// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Runtime.InteropServices;
using System.Threading;
using Microsoft.Win32.SafeHandles;

namespace System.Diagnostics
{
    internal static partial class ProcessUtils
    {
        private static int s_childrenUsingTerminalCount;

        internal static void ConfigureTerminalForChildProcesses(int increment, bool configureConsole = true)
        {
            Debug.Assert(increment != 0);

            int childrenUsingTerminalRemaining = Interlocked.Add(ref s_childrenUsingTerminalCount, increment);
            if (increment > 0)
            {
                Debug.Assert(s_processStartLock.IsReadLockHeld);
                Debug.Assert(configureConsole);

                // At least one child is using the terminal.
                Interop.Sys.ConfigureTerminalForChildProcess(childUsesTerminal: true);
            }
            else
            {
                Debug.Assert(s_processStartLock.IsWriteLockHeld);

                if (childrenUsingTerminalRemaining == 0 && configureConsole)
                {
                    // No more children are using the terminal.
                    Interop.Sys.ConfigureTerminalForChildProcess(childUsesTerminal: false);
                }
            }
        }

        private static unsafe void SetDelayedSigChildConsoleConfigurationHandler()
        {
            Interop.Sys.SetDelayedSigChildConsoleConfigurationHandler(&DelayedSigChildConsoleConfiguration);
        }

        [UnmanagedCallersOnly]
        private static void DelayedSigChildConsoleConfiguration()
        {
            // Lock to avoid races with Process.Start
            s_processStartLock.EnterWriteLock();
            try
            {
                if (s_childrenUsingTerminalCount == 0)
                {
                    // No more children are using the terminal.
                    Interop.Sys.ConfigureTerminalForChildProcess(childUsesTerminal: false);
                }
            }
            finally
            {
                s_processStartLock.ExitWriteLock();
            }
        }

        private static bool AreChildrenUsingTerminal => s_childrenUsingTerminalCount > 0;

        internal static bool IsTerminal(SafeFileHandle? standardHandle) => standardHandle is not null && Interop.Sys.IsATty(standardHandle);
    }
}