using DodoSSH.Client.Ssh;

namespace DodoSSH.Client.App.Tests;

/// <summary>
/// An SSH stack that connects to nothing.
/// </summary>
/// <remarks>
/// The shell suite is about what the view models do, and the real factory would need a reachable
/// sshd — which <c>DodoSSH.Client.Ssh.Tests</c> already covers against a container. What this makes
/// testable is everything the connect path does <em>around</em> the connection.
/// </remarks>
internal sealed class FakeSshConnectionFactory : ISshConnectionFactory, ISftpSessionFactory
{
    /// <summary>Thrown instead of connecting, when set. Used for the host-key paths.</summary>
    internal Exception? Failure { get; set; }

    /// <summary>
    /// Holds a connection open until it is completed, when set.
    /// </summary>
    /// <remarks>
    /// A handshake takes as long as a network takes, and connecting is deliberately no longer allowed to
    /// hold the window still while it does — so there is now behaviour that only exists <em>during</em> a
    /// connection: a tab in the strip with no session behind it. This is how a test gets to look at that
    /// moment rather than at the two on either side of it.
    /// </remarks>
    internal TaskCompletionSource? Gate { get; set; }

    /// <summary>Requests this factory was asked for, in order.</summary>
    internal List<SshConnectionRequest> Requests { get; } = [];

    /// <summary>Every shell this factory has opened, in order.</summary>
    /// <remarks>
    /// Exists so a test can reach one and drop it — see <see cref="FakeSshShellSession.Drop"/>. There was no
    /// reason to hold them while the only ending a session had was the tab being closed, which the shell can
    /// ask for directly.
    /// </remarks>
    internal List<FakeSshShellSession> Shells { get; } = [];

    /// <summary>Requests for a file-transfer session, in order.</summary>
    /// <remarks>
    /// Kept apart from <see cref="Requests"/> deliberately: file transfer is a separate connection, and a
    /// test asserting that opening a terminal did not also open one would have nothing to look at if the two
    /// shared a list.
    /// </remarks>
    internal List<SshConnectionRequest> SftpRequests { get; } = [];

    /// <summary>
    /// The furthest phase a failing attempt reports before <see cref="Failure"/> is thrown, or null for one
    /// that never reports any.
    /// </summary>
    /// <remarks>
    /// <para>
    /// ◆ <b>It is what decides whether the shell goes and probes the endpoint.</b> A connection that stopped
    /// while reaching is worth asking a socket about; one that got a host key has plainly reached the machine,
    /// and one that never reported a phase never dialled at all. See <c>VaultViewModel.ExplainAsync</c>.
    /// </para>
    /// <para>
    /// Defaults to <see cref="SshConnectionPhase.Reaching"/>, which is what this fake reported
    /// unconditionally before the field existed, so every test written against it goes on meaning what it did.
    /// Null models the real factory throwing out of <c>BuildConnectionInfo</c> — a private key that will not
    /// parse — which happens before it reports anything.
    /// </para>
    /// </remarks>
    internal SshConnectionPhase? FailAfter { get; set; } = SshConnectionPhase.Reaching;

    /// <summary>Every phase up to and including <paramref name="furthest"/>, in the order they happen.</summary>
    private static IEnumerable<SshConnectionPhase> PhasesUpTo(SshConnectionPhase? furthest) =>
        furthest is { } limit
            ? Enum.GetValues<SshConnectionPhase>().Where(phase => phase <= limit)
            : [];

    /// <inheritdoc />
    public async Task<ISshConnection> ConnectAsync(
        SshConnectionRequest request,
        IProgress<SshConnectionPhase>? progress,
        CancellationToken cancellationToken)
    {
        Requests.Add(request);

        // Before the gate rather than after it, which is what makes this fake useful for the connecting
        // card: a test that holds Gate open is a connection stuck partway through, and the step list has to
        // show it stuck on a named step rather than on none.
        //
        // How far a failing attempt gets is FailAfter's to say; a succeeding one is always reaching by now.
        foreach (var phase in Failure is null ? [SshConnectionPhase.Reaching] : PhasesUpTo(FailAfter))
        {
            progress?.Report(phase);
        }

        if (Gate is { } gate)
        {
            await gate.Task.WaitAsync(cancellationToken).ConfigureAwait(false);
        }

        if (Failure is { } failure)
        {
            throw failure;
        }

        // Only on the way to succeeding. A failure reported as having authenticated would let a test pass
        // while the card showed a refused connection getting one step further than it did.
        progress?.Report(SshConnectionPhase.CheckingHostKey);
        progress?.Report(SshConnectionPhase.Authenticating);

        return new FakeSshConnection(request, Shells);
    }

    /// <summary>The file-transfer session this factory last handed out, or null when it never has.</summary>
    /// <remarks>
    /// Kept so a test can read back what the screen actually asked the host to do — which path was renamed,
    /// which was deleted, which directories were listed. The screen reports all three in its own status
    /// line, and a suite that asserted only on that would be checking a sentence this code wrote about
    /// itself rather than the operation it claims to have performed.
    /// </remarks>
    internal FakeSftpSession? OpenedSftp { get; private set; }

