using System;
using FFmpeg.AutoGen;
using Unity.Collections;
using Unity.Collections.LowLevel.Unsafe;

namespace ADOFAIRenderer.Util.FFmpeg
{
    /// <summary>
    /// Decodes video files in a streaming fashion using FFmpeg's native C API.
    /// Unlike a standalone player, it allows reading frames sequentially or seeking/skipping forward on demand.
    /// </summary>
    internal sealed unsafe class FFmpegNativeDecoder : IDisposable
    {
        private AVFormatContext* _pFormatContext = null;
        private AVCodecContext* _pCodecContext = null;
        private AVFrame* _pDecodedFrame = null;
        private AVFrame* _pConvertedFrame = null;
        private SwsContext* _pSwsContext = null;
        private AVPacket* _pPacket = null;
        
        private int _videoStreamIndex = -1;
        private long _currentFrameIndex;
        private AVRational _timeBase;
        private bool _isOpened;
        private bool _disposed;
        private bool _isDraining;
        private readonly object _lock = new();

        // Cached frame used to hold matching frames after seeking
        private AVFrame* _pCachedFrame = null;
        private bool _hasCachedFrame;

        // Field to detect SwsContext updates
        private AVPixelFormat _srcPixFmt = AVPixelFormat.AV_PIX_FMT_NONE;
        private AVPixelFormat _dstPixFmt = AVPixelFormat.AV_PIX_FMT_NONE;
        private int _srcWidth;
        private int _srcHeight;

        /// <summary>Video width in pixels.</summary>
        public int Width { get; private set; }

        /// <summary>Video height in pixels.</summary>
        public int Height { get; private set; }

        /// <summary>Frames per second.</summary>
        public double FPS { get; private set; }

        /// <summary>Total duration in seconds.</summary>
        public double Duration { get; private set; }

        /// <summary>Estimated total number of frames.</summary>
        public long TotalFrames { get; private set; }

        /// <summary>Index of the currently read frame.</summary>
        public long CurrentFrameIndex => _currentFrameIndex;

        /// <summary>Current playback time in seconds.</summary>
        public double CurrentTime => _currentFrameIndex / FPS;

        /// <summary>Pixel format of the original video stream.</summary>
        public AVPixelFormat PixelFormat => _pCodecContext != null ? _pCodecContext->pix_fmt : AVPixelFormat.AV_PIX_FMT_NONE;

        /// <summary>Color range of the original video stream.</summary>
        public AVColorRange ColorRange => _pCodecContext != null ? _pCodecContext->color_range : AVColorRange.AVCOL_RANGE_UNSPECIFIED;

        public FFmpegNativeDecoder(string videoPath)
        {
            Open(videoPath);
        }

        private void Open(string videoPath)
        {
            lock (_lock)
            {
                if (_isOpened || _disposed) return;

                try
                {
                    fixed (AVFormatContext** ppFormatCtx = &_pFormatContext)
                    {
                        int ret = ffmpeg.avformat_open_input(ppFormatCtx, videoPath, null, null);
                        if (ret < 0)
                            throw new Exception($"Failed to open video file: {videoPath} ({GetFFmpegErrorString(ret)})");
                    }

                    if (ffmpeg.avformat_find_stream_info(_pFormatContext, null) < 0)
                        throw new Exception("Failed to retrieve stream info.");

                    _videoStreamIndex = -1;
                    for (int i = 0; i < _pFormatContext->nb_streams; i++)
                    {
                        if (_pFormatContext->streams[i]->codecpar->codec_type == AVMediaType.AVMEDIA_TYPE_VIDEO)
                        {
                            _videoStreamIndex = i;
                            break;
                        }
                    }

                    if (_videoStreamIndex == -1)
                        throw new Exception("Failed to find video stream.");

                    var stream = _pFormatContext->streams[_videoStreamIndex];
                    _timeBase = stream->time_base;

