MoneyMap/MoneyMap.Core/Services/PdfToImageConverter.cs

using ImageMagick;

namespace MoneyMap.Services
{
    /// <summary>
    /// Service for converting PDF files to images for AI processing.
    /// </summary>
    public interface IPdfToImageConverter
    {
        /// <summary>
        /// Converts the first page of a PDF to a base64-encoded PNG image.
        /// </summary>
        Task<string> ConvertFirstPageToBase64Async(string pdfPath);

        /// <summary>
        /// Converts PDF bytes to a base64-encoded PNG image.
        /// </summary>
        Task<string> ConvertFirstPageToBase64Async(byte[] pdfBytes);
    }

    public class PdfToImageConverter : IPdfToImageConverter
    {
        private const int DefaultDpi = 220;

        public Task<string> ConvertFirstPageToBase64Async(string pdfPath)
        {
            var pdfBytes = File.ReadAllBytes(pdfPath);
            return ConvertFirstPageToBase64Async(pdfBytes);
        }

        public Task<string> ConvertFirstPageToBase64Async(byte[] pdfBytes)
        {
            return Task.Run(() =>
            {
                var settings = new MagickReadSettings
                {
                    Density = new Density(DefaultDpi),
                    BackgroundColor = MagickColors.White,
                    ColorSpace = ColorSpace.sRGB
                };

                using var pages = new MagickImageCollection();
                pages.Read(pdfBytes, settings);

                if (pages.Count == 0)
                    throw new InvalidOperationException("PDF has no pages");

                using var img = (MagickImage)pages[0].Clone();

                // Ensure we have a clean 8-bit RGB canvas
                img.ColorType = ColorType.TrueColor;
                img.Alpha(AlphaOption.Remove); // flatten onto white
                img.ResetPage();

                // Convert to PNG bytes
                var imageBytes = img.ToByteArray(MagickFormat.Png);
                return Convert.ToBase64String(imageBytes);
            });
        }
    }
}