using FFMediaToolkit.Decoding;
using FFMediaToolkit.Graphics;
using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;

public static class VideoFrameExtractor
{
    public static Bitmap GetFrame200(string videoPath)
    {
        FFMediaToolkit.FFmpegLoader.FFmpegPath = AppDomain.CurrentDomain.BaseDirectory;

        using var mediaFile = MediaFile.Open(videoPath);

        // Read first two frames to estimate frame rate
        if (!mediaFile.Video.TryGetNextFrame(out var firstFrame))
            throw new Exception("Cannot read first frame");
        double firstSeconds = mediaFile.Video.Position.TotalSeconds;

        if (!mediaFile.Video.TryGetNextFrame(out var secondFrame))
            throw new Exception("Cannot read second frame");
        double secondSeconds = mediaFile.Video.Position.TotalSeconds;

        double frameDuration = secondSeconds - firstSeconds;
        if (frameDuration <= 0)
            throw new Exception("Invalid frame duration calculated");

        double frameRate = 1.0 / frameDuration;

        int totalFrames = (int)(mediaFile.Info.Duration.TotalSeconds * frameRate);

        const int targetFrameIndex = 200;
        if (targetFrameIndex >= totalFrames)
            throw new ArgumentOutOfRangeException($"Video has only {totalFrames} frames, cannot extract frame {targetFrameIndex}");

        // Reopen to reset reading
        mediaFile.Dispose();
        using var mediaFile2 = MediaFile.Open(videoPath);

        int currentFrameIndex = 0;
        Bitmap targetFrameBitmap = null;

        while (mediaFile2.Video.TryGetNextFrame(out var frame))
        {
            if (currentFrameIndex == targetFrameIndex)
            {
                targetFrameBitmap = ImageDataToBitmap(frame);
                break;
            }
            currentFrameIndex++;
        }

        if (targetFrameBitmap == null)
            throw new Exception($"Failed to extract frame {targetFrameIndex}");

        return targetFrameBitmap;
    }

    private static Bitmap ImageDataToBitmap(ImageData imageData)
    {
        var bitmap = new Bitmap(imageData.ImageSize.Width, imageData.ImageSize.Height, PixelFormat.Format24bppRgb);
        var bmpData = bitmap.LockBits(
            new Rectangle(0, 0, bitmap.Width, bitmap.Height),
            ImageLockMode.WriteOnly,
            bitmap.PixelFormat);

        // Convert Span<byte> to byte[] for Marshal.Copy
        Marshal.Copy(imageData.Data.ToArray(), 0, bmpData.Scan0, imageData.Data.Length);

        bitmap.UnlockBits(bmpData);

        return bitmap;
    }

}