<?

$bbanFrance = array('30002005500000157841Z25' => true, '11808009101234567890147'=>true, '11808009101234567890146'=>false);

foreach( $bbanFrance as $bban => $expected){
    print $bban;
    if( is_valid_fr_bban($bban) == $expected){
        print " is validated as expected.";
    } else {
        print " VALIDATION ERROR";
    }
    print PHP_EOL;
}


function is_valid_fr_bban($bban){

	$bbanNum = lettersToNumbers($bban);
	if(is_null($bbanNum)){
		print "NULL";
		return false;
	}

    $checksum = substr($bbanNum,-2);

	$bank = substr($bbanNum,0,5);
	$office = substr($bbanNum,5,5);
    $account = substr($bbanNum,10,11);

	$sum = bcadd( bcmul("89", $bank) , bcmul("15", $office));
	$sum = bcadd( $sum, bcmul("3", $account));
	$calcChecksum = bcsub("97", bcmod($sum, "97"));

    return $checksum == $calcChecksum;
}

function lettersToNumbers($bban){
	$allNumbers = "";
	$conversion = array(
		"A" => 1, "B" => 2, "C" => 3, "D" => 4, "E" => 5, "F" => 6, "G" => 7, "H" => 8, "I" => 9,
		"J" => 1, "K" => 2, "L" => 3, "M" => 4, "N" => 5, "O" => 6, "P" => 7, "Q" => 8, "R" => 9,
		"S" => 2, "T" => 3, "U" => 4, "V" => 5, "W" => 6, "X" => 7, "Y" => 8, "Z" => 9
	);
	for ($i=0; $i < strlen($bban); $i++)
	{
		if(is_numeric($bban{$i})){
			$allNumbers .= $bban{$i};
		} else {
			$letter = strtoupper($bban{$i});

			if(array_key_exists($letter, $conversion)){
				$allNumbers .= $conversion[$letter];
			} else {
				return null;
			}
		}
	}
	return $allNumbers;
}

/*
Clé RIB = 97 - ( (
   89 x Code banque +
   15 x Code guichet +
   3 x Numéro de compte ) modulo 97 )$ */