                    // Calculate FPS
                    if (stream->r_frame_rate.num > 0 && stream->r_frame_rate.den > 0)
                    {
                        FPS = ffmpeg.av_q2d(stream->r_frame_rate);
                    }
                    else if (stream->avg_frame_rate.num > 0 && stream->avg_frame_rate.den > 0)
                    {
                        FPS = ffmpeg.av_q2d(stream->avg_frame_rate);
                    }
                    else
                    {
                        FPS = 30.0; // Fallback default
                    }

                    var codecId = stream->codecpar->codec_id;
                    var decoder = ffmpeg.avcodec_find_decoder(codecId);
                    if (decoder == null)
                        throw new Exception($"Unsupported video codec: {codecId}");

                    _pCodecContext = ffmpeg.avcodec_alloc_context3(decoder);
                    if (_pCodecContext == null)
                        throw new Exception("Failed to allocate codec context.");

                    if (ffmpeg.avcodec_parameters_to_context(_pCodecContext, stream->codecpar) < 0)
                        throw new Exception("Failed to copy codec parameters.");

                    // Multi-threading settings for improved decoding performance (auto)
                    _pCodecContext->thread_count = 0;
                    _pCodecContext->thread_type = ffmpeg.FF_THREAD_FRAME;

                    if (ffmpeg.avcodec_open2(_pCodecContext, decoder, null) < 0)
                        throw new Exception("Failed to open codec.");

                    Width = _pCodecContext->width;
                    Height = _pCodecContext->height;

                    // Calculate total frames and duration
                    if (stream->nb_frames > 0)
                    {
                        TotalFrames = stream->nb_frames;
                    }
                    else if (stream->duration > 0)
                    {
                        TotalFrames = (long)Math.Round(stream->duration * ffmpeg.av_q2d(stream->time_base) * FPS);
                    }
                    else if (_pFormatContext->duration > 0)
                    {
                        TotalFrames = (long)Math.Round((_pFormatContext->duration / (double)ffmpeg.AV_TIME_BASE) * FPS);
                    }
                    else
                    {
                        TotalFrames = 0;
                    }

                    Duration = _pFormatContext->duration > 0
                        ? _pFormatContext->duration / (double)ffmpeg.AV_TIME_BASE
                        : (stream->duration > 0 ? stream->duration * ffmpeg.av_q2d(stream->time_base) : 0);

                    _pDecodedFrame = ffmpeg.av_frame_alloc();
                    _pConvertedFrame = ffmpeg.av_frame_alloc();
                    _pCachedFrame = ffmpeg.av_frame_alloc();
                    _pPacket = ffmpeg.av_packet_alloc();

                    _currentFrameIndex = 0;
                    _isOpened = true;
                    _isDraining = false;
                }
                catch (Exception)
                {
                    Dispose();
                    throw;
                }
            }
        }

        private bool ReadAndSendPacket()
        {
            while (true)
            {
                ffmpeg.av_packet_unref(_pPacket);
                int ret = ffmpeg.av_read_frame(_pFormatContext, _pPacket);
                if (ret < 0) return false; // EOF or error

                if (_pPacket->stream_index == _videoStreamIndex)
                {
                    ret = ffmpeg.avcodec_send_packet(_pCodecContext, _pPacket);
                    ffmpeg.av_packet_unref(_pPacket);
                    if (ret < 0)
                    {
                        throw new Exception($"Error sending packet to decoder: {GetFFmpegErrorString(ret)}");
                    }
                    return true;
                }
            }
        }

        private void InitOrUpdateSwsContext(AVPixelFormat srcFormat, int srcWidth, int srcHeight, AVPixelFormat dstFormat)
        {
            if (_pSwsContext != null && _srcPixFmt == srcFormat && _srcWidth == srcWidth && _srcHeight == srcHeight && _dstPixFmt == dstFormat)
            {
                return;
            }

            if (_pSwsContext != null)
            {
                ffmpeg.sws_freeContext(_pSwsContext);
                _pSwsContext = null;
            }

            _srcPixFmt = srcFormat;
            _srcWidth = srcWidth;
            _srcHeight = srcHeight;
            _dstPixFmt = dstFormat;

