RomBytesService.cs

// © Mike Murphy

using EMU7800.Core;
using EMU7800.Services.Dto;
using System;
using System.Security.Cryptography;
using System.Text;

namespace EMU7800.Services;

public class RomBytesService
{
    #region Fields

    const string
        SPECIALBINARY_BIOS78_NTSC_MD5           = "0763f1ffb006ddbe32e52d497ee848ae",
        SPECIALBINARY_BIOS78_NTSC_ALTERNATE_MD5 = "b32526ea179dc9ab9b2e5f8a2662b298",
        SPECIALBINARY_BIOS78_PAL_MD5            = "397bb566584be7b9764e7a68974c4263",
        SPECIALBINARY_HSC78_MD5                 = "c8a73288ab97226c52602204ab894286"
        ;

    const int
        A78FILE_HEADER_SIZE = 0x80,
        A78VERSION          = 0,
        A78CARTSIZE         = 0x31,
        A78CARTTYPE         = 0x35,
        A78TVTYPE           = 0x39,
        A78SAVEDATA         = 0x3a,
        A78XMREQ            = 0x3f
        ;

    static readonly MD5 MD5 = MD5.Create();
    static readonly byte[] Atari7800Tag = [0x41, 0x54, 0x41, 0x52, 0x49, 0x37, 0x38, 0x30, 0x30, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00];
    static readonly uint[] HexStringLookup = CreateHexStringLookupTable();

    #endregion

    public static bool IsA78Format(byte[] bytes)
    {
        if (bytes == null || bytes.Length < A78FILE_HEADER_SIZE)
        {
            return false;
        }

        for (var i = 0; i < Atari7800Tag.Length; i++)
        {
            if (Atari7800Tag[i] != bytes[1 + i])
            {
                if (Atari7800Tag[i] == 0 && bytes[1 + i] == 0x20)
                {
                    continue;
                }
                return false;
            }
        }

        // Not required for identification:
        // at offset 0x64, ACTUAL CART DATA STARTS HERE

        return true;
    }

    public static GameProgramInfo ToGameProgramInfoFromA78Format(byte[] bytes)
    {
        if (bytes == null || bytes.Length < 0x40)
            bytes = new byte[0x40];

        var version  = bytes[A78VERSION];
        var title    = Encoding.UTF8.GetString(bytes, 0x11, 0x20).Trim('\0');
        var cartSize = (bytes[A78CARTSIZE] << 24) | (bytes[A78CARTSIZE+1] << 16) | (bytes[A78CARTSIZE+2] << 8) | bytes[A78CARTSIZE+3];
        var cartType = To78CartType(cartSize, bytes[A78CARTTYPE], bytes[A78CARTTYPE+1]);

        var tvType   = bytes[A78TVTYPE];
        var saveData = version >= 2 ? bytes[A78SAVEDATA] : (byte)0;
        var xmReq    = bytes[A78XMREQ];

        var machineType
            = tvType == 0 && xmReq    == 1 ? MachineType.A7800NTSCxm :
              tvType == 1 && xmReq    == 1 ? MachineType.A7800PALxm :
              tvType == 0 && saveData == 1 ? MachineType.A7800NTSChsc :
              tvType == 1 && saveData == 1 ? MachineType.A7800PALhsc :
              tvType == 0                  ? MachineType.A7800NTSC :
              tvType == 1                  ? MachineType.A7800PAL :
              MachineType.Unknown;

        return new()
        {
            Title       = title,
            MachineType = machineType,
            CartType    = cartType,
            LController = ToController(bytes[0x37]),
            RController = ToController(bytes[0x38]),
        };

        static Controller ToController(byte b)
            => b switch {
                0 => Controller.None,
                1 => Controller.ProLineJoystick,
                2 => Controller.Lightgun,
                _ => Controller.None
            };
    }

    public static byte[] RemoveA78HeaderIfNecessary(byte[] bytes)
    {
        if (!IsA78Format(bytes))
            return bytes;

        var romBytes = new byte[bytes.Length - A78FILE_HEADER_SIZE];
        Buffer.BlockCopy(bytes, A78FILE_HEADER_SIZE, romBytes, 0, romBytes.Length);
        return romBytes;
    }

    public static string ToMD5Key(byte[] bytes)
        => ToHex(MD5.ComputeHash(RemoveA78HeaderIfNecessary(bytes ?? [])));

    public static SpecialBinaryType ToSpecialBinaryType(string md5key)
    {
        if (string.IsNullOrWhiteSpace(md5key))
            return SpecialBinaryType.None;
        if (md5key.Equals(SPECIALBINARY_BIOS78_NTSC_MD5, StringComparison.OrdinalIgnoreCase))
            return SpecialBinaryType.Bios7800Ntsc;
        if (md5key.Equals(SPECIALBINARY_BIOS78_NTSC_ALTERNATE_MD5, StringComparison.OrdinalIgnoreCase))
            return SpecialBinaryType.Bios7800NtscAlternate;
        if (md5key.Equals(SPECIALBINARY_BIOS78_PAL_MD5, StringComparison.OrdinalIgnoreCase))
            return SpecialBinaryType.Bios7800Pal;
        if (md5key.Equals(SPECIALBINARY_HSC78_MD5, StringComparison.OrdinalIgnoreCase))
            return SpecialBinaryType.Hsc7800;
        return SpecialBinaryType.None;
    }

