﻿using System;
using System.Runtime.InteropServices;

namespace tskmgr
{
    /// <summary>
    /// Original code is from: http://stackoverflow.com/a/10028263
    /// </summary>
    public static class PerformanceInfo
    {
        [DllImport("psapi.dll", SetLastError = true)]
        [return: MarshalAs(UnmanagedType.Bool)]
        public static extern bool GetPerformanceInfo([Out] out PerformanceInformation PerformanceInformation, [In] int Size);

        [StructLayout(LayoutKind.Sequential)]
        public struct PerformanceInformation
        {
            public int Size;
            public IntPtr CommitTotal;
            public IntPtr CommitLimit;
            public IntPtr CommitPeak;
            public IntPtr PhysicalTotal;
            public IntPtr PhysicalAvailable;
            public IntPtr SystemCache;
            public IntPtr KernelTotal;
            public IntPtr KernelPaged;
            public IntPtr KernelNonPaged;
            public IntPtr PageSize;
            public int HandlesCount;
            public int ProcessCount;
            public int ThreadCount;
        }

        public static Int64 GetPhysicalAvailableMemoryInMiB()
        {
            PerformanceInformation pi = new PerformanceInformation();
            if (GetPerformanceInfo(out pi, Marshal.SizeOf(pi)))
            {
                return Convert.ToInt64((pi.PhysicalAvailable.ToInt64() * pi.PageSize.ToInt64() / 1048576));
            }
            else
            {
                return -1;
            }
        }

        public static Int64 GetTotalMemoryInMiB()
        {
            PerformanceInformation pi = new PerformanceInformation();
            if (GetPerformanceInfo(out pi, Marshal.SizeOf(pi)))
            {
                return Convert.ToInt64((pi.PhysicalTotal.ToInt64() * pi.PageSize.ToInt64() / 1048576));
            }
            else
            {
                return -1;
            }
        }

        public static int GetUsedMemoryInMiB()
        {
            Int64 phav = PerformanceInfo.GetPhysicalAvailableMemoryInMiB();
            Int64 tot = PerformanceInfo.GetTotalMemoryInMiB();

            return (int)(tot - phav);
        }
    }
}