            _pSwsContext = ffmpeg.sws_getContext(
                srcWidth, srcHeight, srcFormat,
                Width, Height, dstFormat,
                (int)SwsFlags.SWS_BILINEAR, null, null, null
            );

            if (_pSwsContext == null)
            {
                throw new Exception("Failed to initialize SwsContext.");
            }
        }

        private double GetTimestampAndUpdateIndex(AVFrame* frame)
        {
            long ptsValue = frame->best_effort_timestamp;
            if (ptsValue == ffmpeg.AV_NOPTS_VALUE)
            {
                ptsValue = frame->pts;
            }

            double timestamp;
            if (ptsValue == ffmpeg.AV_NOPTS_VALUE)
            {
                timestamp = _currentFrameIndex / FPS;
                _currentFrameIndex++;
            }
            else
            {
                timestamp = ptsValue * ffmpeg.av_q2d(_timeBase);
                _currentFrameIndex = (long)Math.Round(timestamp * FPS);
            }
            return timestamp;
        }

        /// <summary>
        /// Reads the next video frame and copies it in RGBA format.
        /// </summary>
        /// <param name="outBuffer">Pointer to the output buffer storing RGBA data.</param>
        /// <param name="outStride">Byte stride per row of the output buffer (typically Width * 4).</param>
        /// <param name="vflip">Whether to flip vertically to match Unity's texture coordinate system.</param>
        /// <param name="timestamp">Timestamp of the output frame in seconds.</param>
        /// <returns>True if the frame was successfully decoded and copied; false on EOF or failure.</returns>
        private bool TryReadFrame(byte* outBuffer, int outStride, bool vflip, out double timestamp)
        {
            timestamp = 0;
            lock (_lock)
            {
                if (!_isOpened || _disposed) return false;

                if (_hasCachedFrame)
                {
                    timestamp = GetTimestampAndUpdateIndex(_pCachedFrame);
                    InitOrUpdateSwsContext(_pCodecContext->pix_fmt, _pCachedFrame->width, _pCachedFrame->height, AVPixelFormat.AV_PIX_FMT_RGBA);

                    if (vflip)
                    {
                        _pConvertedFrame->data[0] = outBuffer + outStride * (Height - 1);
                        _pConvertedFrame->linesize[0] = -outStride;
                    }
                    else
                    {
                        _pConvertedFrame->data[0] = outBuffer;
                        _pConvertedFrame->linesize[0] = outStride;
                    }

                    ffmpeg.sws_scale(
                        _pSwsContext,
                        _pCachedFrame->data, _pCachedFrame->linesize,
                        0, _pCachedFrame->height,
                        _pConvertedFrame->data, _pConvertedFrame->linesize
                    );

                    ffmpeg.av_frame_unref(_pCachedFrame);
                    _hasCachedFrame = false;
                    return true;
                }

                while (true)
                {
                    int ret = ffmpeg.avcodec_receive_frame(_pCodecContext, _pDecodedFrame);
                    if (ret == 0)
                    {
                        timestamp = GetTimestampAndUpdateIndex(_pDecodedFrame);
                        InitOrUpdateSwsContext(_pCodecContext->pix_fmt, _pDecodedFrame->width, _pDecodedFrame->height, AVPixelFormat.AV_PIX_FMT_RGBA);

                        if (vflip)
                        {
                            _pConvertedFrame->data[0] = outBuffer + outStride * (Height - 1);
                            _pConvertedFrame->linesize[0] = -outStride;
                        }
                        else
                        {
                            _pConvertedFrame->data[0] = outBuffer;
                            _pConvertedFrame->linesize[0] = outStride;
                        }

                        ffmpeg.sws_scale(
                            _pSwsContext,
                            _pDecodedFrame->data, _pDecodedFrame->linesize,
                            0, _pDecodedFrame->height,
                            _pConvertedFrame->data, _pConvertedFrame->linesize
                        );

                        ffmpeg.av_frame_unref(_pDecodedFrame);
                        return true;
                    }

                    if (ret == ffmpeg.AVERROR(ffmpeg.EAGAIN))
                    {
                        if (_isDraining) return false;

