using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Diagnostics;

using Essgee.Exceptions;
using Essgee.EventArguments;
using Essgee.Utilities;

using static Essgee.Emulation.CPU.SM83;

namespace Essgee.Emulation.Video.Nintendo
{
	public class DMGVideo : IVideo
	{
		protected const int displayActiveWidth = 160;
		protected const int displayActiveHeight = 144;
		protected const int numDisplayPixels = displayActiveWidth * displayActiveHeight;

		protected const int displayTotalHeight = 154;

		protected const int numOamSlots = 40;
		protected const int maxSpritesPerLine = 10;

		protected const int mode2Boundary = 80;
		protected const int mode3Boundary = mode2Boundary + 168;

		protected const string layerBackgroundOptionName = "GraphicsLayersShowBackground";
		protected const string layerWindowOptionName = "GraphicsLayersShowWindow";
		protected const string layerSpritesOptionName = "GraphicsLayersShowSprites";

		protected virtual int numSkippedFramesLcdOn => 4;

		protected Action[] modeFunctions;

		protected readonly MemoryReadDelegate memoryReadDelegate;
		protected readonly RequestInterruptDelegate requestInterruptDelegate;

		public virtual (int X, int Y, int Width, int Height) Viewport => (0, 0, displayActiveWidth, displayActiveHeight);

		public virtual event EventHandler<SizeScreenEventArgs> SizeScreen;
		public virtual void OnSizeScreen(SizeScreenEventArgs e) { SizeScreen?.Invoke(this, e); }

		public virtual event EventHandler<RenderScreenEventArgs> RenderScreen;
		public virtual void OnRenderScreen(RenderScreenEventArgs e) { RenderScreen?.Invoke(this, e); }

		public virtual event EventHandler<EventArgs> EndOfScanline;
		public virtual void OnEndOfScanline(EventArgs e) { EndOfScanline?.Invoke(this, e); }

		//

		protected double clockRate, refreshRate;

		//

		[StateRequired]
		protected byte[,] vram;
		[StateRequired]
		protected byte[] oam;

		// FF40 - LCDC
		protected bool lcdEnable, wndMapSelect, wndEnable, bgWndTileSelect, bgMapSelect, objSize, objEnable, bgEnable;

		// FF41 - STAT
		protected bool lycLyInterrupt, m2OamInterrupt, m1VBlankInterrupt, m0HBlankInterrupt, coincidenceFlag;
		protected byte modeNumber;

		// FF42 - SCY
		protected byte scrollY;
		// FF43 - SCX
		protected byte scrollX;

		// FF44 - LY
		protected byte ly;
		// FF45 - LYC
		protected byte lyCompare;

		// FF46 - DMA
		protected byte oamDmaStart;

		// FF47 - BGP
		protected byte bgPalette;
		// FF48 - OBP0
		protected byte obPalette0;
		// FF49 - OBP1
		protected byte obPalette1;

		// FF4A - WY
		protected byte windowY;
		// FF4B - WX
		protected byte windowX;

		//

		protected int numSpritesOnLine, skipFrames;
		protected bool statIrqSignal, vBlankReady;
		protected int[] spritesOnLine;

		readonly byte[][] colorValuesBgr = new byte[][]
		{
			/*              B     G     R */
			new byte[] { 0xF8, 0xF8, 0xF8 },	/* White */
			new byte[] { 0x9B, 0x9B, 0x9B },	/* Light gray */
			new byte[] { 0x3E, 0x3E, 0x3E },	/* Dark gray */
			new byte[] { 0x1F, 0x1F, 0x1F },	/* Black */
		};

		protected const byte screenUsageEmpty = 0;
		protected const byte screenUsageBackground = 1 << 0;
		protected const byte screenUsageWindow = 1 << 1;
		protected const byte screenUsageSprite = 1 << 2;
		protected byte[,] screenUsageFlags, screenUsageSpriteXCoords, screenUsageSpriteSlots;

		protected int cycleCount, cycleDotPause, currentScanline;
		protected byte[] outputFramebuffer;

		protected int clockCyclesPerLine;

		public bool IsDoubleSpeed { get; set; }

		//

		public (string Name, string Description)[] RuntimeOptions => new (string name, string description)[]
		{
			(layerBackgroundOptionName, "Background"),
			(layerWindowOptionName, "Window"),
			(layerSpritesOptionName, "Sprites"),
		};

		protected bool layerBackgroundForceEnable, layerWindowForceEnable, layerSpritesForceEnable;

		public DMGVideo(MemoryReadDelegate memoryRead, RequestInterruptDelegate requestInterrupt)
		{
			vram = new byte[1, 0x2000];
			oam = new byte[0xA0];

