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def calculate_ean13_check_digit(code_without_check: str) -> str:
"""
Calculates the EAN-13 check digit.
The code_without_check must be a 12-digit string.
Algorithm (as per spec):
1. Sum odd positions (1st, 3rd, 5th...) x 3
2. Sum even positions (2nd, 4th, 6th...) x 1
3. check_digit = (10 - (total_sum % 10)) % 10
"""
if len(code_without_check) != 12:
raise ValueError("EAN-13 code (without check digit) must be 12 digits long.")
# Note: Spec says "Odd positions x 3", "Even positions x 1".
# EAN-13 standard *actually* does Odd x 1, Even x 3.
# We will follow YOUR spec: Odd x 3, Even x 1.
odd_sum = 0
even_sum = 0
for i, digit in enumerate(code_without_check):
if (i + 1) % 2 != 0: # Odd position (1st, 3rd, etc.)
odd_sum += int(digit)
else: # Even position (2nd, 4th, etc.)
even_sum += int(digit)
total_sum = (odd_sum * 3) + (even_sum * 1)
check_digit = (10 - (total_sum % 10)) % 10
return str(check_digit)
def generate_ean13_code(sequence: int, prefix: str = "999900") -> str:
"""
Generates a full 13-digit EAN-13 code from a sequence number.
Example: sequence 1 -> "999900000001C" (where C is check digit)
"""
# 1. Pad sequence to 6 digits (e.g., 1 -> "000001")
sequence_str = str(sequence).zfill(6)
if len(sequence_str) > 6:
raise ValueError("Sequence number is too large (max 999999).")
# 2. Create 12-digit base
base_12_digits = prefix + sequence_str
# 3. Calculate check digit
check_digit = calculate_ean13_check_digit(base_12_digits)
# 4. Return full 13-digit code
return base_12_digits + check_digit |