#!/usr/bin/env python3
# Convert PDP-8 .rim format files to ILDEC .oct format
# Created by Luxferre in 2026, released into the public domain

import sys

def print_error(msg):
  sys.stderr.write(f"Error: {msg}\n")

def convert_rim_to_oct(input_path, output_path):
  # Initialize memory to 0
  memory = [0] * 4096

  try:
    with open(input_path, "rb") as f:
      raw_data = f.read()
  except Exception as e:
    print_error(f"Failed to read input file '{input_path}': {e}")
    return False

  # Filter out bytes with MSB set (bit 7)
  data = [b for b in raw_data if not (b & 0x80)]

  i = 0
  words_loaded = 0
  while i < len(data) - 1:
    word = ((data[i] & 0x3F) << 6) | (data[i+1] & 0x3F)
    if data[i] & 0x40 and i + 3 < len(data):
      addr = word
      val = ((data[i+2] & 0x3F) << 6) | (data[i+3] & 0x3F)
      memory[addr] = val
      words_loaded += 1
      i += 4
    else:
      i += 2

  # Output to .oct format
  try:
    with open(output_path, 'w') as f:
      for addr in range(4096):
        if memory[addr] != 0:
          f.write(f"{addr:04o}: {memory[addr]:04o}\n")
  except Exception as e:
    print_error(f"Failed to write output file: {e}")
    return False

  print(f"Successfully converted '{input_path}' to '{output_path}' ({words_loaded} words loaded).")
  return True

def main():
  args = sys.argv if hasattr(sys, 'argv') else []
  if len(args) < 2 or len(args) > 3:
    print("Usage: python3 rim2oct.py <input_rim_file> [output_oct_file]")
    sys.exit(1)

  input_path = args[1]
  if len(args) == 3:
    output_path = args[2]
  else:
    # Generate default output name by replacing extension with .oct
    dot_idx = input_path.rfind('.')
    slash_idx = max(input_path.rfind('/'), input_path.rfind('\\'))
    if dot_idx > slash_idx:
      output_path = input_path[:dot_idx] + ".oct"
    else:
      output_path = input_path + ".oct"

  success = convert_rim_to_oct(input_path, output_path)
  if not success:
    sys.exit(1)

if __name__ == '__main__':
  main()