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 Square : IDMGAudioChannel
		{
			static readonly bool[,] dutyCycleTable = new bool[,]
			{
				{ false, false, false, false, false, false, false, true,  },	// 00000001    12.5%
				{ true,  false, false, false, false, false, false, true,  },	// 10000001    25%
				{ true,  false, false, false, false, true,  true,  true,  },	// 10000111    50%
				{ false, true,  true,  true,  true,  true,  true,  false, }		// 01111110    75%
			};

			// NR10/20
			byte sweepPeriodReload, sweepShift;
			bool sweepNegate;

			// NR11/21
			byte dutyCycle, lengthLoad;

			// NR12/22
			byte envelopeStartingVolume, envelopePeriodReload;
			bool envelopeAddMode;

			// NR13/23
			byte frequencyLSB;

			// NR14/24
			bool trigger, lengthEnable;
			byte frequencyMSB;

			//

			readonly bool channelSupportsSweep;

			// Sweep
			bool isSweepEnabled;
			int sweepCounter, sweepFreqShadow;

			// Frequency
			int frequencyCounter;

			// Envelope
			int volume, envelopeCounter;
			bool isEnvelopeUpdateEnabled;

			// Misc
			bool isChannelEnabled, isDacEnabled;
			int lengthCounter, dutyCounter;

			public int OutputVolume { get; private set; }

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

			public Square(bool hasSweep)
			{
				channelSupportsSweep = hasSweep;
			}

			public void Reset()
			{
				isSweepEnabled = false;
				sweepCounter = sweepFreqShadow = 0;

				frequencyCounter = 0;

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

				isChannelEnabled = isDacEnabled = false;
				lengthCounter = dutyCounter = 0;

				OutputVolume = volume;
			}

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

			public void SweepClock()
			{
				if (!channelSupportsSweep) return;

				sweepCounter--;
				if (sweepCounter == 0)
				{
					sweepCounter = sweepPeriodReload;

					if (isSweepEnabled && sweepPeriodReload != 0)
					{
						var newFrequency = PerformSweepCalculations();
						if (newFrequency <= 2047 && sweepShift != 0)
						{
							sweepFreqShadow = newFrequency;
							frequencyMSB = (byte)((newFrequency >> 8) & 0b111);
							frequencyLSB = (byte)(newFrequency & 0xFF);
							PerformSweepCalculations();
						}
					}
				}
			}

			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;

				frequencyCounter--;
				if (frequencyCounter == 0)
				{
					frequencyCounter = (2048 - ((frequencyMSB << 8) | frequencyLSB)) * 4;
					dutyCounter++;
					dutyCounter %= 8;
				}

				OutputVolume = isDacEnabled && dutyCycleTable[dutyCycle, dutyCounter] ? volume : 0;
			}

			private void Trigger()
			{
				isChannelEnabled = true;

				if (lengthCounter == 0) lengthCounter = 64;

				frequencyCounter = (2048 - ((frequencyMSB << 8) | frequencyLSB)) * 4;
				volume = envelopeStartingVolume;
				envelopeCounter = envelopePeriodReload;
				isEnvelopeUpdateEnabled = true;

				if (channelSupportsSweep)
				{
					sweepFreqShadow = (frequencyMSB << 8) | frequencyLSB;
					sweepCounter = sweepPeriodReload;
					isSweepEnabled = sweepPeriodReload != 0 || sweepShift != 0;
					if (sweepShift != 0)
						PerformSweepCalculations();
				}
			}

			private int PerformSweepCalculations()
			{
				var newFrequency = sweepFreqShadow >> sweepShift;
				if (sweepNegate) newFrequency = -newFrequency;
				newFrequency += sweepFreqShadow;
				if (newFrequency > 2047) isChannelEnabled = false;
				return newFrequency;
			}

			public void WritePort(byte port, byte value)
			{
				switch (port)
				{
					case 0:
						if (channelSupportsSweep)
						{
							sweepPeriodReload = (byte)((value >> 4) & 0b111);
							sweepNegate = ((value >> 3) & 0b1) == 0b1;
							sweepShift = (byte)((value >> 0) & 0b111);
						}
						break;

					case 1:
						dutyCycle = (byte)((value >> 6) & 0b11);
						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:
						frequencyLSB = value;
						break;

					case 4:
						trigger = ((value >> 7) & 0b1) == 0b1;
						lengthEnable = ((value >> 6) & 0b1) == 0b1;
						frequencyMSB = (byte)((value >> 0) & 0b111);

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

			public byte ReadPort(byte port)
			{
				switch (port)
				{
					case 0:
						if (channelSupportsSweep)
						{
							return (byte)(
								0x80 |
								(sweepPeriodReload << 4) |
								(sweepNegate ? (1 << 3) : 0) |
								(sweepShift << 0));
						}
						else
							return 0xFF;

					case 1:
						return (byte)(
							0x3F |
							(dutyCycle << 6));

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