SvgCodec.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Svg.Skia;
using Waher.Content;
using Waher.Content.Images;
using Waher.Runtime.Inventory;
 
namespace NeuroAccessMaui.Helpers
{
    public class SvgCodec : IContentDecoder, IContentEncoder
    {
        public SvgCodec() { }
 
        public static readonly string[] SvgContentTypes = new string[] { ImageCodec.ContentTypeSvg };
        public static readonly string[] SvgFileExtensions = new string[] { ImageCodec.FileExtensionSvg };
        public string[] ContentTypes => SvgContentTypes;
        public string[] FileExtensions => SvgFileExtensions;
 
        public bool Decodes(string ContentType, out Grade Grade)
        {
            if (string.Equals(ContentType, ImageCodec.ContentTypeSvg, StringComparison.OrdinalIgnoreCase))
            {
                Grade = Grade.Excellent;
                return true;
            }
            Grade = Grade.NotAtAll;
            return false;
        }
 
        public Task<ContentResponse> DecodeAsync(string ContentType, byte[] Data, Encoding Encoding,
            KeyValuePair<string, string>[] Fields, Uri BaseUri, ICodecProgress Progress)
        {
            SKSvg Svg;
            try
            {
                Svg = new SKSvg();
                using (MemoryStream ms = new MemoryStream(Data))
                {
                    Svg.Load(ms);
                }
            }
            catch (Exception ex)
            {
                return Task.FromResult(new ContentResponse(ex));
            }
 
            return Task.FromResult(new ContentResponse(ContentType, Svg, Data));
        }
 
        public bool Encodes(object Object, out Grade Grade, params string[] AcceptedContentTypes)
        {
            if (InternetContent.IsAccepted(SvgContentTypes, AcceptedContentTypes))
            {
                if (Object is string s && s.IndexOf("<svg", StringComparison.OrdinalIgnoreCase) >= 0)
                {
                    Grade = Grade.Ok;
                    return true;
                }
                else if (Object is SKSvg)
                {
                    Grade = Grade.Barely; // Cannot re-encode reliably without original XML.
                    return false;
                }
            }
            Grade = Grade.NotAtAll;
            return false;
        }
 
        public Task<ContentResponse> EncodeAsync(object Object, Encoding Encoding, ICodecProgress Progress, params string[] AcceptedContentTypes)
        {
            if (!InternetContent.IsAccepted(SvgContentTypes, out string ContentType, AcceptedContentTypes))
                return Task.FromResult(new ContentResponse(new ArgumentException("Unable to encode object, or content type not accepted.", nameof(Object))));
 
            if (!(Object is string Xml))
                return Task.FromResult(new ContentResponse(new ArgumentException("Encoder expects raw SVG markup string.", nameof(Object))));
 
            if (Xml.IndexOf("<svg", StringComparison.OrdinalIgnoreCase) < 0)
                return Task.FromResult(new ContentResponse(new ArgumentException("Object does not appear to be valid SVG markup.", nameof(Object))));
 
            if (Encoding is null)
            {
                ContentType += "; charset=utf-8";
                Encoding = Encoding.UTF8;
            }
            else
                ContentType += "; charset=" + Encoding.WebName;
 
            return Task.FromResult(new ContentResponse(ContentType, Object, Encoding.GetBytes(Xml)));
        }
 
        public bool TryGetContentType(string FileExtension, out string ContentType)
        {
            if (string.Equals(FileExtension, "svg", StringComparison.OrdinalIgnoreCase))
            {
                ContentType = ImageCodec.ContentTypeSvg;
                return true;
            }
 
            ContentType = string.Empty;
            return false;
        }
 
        public bool TryGetFileExtension(string ContentType, out string FileExtension)
        {
            if (string.Equals(ContentType, ImageCodec.ContentTypeSvg, StringComparison.OrdinalIgnoreCase))
            {
                FileExtension = "svg";
                return true;
            }
 
            FileExtension = string.Empty;
            return false;
        }
    }
}