using System.Globalization;
using System.Text;
using System.Text.RegularExpressions;
using Renci.SshNet;
using Renci.SshNet.Common;

namespace DodoSSH.Client.Ssh.Tests;

/// <summary>
/// The M1 client gate: does a PTY resize actually reach the remote?
/// </summary>
/// <remarks>
/// <para>
/// The plan flagged <c>window-change</c> on <c>ShellStream</c> as unverified, and it decides the
/// terminal's whole design — a terminal that cannot resize is unusable, and the fallback is
/// dropping to <c>IChannelSession</c> and driving the channel requests directly. SSH.NET 2025.1.0
/// does expose <c>ChangeWindowSize</c>, but a method existing is not the remote observing it, so
/// these read the size back from the server rather than asserting the call did not throw.
/// </para>
/// <para>
/// Kept as a permanent regression suite rather than deleted after the spike. An SSH.NET upgrade
/// that silently stopped sending the request would otherwise ship, and the symptom — wrapped
/// output only after the user resizes the window — is easy to blame on the terminal emulator.
/// </para>
/// </remarks>
[Collection(SshCollection.Name)]
public sealed class PtyAndResizeSpikeTests(SshServerFixture fixture)
{
    private static readonly TimeSpan ReadTimeout = TimeSpan.FromSeconds(20);

    /// <summary>
    /// Matches busybox <c>stty size</c> output: rows then columns.
    /// </summary>
    /// <remarks>
    /// Surrounding horizontal whitespace is tolerated, and the caller normalises CR to LF first.
    /// A PTY emits CRLF, so an anchored pattern that does not account for the CR fails on output
    /// that is visibly correct — which reads as "the resize did not work" and sends you looking in
    /// entirely the wrong place.
    /// </remarks>
    private static readonly Regex SizeLine = new(
        @"^[ \t]*(?<rows>[0-9]{1,5})[ \t]+(?<columns>[0-9]{1,5})[ \t]*$",
        RegexOptions.Multiline | RegexOptions.ExplicitCapture,
        TimeSpan.FromSeconds(1));

    [Fact]
    public async Task PasswordAuthentication_Connects()
    {
        using var client = CreatePasswordClient();

        await client.ConnectAsync(TestContext.Current.CancellationToken);

        client.IsConnected.ShouldBeTrue();
    }

    [Fact]
    public async Task PublicKeyAuthentication_Connects()
    {
        // PKCS#1 PEM ("BEGIN RSA PRIVATE KEY"), which SSH.NET has read for years. The vault stores
        // key material in its own format, so this is only about SSH.NET accepting a standard PEM.
        var pem = fixture.ClientKey.ExportRSAPrivateKeyPem();
        using var keyStream = new MemoryStream(Encoding.ASCII.GetBytes(pem));
        using var privateKey = new PrivateKeyFile(keyStream);

        using var client = new SshClient(
            new ConnectionInfo(
                fixture.Host,
                fixture.Port,
                SshServerFixture.Username,
                new PrivateKeyAuthenticationMethod(SshServerFixture.Username, privateKey)));

        await client.ConnectAsync(TestContext.Current.CancellationToken);

        client.IsConnected.ShouldBeTrue();
    }

    [Fact]
    public async Task TheHostKey_ArrivesAsARawBlobWeCanFingerprint()
    {
        // Known-hosts entries are a synced vault entity, so the fingerprint we store has to be
        // computed from the wire blob rather than read off a library property. This confirms the
        // blob is exposed at all, and that our formatting matches OpenSSH's shape.
        using var client = CreatePasswordClient();

        byte[]? blob = null;
        string? algorithm = null;

        client.HostKeyReceived += (_, e) =>
        {
            blob = e.HostKey;
            algorithm = e.HostKeyName;
        };

        await client.ConnectAsync(TestContext.Current.CancellationToken);

        blob.ShouldNotBeNull();
        blob.Length.ShouldBeGreaterThan(0);
        algorithm.ShouldNotBeNullOrEmpty();

        var fingerprint = SshHostKeyFingerprint.Format(blob);

        fingerprint.ShouldStartWith(SshHostKeyFingerprint.Prefix);
        fingerprint.ShouldNotEndWith("=");

        // 32 bytes of SHA-256 render as 43 unpadded base64 characters.
        fingerprint.Length.ShouldBe(SshHostKeyFingerprint.Prefix.Length + 43);
    }