			//

			modeFunctions = new Action[] { StepHBlank, StepVBlank, StepOAMSearch, StepLCDTransfer };

			spritesOnLine = new int[maxSpritesPerLine];

			memoryReadDelegate = memoryRead;
			requestInterruptDelegate = requestInterrupt;

			layerBackgroundForceEnable = true;
			layerWindowForceEnable = true;
			layerSpritesForceEnable = true;
		}

		public object GetRuntimeOption(string name)
		{
			switch (name)
			{
				case layerBackgroundOptionName: return layerBackgroundForceEnable;
				case layerWindowOptionName: return layerWindowForceEnable;
				case layerSpritesOptionName: return layerSpritesForceEnable;
				default: return null;
			}
		}

		public void SetRuntimeOption(string name, object value)
		{
			switch (name)
			{
				case layerBackgroundOptionName: layerBackgroundForceEnable = (bool)value; break;
				case layerWindowOptionName: layerWindowForceEnable = (bool)value; break;
				case layerSpritesOptionName: layerSpritesForceEnable = (bool)value; break;
			}
		}

		public virtual void Startup()
		{
			Reset();

			if (memoryReadDelegate == null) throw new EmulationException("DMGVideo: Memory read delegate is null");
			if (requestInterruptDelegate == null) throw new EmulationException("DMGVideo: Request interrupt delegate is null");

			Debug.Assert(clockRate != 0.0, "Clock rate is zero", "{0} clock rate is not configured", GetType().FullName);
			Debug.Assert(refreshRate != 0.0, "Refresh rate is zero", "{0} refresh rate is not configured", GetType().FullName);
		}

		public virtual void Shutdown()
		{
			//
		}

		public virtual void Reset()
		{
			for (var i = 0; i < vram.GetLength(0); i++) vram[0, i] = 0;
			for (var i = 0; i < oam.Length; i++) oam[i] = 0;

			for (var i = (byte)0x40; i < 0x4C; i++)
			{
				// skip OAM dma
				if (i != 0x46) WritePort(i, 0x00);
			}

			numSpritesOnLine = skipFrames = 0;
			statIrqSignal = vBlankReady = false;

			for (var i = 0; i < spritesOnLine.Length; i++) spritesOnLine[i] = -1;

			ClearScreenUsage();

			cycleCount = cycleDotPause = currentScanline = 0;
		}

		public void SetClockRate(double clock)
		{
			clockRate = clock;

			ReconfigureTimings();
		}

		public void SetRefreshRate(double refresh)
		{
			refreshRate = refresh;

			ReconfigureTimings();
		}

		public virtual void SetRevision(int rev)
		{
			Debug.Assert(rev == 0, "Invalid revision", "{0} revision is invalid; only rev 0 is valid", GetType().FullName);
		}

		protected virtual void ReconfigureTimings()
		{
			/* Calculate cycles/line */
			clockCyclesPerLine = (int)Math.Round((clockRate / refreshRate) / displayTotalHeight);

