using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Text;
using System.Text.RegularExpressions;
using ModelContextProtocol.Tests.Utils;

namespace ModelContextProtocol.ConformanceTests;

/// <summary>
/// Shared fixture that starts a single ConformanceServer instance for all tests in
/// <see cref="ServerConformanceTests"/>. This avoids TCP port TIME_WAIT conflicts
/// that occur when each test starts and stops its own server on the same port.
/// </summary>
public class ConformanceServerFixture : IAsyncLifetime
{
    // Use different ports for each target framework to allow parallel execution
    // net10.0 -> 3001, net9.0 -> 3002, net8.0 -> 3003
    private static int GetPortForTargetFramework()
    {
        var testBinaryDir = AppContext.BaseDirectory;
        var targetFramework = Path.GetFileName(testBinaryDir.TrimEnd(Path.DirectorySeparatorChar));

        return targetFramework switch
        {
            "net10.0" => 3001,
            "net9.0" => 3002,
            "net8.0" => 3003,
            _ => 3001 // Default fallback
        };
    }

    private Task? _serverTask;
    private CancellationTokenSource? _serverCts;

    public string ServerUrl { get; } = $"http://localhost:{GetPortForTargetFramework()}";

    public async ValueTask InitializeAsync()
    {
        _serverCts = new CancellationTokenSource();
        _serverTask = Task.Run(() => ConformanceServer.Program.MainAsync(
            ["--urls", ServerUrl], cancellationToken: _serverCts.Token));

        // Wait for server to be ready (retry for up to 30 seconds)
        var timeout = TimeSpan.FromSeconds(30);
        var stopwatch = Stopwatch.StartNew();
        using var httpClient = new HttpClient { Timeout = TestConstants.HttpClientPollingTimeout };

        while (stopwatch.Elapsed < timeout)
        {
            try
            {
                await httpClient.GetAsync($"{ServerUrl}/health");
                return;
            }
            catch (HttpRequestException)
            {
                // Connection refused means server not ready yet
            }
            catch (TaskCanceledException)
            {
                // Timeout means server might be processing, give it more time
            }

            await Task.Delay(500);
        }

        throw new InvalidOperationException("ConformanceServer failed to start within the timeout period");
    }

    public async ValueTask DisposeAsync()
    {
        if (_serverCts != null)
        {
            _serverCts.Cancel();
            if (_serverTask != null)
            {
                try
                {
                    await _serverTask.WaitAsync(TestConstants.DefaultTimeout);
                }
                catch
                {
                    // Ignore exceptions during shutdown
                }
            }
            _serverCts.Dispose();
        }
    }
}

/// <summary>
/// Runs the official MCP conformance tests against the ConformanceServer.
/// Uses a shared <see cref="ConformanceServerFixture"/> so the server is started once
/// and reused across all tests, avoiding TCP port conflicts on Windows.
/// </summary>
public class ServerConformanceTests(ConformanceServerFixture fixture, ITestOutputHelper output)
    : IClassFixture<ConformanceServerFixture>
{
    [Fact]
    public async Task RunConformanceTests()
    {
        Assert.SkipWhen(!NodeHelpers.IsNodeInstalled(), "Node.js is not installed. Skipping conformance tests.");

        var result = await RunConformanceTestsAsync($"server --url {fixture.ServerUrl}");

        Assert.True(result.Success,
            $"Conformance tests failed.\n\nStdout:\n{result.Output}\n\nStderr:\n{result.Error}");
    }

    [Fact]
    public async Task RunPendingConformanceTest_JsonSchema202012()
    {
        Assert.SkipWhen(!NodeHelpers.IsNodeInstalled(), "Node.js is not installed. Skipping conformance tests.");
        Assert.SkipWhen(
            RuntimeInformation.IsOSPlatform(OSPlatform.Windows),
            "Pending Node-based conformance scenario is unstable on Windows due to a libuv shutdown assertion.");

        var result = await RunConformanceTestsAsync($"server --url {fixture.ServerUrl} --scenario json-schema-2020-12");

        Assert.True(result.Success,
            $"Conformance test failed.\n\nStdout:\n{result.Output}\n\nStderr:\n{result.Error}");
    }

    [Fact]
    public async Task RunPendingConformanceTest_ServerSsePolling()
    {
        Assert.SkipWhen(!NodeHelpers.IsNodeInstalled(), "Node.js is not installed. Skipping conformance tests.");
        Assert.SkipWhen(
            RuntimeInformation.IsOSPlatform(OSPlatform.Windows),
            "Pending Node-based conformance scenario is unstable on Windows due to a libuv shutdown assertion.");

        var result = await RunConformanceTestsAsync($"server --url {fixture.ServerUrl} --scenario server-sse-polling");

        Assert.True(result.Success,
            $"Conformance test failed.\n\nStdout:\n{result.Output}\n\nStderr:\n{result.Error}");
    }

    [Fact]
    public async Task RunConformanceTest_HttpHeaderValidation()
    {
        Assert.SkipWhen(!NodeHelpers.IsNodeInstalled(), "Node.js is not installed. Skipping conformance tests.");
        Assert.SkipWhen(!NodeHelpers.HasSep2243Scenarios(), "SEP-2243 conformance scenarios not yet available.");

        var result = await RunConformanceTestsAsync($"server --url {fixture.ServerUrl} --scenario http-header-validation");

        Assert.True(result.Success,
            $"Conformance test failed.\n\nStdout:\n{result.Output}\n\nStderr:\n{result.Error}");
    }

