using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
using System.IO;

namespace BizHawk.Common.BizInvoke
{
	public sealed class MemoryBlock : IDisposable
	{
		/// <summary>
		/// starting address of the memory block
		/// </summary>
		public ulong Start { get; private set; }
		/// <summary>
		/// total size of the memory block
		/// </summary>
		public ulong Size { get; private set; }
		/// <summary>
		/// ending address of the memory block; equal to start + size
		/// </summary>
		public ulong End { get; private set; }

		/// <summary>
		/// handle returned by CreateFileMapping
		/// </summary>
		private IntPtr _handle;

		/// <summary>
		/// true if this is currently swapped in
		/// </summary>
		public bool Active { get; private set; }

		/// <summary>
		/// stores last set memory protection value for each page
		/// </summary>
		private readonly Protection[] _pageData;

		/// <summary>
		/// snapshot for XOR buffer
		/// </summary>
		private byte[] _snapshot;

		public byte[] XorHash { get; private set; }

		/// <summary>
		/// get a page index within the block
		/// </summary>
		private int GetPage(ulong addr)
		{
			if (addr < Start || addr >= End)
				throw new ArgumentOutOfRangeException();

			return (int)((addr - Start) >> WaterboxUtils.PageShift);
		}

		/// <summary>
		/// get a start address for a page index within the block
		/// </summary>
		private ulong GetStartAddr(int page)
		{
			return ((ulong)page << WaterboxUtils.PageShift) + Start;
		}

		/// <summary>
		/// allocate size bytes at any address
		/// </summary>
		/// <param name="size"></param>
		public MemoryBlock(ulong size)
			: this(0, size)
		{
		}

		/// <summary>
		/// allocate size bytes starting at a particular address
		/// </summary>
		/// <param name="start"></param>
		/// <param name="size"></param>
		public MemoryBlock(ulong start, ulong size)
		{
			if (!WaterboxUtils.Aligned(start))
				throw new ArgumentOutOfRangeException();
			if (size == 0)
				throw new ArgumentOutOfRangeException();
			size = WaterboxUtils.AlignUp(size);

			_handle = Kernel32.CreateFileMapping(Kernel32.INVALID_HANDLE_VALUE, IntPtr.Zero,
				Kernel32.FileMapProtection.PageExecuteReadWrite | Kernel32.FileMapProtection.SectionCommit, (uint)(size >> 32), (uint)size, null);

			if (_handle == IntPtr.Zero)
				throw new InvalidOperationException($"{nameof(Kernel32.CreateFileMapping)}() returned NULL");
			Start = start;
			End = start + size;
			Size = size;
			_pageData = new Protection[GetPage(End - 1) + 1];
		}

		/// <summary>
		/// activate the memory block, swapping it in at the specified address
		/// </summary>
		public void Activate()
		{
			if (Active)
				throw new InvalidOperationException("Already active");
			if (Kernel32.MapViewOfFileEx(_handle, Kernel32.FileMapAccessType.Read | Kernel32.FileMapAccessType.Write | Kernel32.FileMapAccessType.Execute,
				0, 0, Z.UU(Size), Z.US(Start)) != Z.US(Start))
			{
				throw new InvalidOperationException($"{nameof(Kernel32.MapViewOfFileEx)}() returned NULL");
			}
			ProtectAll();
			Active = true;
		}

		/// <summary>
		/// deactivate the memory block, removing it from RAM but leaving it immediately available to swap back in
		/// </summary>
		public void Deactivate()
		{
			if (!Active)
				throw new InvalidOperationException("Not active");
			if (!Kernel32.UnmapViewOfFile(Z.US(Start)))
				throw new InvalidOperationException($"{nameof(Kernel32.UnmapViewOfFile)}() returned NULL");
			Active = false;
		}

		/// <summary>
		/// Memory protection constant
		/// </summary>
		public enum Protection : byte
		{
			None, R, RW, RX
		}

