using System.Diagnostics;
using System.Runtime.InteropServices;
using SpdUp.Core;

namespace SpdUp.Services;

/// <summary>
/// Performs real memory optimizations: working-set trimming + standby-list purge.
/// Requires administrator privileges.
/// </summary>
public sealed class RamOptimizationService
{
    /// <summary>
    /// Trim working sets of all accessible processes – pushes unused pages to the standby list.
    /// </summary>
    public RamCleanupResult TrimWorkingSets()
    {
        int trimmed = 0, failed = 0;
        var ownPid = Environment.ProcessId;

        foreach (var proc in Process.GetProcesses())
        {
            try
            {
                if (proc.Id == ownPid || proc.Id == 0 || proc.Id == 4) continue;

                var hProcess = NativeMethods.OpenProcess(
                    NativeMethods.PROCESS_SET_INFORMATION | NativeMethods.PROCESS_QUERY_INFORMATION,
                    false, proc.Id);

                if (hProcess == IntPtr.Zero) { failed++; continue; }

                try
                {
                    if (NativeMethods.EmptyWorkingSet(hProcess))
                        trimmed++;
                    else
                        failed++;
                }
                finally
                {
                    NativeMethods.CloseHandle(hProcess);
                }
            }
            catch
            {
                failed++;
            }
            finally
            {
                proc.Dispose();
            }
        }

        Logger.Info($"Working-set trim complete: {trimmed} trimmed, {failed} skipped.");
        return new RamCleanupResult(trimmed, failed, 0);
    }

    /// <summary>
    /// Purge the standby memory list. Requires SeProfileSingleProcessPrivilege.
    /// </summary>
    public bool PurgeStandbyList()
    {
        try
        {
            NativeMethods.EnablePrivilege(NativeMethods.SE_PROF_SINGLE_PROCESS_NAME);

            int command = (int)NativeMethods.SYSTEM_MEMORY_LIST_COMMAND.MemoryPurgeStandbyList;
            int status = NativeMethods.NtSetSystemInformation(
                NativeMethods.SystemMemoryListInformation,
                ref command,
                Marshal.SizeOf<int>());

            if (status == 0)
            {
                Logger.Info("Standby list purged successfully.");
                return true;
            }

            Logger.Warn($"NtSetSystemInformation returned NTSTATUS 0x{status:X8}");
            return false;
        }
        catch (Exception ex)
        {
            Logger.Error("Failed to purge standby list", ex);
            return false;
        }
    }

    /// <summary>
    /// Full RAM optimisation: trim working sets + purge standby.
    /// </summary>
    public RamCleanupResult FullCleanup()
    {
        var result = TrimWorkingSets();
        var purged = PurgeStandbyList();
        return result with { StandbyPurged = purged ? 1 : 0 };
    }

    /// <summary>
    /// Returns current memory statistics.
    /// </summary>
    public static (ulong totalMB, ulong availMB, uint loadPercent) GetMemoryStatus()
    {
        var mem = new NativeMethods.MEMORYSTATUSEX { dwLength = (uint)Marshal.SizeOf<NativeMethods.MEMORYSTATUSEX>() };
        NativeMethods.GlobalMemoryStatusEx(ref mem);
        return (mem.ullTotalPhys / 1048576, mem.ullAvailPhys / 1048576, mem.dwMemoryLoad);
    }
}

public record struct RamCleanupResult(int TrimmedCount, int FailedCount, int StandbyPurged);