using Docnet.Core;
using Docnet.Core.Models;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;

public class ImagePreprocessor
{
    // US Letter at 300 DPI — sufficient for Tesseract on clinical scans.
    private const int PdfRenderWidth = 2550;
    private const int PdfRenderHeight = 3300;

    public Stream Preprocess(Stream input, string contentType)
    {
        Stream? pdfRenderStream = null;
        try
        {
            if (contentType == "application/pdf")
            {
                pdfRenderStream = RenderPdfFirstPage(input);
                input = pdfRenderStream;
            }

            using var image = Image.Load(input);

            image.Mutate(ctx => ctx
                .Grayscale()
                .GaussianSharpen(1.5f)
                .BinaryThreshold(0.5f));

            var output = new MemoryStream();
            image.SaveAsPng(output);
            output.Position = 0;
            return output;
        }
        finally
        {
            pdfRenderStream?.Dispose();
        }
    }

    private static Stream RenderPdfFirstPage(Stream pdfStream)
    {
        using var buffer = new MemoryStream();
        pdfStream.CopyTo(buffer);
        var pdfBytes = buffer.ToArray();

        using var docReader = DocLib.Instance.GetDocReader(
            pdfBytes,
            new PageDimensions(PdfRenderWidth, PdfRenderHeight));

        if (docReader.GetPageCount() == 0)
            throw new InvalidOperationException("PDF contains no pages.");

        using var pageReader = docReader.GetPageReader(0);
        var rawBytes = pageReader.GetImage();
        var width = pageReader.GetPageWidth();
        var height = pageReader.GetPageHeight();

        using var image = Image.LoadPixelData<Bgra32>(rawBytes, width, height);
        var output = new MemoryStream();
        image.SaveAsPng(output);
        output.Position = 0;
        return output;
    }
}