WikiSolver.cs

using System.Text.RegularExpressions;

namespace LinkSolver; 
public record struct Node(string Value, int Depth, List<string> Path);

public partial class WikiSolver
{
    private const string WIKI = "/wiki/";
    private const string WIKI_URL_FORMAT = "https://{0}.wikipedia.org/wiki/";

    private readonly Regex _regex = MyRegex();
    private string? _wikiUrl = string.Empty;

    public uint MaximumDepth;

    public WikiSolver(uint maxDepth = 3)
    {
        MaximumDepth = maxDepth;
    }

    public async Task Run(string start, string target, string language = "en")
    {
        if (start == null || start.Length == 0 || target == null || target.Length == 0)
        {
            return;
        }

        _wikiUrl = string.Format(WIKI_URL_FORMAT, language);
        Console.WriteLine("Starting from: " + _wikiUrl + start);

        var queue = new Queue<Node>();
        queue.Enqueue(new Node(start, 0, new List<string>() { start }));

        var found = await IterateOnQueue(queue, target);
        PrintResult(found);
    }

    private async Task<Node> IterateOnQueue(Queue<Node> queue, string target)
    {
        Node found = default;
        var client = new HttpClient();

        while (found == default && queue.Any())
        {
            var current = queue.Dequeue();

            Console.WriteLine($"Working on {current.Value} in depth {current.Depth}");

            if (current.Depth == MaximumDepth)
            {
                continue;
            }

            var wikiPage = await GetWikiPage(client, current.Value);
            found = RunOnLinks(wikiPage, target, current, queue);
        };

        return found;
    }

    private async Task<string> GetWikiPage(HttpClient client, string page) {
        var response = await client.GetAsync($"{_wikiUrl}{page}");
        return await response.Content.ReadAsStringAsync();
    }

    private Node RunOnLinks(string wikiPage, string target, Node current, Queue<Node> queue)
    {
        foreach (var match in _regex.Matches(wikiPage).ToHashSet())
        {
            var value = match.Groups[1].ToString();

            if (!value.StartsWith(WIKI) || value.Contains('.') || value.Contains(':'))
            {
                continue;
            }

            value = value.Replace(WIKI, "", StringComparison.OrdinalIgnoreCase);

            if (value == target)
            {
                current.Path.Add(value);
                return current;
            }

            var list = new List<string>(current.Path) { value };
            queue.Enqueue(new Node(value, current.Depth + 1, list));
        }

        return default;
    }

    private static void PrintResult(Node result)
    {
        var isFound = result != default;
        Console.WriteLine("Result is: " + (isFound ? "Found" : "Can\'t link"));

        if (isFound)
        {
            Console.WriteLine($"The path is: {string.Join(" -> ", result.Path)}");
        }
    }

    [GeneratedRegex("href=\"(.*?)\"")]
    private static partial Regex MyRegex();
}