using System.Runtime.CompilerServices;

namespace System
{
	public enum GCCollectionMode
	{
		Default = 0,
		Forced = 1,
		Optimized = 2
	}

	public enum GCNotificationStatus
	{
		Succeeded = 0,
		Failed = 1,
		Canceled = 2,
		Timeout = 3,
		NotApplicable = 4
	}

	public static partial class GC
	{
		[MethodImplAttribute (MethodImplOptions.InternalCall)]
		extern static int GetCollectionCount (int generation);

		[MethodImplAttribute (MethodImplOptions.InternalCall)]
		extern static int GetMaxGeneration ();

		[MethodImplAttribute (MethodImplOptions.InternalCall)]
		extern static void InternalCollect (int generation);

		[MethodImplAttribute (MethodImplOptions.InternalCall)]
		extern static void RecordPressure (long bytesAllocated);

		// TODO: Move following to ConditionalWeakTable
		[MethodImplAttribute (MethodImplOptions.InternalCall)]
		internal extern static void register_ephemeron_array (Ephemeron[] array);

		[MethodImplAttribute (MethodImplOptions.InternalCall)]
		extern static object get_ephemeron_tombstone ();

		internal static readonly object EPHEMERON_TOMBSTONE = get_ephemeron_tombstone ();

		[MethodImplAttribute (MethodImplOptions.InternalCall)]
		public static extern long GetAllocatedBytesForCurrentThread ();

		public static long GetTotalAllocatedBytes (bool precise = false) => 0;

		public static void AddMemoryPressure (long bytesAllocated)
		{
			if (bytesAllocated <= 0)
				throw new ArgumentOutOfRangeException (nameof (bytesAllocated), SR.ArgumentOutOfRange_NeedPosNum);
			if (IntPtr.Size == 4 && bytesAllocated > Int32.MaxValue)
				throw new ArgumentOutOfRangeException (nameof (bytesAllocated), SR.ArgumentOutOfRange_MustBeNonNegInt32);
			RecordPressure (bytesAllocated);
		}

		public static void RemoveMemoryPressure (long bytesAllocated)
		{
			if (bytesAllocated <= 0)
				throw new ArgumentOutOfRangeException (nameof (bytesAllocated), SR.ArgumentOutOfRange_NeedPosNum);
			if (IntPtr.Size == 4 && bytesAllocated > Int32.MaxValue)
				throw new ArgumentOutOfRangeException (nameof (bytesAllocated), SR.ArgumentOutOfRange_MustBeNonNegInt32);
			RecordPressure (-bytesAllocated);
		}

		[MethodImplAttribute(MethodImplOptions.InternalCall)]
		public static extern int GetGeneration (object obj);

		public static void Collect (int generation)
		{
			Collect (generation, GCCollectionMode.Default);
		}

		public static void Collect ()
		{
			InternalCollect (MaxGeneration);
		}

		public static void Collect (int generation, GCCollectionMode mode) => Collect (generation, mode, true);

		public static void Collect (int generation, GCCollectionMode mode, bool blocking) => Collect (generation, mode, blocking, false);

		public static void Collect (int generation, GCCollectionMode mode, bool blocking, bool compacting)
		{
			if (generation < 0)
				throw new ArgumentOutOfRangeException (nameof (generation), "generation", SR.ArgumentOutOfRange_GenericPositive);
			if ((mode < GCCollectionMode.Default) || (mode > GCCollectionMode.Optimized))
				throw new ArgumentOutOfRangeException (nameof (mode), SR.ArgumentOutOfRange_Enum);

			InternalCollect (generation);
		}

		public static int CollectionCount (int generation)
		{
			if (generation < 0)
				throw new ArgumentOutOfRangeException (nameof (generation), SR.ArgumentOutOfRange_GenericPositive);
			return GetCollectionCount (generation);
		}

		[MethodImplAttribute (MethodImplOptions.NoInlining)] // disable optimizations
		public static void KeepAlive (object obj)
		{
		}

		public static int GetGeneration (WeakReference wo)
		{
			object obj = wo.Target;
			if (obj == null)
				throw new ArgumentException ();
			return GetGeneration (obj);
		}

		public static int MaxGeneration {
			get {
				return GetMaxGeneration ();
			}
		}

		[MethodImplAttribute (MethodImplOptions.InternalCall)]
		public static extern void WaitForPendingFinalizers ();