    public static CartType InferCartTypeFromSize(MachineType machineType, int romByteCount)
        => MachineTypeUtil.Is2600(machineType) ? romByteCount switch
        {
             2048 => CartType.A2K,
             4096 => CartType.A4K,
             8192 => CartType.A8K,
            16384 => CartType.A16K,
            32768 => CartType.A32K,
            _     => CartType.Unknown,
        }
        : MachineTypeUtil.Is7800(machineType) ? romByteCount switch
        {
             8192 => CartType.A7808,
            16384 => CartType.A7816,
            32768 => CartType.A7832,
            49152 => CartType.A7848,
            _     => CartType.Unknown,
        }
        : CartType.Unknown;

    public static void DumpBin(string path, Action<string> printLineFn)
    {
        printLineFn(@$"
File: {path}");

        byte[] bytes;
        try
        {
            bytes = System.IO.File.ReadAllBytes(path);
        }
        catch (Exception ex)
        {
            printLineFn($"Unable to read ROM: {ex.GetType().Name}: {ex.Message}");
            return;
        }

        var isA78Format = IsA78Format(bytes);

        if (isA78Format)
        {
            var gpi = ToGameProgramInfoFromA78Format(bytes);
            printLineFn(@$"
A78 : Title           : {gpi.Title}
      MachineType     : {MachineTypeUtil.ToString(gpi.MachineType)}
      CartType        : {CartTypeUtil.ToString(gpi.CartType)} ({CartTypeUtil.ToCartTypeWordString(gpi.CartType)})
      Left Controller : {ControllerUtil.ToString(gpi.LController)}
      Right Controller: {ControllerUtil.ToString(gpi.RController)}
      Header Version  : {ToHex(bytes[A78VERSION])}
      TV HSC XM       : {ToHex(bytes[A78TVTYPE])} {ToHex(bytes[A78SAVEDATA])} {ToHex(bytes[A78XMREQ])}
      Cart Type       : {ToHex(bytes[A78CARTTYPE+1])} {ToHex(bytes[A78CARTTYPE])}
              pokeyAt4k={(bytes[A78CARTTYPE+1] & (1 << 0)) != 0}
              superGame={(bytes[A78CARTTYPE+1] & (1 << 1)) != 0}
       superGameRamAt4k={(bytes[A78CARTTYPE+1] & (1 << 2)) != 0}
                romAt4k={(bytes[A78CARTTYPE+1] & (1 << 3)) != 0}
                bankset={(bytes[A78CARTTYPE+1] & (1 << 4)) != 0}
             banksetram={(bytes[A78CARTTYPE+1] & (1 << 5)) != 0}
            pokeyAt0450={(bytes[A78CARTTYPE+1] & (1 << 6)) != 0}
          mirrorRamAt4k={(bytes[A78CARTTYPE+1] & (1 << 7)) != 0}
");
        }

        var rawBytes = RemoveA78HeaderIfNecessary(bytes);
        var md5 = ToMD5Key(rawBytes);

        printLineFn(@$"
MD5 : {md5}
Size: {rawBytes.Length} {(isA78Format ? "(excluding A78 header)" : string.Empty)}");
        static string ToHex(byte b) => "$" + b.ToString("X2");
    }

    #region Helpers

    static CartType To78CartType(int cartSize, byte cartType1, byte cartType2)
    {
        // Absolute, e.g., F18 Hornet
        if ((cartType1 & 1) != 0)
        {
            return CartType.A78AB;
        }

        // Activision, e.g., Double Dragon & Rampage
        if ((cartType1 & 2) != 0)
        {
            return CartType.A78AC;
        }

        var pokeyAt4k          = (cartType2 & (1 << 0)) != 0;
        var superGame          = (cartType2 & (1 << 1)) != 0;
        var superGameRamAt4k   = (cartType2 & (1 << 2)) != 0;
        var romAt4k            = (cartType2 & (1 << 3)) != 0;
      //var bankset            = (cartType2 & (1 << 4)) != 0;
      //var banksetram         = (cartType2 & (1 << 5)) != 0;
        var pokeyAt0450        = (cartType2 & (1 << 6)) != 0;
      //var mirrorRamAt4k      = (cartType2 & (1 << 7)) != 0;

        if (superGame)
        {
            if (romAt4k)
            {
                return pokeyAt0450 ? CartType.A78S9PL : CartType.A78S9;  // supergame_large
            }
            if (superGameRamAt4k)
            {
                return CartType.A78SGR; // supergame_ram
            }
            return pokeyAt4k ? CartType.A78SGP : CartType.A78SG;  // supergame
        }

        if (cartSize <= 0x2000)
            return CartType.A7808;
        if (cartSize <= 0x4000)
            return CartType.A7816;
        if (cartSize <= 0x8000)
            return pokeyAt0450 ? CartType.A7832PL : pokeyAt4k ? CartType.A7832P : CartType.A7832;
        if (cartSize <= 0xC000)
            return CartType.A7848;

        return CartType.Unknown;
    }

    static uint[] CreateHexStringLookupTable()
    {
        var result = new uint[0x100];
        for (int i = 0; i < result.Length; i++)
        {
            var s = i.ToString("x2");
            result[i] = s[0] + ((uint)s[1] << 0x10);
        }
        return result;
    }

    static string ToHex(byte[] bytes)
    {
        var result = new char[bytes.Length * 2];
        for (var i = 0; i < bytes.Length; i++)
        {
            var val = HexStringLookup[bytes[i]];
            result[2 * i] = (char)val;
            result[2 * i + 1] = (char)(val >> 0x10);
        }
        return new string(result, 0, result.Length);
    }

    #endregion
}