    /// <inheritdoc />
    public Task<ISftpSession> OpenSftpAsync(
        SshConnectionRequest request,
        CancellationToken cancellationToken)
    {
        SftpRequests.Add(request);

        if (Failure is { } failure)
        {
            return Task.FromException<ISftpSession>(failure);
        }

        OpenedSftp = new FakeSftpSession(request);

        return Task.FromResult<ISftpSession>(OpenedSftp);
    }
}

/// <summary>A remote filesystem with one directory in it.</summary>
/// <remarks>
/// Enough for the shell suite, which is about what the screen does around a session rather than about
/// moving bytes. The queue's own behaviour is covered against a fuller fake in
/// <c>DodoSSH.Client.Transfer.Tests</c>, and the real subsystem against a container in
/// <c>DodoSSH.Client.Ssh.Tests</c>.
/// </remarks>
internal sealed class FakeSftpSession(SshConnectionRequest request) : ISftpSession
{
    /// <inheritdoc />
    public bool IsConnected { get; private set; } = true;

    /// <inheritdoc />
    public string? TransportFailure { get; private set; }

    /// <inheritdoc />
    public event EventHandler? ConnectionLost;

    /// <summary>
    /// Ends this session the way a rebooted host does: the connection is gone and it says so.
    /// </summary>
    /// <remarks>
    /// Latched before the announcement, which is the ordering the real session promises — a screen reading
    /// the reason out of the event would see null if a fake did it the other way round.
    /// </remarks>
    internal void Drop(string reason)
    {
        TransportFailure = reason;
        IsConnected = false;

        ConnectionLost?.Invoke(this, EventArgs.Empty);
    }

    /// <inheritdoc />
    public HostKeyPresentation HostKey { get; } =
        new(request.Host, request.Port, "ssh-ed25519", "SHA256:fake");

    /// <inheritdoc />
    public string Cipher { get; } = "aes256-gcm@openssh.com";

    /// <inheritdoc />
    public string HomeDirectory => $"/home/{request.Username}";

    /// <summary>Every directory this session has been asked to list, in order.</summary>
    /// <remarks>
    /// The evidence that a refresh happened at all. A listing whose contents never change — this one always
    /// answers the same single row — leaves no other trace of having been re-read, which is exactly the
    /// thing the automatic refresh after a transfer has to be proved to do.
    /// </remarks>
    internal List<string> Listed { get; } = [];

    /// <summary>Every rename this session has been asked for, as it was asked.</summary>
    internal List<(string From, string To)> Renamed { get; } = [];

    /// <summary>Every path this session has been asked to delete.</summary>
    internal List<string> Deleted { get; } = [];

    /// <summary>Every mode this session has been asked to set, as it was asked.</summary>
    /// <remarks>
    /// The evidence the screen's own status line cannot be: that sentence is code describing itself, and
    /// what matters is which nine bits actually went to the host.
    /// </remarks>
    internal List<(string Path, int Mode)> PermissionsSet { get; } = [];

    /// <summary>Every timestamp this session has been asked to set.</summary>
    internal List<(string Path, DateTimeOffset When)> TimesSet { get; } = [];

    /// <inheritdoc />
    public Task SetPermissionsAsync(string path, int mode, CancellationToken cancellationToken)
    {
        PermissionsSet.Add((path, mode));

        return Task.CompletedTask;
    }

    /// <inheritdoc />
    public Task SetLastWriteTimeAsync(
        string path,
        DateTimeOffset lastWriteTimeUtc,
        CancellationToken cancellationToken)
    {
        TimesSet.Add((path, lastWriteTimeUtc));

        return Task.CompletedTask;
    }

    /// <inheritdoc />
    public Task<IReadOnlyList<SftpEntry>> ListAsync(string path, CancellationToken cancellationToken)
    {
        Listed.Add(path);

        return Task.FromResult<IReadOnlyList<SftpEntry>>(
        [
            new SftpEntry(
                "notes.txt",
                SftpPath.Combine(path, "notes.txt"),
                SftpEntryKind.File,
                12,
                DateTimeOffset.UnixEpoch,
                "-rw-r--r--"),
        ]);
    }

