using System;

namespace Core.Audio
{
    public class Ay38912
    {
        private readonly byte[] _registers = new byte[16];
        private byte _selectedRegister = 0;

        // The AY-3-8912 uses logarithmic volume, not linear! 
        // This table converts the 0-15 register value into a precise float multiplier.
        private readonly float[] _volumeTable = {
            0.0000f, 0.0137f, 0.0205f, 0.0291f, 0.0423f, 0.0618f, 0.0847f, 0.1369f,
            0.1691f, 0.2647f, 0.3527f, 0.4499f, 0.5704f, 0.6873f, 0.8482f, 1.0000f
        };

        // --- Hardware Port Intercepts ---
        public void SelectRegister(byte register)
        {
            _selectedRegister = (byte)(register & 0x0F); // Only 16 registers exist
        }

        public void WriteRegister(byte value)
        {
            _registers[_selectedRegister] = value;
        }

        public byte ReadRegister()
        {
            return _registers[_selectedRegister];
        }

        // --- Audio Math Generators ---

        // The AY clock on a Spectrum 128 is 1.7734 MHz. 
        // The chip divides this by 16 internally, giving a base clock of ~110,837 Hz.
        private float GetFrequency(int registerLow, int registerHigh)
        {
            int period = _registers[registerLow] | ((_registers[registerHigh] & 0x0F) << 8);
            if (period == 0) return 0f; // Prevent divide-by-zero
            return 110837.5f / period;
        }

        private float GetVolume(int volumeRegister)
        {
            byte vol = _registers[volumeRegister];

            // Bit 4 indicates if the channel is using the hardware Envelope generator.
            // For Version 1 of our chip, if the envelope is active, we will just 
            // output half volume so the game doesn't go silent!
            if ((vol & 0x10) != 0)
            {
                return 0.5f;
            }

            return _volumeTable[vol & 0x0F];
        }

        // --- Public Data for your Audio Engine ---
        public float FreqA => GetFrequency(0, 1);
        public float FreqB => GetFrequency(2, 3);
        public float FreqC => GetFrequency(4, 5);

        // Register 7 is the Mixer. Bit 0, 1, and 2 turn the tone channels OFF when set to 1.
        public float VolA => (_registers[7] & 0x01) == 0 ? GetVolume(8) : 0f;
        public float VolB => (_registers[7] & 0x02) == 0 ? GetVolume(9) : 0f;
        public float VolC => (_registers[7] & 0x04) == 0 ? GetVolume(10) : 0f;
    }
}