			/* Create arrays */
			screenUsageFlags = new byte[displayActiveWidth, displayActiveHeight];
			screenUsageSpriteXCoords = new byte[displayActiveWidth, displayActiveHeight];
			screenUsageSpriteSlots = new byte[displayActiveWidth, displayActiveHeight];
			outputFramebuffer = new byte[numDisplayPixels * 4];

			for (var y = 0; y < displayActiveHeight; y++)
				SetLine(y, 0xFF, 0xFF, 0xFF);
		}

		public virtual void Step(int clockCyclesInStep)
		{
			for (var c = 0; c < clockCyclesInStep; c++)
			{
				if (lcdEnable)
				{
					/* LCD enabled, handle LCD modes */
					modeFunctions[modeNumber]();
				}
				else
				{
					/* LCD disabled */
					modeNumber = 0;
					cycleCount = 0;
					cycleDotPause = 0;

					currentScanline = 0;
					ly = 0;
				}
			}
		}

		/* TODO: dot clock pause! -- https://gbdev.io/pandocs/#properties-of-stat-modes
		 * - non-zero (SCX % 8) causes pause of that many dots
		 * - active window causes pause of *at least* 6 dots?
		 * - sprite dot pauses??
		 * - influence of CGB double-speed mode on this?
		 * Required for: 
		 * - GBVideoPlayer2, pixel column alignment & garbage on left screen edge
		 * - snorpung/pocket demo, vertical scroller right edge of scroll area
		 * - Prehistorik Man, scroller alignment (ex. level start "START" text should be centered on screen)
		 * - ...probably more?
		*/

		protected virtual void StepVBlank()
		{
			// TODO: *should* be 4, but Altered Space hangs w/ any value lower than 8?
			if (cycleCount == 8 && vBlankReady)
			{
				requestInterruptDelegate(InterruptSource.VBlank);
				vBlankReady = false;
			}

			/* V-blank */
			cycleCount++;
			if (cycleCount == clockCyclesPerLine) EndVBlank();
		}

		protected virtual void EndVBlank()
		{
			/* End of scanline reached */
			OnEndOfScanline(EventArgs.Empty);
			currentScanline++;
			ly = (byte)currentScanline;

			/* Check for & request STAT interrupts */
			CheckAndRequestStatInterupt();

			if (currentScanline == displayTotalHeight - 1)
			{
				// TODO: specific cycle this happens?

				/* LY reports as 0 on line 153 */
				ly = 0;

				// TODO: verify if STAT/LYC interrupt is supposed to happen here? currently breaks Shantae's sprites if done
				//CheckAndRequestStatInterupt();
			}
			else if (currentScanline == displayTotalHeight)
			{
				/* End of V-blank reached */
				modeNumber = 2;
				currentScanline = 0;
				ly = 0;

				CheckAndRequestStatInterupt();

				ClearScreenUsage();
			}

			cycleCount = 0;
		}

		protected virtual void StepOAMSearch()
		{
			/* OAM search */

			if ((cycleCount % 2) == 0)
			{
				/* Get object Y coord */
				var objIndex = cycleCount >> 1;
				var objY = oam[(objIndex << 2) + 0] - 16;

				/* Check if object is on current scanline & maximum number of objects was not exceeded, then increment counter */
				if (currentScanline >= objY && currentScanline < (objY + (objSize ? 16 : 8)) && numSpritesOnLine < maxSpritesPerLine)
				{
					var objX = oam[(objIndex << 2) + 1] - 8;
					cycleDotPause += 11 - Math.Min(5, (objX + (objX >= windowX ? (255 - windowX) : scrollX)) % 8);  // TODO: correct?
					spritesOnLine[numSpritesOnLine++] = objIndex;
				}
			}

			/* Increment cycle count & check for next LCD mode */
			cycleCount++;
			if (cycleCount == mode2Boundary) EndOAMSearch();
		}

		protected virtual void EndOAMSearch()
		{
			// 1) GBVideoPlayer2 & Prehistorik Man alignment, 2) GBVideoPlayer2 alignment
			cycleDotPause += (6 << (IsDoubleSpeed ? 1 : 0)) + (scrollX % 8);

			modeNumber = 3;
			CheckAndRequestStatInterupt();
		}

		protected virtual void StepLCDTransfer()
		{
			/* Data transfer to LCD */

			/* Render pixels */
			RenderPixel(currentScanline, cycleCount - mode2Boundary - cycleDotPause);

