/*
 * Copyright (c) 2023 Proton AG
 *
 * This file is part of ProtonVPN.
 *
 * ProtonVPN is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * ProtonVPN is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with ProtonVPN.  If not, see <https://www.gnu.org/licenses/>.
 */
using System;
using System.Text;
using Albireo.Base32;
using ProtonVPN.Configurations.Contracts;
using ProtonVPN.Dns.Contracts.AlternativeRouting;

namespace ProtonVPN.Dns.AlternativeRouting;

public class AlternativeRoutingHostGenerator : IAlternativeRoutingHostGenerator
{
    private const string HOST_FORMAT = "d{0}.protonpro.xyz";

    private Lazy<string> _baseHost;

    public AlternativeRoutingHostGenerator(IConfiguration config)
    {
        _baseHost = new Lazy<string>(() => GenerateBaseHost(config.Urls.ApiUrl));
    }

    private string GenerateBaseHost(string apiUrl)
    {
        string base32ApiUrl = CalculateBase32ApiUrl(apiUrl);
        return string.Format(HOST_FORMAT, base32ApiUrl);
    }

    private string CalculateBase32ApiUrl(string apiUrl)
    {
        Uri apiUri = new(apiUrl);
        return Base32.Encode(Encoding.UTF8.GetBytes(apiUri.Host)).TrimEnd('=');
    }

    public string Generate(string uid)
    {
        return string.IsNullOrEmpty(uid) ? _baseHost.Value : $"{uid}.{_baseHost.Value}";
    }
}