ZXSpectrum48K/Core/Io/TapManager.cs

using System;
using System.Collections.Generic;
using Core.Io;

namespace Core.Io
{
    public class TapManager
    {
        private Queue<byte[]> _blocks = new Queue<byte[]>();
        private byte[] _currentBlock;
        private List<TzxBlock> _tzxBlocks = new List<TzxBlock>();

        // State Machine Tracking
        private enum TapeState { Idle, Pilot, Sync1, Sync2, Data, Pause }
        private TapeState _state = TapeState.Idle;

        public bool EarBit { get; private set; } = false; // The physical audio signal sent to the CPU

        private int _pulseTimer = 0;
        private int _pilotPulsesRemaining = 0;
        private int _byteIndex = 0;
        private int _bitIndex = 0;
        private int _pulseCountForCurrentBit = 0;

        public void LoadTapData(byte[] fileData)
        {
            _blocks.Clear();
            int position = 0;

            while (position < fileData.Length)
            {
                int blockLength = fileData[position] | (fileData[position + 1] << 8);
                position += 2;

                byte[] blockData = new byte[blockLength];
                Array.Copy(fileData, position, blockData, 0, blockLength);
                position += blockLength;

                _blocks.Enqueue(blockData);
            }
        }

        public void Play()
        {
            if (_blocks.Count > 0 && _state == TapeState.Idle)
            {
                LoadNextBlock();
            }
        }

        public void Stop()
        {
            _state = TapeState.Idle;
        }

        private void LoadNextBlock()
        {
            if (_blocks.Count == 0)
            {
                _state = TapeState.Idle;
                return;
            }

            _currentBlock = _blocks.Dequeue();
            _byteIndex = 0;
            _bitIndex = 7; // MSB first
            _pulseCountForCurrentBit = 0;

            // Header blocks (flag 0x00) have longer pilot tones than Data blocks
            bool isHeader = _currentBlock.Length > 0 && _currentBlock[0] == 0;
            _pilotPulsesRemaining = isHeader ? 8063 : 3223;

            _state = TapeState.Pilot;
            _pulseTimer = 2168; // Length of a pilot pulse
            EarBit = false;
        }

        // --- THE ENGINE SYNC ---
        // Call this every time the CPU steps, passing in how many T-States elapsed
        public void Update(int tStatesElapsed)
        {
            if (_state == TapeState.Idle) return;

            _pulseTimer -= tStatesElapsed;

            if (_pulseTimer <= 0)
            {
                EarBit = !EarBit; // Flip the audio square wave
                AdvanceState();
            }
        }

        private void AdvanceState()
        {
            switch (_state)
            {
                case TapeState.Pilot:
                    _pilotPulsesRemaining--;
                    if (_pilotPulsesRemaining > 0)
                    {
                        _pulseTimer += 2168;
                    }
                    else
                    {
                        _state = TapeState.Sync1;
                        _pulseTimer += 667;
                    }
                    break;

                case TapeState.Sync1:
                    _state = TapeState.Sync2;
                    _pulseTimer += 735;
                    break;

                case TapeState.Sync2:
                    _state = TapeState.Data;
                    CalculateNextDataPulse();
                    break;

                case TapeState.Data:
                    _pulseCountForCurrentBit++;
                    if (_pulseCountForCurrentBit < 2)
                    {
                        // A bit requires 2 pulses (one high, one low)
                        CalculateNextDataPulse();
                    }
                    else
                    {
                        // Move to next bit
                        _pulseCountForCurrentBit = 0;
                        _bitIndex--;

                        if (_bitIndex < 0)
                        {
                            // Move to next byte
                            _bitIndex = 7;
                            _byteIndex++;

                            if (_byteIndex >= _currentBlock.Length)
                            {
                                // Block finished! 1 second pause before the next block
                                _state = TapeState.Pause;
                                _pulseTimer += 3500000;
                                return;
                            }
                        }
                        CalculateNextDataPulse();
                    }
                    break;
                //case TapeState.Pause:
                //    // The .TAP Format Auto-Stop Heuristic:
                //    if (_currentBlock != null && _currentBlock.Length > 0 && _currentBlock[0] == 0x00)
                //    {
                //        // 1. It was a Header block. The ROM is waiting for the Data right now! Keep spinning.
                //        LoadNextBlock();
                //    }
                //    else
                //    {
                //        // 2. It was a Data block (or custom). The "file" is done. 
                //        // Auto-Stop the tape deck so we don't accidentally play the next level into the void.
                //        _state = TapeState.Idle;
                //        _currentBlock = null;
                //    }
                //    break;
                case TapeState.Pause:
                    _state = TapeState.Idle;
                    LoadNextBlock();
                    break;
            }
        }

        private void CalculateNextDataPulse()
        {
            // Extract the current bit from the current byte
            bool isBitOne = (_currentBlock[_byteIndex] & (1 << _bitIndex)) != 0;

            // Bit 0 = 855 T-States, Bit 1 = 1710 T-States
            _pulseTimer += isBitOne ? 1710 : 855;
        }

        // --- FAST LOAD METHODS (For ROM Hijack) ---
        //public byte[] GetNextBlock()
        //{
        //    return _blocks.Count > 0 ? _blocks.Dequeue() : null;
        //}

        //public bool HasBlocks => _blocks.Count > 0;
        // Change this line:
        //public bool HasBlocks => _blocks.Count > 0 || _currentBlock != null;
        // Only consider _currentBlock valid if we are actively playing it!
        public bool HasBlocks => _blocks.Count > 0 || (_currentBlock != null && _state != TapeState.Idle && _state != TapeState.Pause);

        public byte[] GetNextBlock()
        {
            // Yank the current block ONLY if it is actively playing
            if (_currentBlock != null && _state != TapeState.Idle && _state != TapeState.Pause)
            {
                byte[] blockToReturn = _currentBlock;
                _state = TapeState.Idle; // Ensure the tape deck is stopped
                _currentBlock = null;
                return blockToReturn;
            }

            // Otherwise, pull directly from the unplayed queue
            _state = TapeState.Idle; // Stop the tape deck just in case
            _currentBlock = null;
            return _blocks.Count > 0 ? _blocks.Dequeue() : null;
        }

        public void LoadTzxData(List<TzxBlock> blocks)
        {
            _tzxBlocks = blocks;

            // Just to prove it works before we build the State Machine!
            System.Diagnostics.Debug.WriteLine($"Successfully loaded {_tzxBlocks.Count} TZX blocks!");
        }
    }
}