                        if (!ReadAndSendPacket())
                        {
                            _isDraining = true;
                            ffmpeg.avcodec_send_packet(_pCodecContext, null);
                        }
                    }
                    else if (ret == ffmpeg.AVERROR_EOF)
                    {
                        return false;
                    }
                    else
                    {
                        throw new Exception($"Error during decoding: {GetFFmpegErrorString(ret)}");
                    }
                }
            }
        }

        public bool TryReadFrame(IntPtr outBuffer, int outStride, bool vflip, out double timestamp)
        {
            return TryReadFrame((byte*)outBuffer.ToPointer(), outStride, vflip, out timestamp);
        }

        public bool TryReadFrame(NativeArray<byte> outBuffer, bool vflip, out double timestamp)
        {
            if (outBuffer.Length < Width * Height * 4)
            {
                throw new ArgumentException("Output buffer size is smaller than video resolution.", nameof(outBuffer));
            }
            int stride = Width * 4;
            return TryReadFrame((byte*)outBuffer.GetUnsafePtr(), stride, vflip, out timestamp);
        }

        /// <summary>
        /// Reads the next video frame and copies its Y, U, and V channel data separately.
        /// If the source format is YUV420P family (YUV420P, YUVJ420P), CPU color conversion (sws_scale) is bypassed
        /// and memory is copied directly for maximum performance.
        /// Other formats are automatically converted to YUV420P before copying.
        /// </summary>
        // ReSharper disable once InconsistentNaming
        private bool TryReadYUV420PFrame(
            byte* yBuffer, int yStride,
            byte* uBuffer, int uStride,
            byte* vBuffer, int vStride,
            out double timestamp)
        {
            timestamp = 0;
            lock (_lock)
            {
                if (!_isOpened || _disposed) return false;

                AVFrame* frame;

                if (_hasCachedFrame)
                {
                    frame = _pCachedFrame;
                    _hasCachedFrame = false;
                }
                else
                {
                    while (true)
                    {
                        int ret = ffmpeg.avcodec_receive_frame(_pCodecContext, _pDecodedFrame);
                        if (ret == 0)
                        {
                            frame = _pDecodedFrame;
                            break;
                        }

                        if (ret == ffmpeg.AVERROR(ffmpeg.EAGAIN))
                        {
                            if (_isDraining) return false;

                            if (!ReadAndSendPacket())
                            {
                                _isDraining = true;
                                ffmpeg.avcodec_send_packet(_pCodecContext, null);
                            }
                        }
                        else if (ret == ffmpeg.AVERROR_EOF)
                        {
                            return false;
                        }
                        else
                        {
                            throw new Exception($"Error during decoding: {GetFFmpegErrorString(ret)}");
                        }
                    }
                }

                if (frame == null) return false;

                timestamp = GetTimestampAndUpdateIndex(frame);

                if (frame->format != (int)AVPixelFormat.AV_PIX_FMT_YUV420P && frame->format != (int)AVPixelFormat.AV_PIX_FMT_YUVJ420P)
                {
                    InitOrUpdateSwsContext((AVPixelFormat)frame->format, frame->width, frame->height, AVPixelFormat.AV_PIX_FMT_YUV420P);

                    _pConvertedFrame->data[0] = yBuffer;
                    _pConvertedFrame->data[1] = uBuffer;
                    _pConvertedFrame->data[2] = vBuffer;
                    _pConvertedFrame->linesize[0] = yStride;
                    _pConvertedFrame->linesize[1] = uStride;
                    _pConvertedFrame->linesize[2] = vStride;

                    ffmpeg.sws_scale(
                        _pSwsContext,
                        frame->data, frame->linesize,
                        0, frame->height,
                        _pConvertedFrame->data, _pConvertedFrame->linesize
                    );
                }
                else
                {
                    int w = frame->width;
                    int h = frame->height;
                    int uvW = w / 2;
                    int uvH = h / 2;

