isbn2 0.4.0

//! A library for handling [International Standard Book Number], or ISBNs.
//!
//! # Examples
//!
//! ```
//! use isbn2::{Isbn10, Isbn13};
//!
//! let isbn_10 = Isbn10::new([8, 9, 6, 6, 2, 6, 1, 2, 6, 4]).unwrap();
//! assert_eq!(isbn_10.hyphenate().unwrap().as_str(), "89-6626-126-4");
//! assert_eq!(isbn_10.registration_group(), Ok("Korea, Republic"));
//! assert_eq!("89-6626-126-4".parse(), Ok(isbn_10));
//!
//! let isbn_13 = Isbn13::new([9, 7, 8, 1, 4, 9, 2, 0, 6, 7, 6, 6, 5]).unwrap();
//! assert_eq!(isbn_13.hyphenate().unwrap().as_str(), "978-1-4920-6766-5");
//! assert_eq!(isbn_13.registration_group(), Ok("English language"));
//! assert_eq!("978-1-4920-6766-5".parse(), Ok(isbn_13));
//! ```
//!
//! [International Standard Book Number]: https://www.isbn-international.org/
#![cfg_attr(not(feature = "runtime-ranges"), no_std)]
#![deny(clippy::missing_errors_doc)]
#![deny(clippy::if_not_else)]

#[cfg(feature = "runtime-ranges")]
pub mod range;
#[cfg(feature = "runtime-ranges")]
pub use range::IsbnRange;
#[cfg(feature = "serialize")]
use serde::{Deserialize, Serialize};

use core::char;
use core::fmt;
use core::num::ParseIntError;
use core::str::FromStr;

use arrayvec::{ArrayString, ArrayVec, CapacityError};

pub type IsbnResult<T> = Result<T, IsbnError>;

include!(concat!(env!("OUT_DIR"), "/generated.rs"));

struct Group<'a> {
    name: &'a str,
    segment_length: usize,
}

trait IsbnObject {
    fn ean_ucc_group(&self) -> Result<Group, IsbnError> {
        Isbn::get_ean_ucc_group(self.prefix_element(), self.segment(0))
    }

    fn hyphenate_with(&self, hyphen_at: [usize; 2]) -> ArrayString<[u8; 17]>;

    fn trait_hyphenate(&self) -> Result<ArrayString<[u8; 17]>, IsbnError> {
        let registration_group_segment_length = self.ean_ucc_group()?.segment_length;
        let registrant_segment_length = Isbn::get_registration_group(
            self.prefix_element(),
            self.group_prefix(registration_group_segment_length),
            self.segment(registration_group_segment_length),
        )?
        .segment_length;

        let hyphen_at = [
            registration_group_segment_length,
            registration_group_segment_length + registrant_segment_length,
        ];
        Ok(self.hyphenate_with(hyphen_at))
    }

    fn trait_registration_group(&self) -> Result<&str, IsbnError> {
        let registration_group_segment_length = self.ean_ucc_group()?.segment_length;

        Ok(Isbn::get_registration_group(
            self.prefix_element(),
            self.group_prefix(registration_group_segment_length),
            self.segment(registration_group_segment_length),
        )?
        .name)
    }

    fn prefix_element(&self) -> u16;

    fn segment(&self, base: usize) -> u32;

    fn group_prefix(&self, length: usize) -> u32;
}

/// An International Standard Book Number, either ISBN10 or ISBN13.
///
/// # Examples
///
/// ```
/// use isbn2::{Isbn, Isbn10, Isbn13};
///
/// let isbn_10 = Isbn::_10(Isbn10::new([8, 9, 6, 6, 2, 6, 1, 2, 6, 4]).unwrap());
/// let isbn_13 = Isbn::_13(Isbn13::new([9, 7, 8, 1, 4, 9, 2, 0, 6, 7, 6, 6, 5]).unwrap());
///
/// assert_eq!("89-6626-126-4".parse(), Ok(isbn_10));
/// assert_eq!("978-1-4920-6766-5".parse(), Ok(isbn_13));
/// ```
#[derive(Debug, PartialEq, Clone, Eq)]
#[cfg_attr(feature = "serialize", derive(Serialize, Deserialize))]
pub enum Isbn {
    _10(Isbn10),
    _13(Isbn13),
}

