namespace Processor;

//
// Source: https://stackoverflow.com/a/20623311/2258393
//

using System;
using System.Diagnostics;
using System.Collections.Generic;
using System.Runtime.InteropServices;

public static class SystemUtil
{
    [StructLayout(LayoutKind.Sequential)]
    private struct RM_UNIQUE_PROCESS
    {
        public readonly int dwProcessId;
        private readonly System.Runtime.InteropServices.ComTypes.FILETIME ProcessStartTime;
    }

    private const int RM_REBOOT_REASON_NONE = 0;
    private const int CCH_RM_MAX_APP_NAME = 255;
    private const int CCH_RM_MAX_SVC_NAME = 63;

    private enum RM_APP_TYPE
    {
        RM_UNKNOWN_APP = 0,
        RM_MAIN_WINDOW = 1,
        RM_OTHER_WINDOW = 2,
        RM_SERVICE = 3,
        RM_EXPLORER = 4,
        RM_CONSOLE = 5,
        RM_CRITICAL = 1000
    }

    [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
    private struct RM_PROCESS_INFO
    {
        public readonly RM_UNIQUE_PROCESS Process;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCH_RM_MAX_APP_NAME + 1)]
        private readonly string strAppName;

        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCH_RM_MAX_SVC_NAME + 1)]
        private readonly string strServiceShortName;

        private readonly RM_APP_TYPE ApplicationType;
        private readonly uint AppStatus;
        private readonly uint TSSessionId;
        
        [MarshalAs(UnmanagedType.Bool)]
        private readonly bool bRestartable;
    }

    [DllImport("rstrtmgr.dll", CharSet = CharSet.Unicode)]
    static extern int RmRegisterResources(uint pSessionHandle, UInt32 nFiles, string[] rgsFilenames, UInt32 nApplications, [In] RM_UNIQUE_PROCESS[] rgApplications, UInt32 nServices, string[] rgsServiceNames);

    [DllImport("rstrtmgr.dll", CharSet = CharSet.Auto)]
    static extern int RmStartSession(out uint pSessionHandle, int dwSessionFlags, string strSessionKey);

    [DllImport("rstrtmgr.dll")]
    static extern int RmEndSession(uint pSessionHandle);

    [DllImport("rstrtmgr.dll")]
    static extern int RmGetList(uint dwSessionHandle, out uint pnProcInfoNeeded, ref uint pnProcInfo, [In, Out] RM_PROCESS_INFO[] rgAffectedApps, ref uint lpdwRebootReasons);

    /// <summary>
    /// Find out what process(es) have a lock on the specified file.
    /// </summary>
    /// <param name="path">Path of the file.</param>
    /// <returns>Processes locking the file</returns>
    /// <remarks>See also:
    /// http://msdn.microsoft.com/en-us/library/windows/desktop/aa373661(v=vs.85).aspx
    /// http://wyupdate.googlecode.com/svn-history/r401/trunk/frmFilesInUse.cs (no copyright in code at time of viewing)
    /// </remarks>
    public static List<Process> WhoIsLocking(string path)
    {
        var key = Guid.NewGuid().ToString();
        var processes = new List<Process>();

        var res = RmStartSession(out var handle, 0, key);
        if (res != 0)
            return processes;

        try
        {
            const int ERROR_MORE_DATA = 234;
            uint pnProcInfoNeeded = 0, pnProcInfo = 0, lpdwRebootReasons = RM_REBOOT_REASON_NONE;
            var resources = new[] { path }; // Just checking on one resource.
            res = RmRegisterResources(handle, (uint)resources.Length, resources, 0, null!, 0, null!);

            if (res != 0)
                return processes;

            //Note: there's a race condition here -- the first call to RmGetList() returns
            //      the total number of process. However, when we call RmGetList() again to get
            //      the actual processes this number may have increased.
            res = RmGetList(handle, out pnProcInfoNeeded, ref pnProcInfo, null!, ref lpdwRebootReasons);
            if (res == ERROR_MORE_DATA)
            {
                // Create an array to store the process results
                var processInfo = new RM_PROCESS_INFO[pnProcInfoNeeded];
                pnProcInfo = pnProcInfoNeeded;

                // Get the list
                res = RmGetList(handle, out pnProcInfoNeeded, ref pnProcInfo, processInfo, ref lpdwRebootReasons);
                if (res == 0)
                {
                    // Enumerate all of the results and add them to the list to be returned
                    for (var i = 0; i < pnProcInfo; i++)
                    {
                        try
                        {
                            processes.Add(Process.GetProcessById(processInfo[i].Process.dwProcessId));
                        }
                        // catch the error -- in case the process is no longer running
                        catch (ArgumentException)
                        {
                        }
                    }
                }
                else
                    return processes;
            }
            else if (res != 0)
                return processes;
        }
        finally
        {
            RmEndSession(handle);
        }

        return processes;
    }
}