		[MethodImplAttribute(MethodImplOptions.InternalCall)]
		static extern void _SuppressFinalize (object o);

		public static void SuppressFinalize (object obj)
		{
			if (obj == null)
				throw new ArgumentNullException (nameof (obj));
			_SuppressFinalize (obj);
		}

		[MethodImplAttribute(MethodImplOptions.InternalCall)]
		static extern void _ReRegisterForFinalize (object o);

		public static void ReRegisterForFinalize (object obj)
		{
			if (obj == null)
				throw new ArgumentNullException (nameof (obj));
			_ReRegisterForFinalize (obj);
		}

		[MethodImplAttribute (MethodImplOptions.InternalCall)]
		public extern static long GetTotalMemory (bool forceFullCollection);

		static bool _RegisterForFullGCNotification(int maxGenerationPercentage, int largeObjectHeapPercentage)
		{
			throw new NotImplementedException ();
		}

		static bool _CancelFullGCNotification ()
		{
			throw new NotImplementedException ();
		}

		static GCNotificationStatus _WaitForFullGCApproach (int millisecondsTimeout)
		{
			throw new NotImplementedException ();
		}

		static GCNotificationStatus _WaitForFullGCComplete (int millisecondsTimeout)
		{
			throw new NotImplementedException ();
		}

		public static void RegisterForFullGCNotification (int maxGenerationThreshold, int largeObjectHeapThreshold)
		{
			if ((maxGenerationThreshold <= 0) || (maxGenerationThreshold >= 100))
				throw new ArgumentOutOfRangeException (nameof (maxGenerationThreshold),
													   String.Format (SR.ArgumentOutOfRange_Bounds_Lower_Upper, 1, 99));
			if ((largeObjectHeapThreshold <= 0) || (largeObjectHeapThreshold >= 100))
				throw new ArgumentOutOfRangeException (nameof (largeObjectHeapThreshold),
													   String.Format (SR.ArgumentOutOfRange_Bounds_Lower_Upper, 1, 99));

			if (!_RegisterForFullGCNotification(maxGenerationThreshold, largeObjectHeapThreshold))
				throw new InvalidOperationException (SR.InvalidOperation_NotWithConcurrentGC);
		}

		public static void CancelFullGCNotification ()
		{
			if (!_CancelFullGCNotification ())
				throw new InvalidOperationException (SR.InvalidOperation_NotWithConcurrentGC);
		}

		public static GCNotificationStatus WaitForFullGCApproach ()
		{
			return (GCNotificationStatus)_WaitForFullGCApproach (-1);
		}

		public static GCNotificationStatus WaitForFullGCApproach (int millisecondsTimeout)
		{
			if (millisecondsTimeout < -1)
				throw new ArgumentOutOfRangeException (nameof (millisecondsTimeout), SR.ArgumentOutOfRange_NeedNonNegOrNegative1);

			return _WaitForFullGCApproach (millisecondsTimeout);
		}

		public static GCNotificationStatus WaitForFullGCComplete ()
		{
			return _WaitForFullGCComplete(-1);
		}

		public static GCNotificationStatus WaitForFullGCComplete (int millisecondsTimeout)
		{
			if (millisecondsTimeout < -1)
				throw new ArgumentOutOfRangeException (nameof (millisecondsTimeout), SR.ArgumentOutOfRange_NeedNonNegOrNegative1);
			return _WaitForFullGCComplete (millisecondsTimeout);
		}

		static bool StartNoGCRegion (long totalSize, bool hasLohSize, long lohSize, bool disallowFullBlockingGC)
		{
			throw new NotImplementedException ();
		}

		public static bool TryStartNoGCRegion (long totalSize) => StartNoGCRegion (totalSize, false, 0, false);

		public static bool TryStartNoGCRegion (long totalSize, long lohSize) => StartNoGCRegion (totalSize, true, lohSize, false);

		public static bool TryStartNoGCRegion (long totalSize, bool disallowFullBlockingGC) => StartNoGCRegion (totalSize, false, 0, disallowFullBlockingGC);

		public static bool TryStartNoGCRegion (long totalSize, long lohSize, bool disallowFullBlockingGC) => StartNoGCRegion (totalSize, true, lohSize, disallowFullBlockingGC);

		public static void EndNoGCRegion ()
		{
			throw new NotImplementedException ();
		}

		internal static ulong GetSegmentSize ()
		{
			// coreclr default
			return 1024 * 1024 * 16;
		}

		public static GCMemoryInfo GetGCMemoryInfo ()
		{
			return default;
		}

		internal static T[] AllocateUninitializedArray<T> (int length)
		{
			return new T [length];
		}
	}
}