impl Isbn {
    /// Hyphenate an ISBN into its parts:
    ///
    /// * GS1 Prefix (ISBN-13 only)
    /// * Registration group
    /// * Registrant
    /// * Publication
    /// * Check digit
    ///
    /// ```
    /// use isbn2::{Isbn, Isbn10, Isbn13};
    ///
    /// let isbn_10 = Isbn::_10(Isbn10::new([8, 9, 6, 6, 2, 6, 1, 2, 6, 4]).unwrap());
    /// let isbn_13 = Isbn::_13(Isbn13::new([9, 7, 8, 1, 4, 9, 2, 0, 6, 7, 6, 6, 5]).unwrap());
    ///
    /// assert_eq!(isbn_10.hyphenate().unwrap().as_str(), "89-6626-126-4");
    /// assert_eq!(isbn_13.hyphenate().unwrap().as_str(), "978-1-4920-6766-5");
    /// ```
    /// # Errors
    /// If the ISBN is not valid, as determined by the current ISBN rules, an error will be
    /// returned.
    pub fn hyphenate(&self) -> Result<ArrayString<[u8; 17]>, IsbnError> {
        match self {
            Isbn::_10(ref c) => c.hyphenate(),
            Isbn::_13(ref c) => c.hyphenate(),
        }
    }

    /// Retrieve the name of the registration group.
    ///
    /// ```
    /// use isbn2::{Isbn, Isbn10, Isbn13};
    ///
    /// let isbn_10 = Isbn::_10(Isbn10::new([8, 9, 6, 6, 2, 6, 1, 2, 6, 4]).unwrap());
    /// let isbn_13 = Isbn::_13(Isbn13::new([9, 7, 8, 1, 4, 9, 2, 0, 6, 7, 6, 6, 5]).unwrap());
    ///
    /// assert_eq!(isbn_10.registration_group(), Ok("Korea, Republic"));
    /// assert_eq!(isbn_13.registration_group(), Ok("English language"));
    /// ```
    ///
    /// # Errors
    /// If the ISBN is not valid, as determined by the current ISBN rules, an error will be
    /// returned.
    pub fn registration_group(&self) -> Result<&str, IsbnError> {
        match self {
            Isbn::_10(ref c) => c.registration_group(),
            Isbn::_13(ref c) => c.registration_group(),
        }
    }
}

impl fmt::Display for Isbn {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Isbn::_10(ref c) => c.fmt(f),
            Isbn::_13(ref c) => c.fmt(f),
        }
    }
}

impl From<Isbn10> for Isbn {
    fn from(isbn10: Isbn10) -> Isbn {
        Isbn::_10(isbn10)
    }
}

impl From<Isbn13> for Isbn {
    fn from(isbn13: Isbn13) -> Isbn {
        Isbn::_13(isbn13)
    }
}

impl FromStr for Isbn {
    type Err = IsbnError;
    fn from_str(s: &str) -> Result<Isbn, IsbnError> {
        Parser::new(s)?.read_isbn()
    }
}

/// Used to convert ISBN digits into chars, excluding the last digit of ISBN10.
fn convert_isbn_body(d: u8) -> char {
    char::from_digit(d.into(), 10).unwrap()
}

/// Used to convert ISBN digits into chars, including the last digit of ISBN10.
fn convert_isbn10_check(d: u8) -> char {
    if d < 11 {
        ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'X'][d as usize]
    } else {
        'X'
    }
}

/// 10-digit ISBN format.
#[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)]
#[cfg_attr(feature = "serialize", derive(Serialize, Deserialize))]
pub struct Isbn10 {
    digits: [u8; 10],
}

impl IsbnObject for Isbn10 {
    /// Applies two hyphens in the middle.
    fn hyphenate_with(&self, hyphen_at: [usize; 2]) -> ArrayString<[u8; 17]> {
        let mut hyphenated = ArrayString::new();

        for (i, &digit) in self.digits[0..9].iter().enumerate() {
            if hyphen_at.contains(&i) {
                hyphenated.push('-')
            }
            hyphenated.push(convert_isbn_body(digit));
        }

        hyphenated.push('-');
        hyphenated.push(convert_isbn10_check(self.digits[9]));

        hyphenated
    }

    fn prefix_element(&self) -> u16 {
        0x978
    }

    fn segment(&self, base: usize) -> u32 {
        (0..7).fold(0, |s, i| {
            s + u32::from(*self.digits.get(base + i).unwrap_or(&0)) * 10_u32.pow(6 - i as u32)
        })
    }

