ZXSpectrum48K/Core/Io/TzxParser.cs

using Core.Io;
using System;
using System.Collections.Generic;
using System.IO;
using static Core.Io.TurboSpeedBlock;

namespace Core.Io
{
    public class TzxParser
    {
        public static List<TzxBlock> Parse(byte[] fileBytes)
        {
            List<TzxBlock> blocks = new List<TzxBlock>();

            using (MemoryStream ms = new MemoryStream(fileBytes))
            using (BinaryReader br = new BinaryReader(ms))
            {
                // 1. Verify the 10-Byte Header
                // Signature is "ZXTape!" followed by EOF (0x1A)
                byte[] signature = br.ReadBytes(8);
                string sigString = System.Text.Encoding.ASCII.GetString(signature);

                if (sigString != "ZXTape!\x1A")
                    throw new Exception("Invalid TZX Signature! Is this a real TZX file?");

                byte majorVersion = br.ReadByte();
                byte minorVersion = br.ReadByte();

                // 2. Read the blocks until we hit the end of the file
                while (ms.Position < ms.Length)
                {
                    byte blockId = br.ReadByte();

                    switch (blockId)
                    {
                        case 0x10: // Standard Speed Data
                            var stdBlock = new StandardSpeedBlock
                            {
                                PauseAfterMs = br.ReadUInt16(),
                                DataLength = br.ReadUInt16()
                            };
                            stdBlock.Data = br.ReadBytes(stdBlock.DataLength);
                            blocks.Add(stdBlock);
                            break;
                        case 0x11: // Turbo Speed Data Block
                            var turboBlock = new TurboSpeedBlock
                            {
                                PilotPulseLength = br.ReadUInt16(),
                                SyncFirstPulseLength = br.ReadUInt16(),
                                SyncSecondPulseLength = br.ReadUInt16(),
                                ZeroBitPulseLength = br.ReadUInt16(),
                                OneBitPulseLength = br.ReadUInt16(),
                                PilotToneLength = br.ReadUInt16(),
                                UsedBitsInLastByte = br.ReadByte(),
                                PauseAfterMs = br.ReadUInt16()
                            };

                            // Z80 files are Little-Endian. Read 3 bytes and combine them into a 24-bit integer.
                            byte len0 = br.ReadByte();
                            byte len1 = br.ReadByte();
                            byte len2 = br.ReadByte();
                            turboBlock.DataLength = len0 | (len1 << 8) | (len2 << 16);

                            // Read the actual tape data
                            turboBlock.Data = br.ReadBytes(turboBlock.DataLength);

                            blocks.Add(turboBlock);
                            break;
                        case 0x12: // Pure Tone Block
                            blocks.Add(new PureToneBlock
                            {
                                PulseLength = br.ReadUInt16(),
                                PulseCount = br.ReadUInt16()
                            });
                            break;
                        case 0x13: // Pulse Sequence Block
                            var seqBlock = new PulseSequenceBlock();

                            byte rawCount = br.ReadByte();
                            // TZX Spec: A raw count of 0 means 256 pulses!
                            seqBlock.PulseCount = (rawCount == 0) ? 256 : rawCount;

                            seqBlock.Pulses = new ushort[seqBlock.PulseCount];
                            for (int i = 0; i < seqBlock.PulseCount; i++)
                            {
                                seqBlock.Pulses[i] = br.ReadUInt16();
                            }

                            blocks.Add(seqBlock);
                            break;
                        case 0x14: // Pure Data Block
                            var pureData = new PureDataBlock
                            {
                                ZeroBitPulseLength = br.ReadUInt16(),
                                OneBitPulseLength = br.ReadUInt16(),
                                UsedBitsInLastByte = br.ReadByte(),
                                PauseAfterMs = br.ReadUInt16()
                            };

                            // Assemble the 24-bit length
                            byte pdLen0 = br.ReadByte();
                            byte pdLen1 = br.ReadByte();
                            byte pdLen2 = br.ReadByte();
                            pureData.DataLength = pdLen0 | (pdLen1 << 8) | (pdLen2 << 16);

                            pureData.Data = br.ReadBytes(pureData.DataLength);
                            blocks.Add(pureData);
                            break;
                        case 0x20: // Pause / Stop Tape Block
                            blocks.Add(new PauseBlock { PauseDurationMs = br.ReadUInt16() });
                            break;

                        case 0x21: // Group Start Block
                            byte groupNameLength = br.ReadByte();
                            string groupName = System.Text.Encoding.ASCII.GetString(br.ReadBytes(groupNameLength));
                            blocks.Add(new GroupStartBlock { GroupName = groupName });
                            break;

                        case 0x22: // Group End Block
                            // This block has no payload data at all! Just the ID.
                            blocks.Add(new GroupEndBlock());
                            break;
                        case 0x30: // Text Description Block
                            byte textLength30 = br.ReadByte();
                            string description = System.Text.Encoding.ASCII.GetString(br.ReadBytes(textLength30));
                            blocks.Add(new TextDescriptionBlock { Description = description });
                            break;
                        
                        case 0x32: // Archive Info Block
                            var archiveBlock = new ArchiveInfoBlock();

                            // The total length of the block (we read it to advance the stream, 
                            // but the string count is what we actually use to loop)
                            ushort totalLength = br.ReadUInt16();
                            byte stringCount = br.ReadByte();

                            for (int i = 0; i < stringCount; i++)
                            {
                                byte textId = br.ReadByte();
                                byte textLength32 = br.ReadByte();

                                // Read the raw bytes and convert them to an ASCII string
                                string text = System.Text.Encoding.ASCII.GetString(br.ReadBytes(textLength32));

                                archiveBlock.Metadata[textId] = text;
                            }

                            blocks.Add(archiveBlock);
                            break;

                        // TODO: Add cases for 0x11 (Turbo), 0x12 (Tone), 0x13 (Pulses), etc.

                        default:
                            throw new NotImplementedException($"TZX Block ID 0x{blockId:X2} is not supported yet!");
                    }
                }
            }

            return blocks;
        }
    }
}