Validates ISBN13 codes

Isbn13Validation.cs

        /// <summary>
        /// Validates ISBN13 codes
        /// </summary>
        /// <param name="isbn13">code to validate</param>
        /// <returns>true, if valid</returns>
        public static bool IsValidIsbn13(string isbn13)
        {
            if (string.IsNullOrEmpty(isbn13))
            {
                return false;
            }
            if (isbn13.Contains("-")) isbn13 = isbn13.Replace("-", "");

            // If the length is not 13 or if it contains any non numeric chars, return false
            long temp;
            if (isbn13.Length != 13 || !long.TryParse(isbn13, out temp)) return false;

            // Comment Source: Wikipedia
            // The calculation of an ISBN-13 check digit begins with the first
            // 12 digits of the thirteen-digit ISBN (thus excluding the check digit itself).
            // Each digit, from left to right, is alternately multiplied by 1 or 3,
            // then those products are summed modulo 10 to give a value ranging from 0 to 9.
            // Subtracted from 10, that leaves a result from 1 to 10. A zero (0) replaces a
            // ten (10), so, in all cases, a single check digit results.
            var sum = 0;
            for (var i = 0; i < 12; i++)
            {
                sum += int.Parse(isbn13[i].ToString()) * (i % 2 == 1 ? 3 : 1);
            }

            var remainder = sum % 10;
            var checkDigit = 10 - remainder;
            if (checkDigit == 10) checkDigit = 0;

            var result = checkDigit == int.Parse(isbn13[12].ToString());

            return result;
        }