    fn group_prefix(&self, length: usize) -> u32 {
        let mut digits = 0;
        for &digit in &self.digits[..length] {
            digits = (digits << 4) | digit as u32;
        }
        digits
    }
}

impl Isbn10 {
    /// Creates a new ISBN10 code from 10 digits. Verifies that the checksum is correct,
    /// and that no digits are out of bounds.
    ///
    /// # Examples
    ///
    /// ```
    /// use isbn2::Isbn10;
    ///
    /// let isbn10 = Isbn10::new([8, 9, 6, 6, 2, 6, 1, 2, 6, 4]).unwrap();
    /// ```
    /// # Errors
    /// If any of the first nine digits exceed nine, or the tenth digit exceeds 10, an error
    /// will be returned. If the check digit is not correct for the ISBN, an error will also
    /// be returned.
    pub fn new(digits: [u8; 10]) -> IsbnResult<Isbn10> {
        if digits[..9].iter().any(|&digit| digit > 9) || digits[9] > 10 {
            Err(IsbnError::DigitTooLarge)
        } else if Isbn10::calculate_check_digit(&digits) == digits[9] {
            Ok(Isbn10 { digits })
        } else {
            Err(IsbnError::InvalidChecksum)
        }
    }

    /// Convert ISBN-13 to ISBN-10, if applicable.
    ///
    /// ```
    /// use isbn2::{Isbn10, Isbn13};
    ///
    /// let isbn_13 = Isbn13::new([9, 7, 8, 1, 4, 9, 2, 0, 6, 7, 6, 6, 5]).unwrap();
    /// assert_eq!(Isbn10::try_from(isbn_13), "1-4920-6766-0".parse());
    /// ```
    /// # Errors
    /// If the ISBN13 does not have a 978 prefix, it can not be downcast to an ISBN10, and an
    /// error will be returned.
    pub fn try_from(isbn13: Isbn13) -> IsbnResult<Self> {
        if isbn13.digits[..3] == [9, 7, 8] {
            let mut a = [0; 10];
            a[..9].clone_from_slice(&isbn13.digits[3..12]);
            a[9] = Isbn10::calculate_check_digit(&a);
            Ok(Isbn10 { digits: a })
        } else {
            Err(IsbnError::InvalidConversion)
        }
    }

    fn calculate_check_digit(digits: &[u8; 10]) -> u8 {
        let sum: usize = digits[..9]
            .iter()
            .enumerate()
            .map(|(i, &d)| d as usize * (10 - i))
            .sum();
        let sum_m = (sum % 11) as u8;
        if sum_m == 0 {
            0
        } else {
            11 - sum_m
        }
    }

    /// Hyphenate an ISBN-10 into its parts:
    ///
    /// * Registration group
    /// * Registrant
    /// * Publication
    /// * Check digit
    ///
    /// ```
    /// use isbn2::Isbn10;
    ///
    /// let isbn_10 = Isbn10::new([8, 9, 6, 6, 2, 6, 1, 2, 6, 4]).unwrap();
    /// assert_eq!(isbn_10.hyphenate().unwrap().as_str(), "89-6626-126-4");
    /// ```
    /// # Errors
    /// If the ISBN is not valid, as determined by the current ISBN rules, an error will be
    /// returned.
    pub fn hyphenate(&self) -> Result<ArrayString<[u8; 17]>, IsbnError> {
        self.trait_hyphenate()
    }

    /// Retrieve the name of the registration group.
    ///
    /// ```
    /// use isbn2::Isbn10;
    ///
    /// let isbn_10 = Isbn10::new([8, 9, 6, 6, 2, 6, 1, 2, 6, 4]).unwrap();
    /// assert_eq!(isbn_10.registration_group(), Ok("Korea, Republic"));
    /// ```
    /// # Errors
    /// If the ISBN is not valid, as determined by the current ISBN rules, an error will be
    /// returned.
    pub fn registration_group(&self) -> Result<&str, IsbnError> {
        self.trait_registration_group()
    }
}

impl fmt::Display for Isbn10 {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let mut s = ArrayString::<[u8; 10]>::new();
        self.digits[0..9]
            .iter()
            .for_each(|&digit| s.push(convert_isbn_body(digit)));
        s.push(convert_isbn10_check(self.digits[9]));
        write!(f, "{}", s)
    }
}

impl FromStr for Isbn10 {
    type Err = IsbnError;
    fn from_str(s: &str) -> Result<Isbn10, IsbnError> {
        let mut p = Parser::new(s)?;
        if p.digits.len() == 10 {
            p.read_isbn10()
        } else {
            Err(IsbnError::InvalidLength)
        }
    }
}

