using System.IO;

namespace MyNes.Core;

internal class VRC6Sawtooth
{
	private byte AccumRate;

	private int accumClock;

	private byte accumulationRegister;

	private int frequency;

	private int freqTimer;

	private int cycles;

	private bool enabled;

	internal int output;

	internal bool Outputable;

	internal void HardReset()
	{
	}

	private void UpdateFrequency()
	{
		freqTimer = (frequency + 1) * 2;
	}

	internal void Write0(ref byte data)
	{
		AccumRate = (byte)(data & 0x3Fu);
	}

	internal void Write1(ref byte data)
	{
		frequency = (frequency & 0xF00) | data;
		UpdateFrequency();
	}

	internal void Write2(ref byte data)
	{
		frequency = (frequency & 0xFF) | ((data & 0xF) << 8);
		enabled = (data & 0x80) == 128;
		UpdateFrequency();
	}

	internal void ClockSingle()
	{
		if (--cycles > 0)
		{
			return;
		}
		cycles = freqTimer;
		if (enabled)
		{
			accumClock++;
			switch (++accumClock)
			{
			case 2:
			case 4:
			case 6:
			case 8:
			case 10:
			case 12:
				accumulationRegister += AccumRate;
				break;
			case 14:
				accumulationRegister = 0;
				accumClock = 0;
				break;
			}
			if (Outputable)
			{
				output = (accumulationRegister >> 3) & 0x1F;
			}
			else
			{
				output = 0;
			}
		}
		else
		{
			output = 0;
		}
	}

	internal void SaveState(ref BinaryWriter stream)
	{
		stream.Write(AccumRate);
		stream.Write(accumClock);
		stream.Write(accumulationRegister);
		stream.Write(frequency);
		stream.Write(freqTimer);
		stream.Write(cycles);
		stream.Write(enabled);
	}

	internal void LoadState(ref BinaryReader stream)
	{
		AccumRate = stream.ReadByte();
		accumClock = stream.ReadInt32();
		accumulationRegister = stream.ReadByte();
		frequency = stream.ReadInt32();
		freqTimer = stream.ReadInt32();
		cycles = stream.ReadInt32();
		enabled = stream.ReadBoolean();
	}
}