namespace ClawdDotNet.Manager.Tests;

/// <summary>
/// An instance process the test controls.
///
/// <para>A real process would only allow checking supervision superficially: a crash at the
/// desired moment, a process that lives and stays silent, a reused
/// process ID — all of that can either not be produced with a running program or only
/// with waiting times, and tests with waiting times are tests that
/// eventually get switched off.</para>
/// </summary>
internal sealed class FakeProcess(int id, DateTimeOffset startedAt) : IInstanceProcess
{
    public int Id { get; } = id;

    public DateTimeOffset StartedAt { get; } = startedAt;

    public bool HasExited { get; private set; }

    public int? ExitCode { get; private set; }

    public bool WasKilled { get; private set; }

    public bool Disposed { get; private set; }

    /// <summary>The process ends — with or without intervention.</summary>
    public void Exit(int code)
    {
        HasExited = true;
        ExitCode = code;
    }

    public void Kill()
    {
        WasKilled = true;
        if (!HasExited) Exit(-1);
    }

    public void Dispose() => Disposed = true;
}

internal sealed class FakeLauncher : IInstanceLauncher
{
    private int _nextId = 1000;

    public FakeProcess? Last { get; private set; }

    public int Starts { get; private set; }

    /// <summary>Which process belongs to which instance directory.</summary>
    public Dictionary<string, FakeProcess> ByDirectory { get; } =
        new(StringComparer.OrdinalIgnoreCase);

    /// <summary>Whether a process is currently alive for this directory.</summary>
    public bool IsRunning(string instanceDirectory)
        => ByDirectory.TryGetValue(Path.GetFullPath(instanceDirectory), out var p)
           && !p.HasExited;

    /// <summary>If set, the start fails with this.</summary>
    public Exception? FailStartWith { get; set; }

    /// <summary>What <see cref="Attach"/> should deliver — already running processes.</summary>
    public Dictionary<int, FakeProcess> Running { get; } = [];

    public DateTimeOffset Now { get; set; } = DateTimeOffset.UnixEpoch;

    public IInstanceProcess Start(string instanceDirectory)
    {
        Starts++;

        if (FailStartWith is not null) throw FailStartWith;

        Last = new FakeProcess(_nextId++, Now);
        Running[Last.Id] = Last;
        ByDirectory[Path.GetFullPath(instanceDirectory)] = Last;
        return Last;
    }

    /// <summary>
    /// A process that was already running before this manager came (E-M6).
    ///
    /// <para>Does not count as a start — exactly therein lies the difference several tests
    /// check: what runs is taken over and not booted a second time.</para>
    /// </summary>
    public FakeProcess StartedElsewhere(string instanceDirectory, int processId)
    {
        var process = new FakeProcess(processId, Now);
        Running[processId] = process;
        ByDirectory[Path.GetFullPath(instanceDirectory)] = process;
        return process;
    }

    public IInstanceProcess? Attach(int processId, DateTimeOffset startedAt)
    {
        if (!Running.TryGetValue(processId, out var process))
            return null;

        // The same check as in real operation: same ID, but a different start time
        // means a different process.
        return (process.StartedAt - startedAt).Duration() > TimeSpan.FromSeconds(2)
            ? null
            : process;
    }
}

/// <summary>The socket that the test lets answer or stay silent.</summary>
internal sealed class FakeChannel : IInstanceChannel
{
    /// <summary>The answer for all directories, unless one of their own is stored.</summary>
    public InstanceIdentity? Answer { get; set; }

    /// <summary>
    /// Answers per instance directory.
    ///
    /// <para>Needed as soon as more than one instance is involved: information that names the same
    /// instance for every directory lets tests turn green that in operation would mix up two
    /// different instances.</para>
    /// </summary>
    public Dictionary<string, InstanceIdentity?> AnswerFor { get; } =
        new(StringComparer.OrdinalIgnoreCase);

    /// <summary>
    /// If set, the socket only answers for instances that this launcher
    /// actually started — as in operation.
    ///
    /// <para><b>Without this a test setup is easily wrong:</b> whoever stores the answer
    /// before the manager comes up says with it "this instance is already running". The manager
    /// then takes it over (E-M6), the launcher is never touched — and the test checks something
    /// other than it claims. That happened to me three times; with this coupling it can
    /// no longer happen.</para>
    ///
    /// <para>Not set means: the stored answer always applies. That is needed by whoever wants to describe an
    /// instance that runs without this manager having started it.</para>
    /// </summary>
    public FakeLauncher? Launcher { get; set; }

    /// <summary>
    /// Directories whose instance has fallen silent: the process lives, the socket is silent.
    ///
    /// <para>The case from #529 — and the only one in which supervision resorts to
    /// force on its own initiative. Without this switch it cannot be reproduced: the coupling
    /// to <see cref="Launcher"/> would otherwise bind the answer to exactly what is supposed to
    /// fall apart here.</para>
    /// </summary>
    public HashSet<string> Verstummt { get; } = new(StringComparer.OrdinalIgnoreCase);

    /// <summary>The instance stops answering without its process ending.</summary>
    public void GoSilent(string instanceDirectory)
        => Verstummt.Add(Path.GetFullPath(instanceDirectory));

    public int Calls { get; private set; }

    /// <summary>How often the instance was asked to end itself.</summary>
    public int StopRequests { get; private set; }

    /// <summary>Whether the request arrives. False means: the instance no longer listens at all.</summary>
    public bool StopRequestArrives { get; set; } = true;

    public Task<InstanceIdentity?> AskAsync(string instanceDirectory, CancellationToken ct = default)
    {
        Calls++;

        if (Verstummt.Contains(Path.GetFullPath(instanceDirectory)))
            return Task.FromResult<InstanceIdentity?>(null);

        if (Launcher is not null && !Launcher.IsRunning(instanceDirectory))
            return Task.FromResult<InstanceIdentity?>(null);

        return Task.FromResult(
            AnswerFor.TryGetValue(Path.GetFullPath(instanceDirectory), out var ownOnes)
                ? ownOnes
                : Answer);
    }

    /// <summary>
    /// #722: What the instance does when the request arrives — typically: end. A test that
    /// ended the process before asking raced the supervisor's own check: under load the check
    /// saw the process gone first and called it a crash, not a stop.
    /// </summary>
    public Action<string>? OnStopRequest { get; set; }

    public Task<bool> RequestStopAsync(string instanceDirectory, CancellationToken ct = default)
    {
        StopRequests++;
        if (StopRequestArrives)
            OnStopRequest?.Invoke(instanceDirectory);
        return Task.FromResult(StopRequestArrives);
    }
}