		/// <summary>
		/// Get a stream that can be used to read or write from part of the block.  Does not check for or change Protect()!
		/// </summary>
		public Stream GetStream(ulong start, ulong length, bool writer)
		{
			if (start < Start)
				throw new ArgumentOutOfRangeException(nameof(start));
			if (start + length > End)
				throw new ArgumentOutOfRangeException(nameof(length));

			return new MemoryViewStream(!writer, writer, (long)start, (long)length, this);
		}

		/// <summary>
		/// get a stream that can be used to read or write from part of the block.
		/// both reads and writes will be XORed against an earlier recorded snapshot
		/// </summary>
		public Stream GetXorStream(ulong start, ulong length, bool writer)
		{
			if (start < Start)
				throw new ArgumentOutOfRangeException(nameof(start));
			if (start + length > End)
				throw new ArgumentOutOfRangeException(nameof(length));
			if (_snapshot == null)
				throw new InvalidOperationException("No snapshot taken!");

			return new MemoryViewXorStream(!writer, writer, (long)start, (long)length, this, _snapshot, (long)(start - Start));
		}

		/// <summary>
		/// take a snapshot of the entire memory block's contents, for use in GetXorStream
		/// </summary>
		public void SaveXorSnapshot()
		{
			if (_snapshot != null)
				throw new InvalidOperationException("Snapshot already taken");
			if (!Active)
				throw new InvalidOperationException("Not active");

			// temporarily switch the entire block to `R`: in case some areas are unreadable, we don't want
			// that to complicate things
			Kernel32.MemoryProtection old;
			if (!Kernel32.VirtualProtect(Z.UU(Start), Z.UU(Size), Kernel32.MemoryProtection.READONLY, out old))
				throw new InvalidOperationException($"{nameof(Kernel32.VirtualProtect)}() returned FALSE!");

			_snapshot = new byte[Size];
			var ds = new MemoryStream(_snapshot, true);
			var ss = GetStream(Start, Size, false);
			ss.CopyTo(ds);
			XorHash = WaterboxUtils.Hash(_snapshot);

			ProtectAll();
		}

		/// <summary>
		/// take a hash of the current full contents of the block, including unreadable areas
		/// </summary>
		/// <returns></returns>
		public byte[] FullHash()
		{
			if (!Active)
				throw new InvalidOperationException("Not active");
			// temporarily switch the entire block to `R`
			Kernel32.MemoryProtection old;
			if (!Kernel32.VirtualProtect(Z.UU(Start), Z.UU(Size), Kernel32.MemoryProtection.READONLY, out old))
				throw new InvalidOperationException($"{nameof(Kernel32.VirtualProtect)}() returned FALSE!");
			var ret = WaterboxUtils.Hash(GetStream(Start, Size, false));
			ProtectAll();
			return ret;
		}

		private static Kernel32.MemoryProtection GetKernelMemoryProtectionValue(Protection prot)
		{
			Kernel32.MemoryProtection p;
			switch (prot)
			{
				case Protection.None: p = Kernel32.MemoryProtection.NOACCESS; break;
				case Protection.R: p = Kernel32.MemoryProtection.READONLY; break;
				case Protection.RW: p = Kernel32.MemoryProtection.READWRITE; break;
				case Protection.RX: p = Kernel32.MemoryProtection.EXECUTE_READ; break;
				default: throw new ArgumentOutOfRangeException(nameof(prot));
			}
			return p;
		}

		/// <summary>
		/// restore all recorded protections
		/// </summary>
		private void ProtectAll()
		{
			int ps = 0;
			for (int i = 0; i < _pageData.Length; i++)
			{
				if (i == _pageData.Length - 1 || _pageData[i] != _pageData[i + 1])
				{
					var p = GetKernelMemoryProtectionValue(_pageData[i]);
					ulong zstart = GetStartAddr(ps);
					ulong zend = GetStartAddr(i + 1);
					Kernel32.MemoryProtection old;
					if (!Kernel32.VirtualProtect(Z.UU(zstart), Z.UU(zend - zstart), p, out old))
						throw new InvalidOperationException($"{nameof(Kernel32.VirtualProtect)}() returned FALSE!");
					ps = i + 1;
				}
			}
		}

