(.*)

using System.Text.RegularExpressions;

namespace Backend.Helper;

public static partial class HttpClientHelper
{
    // Reddit, for example, will block the GET request if you don't have a user agent.
    private const string UserAgentHeader = "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36";
    private const string TitlePattern = "<title>(.*)</title>";
    private const string DescriptionPattern = "<meta name=\"description\" content=\"(.*?)\"";
    private const string StartHeadTag = "<head>";
    private const string EndHeadTag = "</head>";
    
    public static async Task<(string, string)> GetTitleAndDescription(string url, int port)
    {
        using HttpClient client = new();
        
        if (port == 80)
        {
            client.BaseAddress = new($"http://{url}");
        }
        else
        {
            client.BaseAddress = new($"https://{url}");
        }
        
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.UserAgent.ParseAdd(UserAgentHeader);
        client.Timeout = TimeSpan.FromSeconds(30);
        
        HttpResponseMessage? response;
        
        try
        {
            response = await client.GetAsync("/");
        }
        catch
        {
            return ("", "");
        }
        
        if (!response.IsSuccessStatusCode)
        {
            return ("", "");
        }

        string html = await response.Content.ReadAsStringAsync();
        
        int firstIndex = 0;
        int lastIndex = 0;
        
        if (html.Contains(StartHeadTag) && html.Contains(EndHeadTag))
        {
            firstIndex = html.IndexOf(StartHeadTag, StringComparison.Ordinal);
            lastIndex = html.IndexOf(EndHeadTag, StringComparison.Ordinal);
        }
        
        string head = html.AsSpan().Slice(firstIndex, lastIndex).ToString();
        html = "";
        
        string title = "";
        string description = "";
        
        Regex titleRegex = TitleRegEx();
        Match titleMatch = titleRegex.Match(head);
        
        if (titleMatch.Success)
        {
            title = titleMatch.Groups[1].Value;
        }
        
        Regex descriptionRegex = DexcriptionRegEx();
        Match descriptionMatch = descriptionRegex.Match(head);
        
        if (descriptionMatch.Success)
        {
            description = descriptionMatch.Groups[1].Value;
        }
        
        return (title, description);
    }
    
    public static async Task<bool> HasRobotsTxt(string url, int port)
    {
        using HttpClient client = new();
        
        if (port == 80)
        {
            client.BaseAddress = new($"http://{url}");
        }
        else
        {
            client.BaseAddress = new($"https://{url}");
        }
        
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.UserAgent.ParseAdd(UserAgentHeader);
        client.Timeout = TimeSpan.FromSeconds(30);
        
        HttpResponseMessage? response = null;
        
        try
        {
            response = await client.SendAsync(new(HttpMethod.Head, "/robots.txt"));
        }
        catch
        {
            //
        }
        
        return response is not null && response.IsSuccessStatusCode;
    }

    [GeneratedRegex(TitlePattern)]
    private static partial Regex TitleRegEx();
    [GeneratedRegex(DescriptionPattern)]
    private static partial Regex DexcriptionRegEx();
}