// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Diagnostics;
using System.Net.Http;
using System.Text.RegularExpressions;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.NodeServices.Npm;
using Microsoft.AspNetCore.NodeServices.Util;
using Microsoft.AspNetCore.SpaServices.Extensions.Util;
using Microsoft.AspNetCore.SpaServices.Util;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;

namespace Microsoft.AspNetCore.SpaServices.AngularCli;

internal static class AngularCliMiddleware
{
    private const string LogCategoryName = "Microsoft.AspNetCore.SpaServices";
    private static readonly TimeSpan RegexMatchTimeout = TimeSpan.FromSeconds(5); // This is a development-time only feature, so a very long timeout is fine

    public static void Attach(
        ISpaBuilder spaBuilder,
        string scriptName)
    {
        var pkgManagerCommand = spaBuilder.Options.PackageManagerCommand;
        var sourcePath = spaBuilder.Options.SourcePath;
        var devServerPort = spaBuilder.Options.DevServerPort;
        if (string.IsNullOrEmpty(sourcePath))
        {
            throw new ArgumentException("Property 'SourcePath' cannot be null or empty", nameof(spaBuilder));
        }

        if (string.IsNullOrEmpty(scriptName))
        {
            throw new ArgumentException("Cannot be null or empty", nameof(scriptName));
        }

        // Start Angular CLI and attach to middleware pipeline
        var appBuilder = spaBuilder.ApplicationBuilder;
        var applicationStoppingToken = appBuilder.ApplicationServices.GetRequiredService<IHostApplicationLifetime>().ApplicationStopping;
        var logger = LoggerFinder.GetOrCreateLogger(appBuilder, LogCategoryName);
        var diagnosticSource = appBuilder.ApplicationServices.GetRequiredService<DiagnosticSource>();
        var angularCliServerInfoTask = StartAngularCliServerAsync(sourcePath, scriptName, pkgManagerCommand, devServerPort, logger, diagnosticSource, applicationStoppingToken);

        SpaProxyingExtensions.UseProxyToSpaDevelopmentServer(spaBuilder, () =>
        {
            // On each request, we create a separate startup task with its own timeout. That way, even if
            // the first request times out, subsequent requests could still work.
            var timeout = spaBuilder.Options.StartupTimeout;
            return angularCliServerInfoTask.WithTimeout(timeout,
                $"The Angular CLI process did not start listening for requests " +
                $"within the timeout period of {timeout.TotalSeconds} seconds. " +
                $"Check the log output for error information.");
        });
    }

    private static async Task<Uri> StartAngularCliServerAsync(
        string sourcePath, string scriptName, string pkgManagerCommand, int portNumber, ILogger logger, DiagnosticSource diagnosticSource, CancellationToken applicationStoppingToken)
    {
        if (portNumber == default(int))
        {
            portNumber = TcpPortFinder.FindAvailablePort();
        }
        if (logger.IsEnabled(LogLevel.Information))
        {
            logger.LogInformation($"Starting @angular/cli on port {portNumber}...");
        }

        var scriptRunner = new NodeScriptRunner(
            sourcePath, scriptName, $"--port {portNumber}", null, pkgManagerCommand, diagnosticSource, applicationStoppingToken);
        scriptRunner.AttachToLogger(logger);

        Match openBrowserLine;
        using (var stdErrReader = new EventedStreamStringReader(scriptRunner.StdErr))
        {
            try
            {
                openBrowserLine = await scriptRunner.StdOut.WaitForMatch(
                    new Regex("open your browser on (http\\S+)", RegexOptions.None, RegexMatchTimeout));
            }
            catch (EndOfStreamException ex)
            {
                throw new InvalidOperationException(
                    $"The {pkgManagerCommand} script '{scriptName}' exited without indicating that the " +
                    $"Angular CLI was listening for requests. The error output was: " +
                    $"{stdErrReader.ReadAsString()}", ex);
            }
        }

        var uri = new Uri(openBrowserLine.Groups[1].Value);

        // Even after the Angular CLI claims to be listening for requests, there's a short
        // period where it will give an error if you make a request too quickly
        await WaitForAngularCliServerToAcceptRequests(uri);

        return uri;
    }

    private static async Task WaitForAngularCliServerToAcceptRequests(Uri cliServerUri)
    {
        // To determine when it's actually ready, try making HEAD requests to '/'. If it
        // produces any HTTP response (even if it's 404) then it's ready. If it rejects the
        // connection then it's not ready. We keep trying forever because this is dev-mode
        // only, and only a single startup attempt will be made, and there's a further level
        // of timeouts enforced on a per-request basis.
        var timeoutMilliseconds = 1000;
        using (var client = new HttpClient())
        {
            while (true)
            {
                try
                {
                    // If we get any HTTP response, the CLI server is ready
                    using var cancellationTokenSource = new CancellationTokenSource(timeoutMilliseconds);
                    await client.SendAsync(
                        new HttpRequestMessage(HttpMethod.Head, cliServerUri),
                        cancellationTokenSource.Token);
                    return;
                }
                catch (Exception)
                {
                    await Task.Delay(500);

                    // Depending on the host's networking configuration, the requests can take a while
                    // to go through, most likely due to the time spent resolving 'localhost'.
                    // Each time we have a failure, allow a bit longer next time (up to a maximum).
                    // This only influences the time until we regard the dev server as 'ready', so it
                    // doesn't affect the runtime perf (even in dev mode) once the first connection is made.
                    // Resolves https://github.com/aspnet/JavaScriptServices/issues/1611
                    if (timeoutMilliseconds < 10000)
                    {
                        timeoutMilliseconds += 3000;
                    }
                }
            }
        }
    }
}