    /// <summary>
    /// Paths this session admits to already having, and what it says about each.
    /// </summary>
    /// <remarks>
    /// ◆ Empty by default, and that is load-bearing rather than lazy: the transfer queue asks
    /// <see cref="StatAsync"/> whether a destination is taken and refuses to overwrite one that is, so a
    /// fake answering yes for everything would make every upload in this suite fail. What needs a real
    /// answer is editing, which stats the file before each write-back to see whether it moved — so a test
    /// about that puts the one path it is about in here.
    /// </remarks>
    internal Dictionary<string, SftpEntry> Existing { get; } = new(StringComparer.Ordinal);

    /// <summary>What the last write-back actually sent, so an edit's bytes are observable.</summary>
    internal byte[]? Written { get; private set; }

    /// <inheritdoc />
    public Task<SftpEntry?> StatAsync(string path, CancellationToken cancellationToken) =>
        Task.FromResult(Existing.TryGetValue(path, out var entry) ? entry : null);

    /// <inheritdoc />
    public Task<Stream> OpenReadAsync(string path, long offset, CancellationToken cancellationToken) =>
        Task.FromResult<Stream>(new MemoryStream("hello there\n"u8.ToArray(), writable: false));

    /// <inheritdoc />
    /// <remarks>
    /// ◆ A write updates <see cref="Existing"/> only for a path already in it, which is the difference
    /// between modelling a server and breaking every other test in the suite: the transfer queue writes to
    /// part files and stats them to decide whether there is anything to resume from, so a fake that
    /// remembered every write would start answering yes to questions it currently answers no to. What is in
    /// <see cref="Existing"/> is what a test deliberately put there.
    /// </remarks>
    public Task<Stream> OpenWriteAsync(string path, long offset, CancellationToken cancellationToken) =>
        Task.FromResult<Stream>(new RecordingStream(bytes =>
        {
            Written = bytes;

            if (Existing.TryGetValue(path, out var before))
            {
                Existing[path] = before with
                {
                    Length = bytes.Length,
                    LastWriteTimeUtc = before.LastWriteTimeUtc.AddSeconds(1),
                };
            }
        }));

    /// <summary>Every directory this session was asked to make, in the order it was asked.</summary>
    /// <remarks>
    /// The evidence a folder upload actually built the tree before it queued the files. Order matters and is
    /// asserted on: a parent has to exist before its child is asked for, and shortest-first is what
    /// guarantees it.
    /// </remarks>
    internal List<string> Created { get; } = [];

    /// <inheritdoc />
    public Task CreateDirectoryAsync(string path, CancellationToken cancellationToken)
    {
        Created.Add(path);

        return Task.CompletedTask;
    }

    /// <inheritdoc />
    public Task DeleteAsync(string path, CancellationToken cancellationToken)
    {
        Deleted.Add(path);

        return Task.CompletedTask;
    }

    /// <inheritdoc />
    public Task RenameAsync(string fromPath, string toPath, CancellationToken cancellationToken)
    {
        Renamed.Add((fromPath, toPath));

        return Task.CompletedTask;
    }

    /// <inheritdoc />
    public ValueTask DisposeAsync()
    {
        IsConnected = false;
        return ValueTask.CompletedTask;
    }
}

internal sealed class FakeSshConnection(SshConnectionRequest request, List<FakeSshShellSession> shells)
    : ISshConnection
{
    /// <inheritdoc />
    public bool IsConnected { get; private set; } = true;

    /// <inheritdoc />
    public HostKeyPresentation HostKey { get; } =
        new(request.Host, request.Port, "ssh-ed25519", "SHA256:fake");

    /// <inheritdoc />
    public string Cipher { get; } = "aes256-gcm@openssh.com";

    /// <inheritdoc />
    public Task<ISshShellSession> OpenShellAsync(
        TerminalSize size,
        CancellationToken cancellationToken)
    {
        var shell = new FakeSshShellSession();
        shells.Add(shell);

        return Task.FromResult<ISshShellSession>(shell);
    }

    /// <inheritdoc />
    public ValueTask DisposeAsync()
    {
        IsConnected = false;
        return ValueTask.CompletedTask;
    }
}

/// <summary>A write stream that hands its contents over when it is closed.</summary>
/// <remarks>
/// A <see cref="MemoryStream"/> cannot be read after disposal, and disposal is exactly when a write is
/// finished — so a fake that handed one back could observe a transfer starting and never what it sent.
/// </remarks>
internal sealed class RecordingStream(Action<byte[]> onClosed) : MemoryStream
{
    private bool handed;

