using Markdig;
using System.Text.RegularExpressions;

namespace WebApp.Services;

/// <summary>
/// Helper class for rendering markdown to HTML.
/// </summary>
public static class MarkdownHelper
{
    private static readonly MarkdownPipeline _pipeline = new MarkdownPipelineBuilder()
        .UseAdvancedExtensions()
        .Build();

    /// <summary>
    /// Converts markdown text to HTML.
    /// </summary>
    /// <param name="markdown">The markdown text to convert.</param>
    /// <returns>HTML string ready for rendering.</returns>
    public static string ToHtml(string? markdown)
    {
        if (string.IsNullOrWhiteSpace(markdown))
            return string.Empty;

        var html = Markdown.ToHtml(markdown, _pipeline);
        
        // Add target="_blank" and rel="noopener noreferrer" to all links
        html = Regex.Replace(html, @"<a\s+([^>]*?)href=""([^""]*?)""([^>]*?)>", 
            match =>
            {
                var beforeHref = match.Groups[1].Value;
                var href = match.Groups[2].Value;
                var afterHref = match.Groups[3].Value;
                
                // Check if target is already present
                if (Regex.IsMatch(beforeHref + afterHref, @"target\s*=", RegexOptions.IgnoreCase))
                {
                    return match.Value; // Return unchanged if target already exists
                }
                
                // Add target="_blank" and rel="noopener noreferrer"
                return $"<a {beforeHref}href=\"{href}\" target=\"_blank\" rel=\"noopener noreferrer\"{afterHref}>";
            }, 
            RegexOptions.IgnoreCase);
        
        return html;
    }
}