// Copyright (c) StellaOps. All rights reserved.
// Licensed under BUSL-1.1. See LICENSE in the project root.

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Server.Kestrel.Core;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Sockets;
using System.Runtime.InteropServices;
using System.Security.Cryptography.X509Certificates;
using System.Threading;
using System.Threading.Tasks;

namespace StellaOps.Auth.ServerIntegration;

/// <summary>
/// Provides two extension methods for the <c>.stella-ops.local</c> hostname convention:
/// <list type="bullet">
///   <item>
///     <see cref="TryAddStellaOpsLocalBinding"/> — called on <see cref="WebApplicationBuilder"/>
///     before <c>Build()</c>; binds both <c>https://{serviceName}.stella-ops.local</c> (port 443)
///     and <c>http://{serviceName}.stella-ops.local</c> (port 80).
///   </item>
///   <item>
///     <see cref="LogStellaOpsLocalHostname"/> — called on <see cref="WebApplication"/>
///     after <c>Build()</c>; checks DNS for the friendly hostname and logs the result.
///   </item>
/// </list>
/// </summary>
public static class StellaOpsLocalHostnameExtensions
{
    private const string DomainSuffix = ".stella-ops.local";
    private const int HttpsPort = 443;
    private const int HttpPort = 80;
    private const string SetupDocPath = "docs/technical/architecture/port-registry.md";

    /// <summary>
    /// Configuration key used to communicate local-binding status
    /// from the builder phase to the app phase.
    /// </summary>
    internal const string LocalBindingBoundKey = "StellaOps:LocalBindingBound";

    /// <summary>
    /// Configuration key storing the service name for use in the app phase.
    /// </summary>
    internal const string LocalBindingServiceKey = "StellaOps:LocalBindingService";

    /// <summary>
    /// Resolves <c>{serviceName}.stella-ops.local</c> to its dedicated loopback IP
    /// (from the hosts file), then binds <c>https://{hostname}</c> (port 443) and
    /// <c>http://{hostname}</c> (port 80) on that IP. Each service uses a unique
    /// loopback address (e.g. 127.1.0.2) so ports never collide.
    /// </summary>
    public static WebApplicationBuilder TryAddStellaOpsLocalBinding(
        this WebApplicationBuilder builder, string serviceName)
    {
        builder.Configuration[LocalBindingServiceKey] = serviceName;
        var hostname = serviceName + DomainSuffix;

        // Resolve the hostname to find its dedicated loopback IP from the hosts file.
        IPAddress? resolvedIp = null;
        try
        {
            var addresses = Dns.GetHostAddresses(hostname);
            resolvedIp = addresses.FirstOrDefault(a => a.AddressFamily == AddressFamily.InterNetwork);
        }
        catch
        {
            // Hostname does not resolve; skip binding (will warn at startup).
        }

        if (resolvedIp == null)
        {
            builder.Configuration[LocalBindingBoundKey] = "false";
            return builder;
        }

        var httpsAvailable = IsPortAvailable(HttpsPort, resolvedIp);
        var httpAvailable = IsPortAvailable(HttpPort, resolvedIp);

        if (!httpsAvailable && !httpAvailable)
        {
            builder.Configuration[LocalBindingBoundKey] = "false";
            return builder;
        }

        builder.Configuration[LocalBindingBoundKey] = "true";

        // Bind to the specific loopback IP (not hostname) so Kestrel uses only
        // this address, leaving other 127.1.0.x IPs available for other services.
        // UseUrls("https://hostname") would bind to [::]:443 (all interfaces).
        //
        // When ConfigureKestrel uses explicit Listen() calls, Kestrel ignores UseUrls.
        // So we must also re-add the dev-port bindings from launchSettings.json.
        var currentUrls = builder.WebHost.GetSetting(WebHostDefaults.ServerUrlsKey) ?? "";
        var ip = resolvedIp;
        builder.WebHost.ConfigureKestrel((context, kestrel) =>
        {
            // Re-add dev-port bindings from launchSettings.json / ASPNETCORE_URLS
            foreach (var rawUrl in currentUrls.Split(';', StringSplitOptions.RemoveEmptyEntries))
            {
                if (Uri.TryCreate(rawUrl.Trim(), UriKind.Absolute, out var uri))
                {
                    var isHttps = string.Equals(uri.Scheme, "https", StringComparison.OrdinalIgnoreCase);
                    var addr = uri.Host == "localhost"
                        ? IPAddress.Loopback
                        : IPAddress.Parse(uri.Host);

                    if (isHttps)
                    {
                        kestrel.Listen(addr, uri.Port, lo => lo.UseHttps());
                    }
                    else
                    {
                        kestrel.Listen(addr, uri.Port);
                    }
                }
            }

