/*
 * 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.Collections.Generic;
using System.Net.Http;
using System.Threading;
using System.Threading.Tasks;
using ProtonVPN.Common.Core.Extensions;
using ProtonVPN.Common.Core.Networking;
using ProtonVPN.Dns.Contracts;
using ProtonVPN.Dns.Contracts.Exceptions;
using ProtonVPN.Logging.Contracts;
using ProtonVPN.Logging.Contracts.Events.ApiLogs;
using ProtonVPN.Logging.Contracts.Events.DnsLogs;

namespace ProtonVPN.Api.Handlers;

public class DnsHandler : DelegatingHandler
{
    private readonly ILogger _logger;
    private readonly IDnsManager _dnsManager;

    public DnsHandler(ILogger logger, IDnsManager dnsManager)
    {
        _logger = logger;
        _dnsManager = dnsManager;
    }

    protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,
        CancellationToken cancellationToken)
    {
        if (request.RequestUri.HostNameType == UriHostNameType.Dns)
        {
            return await SendRequestToDomainAsync(request, cancellationToken);
        }

        return await SendRequestAsync(request, cancellationToken);
    }

    private async Task<HttpResponseMessage> SendRequestToDomainAsync(HttpRequestMessage request,
        CancellationToken cancellationToken)
    {
        IList<IpAddress> ipAddresses = await _dnsManager.GetAsync(request.RequestUri.IdnHost, cancellationToken);
        if (!ipAddresses.IsNullOrEmpty())
        {
            for (int i = 0; i < ipAddresses.Count; i++)
            {
                try
                {
                    HttpResponseMessage httpResponseMessage = await SendRequestToIpAddressAsync(
                        ipAddresses[i], request, cancellationToken);
                    return httpResponseMessage;
                }
                catch (Exception ex)
                {
                    _logger.Info<DnsLog>($"Attempt {i + 1} failed for IP {ipAddresses[i]}", ex);

                    if (i + 1 == ipAddresses.Count)
                    {
                        throw;
                    }
                }
            }
        }

        throw new DnsException($"No IP addresses to make the API request to '{request.RequestUri}'.");
    }

    private async Task<HttpResponseMessage> SendRequestToIpAddressAsync(IpAddress ipAddress,
        HttpRequestMessage request, CancellationToken token)
    {
        Uri oldRequestUri = request.RequestUri;
        SetRequestHost(request, ipAddress.ToString(), oldRequestUri);
        HttpResponseMessage httpResponseMessage;
        try
        {
            httpResponseMessage = await SendRequestAsync(request, token);
        }
        catch (Exception ex)
        {
            _logger.Error<ApiErrorLog>($"API request '{request.RequestUri}' failed.", ex);
            ResetRequestUri(request, oldRequestUri);
            throw;
        }
        return httpResponseMessage;
    }

    private void SetRequestHost(HttpRequestMessage request, string uriHost, Uri oldRequestUri)
    {
        UriBuilder uriBuilder = new(request.RequestUri) { Host = uriHost };
        request.Headers.Host = oldRequestUri.Host;
        request.RequestUri = uriBuilder.Uri;
    }

    private void ResetRequestUri(HttpRequestMessage request, Uri uri)
    {
        UriBuilder uriBuilder = new(uri) { Host = uri.Host };
        request.Headers.Host = uriBuilder.Host;
        request.RequestUri = uriBuilder.Uri;
    }

    private async Task<HttpResponseMessage> SendRequestAsync(HttpRequestMessage request, CancellationToken token)
    {
        return await base.SendAsync(request, token);
    }
}