// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Reflection;
using System.Runtime.InteropServices;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting.Builder;
using Microsoft.AspNetCore.Hosting.Server;
using Microsoft.AspNetCore.Hosting.Server.Features;
using Microsoft.AspNetCore.Hosting.Views;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Features;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.StackTrace.Sources;

namespace Microsoft.AspNetCore.Hosting.Internal
{
    internal class WebHost : IWebHost
    {
        private static readonly string DeprecatedServerUrlsKey = "server.urls";

        private readonly IServiceCollection _applicationServiceCollection;
        private IStartup _startup;
        private ApplicationLifetime _applicationLifetime;
        private HostedServiceExecutor _hostedServiceExecutor;

        private readonly IServiceProvider _hostingServiceProvider;
        private readonly WebHostOptions _options;
        private readonly IConfiguration _config;
        private readonly AggregateException _hostingStartupErrors;

        private IServiceProvider _applicationServices;
        private RequestDelegate _application;
        private ILogger<WebHost> _logger;

        private bool _stopped;

        // Used for testing only
        internal WebHostOptions Options => _options;

        private IServer Server { get; set; }

        public WebHost(
            IServiceCollection appServices,
            IServiceProvider hostingServiceProvider,
            WebHostOptions options,
            IConfiguration config,
            AggregateException hostingStartupErrors)
        {
            if (appServices == null)
            {
                throw new ArgumentNullException(nameof(appServices));
            }

            if (hostingServiceProvider == null)
            {
                throw new ArgumentNullException(nameof(hostingServiceProvider));
            }

            if (config == null)
            {
                throw new ArgumentNullException(nameof(config));
            }

            _config = config;
            _hostingStartupErrors = hostingStartupErrors;
            _options = options;
            _applicationServiceCollection = appServices;
            _hostingServiceProvider = hostingServiceProvider;
            _applicationServiceCollection.AddSingleton<IApplicationLifetime, ApplicationLifetime>();
            _applicationServiceCollection.AddSingleton<HostedServiceExecutor>();
        }

        public IServiceProvider Services
        {
            get
            {
                EnsureApplicationServices();
                return _applicationServices;
            }
        }

        public IFeatureCollection ServerFeatures
        {
            get
            {
                return Server?.Features;
            }
        }

        public void Initialize()
        {
            if (_application == null)
            {
                _application = BuildApplication();
            }
        }

        public virtual async Task StartAsync(CancellationToken cancellationToken)
        {
            HostingEventSource.Log.HostStart();
            _logger = _applicationServices.GetRequiredService<ILogger<WebHost>>();
            _logger.Starting();

            Initialize();

            _applicationLifetime = _applicationServices.GetRequiredService<IApplicationLifetime>() as ApplicationLifetime;
            _hostedServiceExecutor = _applicationServices.GetRequiredService<HostedServiceExecutor>();
            var diagnosticSource = _applicationServices.GetRequiredService<DiagnosticListener>();
            var httpContextFactory = _applicationServices.GetRequiredService<IHttpContextFactory>();
            var hostingApp = new HostingApplication(_application, _logger, diagnosticSource, httpContextFactory);
            await Server.StartAsync(hostingApp, cancellationToken).ConfigureAwait(false);

            // Fire IApplicationLifetime.Started
            _applicationLifetime?.NotifyStarted();

            // Fire IHostedService.Start
            _hostedServiceExecutor.Start();

            _logger.Started();

            // Log the fact that we did load hosting startup assemblies.
            if (_logger.IsEnabled(LogLevel.Debug))
            {
                foreach (var assembly in _options.HostingStartupAssemblies)
                {
                    _logger.LogDebug("Loaded hosting startup assembly {assemblyName}", assembly);
                }
            }

            if (_hostingStartupErrors != null)
            {
                foreach (var exception in _hostingStartupErrors.InnerExceptions)
                {
                    _logger.HostingStartupAssemblyError(exception);
                }
            }
        }

        private void EnsureApplicationServices()
        {
            if (_applicationServices == null)
            {
                EnsureStartup();
                _applicationServices = _startup.ConfigureServices(_applicationServiceCollection);
            }
        }

        private void EnsureStartup()
        {
            if (_startup != null)
            {
                return;
            }