		/// <summary>
		/// set r/w/x protection on a portion of memory.  rounded to encompassing pages
		/// </summary>
		public void Protect(ulong start, ulong length, Protection prot)
		{
			if (length == 0)
				return;
			int pstart = GetPage(start);
			int pend = GetPage(start + length - 1);

			var p = GetKernelMemoryProtectionValue(prot);
			for (int i = pstart; i <= pend; i++)
				_pageData[i] = prot; // also store the value for later use

			if (Active) // it's legal to Protect() if we're not active; the information is just saved for the next activation
			{
				var computedStart = WaterboxUtils.AlignDown(start);
				var computedEnd = WaterboxUtils.AlignUp(start + length);
				var computedLength = computedEnd - computedStart;

				Kernel32.MemoryProtection old;
				if (!Kernel32.VirtualProtect(Z.UU(computedStart),
					Z.UU(computedLength), p, out old))
					throw new InvalidOperationException($"{nameof(Kernel32.VirtualProtect)}() returned FALSE!");
			}
		}

		public void Dispose()
		{
			Dispose(true);
			GC.SuppressFinalize(this);
		}

		private void Dispose(bool disposing)
		{
			if (_handle != IntPtr.Zero)
			{
				if (Active)
					Deactivate();
				Kernel32.CloseHandle(_handle);
				_handle = IntPtr.Zero;
			}
		}

		~MemoryBlock()
		{
			Dispose(false);
		}

		private class MemoryViewStream : Stream
		{
			public MemoryViewStream(bool readable, bool writable, long ptr, long length, MemoryBlock owner)
			{
				_readable = readable;
				_writable = writable;
				_ptr = ptr;
				_length = length;
				_owner = owner;
				_pos = 0;
			}

			private void EnsureNotDisposed()
			{
				if (_owner.Start == 0)
					throw new ObjectDisposedException(nameof(MemoryBlock));
			}

			private MemoryBlock _owner;

			private readonly bool _readable;
			private readonly bool _writable;

			private long _length;
			private long _pos;
			private readonly long _ptr;

			public override bool CanRead => _readable;
			public override bool CanSeek => true;
			public override bool CanWrite => _writable;
			public override void Flush() { }
			public override long Length => _length;

			public override long Position
			{
				get { return _pos; }
				set
				{
					if (value < 0 || value > _length)
						throw new ArgumentOutOfRangeException();
					_pos = value;
				}
			}

			public override int Read(byte[] buffer, int offset, int count)
			{
				if (!_readable)
					throw new InvalidOperationException();
				if (count < 0 || count + offset > buffer.Length)
					throw new ArgumentOutOfRangeException();
				EnsureNotDisposed();
				count = (int)Math.Min(count, _length - _pos);
				Marshal.Copy(Z.SS(_ptr + _pos), buffer, offset, count);
				_pos += count;
				return count;
			}

			public override long Seek(long offset, SeekOrigin origin)
			{
				long newpos;
				switch (origin)
				{
					default:
					case SeekOrigin.Begin:
						newpos = offset;
						break;
					case SeekOrigin.Current:
						newpos = _pos + offset;
						break;
					case SeekOrigin.End:
						newpos = _length + offset;
						break;
				}
				Position = newpos;
				return newpos;
			}

			public override void SetLength(long value)
			{
				throw new InvalidOperationException();
			}

			public override void Write(byte[] buffer, int offset, int count)
			{
				if (!_writable)
					throw new InvalidOperationException();
				if (count < 0 || count + offset > buffer.Length)
					throw new ArgumentOutOfRangeException();
				if (count > _length - _pos)
					throw new ArgumentOutOfRangeException();
				EnsureNotDisposed();
				Marshal.Copy(buffer, offset, Z.SS(_ptr + _pos), count);
				_pos += count;
			}
		}

		private class MemoryViewXorStream : MemoryViewStream
		{
			public MemoryViewXorStream(bool readable, bool writable, long ptr, long length, MemoryBlock owner,
				byte[] initial, long offset)
				: base(readable, writable, ptr, length, owner)
			{
				_initial = initial;
				_offset = (int)offset;
			}

