using System;
using System.IO;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Formats.Png;
using SixLabors.ImageSharp.Processing;

namespace Gott.Services;

public class ImageService
{
    private const int MaxSideLength = 512;

    /// <summary>
    /// Nimmt eine Base64-Data-URL (z.B. "data:image/png;base64,..."), skaliert das Bild
    /// auf max 512px Seitenlänge und gibt eine neue Data-URL zurück.
    /// Gibt null zurück wenn input null/leer ist.
    /// </summary>
    public string ResizeDataUrl(string dataUrl)
    {
        if (string.IsNullOrEmpty(dataUrl)) return null;

        // Data-URL parsen: "data:<mediaType>;base64,<data>"
        var commaIndex = dataUrl.IndexOf(',');
        if (commaIndex < 0) return dataUrl;

        var base64 = dataUrl.Substring(commaIndex + 1);
        var bytes = Convert.FromBase64String(base64);

        using var image = Image.Load(bytes);

        // Nur skalieren wenn nötig
        if (image.Width <= MaxSideLength && image.Height <= MaxSideLength)
            return dataUrl;

        image.Mutate(x => x.Resize(new ResizeOptions
        {
            Size = new Size(MaxSideLength, MaxSideLength),
            Mode = ResizeMode.Max
        }));

        using var ms = new MemoryStream();
        image.Save(ms, new PngEncoder());
        var resizedBase64 = Convert.ToBase64String(ms.ToArray());

        return "data:image/png;base64," + resizedBase64;
    }
}