            // Add .stella-ops.local bindings on the dedicated loopback IP
            if (httpsAvailable)
            {
                kestrel.Listen(ip, HttpsPort, listenOptions =>
                {
                    listenOptions.UseHttps();
                });
            }

            if (httpAvailable)
            {
                kestrel.Listen(ip, HttpPort);
            }
        });

        return builder;
    }

    /// <summary>
    /// Backwards-compatible overload — reads the service name from configuration
    /// set by <see cref="TryAddStellaOpsLocalBinding"/>.
    /// </summary>
    [System.Obsolete("Use TryAddStellaOpsLocalBinding(builder, serviceName) instead of TryAddStellaOpsSharedPort(). This overload will be removed.")]
    public static WebApplicationBuilder TryAddStellaOpsSharedPort(
        this WebApplicationBuilder builder)
    {
        // No-op fallback for any callers not yet migrated; the binding happens
        // in TryAddStellaOpsLocalBinding which should be called instead.
        return builder;
    }

    /// <summary>
    /// Registers a startup callback that checks DNS for
    /// <c>{serviceName}.stella-ops.local</c> and logs the result.
    /// Also warns if the local bindings were skipped.
    /// </summary>
    public static WebApplication LogStellaOpsLocalHostname(
        this WebApplication app, string serviceName)
    {
        var hostname = serviceName + DomainSuffix;
        var localBindingBound = string.Equals(
            app.Configuration[LocalBindingBoundKey], "true", StringComparison.OrdinalIgnoreCase);
        var lifetime = app.Services.GetRequiredService<IHostApplicationLifetime>();

        lifetime.ApplicationStarted.Register(() =>
        {
            var logger = app.Services.GetRequiredService<ILoggerFactory>()
                .CreateLogger("StellaOps.LocalHostname");

            if (!localBindingBound)
            {
                logger.LogWarning(
                    "Ports {HttpsPort}/{HttpPort} are already in use; skipping {Hostname} bindings. " +
                    "This is expected when running multiple services locally.",
                    HttpsPort, HttpPort, hostname);
            }

            _ = Task.Run(async () =>
            {
                try
                {
                    using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(2));
                    var resolved = await Dns.GetHostAddressesAsync(hostname, cts.Token);

                    if (resolved.Length > 0)
                    {
                        if (localBindingBound)
                        {
                            logger.LogInformation(
                                "Also accessible at https://{Hostname} and http://{Hostname}",
                                hostname, hostname);
                        }
                        else
                        {
                            logger.LogInformation(
                                "Hostname {Hostname} resolves but ports {HttpsPort}/{HttpPort} are unavailable; " +
                                "use the dev port instead.",
                                hostname, HttpsPort, HttpPort);
                        }
                    }
                }
                catch
                {
                    var hostsPath = RuntimeInformation.IsOSPlatform(OSPlatform.Windows)
                        ? @"C:\Windows\System32\drivers\etc\hosts"
                        : "/etc/hosts";

                    logger.LogWarning(
                        "Hostname {Hostname} does not resolve. " +
                        "To enable friendly .stella-ops.local URLs, add hosts-file entries " +
                        "as described in {SetupDoc}. " +
                        "Edit {HostsFile} and add a unique 127.1.0.x entry for {Hostname}",
                        hostname, SetupDocPath, hostsPath, hostname);
                }
            });
        });

        return app;
    }

    private static bool IsPortAvailable(int port, IPAddress address)
    {
        try
        {
            using var listener = new TcpListener(address, port);
            listener.Start();
            listener.Stop();
            return true;
        }
        catch
        {
            return false;
        }
    }
}