PHP - Date Format Check

function checkDateFormat($date, $empty = '0', $sep = '/')
{
    $date = preg_replace('/[^\d\-\. \/]/', '', $date); // remove non-numeric and non-date separaters
    
    $check = preg_split('/[ \-\.\/]/', $date);
    if(empty($check)) return '0';
    
    foreach($check as &$item)
      $item = str_pad($item, 2, '0', STR_PAD_LEFT);
    $date = implode('-', $check);
    
    // matches for all format dates, with space, hyphen, period, or slash separators
    // correct format needed is Y-m-d
    // 100 is used as the final check to keep room open for later additions
    $patterns = array(
              0 => '/(9999)[- \.\/](09)[- \.\/](09)/', // one of the many different "blank" values used
              1 => '/(0[1-9]|1[012])[- \.\/](0[1-9]|1[012])[- \.\/](\d{4,4})/', // unknown d-m order, Y at end
              2 => '/(\d{4,4})[- \.\/](0[1-9]|1[012])[- \.\/](0[1-9]|1[012])/', // unknown d-m order, Y at front
              3 => '/(0[1-9]|1[012])[- \.\/](0[1-9]|[12][0-9]|3[01])[- \.\/](\d{4,4})/', // m-d-Y
              4 => '/(\d{4,4})[- \.\/](0[1-9]|1[012])[- \.\/](0[1-9]|[12][0-9]|3[01])/', // Y-m-d (aka already correct)
              5 => '/(0[1-9]|[12][0-9]|3[01])[- \.\/](0[1-9]|1[012])[- \.\/](\d{4,4})/', // d-m-Y
              6 => '/(\d{4,4})[- \.\/](0[1-9]|[12][0-9]|3[01])[- \.\/](0[1-9]|1[012])/', // Y-d-m
              99 => '/ |[s(\302\240|\240)]+|[W]+/', // blank, empty, or placeholder
              100 => '/(\d{2,2})[- \.\/](\d{2,2})[- \.\/](\d{2,2})/' // unknown all double digits
            );
    
    // for unknown d-m order assume month is first
    $replace = array(
              0 => $empty,
              1 => "$3{$sep}$1{$sep}$2", // unknown d-m order, Y at end -> Y-m-d
              2 => "$1{$sep}$2{$sep}$3", // unknown d-m order, Y at front -> Y-m-d
              3 => "$3{$sep}$1{$sep}$2", // m-d-Y -> Y-m-d
              4 => "$1{$sep}$2{$sep}$3", // Y-m-d -> Y-m-d
              5 => "$3{$sep}$2{$sep}$1", // d-m-Y -> Y-m-d
              6 => "$3{$sep}$1{$sep}$2", // Y-d-m -> Y-m-d
              99 => "$0",
              100 => $empty
            );
    
    foreach($patterns as $index => $pattern)
      if(preg_match($pattern, $date))
        return preg_replace($pattern, $replace[$index], $date);
    
    return $empty;
}

100 => "$1-$2-$3"