			/* Increment cycle count & check for next LCD mode */
			cycleCount++;
			// 3) snorpung/pocket scroller width
			if (cycleCount == mode3Boundary + cycleDotPause + (wndEnable ? 12 : 0)) EndLCDTransfer();
		}

		protected virtual void EndLCDTransfer()
		{
			modeNumber = 0;
			CheckAndRequestStatInterupt();
		}

		protected virtual void StepHBlank()
		{
			/* H-blank */

			/* Increment cycle count & check for next LCD mode */
			cycleCount++;
			if (cycleCount == clockCyclesPerLine) EndHBlank();
		}

		protected virtual void EndHBlank()
		{
			/* End of scanline reached */
			OnEndOfScanline(EventArgs.Empty);
			currentScanline++;
			ly = (byte)currentScanline;

			CheckAndRequestStatInterupt();

			for (var i = 0; i < spritesOnLine.Length; i++) spritesOnLine[i] = -1;
			numSpritesOnLine = 0;

			if (currentScanline == displayActiveHeight)
			{
				modeNumber = 1;
				CheckAndRequestStatInterupt();

				/* Reached V-blank, request V-blank interrupt */
				vBlankReady = true;

				if (skipFrames > 0) skipFrames--;

				/* Submit screen for rendering */
				OnRenderScreen(new RenderScreenEventArgs(displayActiveWidth, displayActiveHeight, outputFramebuffer.Clone() as byte[]));
			}
			else
			{
				modeNumber = 2;
				CheckAndRequestStatInterupt();
			}

			cycleCount = 0;
			cycleDotPause = 0;
		}

		protected void CheckAndRequestStatInterupt()
		{
			if (!lcdEnable) return;

			var oldSignal = statIrqSignal;
			statIrqSignal = false;

			if (modeNumber == 0 && m0HBlankInterrupt) statIrqSignal = true;
			if (modeNumber == 1 && m1VBlankInterrupt) statIrqSignal = true;
			if (modeNumber == 2 && m2OamInterrupt) statIrqSignal = true;

			coincidenceFlag = (ly == lyCompare);
			if (coincidenceFlag && lycLyInterrupt) statIrqSignal = true;

			if (!oldSignal && statIrqSignal)
				requestInterruptDelegate(InterruptSource.LCDCStatus);
		}

		protected virtual void RenderPixel(int y, int x)
		{
			if (x < 0 || x >= displayActiveWidth || y < 0 || y >= displayActiveHeight) return;

			if (skipFrames > 0)
			{
				SetPixel(y, x, 0xFF, 0xFF, 0xFF);
				return;
			}

			screenUsageFlags[x, y] = screenUsageEmpty;

			if (bgEnable)
			{
				RenderBackground(y, x);
				if (wndEnable) RenderWindow(y, x);
			}
			else
				SetPixel(y, x, 0xFF, 0xFF, 0xFF);

			if (objEnable) RenderSprites(y, x);
		}

		protected virtual void RenderBackground(int y, int x)
		{
			// Get base addresses
			var tileBase = (ushort)(bgWndTileSelect ? 0x0000 : 0x0800);
			var mapBase = (ushort)(bgMapSelect ? 0x1C00 : 0x1800);

			// Calculate tilemap address & get tile
			var yTransformed = (byte)(scrollY + y);
			var xTransformed = (byte)(scrollX + x);
			var mapAddress = mapBase + ((yTransformed >> 3) << 5) + (xTransformed >> 3);
			var tileNumber = vram[0, mapAddress];
			if (!bgWndTileSelect)
				tileNumber = (byte)(tileNumber ^ 0x80);

			// Calculate tile address & get pixel color index
			var tileAddress = tileBase + (tileNumber << 4) + ((yTransformed & 7) << 1);
			var ba = (vram[0, tileAddress + 0] >> (7 - (xTransformed % 8))) & 0b1;
			var bb = (vram[0, tileAddress + 1] >> (7 - (xTransformed % 8))) & 0b1;
			var c = (byte)((bb << 1) | ba);

			// If color is not 0, note that a BG pixel exists here
			if (c != 0)
				screenUsageFlags[x, y] |= screenUsageBackground;