    [Fact]
    public async Task RefusingTheHostKey_AbortsTheConnection()
    {
        // The mismatch path has to be a hard block, not a warning. If CanTrust were advisory the
        // TOFU dialog would be decoration.
        using var client = CreatePasswordClient();

        client.HostKeyReceived += (_, e) => e.CanTrust = false;

        await Should.ThrowAsync<SshConnectionException>(
            async () => await client.ConnectAsync(TestContext.Current.CancellationToken));

        client.IsConnected.ShouldBeFalse();
    }

    [Fact]
    public async Task APtyShell_ReportsTheSizeItWasCreatedWith()
    {
        using var client = CreatePasswordClient();
        await client.ConnectAsync(TestContext.Current.CancellationToken);

        using var shell = client.CreateShellStream("xterm-256color", 80, 24, 800, 600, 4096);

        var (rows, columns) = await ReadSizeAsync(shell);

        rows.ShouldBe(24);
        columns.ShouldBe(80);
    }

    [Fact]
    public async Task ChangeWindowSize_IsObservedByTheRemote()
    {
        // The gate. Reads the size back from the server after resizing, so this fails if
        // ChangeWindowSize silently does nothing.
        using var client = CreatePasswordClient();
        await client.ConnectAsync(TestContext.Current.CancellationToken);

        using var shell = client.CreateShellStream("xterm-256color", 80, 24, 800, 600, 4096);

        var initial = await ReadSizeAsync(shell);
        initial.ShouldBe((24, 80));

        shell.ChangeWindowSize(columns: 132, rows: 43, width: 1320, height: 1075);

        var resized = await ReadSizeAsync(shell);

        resized.ShouldBe(
            (43, 132),
            "The remote did not observe the window-change request. ShellStream.ChangeWindowSize is "
            + "not usable, and the terminal must drive IChannelSession directly instead.");
    }

    [Fact]
    public async Task ChangeWindowSize_CanBeCalledRepeatedly()
    {
        // A user dragging a window edge produces a stream of these. If only the first took effect,
        // the terminal would settle on whatever size the drag started at.
        using var client = CreatePasswordClient();
        await client.ConnectAsync(TestContext.Current.CancellationToken);

        using var shell = client.CreateShellStream("xterm-256color", 80, 24, 800, 600, 4096);
        await ReadSizeAsync(shell);

        foreach (var (columns, rows) in new[] { (100u, 30u), (120u, 40u), (90u, 25u) })
        {
            shell.ChangeWindowSize(columns, rows, columns * 10, rows * 25);

            var observed = await ReadSizeAsync(shell);
            observed.ShouldBe(((int)rows, (int)columns));
        }
    }

    // ---- Helpers ----

    private SshClient CreatePasswordClient() =>
        new(fixture.Host, fixture.Port, SshServerFixture.Username, SshServerFixture.Password);

    /// <summary>Asks the remote what size it thinks the terminal is.</summary>
    /// <remarks>
    /// The marker is written split — <c>"MAR""KER"</c> — so the PTY's echo of the command line
    /// does not contain it. Without that the read completes on the echo and never sees the output,
    /// which looks exactly like a resize that did not take effect.
    /// </remarks>
    private static async Task<(int Rows, int Columns)> ReadSizeAsync(ShellStream shell)
    {
        shell.WriteLine("""stty size; echo "MAR""KER" """);

        var output = (await ReadUntilAsync(shell, "MARKER")).Replace('\r', '\n');

        var matches = SizeLine.Matches(output);
        matches.Count.ShouldBeGreaterThan(0, $"No 'rows cols' line in output:\n{output}");

        // The last match, not the first. A read can begin with output still buffered from the
        // previous command, including its size line — taking the first match would report the size
        // from before the resize and turn a working resize into a failing test.
        var match = matches[^1];

        return (
            int.Parse(match.Groups["rows"].Value, CultureInfo.InvariantCulture),
            int.Parse(match.Groups["columns"].Value, CultureInfo.InvariantCulture));
    }

    /// <remarks>
    /// Raced against a timeout rather than cancelled. <c>ShellStream</c> does not override
    /// <c>ReadAsync</c>, so the base implementation runs the blocking read on a pool thread and
    /// cannot observe a token once it has started — passing one would produce a test that hangs
    /// instead of failing. The abandoned read dies with the process.
    /// </remarks>
    private static async Task<string> ReadUntilAsync(ShellStream shell, string marker)
    {
        var accumulated = new StringBuilder();
        var deadline = TimeProvider.System.GetUtcNow() + ReadTimeout;

        while (TimeProvider.System.GetUtcNow() < deadline)
        {
            var buffer = new byte[4096];
            var read = shell.ReadAsync(buffer.AsMemory()).AsTask();

            var remaining = deadline - TimeProvider.System.GetUtcNow();
            if (remaining <= TimeSpan.Zero || await Task.WhenAny(read, Task.Delay(remaining)) != read)
            {
                break;
            }

            var count = await read;
            if (count == 0)
            {
                break;
            }

            accumulated.Append(Encoding.UTF8.GetString(buffer, 0, count));

            if (accumulated.ToString().Contains(marker, StringComparison.Ordinal))
            {
                return accumulated.ToString();
            }
        }

        throw new TimeoutException(
            $"Did not see '{marker}' within {ReadTimeout}. Output so far:\n{accumulated}");
    }
}