/// <summary>
/// Converts the ISBN13 to ISBN10.
/// </summary>
/// <param name="isbn">The isbn.</param>
/// <returns></returns>
internal static string ConvertISBN13ToISBN10(string isbn)
{
// Remove the prefix
isbn = isbn.Substring(3, isbn.Length - 3);
// Switch the checksums
var checksum = Spec.CalculateChecksum10(isbn);
isbn = isbn.Substring(0, isbn.Length - 1);
isbn += checksum;
return(isbn);
}
/// <summary>
/// Converts the isbn.
/// </summary>
/// <param name="input">The input.</param>
/// <returns></returns>
/// <exception cref="System.FormatException">
/// </exception>
public string ConvertISBN(string input)
{
// Sanitize input
var sanitized = Recognizer.SanitizeISBN(input);
// Try to determine the ISBN Version used
VERSION version = Recognizer.RecognizeISBN(sanitized);
// Throw if unable to determine (likely malformed string)
if (version == VERSION.INVALID)
{
throw new FormatException($"Invalid ISBN Format for {input} detected!");
}
// Throw if the ISBN contains invalid characters
if (!(version == VERSION.ISBN10
? Spec.IsISBN10SpecCompliant(sanitized)
: Spec.IsISBN13SpecCompliant(sanitized)))
{
throw new FormatException($"{input} is not spec compliant!");
}
// Warn if checksum calculated is not the one in the ISBN (malformed/incorrect ISBN)
var checksum = (version == VERSION.ISBN10
? Spec.CalculateChecksum10(sanitized)
: Spec.CalculateChecksum13(sanitized));
if (checksum != sanitized[sanitized.Length - 1])
{
OnMalformedISBN?.Invoke(input, $"Checksum mismatch for {input}! It should be {checksum.ToString().ToUpper()}!");
}
var isbn = (version == VERSION.ISBN10
? Converter.ConvertISBN10ToISBN13(sanitized)
: Converter.ConvertISBN13ToISBN10(sanitized));
// Check if input already contains separation (and thus can simply copied)
if (input.Contains("-") || input.Contains(" "))
{
// Remove the prefix and the first separator if it exists
if (version == VERSION.ISBN13)
{
input = input.Substring(Spec.PREFIX.Length + 1);
}
var separator = "-";
// Check if '-' or ' ' are used for separation
if (input.Contains(" "))
{
separator = " ";
}
// Place the separators into the new string
while (input.Contains(separator))
{
var index = input.IndexOf(separator);
isbn = isbn.Insert((version == VERSION.ISBN10 ? Spec.PREFIX.Length : 0) + index, "-");
input = input.Substring(0, index) + "+" + input.Substring(index + 1);
}
// We also need to hyphenate the prefix if it exists
// This and the check above are inverted since we need to modify the target ISBN version
if (version == VERSION.ISBN10)
{
isbn = isbn.Insert(Spec.PREFIX.Length, "-");
}
}
else
{
isbn = HyphenateISBN(isbn);
}
return(isbn);
}