			// Draw pixel
			if (layerBackgroundForceEnable)
				SetPixel(y, x, (byte)((bgPalette >> (c << 1)) & 0x03));
			else
				SetPixel(y, x, (byte)(bgPalette & 0x03));
		}

		protected virtual void RenderWindow(int y, int x)
		{
			// Check if current coords are inside window
			if (y < windowY) return;
			if (x < (windowX - 7)) return;

			// Get base addresses
			var tileBase = (ushort)(bgWndTileSelect ? 0x0000 : 0x0800);
			var mapBase = (ushort)(wndMapSelect ? 0x1C00 : 0x1800);

			// Calculate tilemap address & get tile
			var yTransformed = (byte)(y - windowY);
			var xTransformed = (byte)((7 - windowX) + x);
			var mapAddress = mapBase + ((yTransformed >> 3) << 5) + (xTransformed >> 3);
			var tileNumber = vram[0, mapAddress];
			if (!bgWndTileSelect)
				tileNumber = (byte)(tileNumber ^ 0x80);

			// Calculate tile address & get pixel color index
			var tileAddress = tileBase + (tileNumber << 4) + ((yTransformed & 7) << 1);
			var ba = (vram[0, tileAddress + 0] >> (7 - (xTransformed % 8))) & 0b1;
			var bb = (vram[0, tileAddress + 1] >> (7 - (xTransformed % 8))) & 0b1;
			var c = (byte)((bb << 1) | ba);

			// If color is not 0, note that a Window pixel exists here
			if (c != 0)
				screenUsageFlags[x, y] |= screenUsageWindow;

			// Draw pixel
			if (layerWindowForceEnable)
				SetPixel(y, x, (byte)((bgPalette >> (c << 1)) & 0x03));
			else
				SetPixel(y, x, (byte)(bgPalette & 0x03));
		}

		protected virtual void RenderSprites(int y, int x)
		{
			var objHeight = objSize ? 16 : 8;

			// Iterate over sprite on line
			for (var s = 0; s < numSpritesOnLine; s++)
			{
				var i = spritesOnLine[s];

				// Get sprite Y coord & if sprite is not on current scanline, continue to next slot
				var objY = (short)(oam[(i * 4) + 0] - 16);
				if (y < objY || y >= (objY + objHeight)) continue;

				// Get sprite X coord, tile number & attributes
				var objX = (byte)(oam[(i * 4) + 1] - 8);
				var objTileNumber = oam[(i * 4) + 2];
				var objAttributes = oam[(i * 4) + 3];

				// Extract attributes
				var objFlipY = ((objAttributes >> 6) & 0b1) == 0b1;
				var objFlipX = ((objAttributes >> 5) & 0b1) == 0b1;
				var objPalNumber = (objAttributes >> 4) & 0b1;

				// Iterate over pixels
				for (var px = 0; px < 8; px++)
				{
					// If sprite pixel X coord does not equal current rendering X coord, continue to next pixel
					if (x != (byte)(objX + px)) continue;

					// Calculate tile address
					var xShift = objFlipX ? (px % 8) : (7 - (px % 8));
					var yShift = objFlipY ? (7 - ((y - objY) % 8)) : ((y - objY) % 8);
					if (objSize)
					{
						objTileNumber &= 0xFE;
						if ((objFlipY && y < (objY + 8)) || (!objFlipY && y >= (objY + 8)))
							objTileNumber |= 0x01;
					}
					var tileAddress = (objTileNumber << 4) + (yShift << 1);

					// Get palette & bitplanes
					var pal = objPalNumber == 0 ? obPalette0 : obPalette1;
					var ba = (vram[0, tileAddress + 0] >> xShift) & 0b1;
					var bb = (vram[0, tileAddress + 1] >> xShift) & 0b1;

					// Combine to color index, continue drawing if color is not 0
					var c = (byte)((bb << 1) | ba);
					if (c != 0)
					{
						// If sprite does not have priority i.e. if sprite should not be drawn, continue to next pixel
						if (!HasSpritePriority(y, x, i)) continue;

						screenUsageFlags[x, y] |= screenUsageSprite;
						screenUsageSpriteSlots[x, y] = (byte)i;
						screenUsageSpriteXCoords[x, y] = objX;

