// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
 
#nullable disable
 
using System;
using System.Collections.Generic;
using System.Threading;
 
namespace Roslyn.Hosting.Diagnostics.PerfMargin;
 
/// <summary>
/// Represents whether each feature is active or inactive.
/// 
/// The IsActive property indicates whether a given feature is currently in the
/// middle of an operation.  Features can be grouped into a parent ActivityLevel
/// which is active when any of its children are active.
/// </summary>
internal sealed class ActivityLevel
{
    private int _isActive;
    private readonly List<ActivityLevel> _children;
    private readonly ActivityLevel _parent;
 
    public ActivityLevel(string name)
    {
        Name = name;
        _children = [];
    }
 
    public ActivityLevel(string name, ActivityLevel parent, bool createChildList)
    {
        Name = name;
        _parent = parent;
        _parent._children.Add(this);
 
        if (createChildList)
        {
            _children = [];
        }
    }
 
    public event EventHandler IsActiveChanged;
 
    public string Name { get; }
 
    public bool IsActive
        => _isActive > 0;
 
    public void Start()
    {
        var current = Interlocked.Increment(ref _isActive);
        if (current == 1)
        {
            ActivityLevelChanged();
        }
 
        _parent?.Start();
    }
 
    public void Stop()
    {
        var current = Interlocked.Decrement(ref _isActive);
        if (current == 0)
        {
            ActivityLevelChanged();
        }
 
        _parent?.Stop();
    }
 
    internal void SortChildren()
    {
        if (_children != null)
        {
            _children.Sort(new Comparison<ActivityLevel>((a, b) => string.CompareOrdinal(a.Name, b.Name)));
            foreach (var child in _children)
            {
                child.SortChildren();
            }
        }
    }
 
    private void ActivityLevelChanged()
    {
        IsActiveChanged?.Invoke(this, EventArgs.Empty);
    }
 
    public IReadOnlyCollection<ActivityLevel> Children
        => _children;
}