ZX Spectrum P-File decoder (incomplete)

pfiler.cs

using System;
using System.IO;
using System.Linq;
using System.Text;

internal class Program
{
    static void Main(string[] args)
    {
        var pFileName = "EasyList.P";

        using var reader = new BinaryReader(File.OpenRead(pFileName));

        var version = reader.ReadByte();

        while (reader.BaseStream.Position < reader.BaseStream.Length)
        {
            var fileName = new String(reader.ReadChars(10)).TrimEnd();
            var length = reader.ReadUInt16();
            var param1 = reader.ReadUInt16();
            var param2 = reader.ReadUInt16();
            var unknown = reader.ReadBytes(3);

            Console.WriteLine($"{fileName} length {length} ({param1}/{param2}/{String.Join("", unknown.Select(b => b.ToString("x2")).ToArray())})");

            string text;
            if (fileName.EndsWith("_T"))
                text = GetFixedText(reader, length);
            else
                text = GetBasic(reader, length);
            Console.WriteLine(text);
        }

    }

    static readonly char[] textBuffer = new char[65536];
    static readonly char[] noSpaceAfter = new char[] { ' ', '(', ')', ';', '=', '#', '<', '>', '*', '+', '/', '-' };

    static string GetBasic(BinaryReader reader, int length)
    {
        var sb = new StringBuilder();
        var endOfBasicPosition = reader.BaseStream.Position + length;

        while (reader.BaseStream.Position < endOfBasicPosition)
        {
            var lineNumber = (reader.ReadByte() * 256) + reader.ReadByte();
            if (lineNumber > 9999) break;
            var lineLength = reader.ReadUInt16();

            var endOfLinePosition = reader.BaseStream.Position + lineLength;

            var line = lineNumber.ToString();

            while (reader.BaseStream.Position < endOfLinePosition)
            {
                var b = reader.ReadByte();
                var t = GetToken(b);
                var lastChar = line[line.Length - 1];
                if (noSpaceAfter.Contains(lastChar))
                    line += t.TrimStart();
                else
                    line += t;
            }

            sb.AppendLine(line);
        }

        return sb.ToString();
    }


    static string GetFixedText(BinaryReader reader, int length)
    {
        int i = 0;
        do
        {
            char c = reader.ReadChar();
            switch (c)
            {
                case (char)0x0D:
                    textBuffer[i++] = '\n';
                    break;
                default:
                    textBuffer[i++] = c;
                    break;
            }
        } while (i <= length);

        return new String(textBuffer, 0, i);
    }

    static string GetToken(byte b)
    {
        return b switch
        {
            0x60 => "£",
            127 => "©",
            165 => " RND ",
            166 => " INKEY$ ",
            167 => " PI ",
            168 => " FN ",
            169 => " POINT ",
            170 => " SCREEN$ ",
            171 => " ATTR ",
            172 => " AT ",
            173 => " TAB ",
            174 => " VAL$ ",
            175 => " CODE ",
            176 => " VAL ",
            177 => " LEN ",
            178 => " SIN ",
            179 => " COS ",
            180 => " TAN ",
            181 => " ASN ",
            182 => " ACS ",
            183 => " ATN ",
            184 => " LN ",
            185 => " EXP ",
            186 => " INT ",
            187 => " SQR ",
            188 => " SGN ",
            189 => " ABS ",
            190 => " PEEK ",
            191 => " IN ",
            192 => " USR ",
            193 => " STR$ ",
            194 => " CHR$ ",
            195 => " NOT ",
            196 => " BIN ",
            197 => " OR ",
            198 => " AND ",
            199 => "<= ",
            200 => ">= ",
            201 => "<> ",
            202 => " LINE ",
            203 => " THEN ",
            204 => " TO ",
            205 => " STEP ",
            206 => " DEF FN ",
            207 => " CAT ",
            208 => " FORMAT ",
            209 => " MOVE ",
            210 => " ERASE ",
            211 => " OPEN #",
            212 => " CLOSE #",
            213 => " MERGE ",
            214 => " VERIFY ",
            215 => " BEEP ",
            216 => " CIRCLE ",
            217 => " INK ",
            218 => " PAPER ",
            219 => " FLASH ",
            220 => " BRIGHT ",
            221 => " INVERSE ",
            222 => " OVER ",
            223 => " OUT ",
            224 => " LPRINT ",
            225 => " LLIST ",
            226 => " STOP ",
            227 => " READ ",
            228 => " DATA ",
            229 => " RESTORE ",
            230 => " NEW ",
            231 => " BORDER ",
            232 => " CONTINUE ",
            233 => " DIM ",
            234 => " REM ",
            235 => " FOR ",
            236 => " GO TO ",
            237 => " GO SUB ",
            238 => " INPUT ",
            239 => " LOAD ",
            240 => " LIST ",
            241 => " LET ",
            242 => " PAUSE ",
            243 => " NEXT ",
            244 => " POKE ",
            245 => " PRINT ",
            246 => " PLOT ",
            247 => " RUN ",
            248 => " SAVE ",
            249 => " RANDOMIZE ",
            250 => " IF ",
            251 => " CLS ",
            252 => " DRAW ",
            253 => " CLEAR ",
            254 => " RETURN ",
            255 => " COPY ",
            _ => new String((char)b, 1)
        };
    }
}