namespace OcrDaemon;

using System.Drawing;
using OpenCvSharp;
using OpenCvSharp.Extensions;

static class ImagePreprocessor
{
    /// <summary>
    /// Pre-process an image for OCR using morphological white top-hat filtering.
    /// Isolates bright tooltip text, suppresses dim background text visible through overlay.
    /// Pipeline: grayscale → morphological top-hat → Otsu binary → 2x upscale
    /// </summary>
    public static Bitmap PreprocessForOcr(Bitmap src, OcrOptions? options = null)
    {
        if (options != null && !options.Preprocess)
            return CloneArgb(src);

        int kernelSize = options?.KernelSize ?? 25;
        if (kernelSize < 3) kernelSize = 3;
        if (kernelSize % 2 == 0) kernelSize += 1;

        int scale = options?.Scale ?? 2;
        if (scale < 1) scale = 1;

        using var mat = BitmapConverter.ToMat(src);
        using var gray = new Mat();
        Cv2.CvtColor(mat, gray, ColorConversionCodes.BGRA2GRAY);

        // Morphological white top-hat: isolates bright text on dark background
        // Kernel size 25x25 captures text strokes, suppresses dim background text
        using var kernel = Cv2.GetStructuringElement(MorphShapes.Rect, new OpenCvSharp.Size(kernelSize, kernelSize));
        using var tophat = new Mat();
        Cv2.MorphologyEx(gray, tophat, MorphTypes.TopHat, kernel);

        // Otsu binarization: automatic threshold, black text on white
        using var binary = new Mat();
        Cv2.Threshold(tophat, binary, 0, 255, ThresholdTypes.BinaryInv | ThresholdTypes.Otsu);

        // 2x upscale for better LSTM recognition
        if (scale == 1)
            return BitmapConverter.ToBitmap(binary);

        using var upscaled = new Mat();
        Cv2.Resize(binary, upscaled, new OpenCvSharp.Size(binary.Width * scale, binary.Height * scale),
            interpolation: InterpolationFlags.Cubic);

        return BitmapConverter.ToBitmap(upscaled);
    }

    private static Bitmap CloneArgb(Bitmap src)
    {
        var rect = new Rectangle(0, 0, src.Width, src.Height);
        return src.Clone(rect, System.Drawing.Imaging.PixelFormat.Format32bppArgb);
    }
}