						// Draw pixel
						if (layerSpritesForceEnable)
							SetPixel(y, x, (byte)((pal >> (c << 1)) & 0x03));
					}
				}
			}
		}

		protected virtual bool HasSpritePriority(int y, int x, int objSlot)
		{
			// Get new sprite X coord
			var objX = (byte)(oam[(objSlot * 4) + 1] - 8);

			// Get potentially existing sprite X coord and slot
			var prevX = screenUsageSpriteXCoords[x, y];
			var prevSlot = screenUsageSpriteSlots[x, y];

			// If existing sprite has lower X coord -or- both sprites have same X coord BUT existing sprite has lower slot, new sprite does not have priority
			if (prevX < objX || (prevX == objX && prevSlot < objSlot))
				return false;

			// Get new sprite OBJ-to-BG priority attribute
			var objIsBehindBg = ((oam[(objSlot * 4) + 3] >> 7) & 0b1) == 0b1;

			// If new sprite is shown behind BG/Window -and- a BG/Window pixel has already been drawn, new sprite does not have priority
			if (objIsBehindBg &&
				(IsScreenUsageFlagSet(y, x, screenUsageBackground) || IsScreenUsageFlagSet(y, x, screenUsageWindow))) return false;

			// New sprite has priority
			return true;
		}

		protected void SetLine(int y, byte c)
		{
			for (int x = 0; x < displayActiveWidth; x++)
				SetPixel(y, x, c);
		}

		protected void SetLine(int y, byte b, byte g, byte r)
		{
			for (int x = 0; x < displayActiveWidth; x++)
				SetPixel(y, x, b, g, r);
		}

		protected void SetPixel(int y, int x, byte c)
		{
			WriteColorToFramebuffer(c, ((y * displayActiveWidth) + (x % displayActiveWidth)) * 4);
		}

		protected void SetPixel(int y, int x, byte b, byte g, byte r)
		{
			WriteColorToFramebuffer(b, g, r, ((y * displayActiveWidth) + (x % displayActiveWidth)) * 4);
		}

		protected virtual void WriteColorToFramebuffer(byte c, int address)
		{
			outputFramebuffer[address + 0] = colorValuesBgr[c & 0x03][0];
			outputFramebuffer[address + 1] = colorValuesBgr[c & 0x03][1];
			outputFramebuffer[address + 2] = colorValuesBgr[c & 0x03][2];
			outputFramebuffer[address + 3] = 0xFF;
		}

		protected virtual void WriteColorToFramebuffer(byte b, byte g, byte r, int address)
		{
			outputFramebuffer[address + 0] = b;
			outputFramebuffer[address + 1] = g;
			outputFramebuffer[address + 2] = r;
			outputFramebuffer[address + 3] = 0xFF;
		}

		protected virtual void ClearScreenUsage()
		{
			for (var y = 0; y < displayActiveHeight; y++)
			{
				for (var x = 0; x < displayActiveWidth; x++)
				{
					screenUsageFlags[x, y] = screenUsageEmpty;
					screenUsageSpriteXCoords[x, y] = 255;
					screenUsageSpriteSlots[x, y] = numOamSlots;
				}
			}
		}

		protected bool IsScreenUsageFlagSet(int y, int x, byte flag)
		{
			return (screenUsageFlags[x, y] & flag) == flag;
		}

		public virtual byte ReadVram(ushort address)
		{
			if (modeNumber != 3)
				return vram[0, address & (vram.Length - 1)];
			else
				return 0xFF;
		}

		public virtual void WriteVram(ushort address, byte value)
		{
			if (modeNumber != 3)
				vram[0, address & (vram.Length - 1)] = value;
		}

		public virtual byte ReadOam(ushort address)
		{
			if (modeNumber != 2 && modeNumber != 3)
				return oam[address - 0xFE00];
			else
				return 0xFF;
		}

		public virtual void WriteOam(ushort address, byte value)
		{
			if (modeNumber != 2 && modeNumber != 3)
				oam[address - 0xFE00] = value;
		}

