using System;
using System.Collections.Generic;
using System.Linq;

namespace WhiteMagic.Thread;

/// <summary>
/// A disposable scope that tracks a set of threads frozen by <see cref="ThreadFactory.Freeze"/>.
/// Disposing the scope resumes exactly those threads, in reverse order, even if the guarded
/// body throws.
/// </summary>
public sealed class FrozenThread : IDisposable
{
    private readonly IReadOnlyList<RemoteThread> _threads;
    private bool _disposed;

    internal FrozenThread(IReadOnlyList<RemoteThread> threads)
    {
        _threads = threads ?? throw new ArgumentNullException(nameof(threads));
    }

    /// <summary>The threads suspended by this freeze scope.</summary>
    public IEnumerable<RemoteThread> Threads => _threads;

    /// <summary>
    /// Resumes the frozen threads in reverse order. The original call is responsible for
    /// disposing the <see cref="RemoteThread"/> instances afterwards.
    /// </summary>
    public void Dispose()
    {
        if (_disposed)
            return;

        _disposed = true;

        foreach (RemoteThread thread in _threads.Reverse())
        {
            try
            {
                thread.Resume();
            }
            catch
            {
                // Resume-on-dispose is best-effort; callers keep the thread handles so
                // they can diagnose or recover separately.
            }
        }
    }
}