			/// <summary>
			/// the initial data to XOR against for both reading and writing
			/// </summary>
			private readonly byte[] _initial;
			/// <summary>
			/// offset into the XOR data that this stream is representing
			/// </summary>
			private readonly int _offset;

			public override int Read(byte[] buffer, int offset, int count)
			{
				int pos = (int)Position;
				count = base.Read(buffer, offset, count);
				XorTransform(_initial, _offset + pos, buffer, offset, count);
				return count;
			}

			public override void Write(byte[] buffer, int offset, int count)
			{
				int pos = (int)Position;
				if (count < 0 || count + offset > buffer.Length)
					throw new ArgumentOutOfRangeException();
				if (count > Length - pos)
					throw new ArgumentOutOfRangeException();
				// is mutating the buffer passed to Stream.Write kosher?
				XorTransform(_initial, _offset + pos, buffer, offset, count);
				base.Write(buffer, offset, count);
			}

			private static unsafe void XorTransform(byte[] source, int sourceOffset, byte[] dest, int destOffset, int length)
			{
				// we don't do any bounds check because MemoryViewStream.Read and MemoryViewXorStream.Write already did it

				// TODO: C compilers can make this pretty snappy, but can the C# jitter?  Or do we need intrinsics
				fixed (byte* _s = source, _d = dest)
				{
					byte* s = _s + sourceOffset;
					byte* d = _d + destOffset;
					byte* sEnd = s + length;
					while (s < sEnd)
					{
						*d++ ^= *s++;
					}
				}
			}
		}

		private static class Kernel32
		{
			[DllImport("kernel32.dll", SetLastError = true)]
			public static extern bool VirtualProtect(UIntPtr lpAddress, UIntPtr dwSize,
			   MemoryProtection flNewProtect, out MemoryProtection lpflOldProtect);

			[Flags]
			public enum MemoryProtection : uint
			{
				EXECUTE = 0x10,
				EXECUTE_READ = 0x20,
				EXECUTE_READWRITE = 0x40,
				EXECUTE_WRITECOPY = 0x80,
				NOACCESS = 0x01,
				READONLY = 0x02,
				READWRITE = 0x04,
				WRITECOPY = 0x08,
				GUARD_Modifierflag = 0x100,
				NOCACHE_Modifierflag = 0x200,
				WRITECOMBINE_Modifierflag = 0x400
			}

			[DllImport("kernel32.dll", SetLastError = true)]
			public static extern IntPtr CreateFileMapping(
				IntPtr hFile,
				IntPtr lpFileMappingAttributes,
				FileMapProtection flProtect,
				uint dwMaximumSizeHigh,
				uint dwMaximumSizeLow,
				string lpName);

			[Flags]
			public enum FileMapProtection : uint
			{
				PageReadonly = 0x02,
				PageReadWrite = 0x04,
				PageWriteCopy = 0x08,
				PageExecuteRead = 0x20,
				PageExecuteReadWrite = 0x40,
				SectionCommit = 0x8000000,
				SectionImage = 0x1000000,
				SectionNoCache = 0x10000000,
				SectionReserve = 0x4000000,
			}

			[DllImport("kernel32.dll", SetLastError = true)]
			public static extern bool CloseHandle(IntPtr hObject);

			[DllImport("kernel32.dll", SetLastError = true)]
			public static extern bool UnmapViewOfFile(IntPtr lpBaseAddress);

			[DllImport("kernel32.dll")]
			public static extern IntPtr MapViewOfFileEx(IntPtr hFileMappingObject,
			   FileMapAccessType dwDesiredAccess, uint dwFileOffsetHigh, uint dwFileOffsetLow,
			   UIntPtr dwNumberOfBytesToMap, IntPtr lpBaseAddress);

			[Flags]
			public enum FileMapAccessType : uint
			{
				Copy = 0x01,
				Write = 0x02,
				Read = 0x04,
				AllAccess = 0x08,
				Execute = 0x20,
			}

			public static readonly IntPtr INVALID_HANDLE_VALUE = Z.US(0xffffffffffffffff);
		}
	}
}