/**
* downformat "any" ISBN Number to the very basics
* an isbn number is a 10 or 13 digit. with the
* 10 digit string, the last digit can be 0-9 and
* X as well, all other are 0-9 only
* additionally this fucntion can be used to validate
* the isbn against correct length and chars
*
* @param string $isbn ISBN String to normalise
*
* @return string|false normalised ISBN Number or false if the function was
* not able to normalise the input
*
* @access private
*/
function _normaliseISBN($isbn)
{
/* validate input */
$r = settype($isbn, 'string');
if ($r === false) {
return false;
}
/* normalize (trim & case)*/
$isbn = trim($isbn);
$isbn = strtoupper($isbn);
/* remove lang specific prefix (if any) */
$isbn = ISBN::_normaliseISBNremoveLangSpecific($isbn);
/* remove ISBN-10: or ISBN-13: prefix (if any) */
if (strlen($isbn > 8)) {
$prefix = substr($isbn, 0, 8);
if ($prefix == 'ISBN-10:' || $prefix == 'ISBN-13:') {
$isbn = substr($isbn, 8);
$isbn = ltrim($isbn);
}
}
/* remove lang specific prefix again (if any) */
$isbn = ISBN::_normaliseISBNremoveLangSpecific($isbn);
/* remove "ISBN" prefix (if any)*/
if (substr($isbn, 0, 4) == 'ISBN') {
$isbn = substr($isbn, 4);
}
/* remove cosmetic chars and different type of spaces */
$isbn = str_replace(array('-', ' ', '\\t', '\\n'), '', $isbn);
/* take the length to check and differ between versions
* sothat a syntaxcheck can be made */
$l = strlen($isbn);
if ($l != 10 && $l != 13) {
return false;
} elseif ($l == 10) {
if (!preg_match('/^[0-9]{9}[0-9X]$/', $isbn)) {
return false;
}
} elseif ($l == 13) {
if (!ctype_digit($isbn)) {
return false;
}
}
return $isbn;
}