    [Fact]
    public async Task RunConformanceTest_HttpCustomHeaderServerValidation()
    {
        Assert.SkipWhen(!NodeHelpers.IsNodeInstalled(), "Node.js is not installed. Skipping conformance tests.");
        Assert.SkipWhen(!NodeHelpers.HasSep2243Scenarios(), "SEP-2243 conformance scenarios not yet available.");

        var result = await RunConformanceTestsAsync($"server --url {fixture.ServerUrl} --scenario http-custom-header-server-validation");

        Assert.True(result.Success,
            $"Conformance test failed.\n\nStdout:\n{result.Output}\n\nStderr:\n{result.Error}");
    }

    // SEP-2322 (Multi Round-Trip Requests / IncompleteResult) conformance scenarios.
    // The csharp-sdk ConformanceServer surfaces the matching tools/prompts via
    // ConformanceServer.Tools.IncompleteResultTools and ConformanceServer.Prompts.IncompleteResultPrompts.
    // Each scenario uses the conformance harness's RawMcpSession, which negotiates DRAFT-2026-v1
    // so the csharp-sdk emits InputRequiredResult on the wire. These tests skip until the
    // upstream conformance package ships with SEP-2322 scenarios
    // (https://github.com/modelcontextprotocol/conformance/pull/188).
    [Theory]
    [InlineData("incomplete-result-basic-elicitation")]
    [InlineData("incomplete-result-basic-sampling")]
    [InlineData("incomplete-result-basic-list-roots")]
    [InlineData("incomplete-result-request-state")]
    [InlineData("incomplete-result-multiple-input-requests")]
    [InlineData("incomplete-result-multi-round")]
    [InlineData("incomplete-result-missing-input-response")]
    [InlineData("incomplete-result-non-tool-request")]
    public async Task RunMrtrConformanceTest(string scenario)
    {
        Assert.SkipWhen(!NodeHelpers.IsNodeInstalled(), "Node.js is not installed. Skipping conformance tests.");
        Assert.SkipWhen(!NodeHelpers.HasMrtrScenarios(), "SEP-2322 MRTR conformance scenarios not yet available in the published @modelcontextprotocol/conformance package.");

        var result = await RunConformanceTestsAsync(
            $"server --url {fixture.ServerUrl} --scenario {scenario}");

        Assert.True(result.Success,
            $"MRTR conformance test '{scenario}' failed.\n\nStdout:\n{result.Output}\n\nStderr:\n{result.Error}");
    }

    private async Task<(bool Success, string Output, string Error)> RunConformanceTestsAsync(string arguments)
    {
        var startInfo = NodeHelpers.ConformanceTestStartInfo(arguments);

        var outputBuilder = new StringBuilder();
        var errorBuilder = new StringBuilder();

        var process = new Process { StartInfo = startInfo };

        // Protect callbacks with try/catch to prevent ITestOutputHelper from
        // throwing on a background thread if events arrive after the test completes.
        DataReceivedEventHandler outputHandler = (sender, e) =>
        {
            if (e.Data != null)
            {
                try { output.WriteLine(e.Data); } catch { }
                outputBuilder.AppendLine(e.Data);
            }
        };

        DataReceivedEventHandler errorHandler = (sender, e) =>
        {
            if (e.Data != null)
            {
                try { output.WriteLine(e.Data); } catch { }
                errorBuilder.AppendLine(e.Data);
            }
        };

        process.OutputDataReceived += outputHandler;
        process.ErrorDataReceived += errorHandler;

        process.Start();
        process.BeginOutputReadLine();
        process.BeginErrorReadLine();

        using var cts = new CancellationTokenSource(TimeSpan.FromMinutes(5));
        try
        {
            await process.WaitForExitAsync(cts.Token);
        }
        catch (OperationCanceledException)
        {
            process.Kill(entireProcessTree: true);
            process.OutputDataReceived -= outputHandler;
            process.ErrorDataReceived -= errorHandler;
            return (
                Success: false,
                Output: outputBuilder.ToString(),
                Error: errorBuilder.ToString() + "\nProcess timed out after 5 minutes and was killed."
            );
        }

        process.OutputDataReceived -= outputHandler;
        process.ErrorDataReceived -= errorHandler;

        var stdoutText = outputBuilder.ToString();
        var stderrText = errorBuilder.ToString();

        // The Node.js conformance runner can crash during cleanup on Windows with a libuv
        // assertion ("!(handle->flags & UV_HANDLE_CLOSING)") that produces a non-zero exit
        // code even though every conformance check passed. When that happens, fall back to
        // parsing the "Test Results:" summary in stdout to decide success.
        bool success = process.ExitCode == 0 || ConformanceOutputIndicatesSuccess(stdoutText);

        return (
            Success: success,
            Output: stdoutText,
            Error: stderrText
        );
    }

    /// <summary>
    /// Parses the conformance runner output for a "Test Results:" line such as
    /// "Passed: 3/3, 0 failed, 0 warnings" and returns true when all checks passed
    /// and none failed.
    /// </summary>
    private static bool ConformanceOutputIndicatesSuccess(string output)
    {
        // Match lines like "Passed: 3/3, 0 failed, 0 warnings"
        var match = Regex.Match(output, @"Passed:\s*(\d+)/(\d+),\s*(\d+)\s*failed");
        if (!match.Success)
        {
            return false;
        }

        int passed = int.Parse(match.Groups[1].Value);
        int total = int.Parse(match.Groups[2].Value);
        int failed = int.Parse(match.Groups[3].Value);

        return passed == total && failed == 0 && total > 0;
    }
}