs;
            }

            return 0;
        }

        [DllImport("kernel32.dll")]
        static extern uint GetTickCount();

        /// <summary>
        /// 检测是否有媒体正在播放（视频或音频）
        /// </summary>
        /// <returns>如果有媒体正在播放返回 true，否则返回 false</returns>
        public static bool IsMediaPlaying()
        {
            EnsureMediaPlaybackStatusFresh();
            return Volatile.Read(ref _mediaPlaying);
        }

        private static bool _mediaPlaying;
        private static long _mediaLastUpdateMs = -1;
        private static int _mediaUpdateInProgress;

        private static void EnsureMediaPlaybackStatusFresh()
        {
            long now = Environment.TickCount64;
            long last = Interlocked.Read(ref _mediaLastUpdateMs);
            if (last >= 0 && now - last < 3000)
            {
                return;
            }

            if (Interlocked.Exchange(ref _mediaUpdateInProgress, 1) == 1)
            {
                return;
            }

            _ = Task.Run(async () =>
            {
                bool playing = false;
                try
                {
                    await Task.Yield();
                    playing = TryIsAudioPlaying();
                }
                catch
                {
                    playing = false;
                }
                finally
                {
                    Volatile.Write(ref _mediaPlaying, playing);
                    Interlocked.Exchange(ref _mediaLastUpdateMs, Environment.TickCount64);
                    Interlocked.Exchange(ref _mediaUpdateInProgress, 0);
                }
            });
        }

        private static bool TryIsAudioPlaying()
        {
            object? deviceEnumeratorObj = null;
            IMMDeviceEnumerator? deviceEnumerator = null;
            IMMDevice? device = null;
            object? sessionManagerObj = null;
            IAudioSessionManager2? sessionManager = null;
            IAudioSessionEnumerator? sessionEnumerator = null;

            try
            {
                Type? enumeratorType = Type.GetTypeFromCLSID(CLSID_MMDeviceEnumerator);
                if (enumeratorType is null)
                    return false;

                deviceEnumeratorObj = Activator.CreateInstance(enumeratorType);
                if (deviceEnumeratorObj is null)
                    return false;
                deviceEnumerator = (IMMDeviceEnumerator)deviceEnumeratorObj;

                Marshal.ThrowExceptionForHR(deviceEnumerator.GetDefaultAudioEndpoint(EDataFlow.eRender, ERole.eMultimedia, out device));

                Guid iid = typeof(IAudioSessionManager2).GUID;
                Marshal.ThrowExceptionForHR(device.Activate(ref iid, CLSCTX.CLSCTX_ALL, IntPtr.Zero, out sessionManagerObj));
                if (sessionManagerObj is null)
                    return false;
                sessionManager = (IAudioSessionManager2)sessionManagerObj;

                Marshal.ThrowExceptionForHR(sessionManager.GetSessionEnumerator(out sessionEnumerator));
                Marshal.ThrowExceptionForHR(sessionEnumerator.GetCount(out int count));

                for (int i = 0; i < count; i++)
                {
                    Marshal.ThrowExceptionForHR(sessionEnumerator.GetSession(i, out IAudioSessionControl? sessionControl));
                    if (sessionControl is null)
                        continue;

                    try
                    {
                        Marshal.ThrowExceptionForHR(sessionControl.GetState(out AudioSessionState state));
                        if (state != AudioSessionState.Active)
                            continue;

                        if (sessionControl is IAudioMeterInformation meter)
                        {
                            Marshal.ThrowExceptionForHR(meter.GetPeakValue(out float peak));
                            if (peak > 0.001f)
                                return true;
                        }
                        else
                        {
                            return true;
                        }
                    }
                    finally
                    {
                        Marshal.FinalReleaseComObject(sessionControl);
                    }
                }

                return false;
            }
            catch
            {
                return false;
            }
            finally
            {
                if (sessionEnumerator is not null) Marshal.FinalReleaseComObject(sessionEnumerator);
                if (sessionManagerObj is not null) Marshal.FinalReleaseComObject(sessionManagerObj);
                if (device is not null) Marshal.FinalReleaseComObject(device);
                if (deviceEnumeratorObj is not null) Marshal.FinalReleaseComObject(deviceEnumeratorObj);
            }
        }

        private static readonly Guid CLSID_MMDeviceEnumerator = new Guid("BCDE0395-E52F-467C-8E3D-C4579291692E");

        private enum EDataFlow
        {
            eRender = 0,
            eCapture = 1,
            eAll = 2
        }

        private enum ERole
        {
            eConsole = 0,
            eMultimedia = 1,
            eCommunications = 2
        }

        private enum AudioSessionState
        {
            Inactive = 0,
            Active = 1,
            Expired = 2
        }

        [Flags]
        private enum CLSCTX : uint
        {
            CLSCTX_INPROC_SERVER = 0x1,
            CLSCTX_INPROC_HANDLER = 0x2,
            CLSCTX_LOCAL_SERVER = 0x4,
            CLSCTX_REMOTE_SERVER = 0x10,
            CLSCTX_ALL = CLSCTX_INPROC_SERVER | CLSCTX_INPROC_HANDLER | CLSCTX_LOCAL_SERVER | CLSCTX_REMOTE_SERVER
        }

        [ComImport]
        [Guid("A95664D2-9614-4F35-A746-DE8DB63617E6")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        private interface IMMDeviceEnumerator
        {
            int NotImpl1();
            int GetDefaultAudioEndpoint(EDataFlow dataFlow, ERole role, out IMMDevice ppDevice);
        }

        [ComImport]
        [Guid("D666063F-1587-4E43-81F1-B948E807363F")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        private interface IMMDevice
        {
            int Activate(ref Guid iid, CLSCTX dwClsCtx, IntPtr pActivationParams, [MarshalAs(UnmanagedType.IUnknown)] out object ppInterface);
        }

        [ComImport]
        [Guid("77AA99A0-1BD6-484F-8BC7-2C654C9A9B6F")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        private interface IAudioSessionManager2
        {
            int NotImpl1();
            int NotImpl2();
            int GetSessionEnumerator(out IAudioSessionEnumerator sessionEnum);
        }

        [ComImport]
        [Guid("E2F5BB11-0570-40CA-ACDD-3AA01277DEE8")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        private interface IAudioSessionEnumerator
        {
            int GetCount(out int sessionCount);
            int GetSession(int sessionCount, out IAudioSessionControl session);
        }

        [ComImport]
        [Guid("F4B1A599-7266-4319-A8CA-E70ACB11E8CD")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        private interface IAudioSessionControl
        {
            int NotImpl1();
            int GetState(out AudioSessionState state);
        }

        [ComImport]
        [Guid("C02216F6-8C67-4B5B-9D00-D008E73E0064")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        private interface IAudioMeterInformation
        {
            int GetPeakValue(out float peak);
        }
    }
}