check isbn in objc

checkISBN.m

#pragma mark - ISBN Logic

- (BOOL)checkISBN:(NSString *)ISBN error:(NSError * __autoreleasing *)error
{
    if (ISBN.length != 10 || ISBN.length != 13) {
        
        NSInteger checkSum = 0;
        NSInteger length = ISBN.length;
        
        if (length == 10) {
            // !!!: 10
            NSInteger modulo = 11;
            NSInteger checkDigit = [[ISBN substringWithRange:NSMakeRange(length - 1, 1)] integerValue];
            
            for (NSInteger index = 0; index < length - 1; index ++) {
                NSInteger digit = [[ISBN substringWithRange:NSMakeRange(index, 1)] integerValue];
                checkSum += digit * (index + 1);
            }
            
            if (checkSum % modulo == checkDigit) {
                return YES;
            } else {
                if (error) {
                    *error = [NSError errorWithDomain:@"tw.com.springhouse.klife" code:1 userInfo:@{NSLocalizedDescriptionKey:@"The checkSum of ISBN-10 did not pass."}];
                }
                return NO;
            }
            
        } else {
            // !!!: 13
            NSInteger modulo = 10;
            NSInteger checkDigit = [[ISBN substringWithRange:NSMakeRange(length - 1, 1)] integerValue];
            
            for (NSInteger index = 0; index < length - 1; index ++) {
                NSInteger digit = [[ISBN substringWithRange:NSMakeRange(index, 1)] integerValue];
                if (index % 2) {
                    checkSum += digit * 3;
                } else {
                    checkSum += digit * 1;
                }
            }
            
            if (modulo - (checkSum % modulo) == checkDigit) {
                return YES;
            } else {
                if (error) {
                    *error = [NSError errorWithDomain:@"tw.com.springhouse.klife" code:2 userInfo:@{NSLocalizedDescriptionKey:@"The checkSum of ISBN-13 did not pass."}];
                }
                return NO;
            }
        }
    } else {
        if (error) {
            *error = [NSError errorWithDomain:@"tw.com.springhouse.klife" code:3 userInfo:@{NSLocalizedDescriptionKey:@"The length of ISBN should be 10 or 13 digits."}];
        }
        return NO;
    }
}