/// 13-digit ISBN format.
#[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)]
#[cfg_attr(feature = "serialize", derive(Serialize, Deserialize))]
pub struct Isbn13 {
    digits: [u8; 13],
}

impl IsbnObject for Isbn13 {
    fn hyphenate_with(&self, hyphen_at: [usize; 2]) -> ArrayString<[u8; 17]> {
        let mut hyphenated = ArrayString::new();

        for &digit in &self.digits[0..3] {
            hyphenated.push(convert_isbn_body(digit))
        }
        hyphenated.push('-');

        for (i, &digit) in self.digits[3..12].iter().enumerate() {
            if hyphen_at.contains(&i) {
                hyphenated.push('-')
            }
            hyphenated.push(convert_isbn_body(digit));
        }

        hyphenated.push('-');
        hyphenated.push(convert_isbn_body(self.digits[12]));

        hyphenated
    }

    fn prefix_element(&self) -> u16 {
        ((self.digits[0] as u16) << 8) | ((self.digits[1] as u16) << 4) | (self.digits[2] as u16)
    }

    fn segment(&self, base: usize) -> u32 {
        (3..9).fold(0, |s, i| {
            s + u32::from(*self.digits.get(base + i).unwrap_or(&0)) * 10_u32.pow(9 - i as u32)
        })
    }

    fn group_prefix(&self, length: usize) -> u32 {
        let mut digits = 0;
        for &digit in &self.digits[3..length + 3] {
            digits = (digits << 4) | digit as u32;
        }
        digits
    }
}

impl Isbn13 {
    /// Creates a new ISBN13 code from 13 digits. Verifies that the checksum is correct,
    /// and that no digits are out of bounds.
    ///
    /// # Examples
    ///
    /// ```
    /// use isbn2::Isbn13;
    ///
    /// let isbn13 = Isbn13::new([9, 7, 8, 1, 4, 9, 2, 0, 6, 7, 6, 6, 5]).unwrap();
    /// ```
    /// # Errors
    /// If any of the digits exceed nine, an error will be returned. If the check digit is not
    /// correct for the ISBN, an error will also be returned.
    pub fn new(digits: [u8; 13]) -> IsbnResult<Isbn13> {
        if digits.iter().any(|&digit| digit > 9) {
            Err(IsbnError::DigitTooLarge)
        } else if Isbn13::calculate_check_digit(&digits) == digits[12] {
            Ok(Isbn13 { digits })
        } else {
            Err(IsbnError::InvalidChecksum)
        }
    }

    fn calculate_check_digit(digits: &[u8; 13]) -> u8 {
        let mut sum = 0;
        for i in 0..6 {
            sum += u16::from(digits[i * 2] + 3 * digits[i * 2 + 1]);
        }
        let sum_m = (sum % 10) as u8;
        if sum_m == 0 {
            0
        } else {
            10 - sum_m
        }
    }

    /// Hyphenate an ISBN-13 into its parts:
    ///
    /// * GS1 Prefix
    /// * Registration group
    /// * Registrant
    /// * Publication
    /// * Check digit
    ///
    /// ```
    /// use isbn2::Isbn13;
    ///
    /// let isbn_13 = Isbn13::new([9, 7, 8, 1, 4, 9, 2, 0, 6, 7, 6, 6, 5]).unwrap();
    /// assert_eq!(isbn_13.hyphenate().unwrap().as_str(), "978-1-4920-6766-5");
    /// ```
    /// # Errors
    /// If the ISBN is not valid, as determined by the current ISBN rules, an error will be
    /// returned.
    pub fn hyphenate(&self) -> Result<ArrayString<[u8; 17]>, IsbnError> {
        self.trait_hyphenate()
    }