		public virtual byte ReadPort(byte port)
		{
			switch (port)
			{
				case 0x40:
					// LCDC
					return (byte)(
						(lcdEnable ? (1 << 7) : 0) |
						(wndMapSelect ? (1 << 6) : 0) |
						(wndEnable ? (1 << 5) : 0) |
						(bgWndTileSelect ? (1 << 4) : 0) |
						(bgMapSelect ? (1 << 3) : 0) |
						(objSize ? (1 << 2) : 0) |
						(objEnable ? (1 << 1) : 0) |
						(bgEnable ? (1 << 0) : 0));

				case 0x41:
					// STAT
					return (byte)(
						0x80 |
						(lycLyInterrupt ? (1 << 6) : 0) |
						(m2OamInterrupt ? (1 << 5) : 0) |
						(m1VBlankInterrupt ? (1 << 4) : 0) |
						(m0HBlankInterrupt ? (1 << 3) : 0) |
						(coincidenceFlag ? (1 << 2) : 0) |
						((modeNumber & 0b11) << 0));

				case 0x42:
					// SCY
					return scrollY;

				case 0x43:
					// SCX
					return scrollX;

				case 0x44:
					// LY
					return ly;

				case 0x45:
					// LYC
					return lyCompare;

				case 0x46:
					// DMA
					return oamDmaStart;

				case 0x47:
					// BGP
					return bgPalette;

				case 0x48:
					// OBP0
					return obPalette0;

				case 0x49:
					// OBP1
					return obPalette1;

				case 0x4A:
					// WY
					return windowY;

				case 0x4B:
					//WX
					return windowX;

				default:
					return 0xFF;
			}
		}

		public virtual void WritePort(byte port, byte value)
		{
			switch (port)
			{
				case 0x40:
					// LCDC
					{
						var newLcdEnable = ((value >> 7) & 0b1) == 0b1;
						if (lcdEnable != newLcdEnable)
						{
							modeNumber = 2;
							currentScanline = 0;
							ly = 0;

							CheckAndRequestStatInterupt();

							if (newLcdEnable)
								skipFrames = numSkippedFramesLcdOn;
						}

						lcdEnable = newLcdEnable;
						wndMapSelect = ((value >> 6) & 0b1) == 0b1;
						wndEnable = ((value >> 5) & 0b1) == 0b1;
						bgWndTileSelect = ((value >> 4) & 0b1) == 0b1;
						bgMapSelect = ((value >> 3) & 0b1) == 0b1;
						objSize = ((value >> 2) & 0b1) == 0b1;
						objEnable = ((value >> 1) & 0b1) == 0b1;
						bgEnable = ((value >> 0) & 0b1) == 0b1;
					}
					break;

				case 0x41:
					// STAT
					lycLyInterrupt = ((value >> 6) & 0b1) == 0b1;
					m2OamInterrupt = ((value >> 5) & 0b1) == 0b1;
					m1VBlankInterrupt = ((value >> 4) & 0b1) == 0b1;
					m0HBlankInterrupt = ((value >> 3) & 0b1) == 0b1;

					CheckAndRequestStatInterupt();

					// TODO: correct?
					if (lcdEnable && modeNumber == 1 && currentScanline != 0)
						requestInterruptDelegate(InterruptSource.LCDCStatus);
					break;

				case 0x42:
					// SCY
					scrollY = value;
					break;

				case 0x43:
					// SCX
					scrollX = value;
					break;

				case 0x44:
					// LY
					break;

				case 0x45:
					// LYC
					lyCompare = value;
					CheckAndRequestStatInterupt();
					break;

				case 0x46:
					// DMA
					oamDmaStart = value;
					for (int src = 0, dst = oamDmaStart << 8; src < 0xA0; src++, dst++)
						oam[src] = memoryReadDelegate((ushort)dst);
					break;

				case 0x47:
					// BGP
					bgPalette = value;
					break;

				case 0x48:
					// OBP0
					obPalette0 = value;
					break;

				case 0x49:
					// OBP1
					obPalette1 = value;
					break;

				case 0x4A:
					// WY
					windowY = value;
					break;

				case 0x4B:
					// WX
					windowX = value;
					break;
			}
		}
	}
}