    /// <inheritdoc />
    protected override void Dispose(bool disposing)
    {
        if (disposing && !handed)
        {
            handed = true;
            onClosed(ToArray());
        }

        base.Dispose(disposing);
    }
}

/// <summary>A shell that is open, silent and closes only when it is told to.</summary>
/// <remarks>
/// <see cref="ReadAsync"/> blocks rather than returning 0. Returning 0 means the remote closed the
/// channel, which would end the session the moment it was opened and make the test assert against a
/// connection that had already gone. <see cref="Drop"/> and <see cref="Exit"/> are the two ways out.
/// </remarks>
internal sealed class FakeSshShellSession : ISshShellSession
{
    private readonly CancellationTokenSource closed = new();

    /// <inheritdoc />
    public bool IsOpen { get; private set; } = true;

    /// <inheritdoc />
    public string? TransportFailure { get; private set; }

    /// <summary>
    /// Ends this shell the way a rebooted machine does: the read stops, with a transport failure latched.
    /// </summary>
    /// <remarks>
    /// Latched before the read is released, which is the ordering the real session promises and the whole
    /// reason the distinction is race-free — see <see cref="ISshShellSession.TransportFailure"/>. A fake
    /// that set it afterwards would be testing a guarantee the product does not make.
    /// </remarks>
    internal void Drop(string reason)
    {
        TransportFailure = reason;
        closed.Cancel();
    }

    /// <summary>Ends this shell the way <c>exit</c> does: the read stops, with nothing wrong underneath.</summary>
    internal void Exit() => closed.Cancel();

    /// <inheritdoc />
    public async ValueTask<int> ReadAsync(Memory<byte> buffer, CancellationToken cancellationToken)
    {
        try
        {
            await Task.Delay(Timeout.InfiniteTimeSpan, closed.Token).ConfigureAwait(false);
        }
        catch (OperationCanceledException) when (!cancellationToken.IsCancellationRequested)
        {
            // This shell ending, not the pump being asked to stop. Reported as end of stream rather than
            // rethrown, because that is what a real read does for both of the endings above: the channel
            // stops producing bytes, and what happened to the transport is told by the latch, not by an
            // exception coming out of here.
            return 0;
        }

        cancellationToken.ThrowIfCancellationRequested();

        return 0;
    }

    /// <inheritdoc />
    public ValueTask WriteAsync(ReadOnlyMemory<byte> data, CancellationToken cancellationToken) =>
        ValueTask.CompletedTask;

    /// <inheritdoc />
    public void Resize(TerminalSize size)
    {
    }

    /// <inheritdoc />
    public async ValueTask DisposeAsync()
    {
        IsOpen = false;

        await closed.CancelAsync().ConfigureAwait(false);

        closed.Dispose();
    }
}

/// <summary>
/// A reachability probe that answers from a script instead of from the network.
/// </summary>
/// <remarks>
/// <para>
/// ◆ <b>Every shell in this suite is given one, and that is not only about speed.</b> The real probe resolves
/// a name and opens a socket — see <see cref="SshReachabilityProbe"/> — so a fixture without this would put a
/// live DNS lookup for <c>db.internal</c> and a live TCP connect in the middle of a unit suite, on every test
/// where a connection fails. That is slow, it needs a network, and it is worse than either: <c>db.internal</c>
/// resolves on any machine whose resolver has a search domain that makes it resolve, so the sentence the
/// assertions read would depend on whose network the suite was run from.
/// </para>
/// <para>
/// <see cref="Summary"/> defaults to empty, which is what keeps the tests that predate the probe asserting
/// the exact message they always did: an empty finding appends nothing, so those cases go on describing a
/// failure and nothing else. A test that is about the diagnosis sets it.
/// </para>
/// </remarks>
internal sealed class FakeReachabilityProbe : ISshReachabilityProbe
{
    /// <summary>What every probe comes back with. Empty adds nothing to the failure it explains.</summary>
    internal string Summary { get; set; } = string.Empty;

    /// <summary>What it was asked about, in order, so a test can assert it was not asked at all.</summary>
    internal List<string> Probed { get; } = [];

    /// <inheritdoc />
    public ValueTask<SshReachabilityReport> ProbeAsync(
        string host,
        int port,
        CancellationToken cancellationToken)
    {
        Probed.Add($"{host}:{port}");

        return ValueTask.FromResult(
            new SshReachabilityReport(SshReach.Open, host, port, host, TimeSpan.Zero, Summary));
    }
}