                    // Copy Y plane
                    for (int y = 0; y < h; y++)
                    {
                        Buffer.MemoryCopy(
                            frame->data[0] + y * frame->linesize[0],
                            yBuffer + y * yStride,
                            w, w
                        );
                    }

                    // Copy U plane
                    for (int y = 0; y < uvH; y++)
                    {
                        Buffer.MemoryCopy(
                            frame->data[1] + y * frame->linesize[1],
                            uBuffer + y * uStride,
                            uvW, uvW
                        );
                    }

                    // Copy V plane
                    for (int y = 0; y < uvH; y++)
                    {
                        Buffer.MemoryCopy(
                            frame->data[2] + y * frame->linesize[2],
                            vBuffer + y * vStride,
                            uvW, uvW
                        );
                    }
                }

                ffmpeg.av_frame_unref(frame);
                return true;
            }
        }

        // ReSharper disable once InconsistentNaming
        public bool TryReadYUV420PFrame(
            NativeArray<byte> yBuffer,
            NativeArray<byte> uBuffer,
            NativeArray<byte> vBuffer,
            out double timestamp)
        {
            int w = Width;
            int h = Height;
            int uvW = w / 2;
            int uvH = h / 2;

            if (yBuffer.Length < w * h || uBuffer.Length < uvW * uvH || vBuffer.Length < uvW * uvH)
            {
                throw new ArgumentException("Buffer size is smaller than video YUV plane resolution.");
            }

            return TryReadYUV420PFrame(
                (byte*)yBuffer.GetUnsafePtr(), w,
                (byte*)uBuffer.GetUnsafePtr(), uvW,
                (byte*)vBuffer.GetUnsafePtr(), uvW,
                out timestamp
            );
        }

        /// <summary>
        /// Reads the next video frame and copies its NV12 format Y and UV channel data separately.
        /// If the source format is NV12 family, CPU color conversion (sws_scale) is bypassed
        /// and memory is copied directly for maximum performance.
        /// Other formats are automatically converted to NV12 before copying.
        /// </summary>
        // ReSharper disable once InconsistentNaming
        private bool TryReadNV12Frame(
            byte* yBuffer, int yStride,
            byte* uvBuffer, int uvStride,
            out double timestamp)
        {
            timestamp = 0;
            lock (_lock)
            {
                if (!_isOpened || _disposed) return false;

                AVFrame* frame;

                if (_hasCachedFrame)
                {
                    frame = _pCachedFrame;
                    _hasCachedFrame = false;
                }
                else
                {
                    while (true)
                    {
                        int ret = ffmpeg.avcodec_receive_frame(_pCodecContext, _pDecodedFrame);
                        if (ret == 0)
                        {
                            frame = _pDecodedFrame;
                            break;
                        }

                        if (ret == ffmpeg.AVERROR(ffmpeg.EAGAIN))
                        {
                            if (_isDraining) return false;

                            if (!ReadAndSendPacket())
                            {
                                _isDraining = true;
                                ffmpeg.avcodec_send_packet(_pCodecContext, null);
                            }
                        }
                        else if (ret == ffmpeg.AVERROR_EOF)
                        {
                            return false;
                        }
                        else
                        {
                            throw new Exception($"Error during decoding: {GetFFmpegErrorString(ret)}");
                        }
                    }
                }

                if (frame == null) return false;

                timestamp = GetTimestampAndUpdateIndex(frame);

                if (frame->format != (int)AVPixelFormat.AV_PIX_FMT_NV12)
                {
                    InitOrUpdateSwsContext((AVPixelFormat)frame->format, frame->width, frame->height, AVPixelFormat.AV_PIX_FMT_NV12);

                    _pConvertedFrame->data[0] = yBuffer;
                    _pConvertedFrame->data[1] = uvBuffer;
                    _pConvertedFrame->linesize[0] = yStride;
                    _pConvertedFrame->linesize[1] = uvStride;

                    ffmpeg.sws_scale(
                        _pSwsContext,
                        frame->data, frame->linesize,
                        0, frame->height,
                        _pConvertedFrame->data, _pConvertedFrame->linesize
                    );
                }
                else
                {
                    int w = frame->width;
                    int h = frame->height;
                    int uvH = h / 2;