    /// Retrieve the name of the registration group.
    ///
    /// ```
    /// use isbn2::Isbn13;
    ///
    /// let isbn_13 = Isbn13::new([9, 7, 8, 1, 4, 9, 2, 0, 6, 7, 6, 6, 5]).unwrap();
    /// assert_eq!(isbn_13.registration_group(), Ok("English language"));
    /// ```
    /// # Errors
    /// If the ISBN is not valid, as determined by the current ISBN rules, an error will be
    /// returned.
    pub fn registration_group(&self) -> Result<&str, IsbnError> {
        self.trait_registration_group()
    }
}

impl fmt::Display for Isbn13 {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        let mut s = ArrayString::<[u8; 13]>::new();
        self.digits
            .iter()
            .for_each(|&digit| s.push(convert_isbn_body(digit)));
        write!(f, "{}", s)
    }
}

impl From<Isbn10> for Isbn13 {
    fn from(isbn10: Isbn10) -> Isbn13 {
        let mut digits = [0; 13];
        digits[..3].clone_from_slice(&[9, 7, 8]);
        digits[3..12].clone_from_slice(&isbn10.digits[0..9]);
        digits[12] = Isbn13::calculate_check_digit(&digits);
        Isbn13 { digits }
    }
}

impl FromStr for Isbn13 {
    type Err = IsbnError;
    fn from_str(s: &str) -> Result<Isbn13, IsbnError> {
        let mut p = Parser::new(s)?;
        if p.digits.len() == 13 {
            p.read_isbn13()
        } else {
            Err(IsbnError::InvalidLength)
        }
    }
}

/// An error which can be returned when parsing an ISBN.
#[derive(Debug, PartialEq)]
pub enum IsbnError {
    /// The given string is too short or too long to be an ISBN.
    InvalidLength,
    /// Encountered an invalid digit while parsing.
    InvalidDigit,
    /// Encountered an invalid ISBN registration group.
    InvalidGroup,
    /// Encountered a range not defined for use at this time.
    UndefinedRange,
    /// Failed to validate checksum.
    InvalidChecksum,
    /// Failed to convert to ISBN10.
    InvalidConversion,
    /// One or supplied more digits were too large.
    DigitTooLarge,
}

impl fmt::Display for IsbnError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            IsbnError::InvalidLength => write!(
                f,
                "The given string is too short or too long to be an ISBN."
            ),
            IsbnError::InvalidDigit => write!(f, "Encountered an invalid digit while parsing."),
            IsbnError::InvalidGroup => write!(f, "Encountered an invalid ISBN registration group."),
            IsbnError::UndefinedRange => {
                write!(f, "Encountered a range not defined for use at this time.")
            }
            IsbnError::InvalidChecksum => write!(f, "Failed to validate checksum."),
            IsbnError::InvalidConversion => write!(f, "Failed to convert to ISBN10."),
            IsbnError::DigitTooLarge => write!(
                f,
                "A supplied digit was larger than 9, or the ISBN10 check digit was larger than 10."
            ),
        }
    }
}

impl From<ParseIntError> for IsbnError {
    fn from(_: ParseIntError) -> Self {
        IsbnError::InvalidDigit
    }
}

impl From<CapacityError<u8>> for IsbnError {
    fn from(_: CapacityError<u8>) -> Self {
        IsbnError::InvalidLength
    }
}

#[derive(Debug, Clone)]
struct Parser {
    digits: ArrayVec<[u8; 13]>,
}

impl Parser {
    pub fn new<S: AsRef<str>>(s: S) -> Result<Parser, IsbnError> {
        let mut digits = ArrayVec::new();
        let mut has_x = false;

        for c in s.as_ref().chars() {
            match c {
                '-' | ' ' => {}
                'X' => {
                    if digits.len() == 9 {
                        has_x = true;
                        digits.push(10);
                    } else {
                        return Err(IsbnError::InvalidDigit);
                    }
                }
                '0'..='9' => {
                    if has_x {
                        return Err(IsbnError::InvalidDigit);
                    } else {
                        digits.try_push(c.to_digit(10).unwrap() as u8)?
                    }
                }
                _ => return Err(IsbnError::InvalidDigit),
            }
        }
        Ok(Parser { digits })
    }

    fn read_isbn(&mut self) -> Result<Isbn, IsbnError> {
        match self.digits.len() {
            10 => self.read_isbn10().map(Isbn::_10),
            13 => self.read_isbn13().map(Isbn::_13),
            _ => Err(IsbnError::InvalidLength),
        }
    }

