using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Sockets;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using PuppeteerSharp;

namespace AyaNova.Util
{
    /// <summary>
    /// Where the report page's API calls are sent when AyaNova runs inside IIS: the address and port a user's request
    /// arrived on, with the host name and scheme of that request
    /// </summary>
    internal sealed class ReportApiTarget
    {
        public string Scheme { get; set; }
        public string Host { get; set; }//host header value, with the port when the request had one
        public string Address { get; set; }
        public int Port { get; set; }

        internal string BaseUrl => $"{Scheme}://{Host}/api/{AyaNovaVersion.CurrentApiVersion}/";
        public override string ToString() => $"{Scheme}://{Host} via {Address}:{Port}";
    }

    /// <summary>
    /// case 4632: inside IIS (in-process hosting) AyaNova has no port of its own: nothing listens on AYANOVA_USE_URLS, and
    /// the port of the user's request is IIS's, often https-only and bound to a host name. So the report page could not
    /// reach the API at http://127.0.0.1:port (user reports, or notification reports at the AYANOVA_USE_URLS port), and the
    /// override setting only helped where the server can reach itself by its public name. Under IIS the report page's
    /// requests to the API URL are intercepted and made here instead, to the local address and port a user's request
    /// arrived on, with that request's host name and scheme: the IIS binding and certificate match, and no DNS or router
    /// is involved. Outside IIS nothing changes (the page calls http://127.0.0.1:port itself, which works with Kestrel)
    /// </summary>
    internal static class ReportApiRelay
    {
        //path the page is first opened at, so it has the API's origin and its API calls are same-origin (no CORS preflight,
        //which the browser would send itself, past the interception)
        private const string PAGE_PATH = "ay-report-render-page";

        private static volatile ReportApiTarget _lastSeen;

        /// <summary>
        /// The address, port, host name and scheme this request arrived with, for relaying a report started by it
        /// </summary>
        internal static ReportApiTarget FromRequest(HttpContext context)
        {
            var address = context.Connection.LocalIpAddress;
            if (address == null)
                return null;
            if (address.IsIPv4MappedToIPv6)
                address = address.MapToIPv4();
            //the IIS server variable says if this connection is TLS; Request.Scheme may come from a proxy's X-Forwarded-Proto
            var https = string.Equals(context.GetServerVariable("HTTPS"), "on", StringComparison.OrdinalIgnoreCase);
            return new ReportApiTarget
            {
                Scheme = https ? "https" : "http",
                Host = context.Request.Host.HasValue ? context.Request.Host.Value : address.ToString(),
                Address = address.ToString(),
                Port = context.Connection.LocalPort
            };
        }

        /// <summary>
        /// Keeps the target of the latest signed-in request, for reports rendered without one (customer notifications)
        /// </summary>
        internal static void Remember(HttpContext context)
        {
            if (!ServerBootConfig.HOSTED_IN_IIS)
                return;
            var target = FromRequest(context);
            var last = _lastSeen;
            if (target != null && (last == null || last.ToString() != target.ToString()))
                _lastSeen = target;
        }

        /// <summary>
        /// Target for a report rendered without a user request: the latest signed-in request, else the override URL
        /// sent to this machine; null outside IIS or when neither is known
        /// </summary>
        internal static ReportApiTarget ForBackgroundRender()
        {
            if (!ServerBootConfig.HOSTED_IN_IIS)
                return null;
            if (_lastSeen != null)
                return _lastSeen;
            if (Uri.TryCreate(ServerBootConfig.AYANOVA_REPORT_RENDER_API_URL_OVERRIDE?.Trim(), UriKind.Absolute, out var o))
                return new ReportApiTarget { Scheme = o.Scheme, Host = o.Authority, Address = IPAddress.Loopback.ToString(), Port = o.Port };
            return null;
        }

        /// <summary>
        /// Opens the page at the API URL's origin and relays the page's requests under the API URL to the target.
        /// Returns the HTTP client to dispose when the page is done
        /// </summary>
        internal static async Task<IDisposable> AttachAsync(IPage page, string apiUrl, ReportApiTarget target, TimeSpan timeout, Action<string> pageLog, ILogger log)
        {
            var handler = new SocketsHttpHandler
            {
                AllowAutoRedirect = false,
                UseCookies = false,
                UseProxy = false,
                //always the local address, whatever the URL's host name resolves to; TLS still checks the certificate for that name
                ConnectCallback = async (context, cancel) =>
                {
                    var address = IPAddress.Parse(target.Address);
                    var socket = new Socket(address.AddressFamily, SocketType.Stream, System.Net.Sockets.ProtocolType.Tcp) { NoDelay = true };
                    try
                    {
                        await socket.ConnectAsync(new IPEndPoint(address, target.Port), cancel);
                        return new NetworkStream(socket, ownsSocket: true);
                    }
                    catch
                    {
                        socket.Dispose();
                        throw;
                    }
                }
            };
            var client = new HttpClient(handler) { Timeout = timeout };
            var pageUrl = apiUrl + PAGE_PATH;

            await page.SetRequestInterceptionAsync(true);
            page.Request += async (sender, e) =>
            {
                var request = e.Request;
                try
                {
                    if (request.Url == pageUrl)
                    {
                        await request.RespondAsync(new ResponseData { Status = HttpStatusCode.OK, ContentType = "text/html", Body = "<!DOCTYPE html><html><head></head><body></body></html>" });
                        return;
                    }
                    if (!request.Url.StartsWith(apiUrl, StringComparison.OrdinalIgnoreCase))
                    {
                        await request.ContinueAsync();
                        return;
                    }
                    using var message = new HttpRequestMessage(request.Method, target.BaseUrl + request.Url.Substring(apiUrl.Length));
                    if (request.HasPostData)
                        message.Content = new StringContent(request.PostData ?? await request.FetchPostDataAsync() ?? string.Empty);
                    foreach (var header in request.Headers)
                    {
                        if (header.Key.Equals("Host", StringComparison.OrdinalIgnoreCase) || header.Key.Equals("Content-Length", StringComparison.OrdinalIgnoreCase))
                            continue;
                        if (!message.Headers.TryAddWithoutValidation(header.Key, header.Value) && message.Content != null)
                        {
                            message.Content.Headers.Remove(header.Key);
                            message.Content.Headers.TryAddWithoutValidation(header.Key, header.Value);
                        }
                    }
                    using var response = await client.SendAsync(message);                    var headers = new Dictionary<string, object>(StringComparer.OrdinalIgnoreCase);
                    foreach (var header in response.Headers.Concat(response.Content.Headers))
                    {
                        if (header.Key.Equals("Transfer-Encoding", StringComparison.OrdinalIgnoreCase) || header.Key.Equals("Connection", StringComparison.OrdinalIgnoreCase) || header.Key.Equals("Content-Length", StringComparison.OrdinalIgnoreCase))
                            continue;
                        headers[header.Key] = string.Join(", ", header.Value);
                    }
                    await request.RespondAsync(new ResponseData { Status = response.StatusCode, Headers = headers, BodyData = await response.Content.ReadAsByteArrayAsync() });
                }
                catch (Exception ex)
                {
                    var reason = ex.InnerException != null ? $"{ex.Message} ({ex.InnerException.Message})" : ex.Message;
                    pageLog($"ERROR: AyaNova API request {request.Method} {request.Url} via {target} failed: {reason}");
                    log.LogWarning($"Report API request {request.Method} {request.Url} via {target} failed: {reason}");
                    try { await request.AbortAsync(); } catch { }
                }
            };
            await page.GoToAsync(pageUrl);
            return client;
        }
    }
}