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

namespace Essgee.Emulation.Audio
{
	public partial class DMGAudio
	{
		public class Noise : IDMGAudioChannel
		{
			static readonly int[] divisors = new int[]
			{
				8, 16, 32, 48, 64, 80, 96, 112
			};

			// NR41
			byte lengthLoad;

			// NR42
			byte envelopeStartingVolume, envelopePeriodReload;
			bool envelopeAddMode;

			// NR43
			byte clockShift, divisorCode;
			bool lfsrWidthMode;

			// NR44
			bool trigger, lengthEnable;

			//

			// Noise
			int noiseCounter;
			ushort lfsr;

			// Envelope
			int volume, envelopeCounter;
			bool isEnvelopeUpdateEnabled;

			// Misc
			bool isChannelEnabled, isDacEnabled;
			int lengthCounter;

			public int OutputVolume { get; private set; }

			public bool IsActive { get { return lengthCounter != 0; } }

			public Noise()
			{
				//
			}

			public void Reset()
			{
				noiseCounter = 0;
				lfsr = 0;

				volume = 15;
				envelopeCounter = 0;
				isEnvelopeUpdateEnabled = false;

				isChannelEnabled = isDacEnabled = false;
				lengthCounter = 0;

				OutputVolume = volume;
			}

			public void LengthCounterClock()
			{
				if (lengthCounter > 0 && lengthEnable)
				{
					lengthCounter--;
					if (lengthCounter == 0)
						isChannelEnabled = false;
				}
			}

			public void SweepClock()
			{
				throw new Exception("Channel type does not support sweep");
			}

			public void VolumeEnvelopeClock()
			{
				envelopeCounter--;
				if (envelopeCounter == 0)
				{
					envelopeCounter = envelopePeriodReload;

					if (isEnvelopeUpdateEnabled)
					{
						var newVolume = volume;
						if (envelopeAddMode) newVolume++;
						else newVolume--;

						if (newVolume >= 0 && newVolume <= 15)
							volume = newVolume;
						else
							isEnvelopeUpdateEnabled = false;
					}
				}
			}

			public void Step()
			{
				if (!isChannelEnabled) return;

				noiseCounter--;
				if (noiseCounter == 0)
				{
					noiseCounter = divisors[divisorCode] << clockShift;

					var result = (lfsr & 0b1) ^ ((lfsr >> 1) & 0b1);
					lfsr = (ushort)((lfsr >> 1) | (result << 14));

					if (lfsrWidthMode)
						lfsr = (ushort)((lfsr & 0b10111111) | (result << 6));
				}

				OutputVolume = isDacEnabled && ((lfsr & 0b1) == 0) ? volume : 0;
			}

			private void Trigger()
			{
				isChannelEnabled = true;

				if (lengthCounter == 0) lengthCounter = 64;

				noiseCounter = divisors[divisorCode] << clockShift;
				volume = envelopeStartingVolume;
				envelopeCounter = envelopePeriodReload;
				isEnvelopeUpdateEnabled = true;

				lfsr = 0x7FFF;
			}

			public void WritePort(byte port, byte value)
			{
				switch (port)
				{
					case 0:
						break;

					case 1:
						lengthLoad = (byte)((value >> 0) & 0b111111);

						lengthCounter = 64 - lengthLoad;
						break;

					case 2:
						envelopeStartingVolume = (byte)((value >> 4) & 0b1111);
						envelopeAddMode = ((value >> 3) & 0b1) == 0b1;
						envelopePeriodReload = (byte)((value >> 0) & 0b111);

						isDacEnabled = ((value >> 3) & 0b11111) != 0;
						break;

					case 3:
						clockShift = (byte)((value >> 4) & 0b1111);
						lfsrWidthMode = ((value >> 3) & 0b1) == 0b1;
						divisorCode = (byte)((value >> 0) & 0b111);
						break;

					case 4:
						trigger = ((value >> 7) & 0b1) == 0b1;
						lengthEnable = ((value >> 6) & 0b1) == 0b1;

						if (trigger) Trigger();
						break;
				}
			}

			public byte ReadPort(byte port)
			{
				switch (port)
				{
					case 0:
						return 0xFF;

					case 1:
						return 0xFF;

					case 2:
						return (byte)(
							(envelopeStartingVolume << 4) |
							(envelopeAddMode ? (1 << 3) : 0) |
							(envelopePeriodReload << 0));

					case 3:
						return (byte)(
							(clockShift << 4) |
							(lfsrWidthMode ? (1 << 3) : 0) |
							(divisorCode << 0));

					case 4:
						return (byte)(
							0xBF |
							(lengthEnable ? (1 << 6) : 0));

					default:
						return 0xFF;
				}
			}

			public void WriteWaveRam(byte offset, byte value)
			{
				throw new Exception("Channel type does have Wave RAM");
			}

			public byte ReadWaveRam(byte offset)
			{
				throw new Exception("Channel type does have Wave RAM");
			}
		}
	}
}