Beam/Beam.Dynamic/DropDownDataProvider.cs

using HtmlAgilityPack;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.Marshalling;
using System.Text;
using System.Text.Json;
using System.Threading.Tasks;

namespace Beam.Dynamic {
    public class DropDownDataProvider
            : IDataProvider<string>, 
              IDataProvider<string[]>, 
              IDataProvider<SourceLink[]> {
        public IBinding? Content { get; set; }
        public string? RelativeTo { get; set; } 

        private string GetAbsolute(string? @base, string relative) {
            if (@base is null)
                return relative;

            if (@base.EndsWith('/'))
                @base = @base[..^1];
            if (relative.StartsWith('/'))
                relative = relative[1..];
            return @base + '/' + relative;
        }

        public SourceLink[] Get(HtmlDocument document) {
            if (Content is null)
                return [];
            var node = Content.Select(document);
            if (node is null)
                return [];
            List<SourceLink> links = [];
            foreach (var child in node.ChildNodes.Where(x => x.Name == "option")) {
                var childValue = child.GetAttributeValue("value", null);
                if (!Uri.TryCreate(GetAbsolute(RelativeTo, childValue), UriKind.Absolute, out _))
                    continue;
                links.Add(new SourceLink(GetAbsolute(RelativeTo, childValue)));
            }

            return links.ToArray();
        }

        string[] IDataProvider<string[]>.Get(HtmlDocument document) {
            return this.Get(document).Select(x => x.Link.AbsoluteUri).ToArray();
        }

        string IDataProvider<string>.Get(HtmlDocument document) {
            return JsonSerializer.Serialize(this.Get(document));
        }
    }
}