notesnook-sync-server_customPrivateV1/Streetwriters.Identity/Services/EmailAddressValidator.cs

using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Threading.Tasks;
using Microsoft.Extensions.Logging;
using Streetwriters.Common;
using System.Linq;

namespace Streetwriters.Identity.Services
{
    public class EmailAddressValidator
    {
        private static DateTimeOffset LAST_FETCH_TIME = DateTimeOffset.MinValue;
        private static HashSet<string> BLACKLISTED_DOMAINS = new();
        private readonly ILogger<EmailAddressValidator> logger;

        public EmailAddressValidator(ILogger<EmailAddressValidator> logger)
        {
            this.logger = logger;
        }

        public async Task<bool> IsEmailAddressValidAsync(string email)
        {
            var domain = email.ToLowerInvariant().Split("@")[1];
            try
            {
                if (LAST_FETCH_TIME.AddDays(1) < DateTimeOffset.UtcNow)
                {
                    var httpClient = new HttpClient();
                    var domainsList = await httpClient.GetStringAsync("https://raw.githubusercontent.com/disposable-email-domains/disposable-email-domains/master/disposable_email_blocklist.conf");
                    var domains = domainsList.Split('\n').Where(line => !string.IsNullOrWhiteSpace(line) && !line.TrimStart().StartsWith("//"));
                    BLACKLISTED_DOMAINS = new HashSet<string>(domains, StringComparer.OrdinalIgnoreCase);
                    LAST_FETCH_TIME = DateTimeOffset.UtcNow;
                }

                return !BLACKLISTED_DOMAINS.Contains(domain);
            }
            catch (Exception ex)
            {
                logger.LogError(ex, "Failed to validate email address: {Email}", email);
                return BLACKLISTED_DOMAINS.Count > 0 ? !BLACKLISTED_DOMAINS.Contains(domain) : true;
            }
        }
    }
}