                    // Copy Y plane
                    for (int y = 0; y < h; y++)
                    {
                        Buffer.MemoryCopy(
                            frame->data[0] + y * frame->linesize[0],
                            yBuffer + y * yStride,
                            w, w
                        );
                    }

                    // Copy UV plane
                    for (int y = 0; y < uvH; y++)
                    {
                        Buffer.MemoryCopy(
                            frame->data[1] + y * frame->linesize[1],
                            uvBuffer + y * uvStride,
                            w, w
                        );
                    }
                }

                ffmpeg.av_frame_unref(frame);
                return true;
            }
        }

        // ReSharper disable once InconsistentNaming
        public bool TryReadNV12Frame(
            NativeArray<byte> yBuffer,
            NativeArray<byte> uvBuffer,
            out double timestamp)
        {
            int w = Width;
            int h = Height;
            int uvH = h / 2;

            if (yBuffer.Length < w * h || uvBuffer.Length < w * uvH)
            {
                throw new ArgumentException("Buffer size is smaller than video NV12 plane resolution.");
            }

            return TryReadNV12Frame(
                (byte*)yBuffer.GetUnsafePtr(), w,
                (byte*)uvBuffer.GetUnsafePtr(), w,
                out timestamp
            );
        }

        /// <summary>
        /// Decodes and discards a specified number of frames immediately (for fast forward skipping).
        /// </summary>
        /// <param name="count">Number of frames to discard.</param>
        private void SkipFrames(int count)
        {
            lock (_lock)
            {
                if (!_isOpened || _disposed) return;
                if (count <= 0) return;

                int skipped = 0;
                if (_hasCachedFrame)
                {
                    ffmpeg.av_frame_unref(_pCachedFrame);
                    _hasCachedFrame = false;
                    skipped++;
                }

                while (skipped < count)
                {
                    int ret = ffmpeg.avcodec_receive_frame(_pCodecContext, _pDecodedFrame);
                    if (ret == 0)
                    {
                        GetTimestampAndUpdateIndex(_pDecodedFrame);
                        ffmpeg.av_frame_unref(_pDecodedFrame);
                        skipped++;
                        continue;
                    }

                    if (ret == ffmpeg.AVERROR(ffmpeg.EAGAIN))
                    {
                        if (_isDraining) break;

                        if (!ReadAndSendPacket())
                        {
                            _isDraining = true;
                            ffmpeg.avcodec_send_packet(_pCodecContext, null);
                        }
                    }
                    else if (ret == ffmpeg.AVERROR_EOF)
                    {
                        break;
                    }
                    else
                    {
                        throw new Exception($"Error skipping frames: {GetFFmpegErrorString(ret)}");
                    }
                }
            }
        }

        /// <summary>
        /// Seeks to a specific playback time in seconds.
        /// </summary>
        /// <param name="timeSeconds">Target time in seconds to seek to.</param>
        public void SeekToTime(double timeSeconds)
        {
            lock (_lock)
            {
                if (!_isOpened || _disposed) return;

                if (timeSeconds < 0) timeSeconds = 0;
                double targetFrameIndex = timeSeconds * FPS;

                // If already at target index or very close future, skip frames instead of seek to avoid I-frame overhead
                bool useSkip = targetFrameIndex >= _currentFrameIndex && targetFrameIndex - _currentFrameIndex < 60;
                if (useSkip)
                {
                    SkipFrames((int)(targetFrameIndex - _currentFrameIndex));
                    return;
                }

                if (_hasCachedFrame)
                {
                    ffmpeg.av_frame_unref(_pCachedFrame);
                    _hasCachedFrame = false;
                }

                long targetPts = (long)Math.Round(timeSeconds / ffmpeg.av_q2d(_timeBase));
                int ret = ffmpeg.av_seek_frame(_pFormatContext, _videoStreamIndex, targetPts, ffmpeg.AVSEEK_FLAG_BACKWARD);
                if (ret < 0)
                {
                    // Fallback to start of file on seek failure
                    ret = ffmpeg.av_seek_frame(_pFormatContext, _videoStreamIndex, 0, ffmpeg.AVSEEK_FLAG_BACKWARD);
                    if (ret < 0)
                    {
                        throw new Exception($"Seek failed: {GetFFmpegErrorString(ret)}");
                    }
                }

