#!/usr/bin/env python3
#
# (c) 2007 Matt Godbolt.
# Use however you like, as long as you put credit where credit's due.
# Some information obtained from source code from RISC OS Open.
# v0.01 - first release. Doesn't deal with GOTO line numbers.
import getopt
import re
import struct
import sys
# fmt: off
# The list of BBC BASIC V tokens:
# Base tokens, starting at 0x7f
tokens = [
 'OTHERWISE', # 7f
 'AND', 'DIV', 'EOR', 'MOD', 'OR', 'ERROR', 'LINE', 'OFF',
 'STEP', 'SPC', 'TAB(', 'ELSE', 'THEN', '<line>' # TODO
 , 'OPENIN', 'PTR',
 'PAGE', 'TIME', 'LOMEM', 'HIMEM', 'ABS', 'ACS', 'ADVAL', 'ASC',
 'ASN', 'ATN', 'BGET', 'COS', 'COUNT', 'DEG', 'ERL', 'ERR',
 'EVAL', 'EXP', 'EXT', 'FALSE', 'FN', 'GET', 'INKEY', 'INSTR(',
 'INT', 'LEN', 'LN', 'LOG', 'NOT', 'OPENUP', 'OPENOUT', 'PI',
 'POINT(', 'POS', 'RAD', 'RND', 'SGN', 'SIN', 'SQR', 'TAN',
 'TO', 'TRUE', 'USR', 'VAL', 'VPOS', 'CHR$', 'GET$', 'INKEY$',
 'LEFT$(', 'MID$(', 'RIGHT$(', 'STR$', 'STRING$(', 'EOF',
 '<escfn>', '<esccom>', '<escstmt>',
 'WHEN', 'OF', 'ENDCASE', 'ELSE' # ELSE2
 , 'ENDIF', 'ENDWHILE', 'PTR',
 'PAGE', 'TIME', 'LOMEM', 'HIMEM', 'SOUND', 'BPUT', 'CALL', 'CHAIN',
 'CLEAR', 'CLOSE', 'CLG', 'CLS', 'DATA', 'DEF', 'DIM', 'DRAW',
 'END', 'ENDPROC', 'ENVELOPE', 'FOR', 'GOSUB', 'GOTO', 'GCOL', 'IF',
 'INPUT', 'LET', 'LOCAL', 'MODE', 'MOVE', 'NEXT', 'ON', 'VDU',
 'PLOT', 'PRINT', 'PROC', 'READ', 'REM', 'REPEAT', 'REPORT', 'RESTORE',
 'RETURN', 'RUN', 'STOP', 'COLOUR', 'TRACE', 'UNTIL', 'WIDTH', 'OSCLI']
# Referred to as "ESCFN" tokens in the source, starting at 0x8e.
cfnTokens = [
 'SUM', 'BEAT']
# Referred to as "ESCCOM" tokens in the source, starting at 0x8e.
comTokens = [
 'APPEND', 'AUTO', 'CRUNCH', 'DELET', 'EDIT', 'HELP', 'LIST', 'LOAD',
 'LVAR', 'NEW', 'OLD', 'RENUMBER', 'SAVE', 'TEXTLOAD', 'TEXTSAVE', 'TWIN'
 'TWINO', 'INSTALL']
# Referred to as "ESCSTMT", starting at 0x8e.
stmtTokens= [
 'CASE', 'CIRCLE', 'FILL', 'ORIGIN', 'PSET', 'RECT', 'SWAP', 'WHILE',
 'WAIT', 'MOUSE', 'QUIT', 'SYS', 'INSTALL', 'LIBRARY', 'TINT', 'ELLIPSE',
 'BEATS', 'TEMPO', 'VOICES', 'VOICE', 'STEREO', 'OVERLAY']
# fmt: on
def Detokenise(line):
 """Replace all tokens in the line 'line' with their ASCII equivalent."""
 # Internal function used as a callback to the regular expression
 # to replace tokens with their ASCII equivalents.
 def ReplaceFunc(match):
 ext, token = match.groups()
 tokenOrd = ord(token[0])
 if ext: # An extended opcode, CASE/WHILE/SYS etc
 if ext == "\xc6":
 return cfnTokens[tokenOrd - 0x8E]
 if ext == "\xc7":
 return comTokens[tokenOrd - 0x8E]
 if ext == "\xc8":
 return stmtTokens[tokenOrd - 0x8E]
 raise RuntimeError("Bad token")
 else: # Normal token, plus any extra characters
 return tokens[tokenOrd - 127] + token[1:]
 # This regular expression is essentially:
 # (Optional extension token) followed by
 # (REM token followed by the rest of the line)
 # -- this ensures we don't detokenise the REM statement itself
 # OR
 # (any token)
 return re.sub(r"([\xc6-\xc8])?(\xf4.*&#124;[\x7f-\xff])", ReplaceFunc, line)
def ReadLines(data):
 """Returns a list of [line number, tokenised line] from a binary
 BBC BASIC V format file."""
 lines = []
 while True:
 if len(data) < 2: raise RuntimeError("Bad program") if data[0] != "\r": print(data) raise RuntimeError("Bad program") if data[1] == "\xff": break lineNumber, length = struct.unpack(">hB", data[1:4])
 lineData = data[4:length]
 lines.append([lineNumber, lineData])
 data = data[length:]
 return lines
def Decode(data, output):
 """Decode binary data 'data' and write the result to 'output'."""
 lines = ReadLines(data)
 for lineNumber, line in lines:
 lineData = Detokenise(line)
 output.write(lineData + "\n")
if __name__ == "__main__":
 optlist, args = getopt.getopt(sys.argv[1:], "")
 if len(args) != 2:
 print("Usage: %s INPUT OUTPUT" % sys.argv[0])
 sys.exit(1)
 entireFile = open(args[0], "rb").read()
 output = open(args[1], "w")
 Decode(entireFile, output)
 output.close()
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