    /// Reads an ISBN13 from self. Requires that length is checked beforehand.
    fn read_isbn13(&mut self) -> Result<Isbn13, IsbnError> {
        let mut digits = [0; 13];
        digits.clone_from_slice(&self.digits);
        let check_digit = Isbn13::calculate_check_digit(&digits);
        if check_digit == digits[12] {
            Ok(Isbn13 { digits })
        } else {
            Err(IsbnError::InvalidDigit)
        }
    }

    /// Reads an ISBN10 from self. Requires that length is checked beforehand.
    fn read_isbn10(&mut self) -> Result<Isbn10, IsbnError> {
        let mut digits = [0; 10];
        digits.clone_from_slice(&self.digits);
        let check_digit = Isbn10::calculate_check_digit(&digits);
        if check_digit == digits[9] {
            Ok(Isbn10 { digits })
        } else {
            Err(IsbnError::InvalidDigit)
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_from_str_isbn10() {
        // Wikipedia ISBN-10 check digit calculation example
        assert!(Isbn::from_str("0-306-40615-2").is_ok());

        // Wikipedia ISBN-10 check digit calculation invalid example
        assert!(Isbn::from_str("99999-999-9-X").is_err());

        // Wikipedia Registrant element examples
        assert!(Isbn::from_str("99921-58-10-7").is_ok());
        assert!(Isbn::from_str("9971-5-0210-0").is_ok());
        assert!(Isbn::from_str("9971-5-0210-0").is_ok());
        assert!(Isbn::from_str("960-425-059-0").is_ok());
        assert!(Isbn::from_str("80-902734-1-6").is_ok());
        assert!(Isbn::from_str("85-359-0277-5").is_ok());
        assert!(Isbn::from_str("1-84356-028-3").is_ok());
        assert!(Isbn::from_str("0-684-84328-5").is_ok());
        assert!(Isbn::from_str("0-8044-2957-X").is_ok());
        assert!(Isbn::from_str("0-85131-041-9").is_ok());
        assert!(Isbn::from_str("0-943396-04-2").is_ok());
        assert!(Isbn::from_str("0-9752298-0-X").is_ok());
    }

    #[test]
    fn test_hyphens_no_panic() {
        assert!(Isbn::from_str("0-9752298-0-X").unwrap().hyphenate().is_ok());
        assert!(Isbn::from_str("978-3-16-148410-0")
            .unwrap()
            .hyphenate()
            .is_ok());
    }

    #[test]
    fn test_from_str_isbn13() {
        // Wikipedia Example
        assert!(Isbn13::from_str("978-3-16-148410-0").is_ok());

        // Wikipedia ISBN-13 check digit calculation example
        assert!(Isbn13::from_str("978-0-306-40615-7").is_ok());
    }

    #[test]
    fn test_invalid_isbn_strings_no_panic() {
        assert!(Isbn::from_str("L").is_err());
        assert!(Isbn::from_str("").is_err());
        assert!(Isbn::from_str("01234567890123456789").is_err());
        assert!(Isbn::from_str("ⱧňᚥɂᛢĞžᚪ©ᛟƚ¶G").is_err());

        assert!(Isbn10::from_str("").is_err());
        assert!(Isbn10::from_str("01234567890").is_err());
        assert!(Isbn10::from_str("01234567X9").is_err());
        assert!(Isbn10::from_str("012345678").is_err());

        assert!(Isbn13::from_str("").is_err());
        assert!(Isbn13::from_str("012345678901X").is_err());
        assert!(Isbn13::from_str("01234567890X2").is_err());
        assert!(Isbn13::from_str("012345678").is_err());
        assert!(Isbn13::from_str("0123456789012345").is_err());
    }

    #[test]
    fn test_isbns_do_not_accept_larger_digits() {
        let mut a = [10; 10];
        // Everything except check digit must be <= 9.
        a[9] = Isbn10::calculate_check_digit(&a);
        assert!(Isbn10::new(a).is_err());
        // Check digit can be 10.
        assert!(Isbn10::new([0, 9, 7, 5, 2, 2, 9, 8, 0, 10]).is_ok());
        // Check digits which are larger than 10 are implicitly handled by
        // the fact that calculate_check_digit returns a number from 0 to 10.
        let mut a = [10; 13];
        a[12] = Isbn13::calculate_check_digit(&a);
        assert!(Isbn13::new(a).is_err());
    }
}