import argparse
from typing import Optional

def get_next_bit(left: str, center: str, right: str) -> str:
    """Rule 30 implementation:
    111 -> 0
    110 -> 0
    101 -> 0
    100 -> 1
    011 -> 1
    010 -> 1
    001 -> 1
    000 -> 0
    """
    pattern = left + center + right
    rule30_map = {
        "111": "0", "110": "0", "101": "0", "100": "1",
        "011": "1", "010": "1", "001": "1", "000": "0"
    }
    return rule30_map[pattern]

def validate_sequence(bits: str) -> tuple[bool, Optional[int]]:
    """Validate if a sequence follows Rule 30.
    Returns (is_valid, first_error_position)
    """
    if not all(bit in '01' for bit in bits):
        return False, 0
    
    # Pad with zeros for edge cases
    padded = '0' + bits + '0'
    
    for i in range(1, len(bits) + 1):
        expected = get_next_bit(
            padded[i-1], 
            padded[i], 
            padded[i+1]
        )
        if i < len(bits) and bits[i] != expected:
            return False, i
            
    return True, None

def main():
    parser = argparse.ArgumentParser(description='Validate a binary sequence against Rule 30')
    parser.add_argument('file', help='Path to file containing binary sequence')
    args = parser.parse_args()
    
    try:
        with open(args.file, 'r') as f:
            bits = f.read().strip()
            
        is_valid, error_pos = validate_sequence(bits)
        
        if is_valid:
            print("✅ Sequence follows Rule 30")
            return 0
        else:
            print(f"❌ Sequence violates Rule 30 at position {error_pos}")
            return 1
            
    except FileNotFoundError:
        print(f"Error: File {args.file} not found")
        return 2
    except Exception as e:
        print(f"Error: {str(e)}")
        return 3

if __name__ == "__main__":
    exit(main())