namespace StoicGoose.Core.Sound
{
	/* Channel 4, supports noise */
	public sealed class SoundChannel4
	{
		const int counterReload = 2048;

		readonly static byte[] noiseLfsrTaps = { 14, 10, 13, 4, 8, 6, 9, 11 };

		ushort counter;
		byte pointer;

		public byte OutputLeft { get; set; }
		public byte OutputRight { get; set; }

		readonly WaveTableReadDelegate waveTableReadDelegate;

		/* REG_SND_CH4_PITCH */
		public ushort Pitch { get; set; }
		/* REG_SND_CH4_VOL */
		public byte VolumeLeft { get; set; }
		public byte VolumeRight { get; set; }
		/* REG_SND_CTRL */
		public bool IsEnabled { get; set; }
		public bool IsNoiseEnabled { get; set; }

		/* REG_SND_NOISE */
		public byte NoiseMode { get; set; }
		public bool NoiseReset { get; set; }
		public bool NoiseEnable { get; set; }
		/* REG_SND_RANDOM */
		public ushort NoiseLfsr { get; set; }

		public SoundChannel4(WaveTableReadDelegate waveTableRead) => waveTableReadDelegate = waveTableRead;

		public void Reset()
		{
			counter = counterReload;
			pointer = 0;
			OutputLeft = OutputRight = 0;

			Pitch = 0;
			VolumeLeft = VolumeRight = 0;
			IsEnabled = false;

			IsNoiseEnabled = false;

			NoiseMode = 0;
			NoiseReset = NoiseEnable = false;
			NoiseLfsr = 0;
		}

		public void Step()
		{
			counter--;
			if (counter == Pitch)
			{
				if (NoiseEnable)
				{
					var tap = noiseLfsrTaps[NoiseMode];
					var noise = (1 ^ (NoiseLfsr >> 7) ^ (NoiseLfsr >> tap)) & 0b1;
					NoiseLfsr = (ushort)(((NoiseLfsr << 1) | noise) & 0x7FFF);
				}

				var data = IsNoiseEnabled ? ((NoiseLfsr & 0b1) * 0x0F) : waveTableReadDelegate((ushort)(pointer >> 1));
				if (!IsNoiseEnabled)
				{
					if ((pointer & 0b1) == 0b1) data >>= 4;
					data &= 0x0F;
				}

				OutputLeft = (byte)(data * VolumeLeft);
				OutputRight = (byte)(data * VolumeRight);

				if (NoiseReset)
				{
					NoiseLfsr = 0;
					OutputLeft = OutputRight = 0;
					NoiseReset = false;
				}

				pointer++;
				pointer &= 0b11111;
				counter = counterReload;
			}
		}
	}
}