// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using System.Diagnostics;
using System.Threading;
 
namespace Microsoft.Build.TaskHost.Utilities;
 
internal static partial class EnvironmentUtilities
{
    private static volatile int s_processId;
    private static volatile string? s_processPath;
    private static int? s_processSessionId;
 
    /// <summary>Gets the unique identifier for the current process.</summary>
    public static int CurrentProcessId
    {
        get
        {
            // copied from Environment.ProcessId
            int processId = s_processId;
            if (processId == 0)
            {
                using Process currentProcess = Process.GetCurrentProcess();
                s_processId = processId = currentProcess.Id;
 
                // Assume that process Id zero is invalid for user processes. It holds for all mainstream operating systems.
                Debug.Assert(processId != 0);
            }
 
            return processId;
        }
    }
 
    /// <summary>
    /// Returns the path of the executable that started the currently executing process. Returns null when the path is not available.
    /// </summary>
    /// <returns>Path of the executable that started the currently executing process</returns>
    /// <remarks>
    /// If the executable is renamed or deleted before this property is first accessed, the return value is undefined and depends on the operating system.
    /// </remarks>
    public static string? ProcessPath
    {
        get
        {
            // copied from Environment.ProcessPath
            string? processPath = s_processPath;
            if (processPath == null)
            {
                // The value is cached both as a performance optimization and to ensure that the API always returns
                // the same path in a given process.
                using Process currentProcess = Process.GetCurrentProcess();
                Interlocked.CompareExchange(ref s_processPath, currentProcess.MainModule.FileName ?? "", null);
                processPath = s_processPath;
                Debug.Assert(processPath != null);
            }
 
            return (processPath?.Length != 0) ? processPath : null;
        }
    }
 
    public static int ProcessSessionId
    {
        get
        {
            return s_processSessionId ??= GetProcessSessionId();
 
            static int GetProcessSessionId()
            {
                using Process currentProcess = Process.GetCurrentProcess();
                return currentProcess.SessionId;
            }
        }
    }
}