// 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.
 
using System;
using System.Runtime.InteropServices;
using Microsoft.CodeAnalysis.CommandLine;
using Roslyn.Utilities;
 
namespace Microsoft.CodeAnalysis.CompilerServer
{
    /// <summary>
    /// Uses p/invoke to gain access to information about how much memory this process is using
    /// and how much is still available.
    /// </summary>
    [StructLayout(LayoutKind.Sequential)]
    internal sealed class MemoryHelper
    {
        private MemoryHelper()
        {
            this.Length = (int)Marshal.SizeOf(this);
        }
 
        // The length field must be set to the size of this data structure.
        public int Length;
        public int PercentPhysicalUsed;
        public ulong MaxPhysical;
        public ulong AvailablePhysical;
        public ulong MaxPageFile;
        public ulong AvailablePageFile;
        public ulong MaxVirtual;
        public ulong AvailableVirtual;
        public ulong Reserved; //always 0
 
        public static bool IsMemoryAvailable(ICompilerServerLogger logger)
        {
            if (!PlatformInformation.IsWindows)
            {
                // assume we have enough memory on non-Windows machines
                return true;
            }
 
            MemoryHelper status = new MemoryHelper();
            GlobalMemoryStatusEx(status);
            ulong max = status.MaxVirtual;
            ulong free = status.AvailableVirtual;
 
            int shift = 20;
            string unit = "MB";
            if (free >> shift == 0)
            {
                shift = 10;
                unit = "KB";
            }
 
            logger.Log("Free memory: {1}{0} of {2}{0}.", unit, free >> shift, max >> shift);
 
            return free >= 800 << 20; // Value (500MB) is arbitrary; feel free to improve.
        }
 
        [DllImport("kernel32.dll", SetLastError = true)]
        private static extern bool GlobalMemoryStatusEx([In, Out] MemoryHelper buffer);
    }
}