                // Flush decoder internal cache
                ffmpeg.avcodec_flush_buffers(_pCodecContext);
                _isDraining = false;

                // Decode and discard frames until the first frame past the specified time is found
                while (true)
                {
                    ret = ffmpeg.avcodec_receive_frame(_pCodecContext, _pDecodedFrame);
                    if (ret == 0)
                    {
                        double currentPts = GetTimestampAndUpdateIndex(_pDecodedFrame);

                        // Check from half frame earlier to account for floating point errors
                        if (currentPts >= timeSeconds - (0.5 / FPS))
                        {
                            // Cache the first matching frame so it will be consumed by the next TryReadFrame call
                            ffmpeg.av_frame_move_ref(_pCachedFrame, _pDecodedFrame);
                            _hasCachedFrame = true;
                            break;
                        }

                        ffmpeg.av_frame_unref(_pDecodedFrame);
                        continue;
                    }

                    if (ret == ffmpeg.AVERROR(ffmpeg.EAGAIN))
                    {
                        if (_isDraining) break;

                        if (!ReadAndSendPacket())
                        {
                            _isDraining = true;
                            ffmpeg.avcodec_send_packet(_pCodecContext, null);
                        }
                    }
                    else if (ret == ffmpeg.AVERROR_EOF)
                    {
                        break;
                    }
                    else
                    {
                        throw new Exception($"Error during seek decoding: {GetFFmpegErrorString(ret)}");
                    }
                }
            }
        }

        /// <summary>
        /// Seeks to a specific frame index.
        /// </summary>
        /// <param name="frameIndex">Target frame index to seek to.</param>
        public void SeekToFrame(long frameIndex)
        {
            SeekToTime(frameIndex / FPS);
        }

        private string GetFFmpegErrorString(int errnum)
        {
            const ulong bufferSize = 1024;
            byte* buffer = stackalloc byte[(int)bufferSize];
            if (ffmpeg.av_strerror(errnum, buffer, bufferSize) >= 0)
            {
                return System.Runtime.InteropServices.Marshal.PtrToStringAnsi((IntPtr)buffer) ?? $"Unknown error (Code: {errnum})";
            }
            return $"Unknown error (Code: {errnum})";
        }

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

                if (_pSwsContext != null)
                {
                    ffmpeg.sws_freeContext(_pSwsContext);
                    _pSwsContext = null;
                }

                if (_pDecodedFrame != null)
                {
                    var pFrame = _pDecodedFrame;
                    ffmpeg.av_frame_free(&pFrame);
                    _pDecodedFrame = null;
                }

                if (_pCachedFrame != null)
                {
                    var pFrame = _pCachedFrame;
                    ffmpeg.av_frame_free(&pFrame);
                    _pCachedFrame = null;
                }

                if (_pConvertedFrame != null)
                {
                    var pFrame = _pConvertedFrame;
                    ffmpeg.av_frame_free(&pFrame);
                    _pConvertedFrame = null;
                }

                if (_pPacket != null)
                {
                    var pPacket = _pPacket;
                    ffmpeg.av_packet_free(&pPacket);
                    _pPacket = null;
                }

                if (_pCodecContext != null)
                {
                    var pCodecCtx = _pCodecContext;
                    ffmpeg.avcodec_free_context(&pCodecCtx);
                    _pCodecContext = null;
                }

                if (_pFormatContext != null)
                {
                    var pFormatCtx = _pFormatContext;
                    ffmpeg.avformat_close_input(&pFormatCtx);
                    _pFormatContext = null;
                }

                _isOpened = false;
                GC.SuppressFinalize(this);
            }
        }

        ~FFmpegNativeDecoder()
        {
            Dispose();
        }
    }
}