            _startup = _hostingServiceProvider.GetRequiredService<IStartup>();
        }

        private RequestDelegate BuildApplication()
        {
            try
            {
                EnsureApplicationServices();
                EnsureServer();

                var builderFactory = _applicationServices.GetRequiredService<IApplicationBuilderFactory>();
                var builder = builderFactory.CreateBuilder(Server.Features);
                builder.ApplicationServices = _applicationServices;

                var startupFilters = _applicationServices.GetService<IEnumerable<IStartupFilter>>();
                Action<IApplicationBuilder> configure = _startup.Configure;
                foreach (var filter in startupFilters.Reverse())
                {
                    configure = filter.Configure(configure);
                }

                configure(builder);

                return builder.Build();
            }
            catch (Exception ex) when (_options.CaptureStartupErrors)
            {
                // EnsureApplicationServices may have failed due to a missing or throwing Startup class.
                if (_applicationServices == null)
                {
                    _applicationServices = _applicationServiceCollection.BuildServiceProvider();
                }

                EnsureServer();

                // Write errors to standard out so they can be retrieved when not in development mode.
                Console.Out.WriteLine("Application startup exception: " + ex.ToString());
                var logger = _applicationServices.GetRequiredService<ILogger<WebHost>>();
                logger.ApplicationError(ex);

                // Generate an HTML error page.
                var hostingEnv = _applicationServices.GetRequiredService<IHostingEnvironment>();
                var showDetailedErrors = hostingEnv.IsDevelopment() || _options.DetailedErrors;

                var model = new ErrorPageModel
                {
                    RuntimeDisplayName = RuntimeInformation.FrameworkDescription
                };
                var systemRuntimeAssembly = typeof(System.ComponentModel.DefaultValueAttribute).GetTypeInfo().Assembly;
                var assemblyVersion = new AssemblyName(systemRuntimeAssembly.FullName).Version.ToString();
                var clrVersion = assemblyVersion;
                model.RuntimeArchitecture = RuntimeInformation.ProcessArchitecture.ToString();
                var currentAssembly = typeof(ErrorPage).GetTypeInfo().Assembly;
                model.CurrentAssemblyVesion = currentAssembly
                    .GetCustomAttribute<AssemblyInformationalVersionAttribute>()
                    .InformationalVersion;
                model.ClrVersion = clrVersion;
                model.OperatingSystemDescription = RuntimeInformation.OSDescription;

                if (showDetailedErrors)
                {
                    var exceptionDetailProvider = new ExceptionDetailsProvider(
                        hostingEnv.ContentRootFileProvider,
                        sourceCodeLineCount: 6);

                    model.ErrorDetails = exceptionDetailProvider.GetDetails(ex);
                }
                else
                {
                    model.ErrorDetails = new ExceptionDetails[0];
                }

                var errorPage = new ErrorPage(model);
                return context =>
                {
                    context.Response.StatusCode = 500;
                    context.Response.Headers["Cache-Control"] = "no-cache";
                    return errorPage.ExecuteAsync(context);
                };
            }
        }

        private void EnsureServer()
        {
            if (Server == null)
            {
                Server = _applicationServices.GetRequiredService<IServer>();

                var serverAddressesFeature = Server.Features?.Get<IServerAddressesFeature>();
                var addresses = serverAddressesFeature?.Addresses;
                if (addresses != null && !addresses.IsReadOnly && addresses.Count == 0)
                {
                    var urls = _config[WebHostDefaults.ServerUrlsKey] ?? _config[DeprecatedServerUrlsKey];
                    if (!string.IsNullOrEmpty(urls))
                    {
                        serverAddressesFeature.PreferHostingUrls = WebHostUtilities.ParseBool(_config, WebHostDefaults.PreferHostingUrlsKey);

                        foreach (var value in urls.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries))
                        {
                            addresses.Add(value);
                        }
                    }
                }
            }
        }

        public async Task StopAsync(CancellationToken cancellationToken)
        {
            if (_stopped)
            {
                return;
            }
            _stopped = true;

            _logger?.Shutdown();

            var timeoutToken = new CancellationTokenSource(Options.ShutdownTimeout).Token;
            if (!cancellationToken.CanBeCanceled)
            {
                cancellationToken = timeoutToken;
            }
            else
            {
                cancellationToken = CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, timeoutToken).Token;
            }

            // Fire IApplicationLifetime.Stopping
            _applicationLifetime?.StopApplication();

            if (Server != null)
            {
                await Server.StopAsync(cancellationToken).ConfigureAwait(false);
            }

            // Fire the IHostedService.Stop
            _hostedServiceExecutor?.Stop();

            // Fire IApplicationLifetime.Stopped
            _applicationLifetime?.NotifyStopped();

            HostingEventSource.Log.HostStop();
        }

        public void Dispose()
        {
            if (!_stopped)
            {
                try
                {
                    this.StopAsync().GetAwaiter().GetResult();
                }
                catch (Exception ex)
                {
                    _logger?.ServerShutdownException(ex);
                }
            }

            (_applicationServices as IDisposable)?.Dispose();
            (_hostingServiceProvider as IDisposable)?.Dispose();
        }
    }
}