MySQL Date Validation and Conversion

<?
/*
	Function Name: date_validate
  
	Author: Eric Sammons, Vansam Software, Inc. (www.vansam.com)
	Email: [email protected]

	Date: 2001-09-01
	Version 1.0.0

	Purpose:
		Receives various date field formats, validates them, and then and 
		converts them to MySQL standard date format

	Valid date fields:
		mm-dd-yyyy, mm/dd/yyyy, yyyy-mm-dd, yyyy/mm/dd

	Returns:
		if valid input, the date in MySQL standard format
		if invalid input, error message with "Error:" at the beginning of message

	Sample Use:
		$MySQLDate=date_validate($datefield);
		if (substr($MySQLDate, 0, 5)=="Error") {
			// Insert Error Code
		} else {
			// Insert Valid Date Code
		}
*/

function date_validate ($datefield) {

	// First check to see if the input ($datefield) is in one of the accepted formats
	
	// Check for delimiters ("-" or "/") and put three fields into an array
	if (strpos($datefield, "-")) {
	  $datesplit = explode("-", $datefield);
	} elseif (strpos($datefield, "/")) {
	  $datesplit = explode("/", $datefield);
	} else {
	    $date_err="Error: Invalid date field. No proper delimiters (- or /) found";
		return $date_err;
	}

	// Check for three input fields (month, day, year)
	if (count($datesplit)>3) {
	    $date_err="Error: Invalid date field. Too many fields (".count($datesplit).") found";
		return $date_err;
	}

	// Put date array into single format
	if (strlen($datesplit[2])==4) { // The year is listed last - switch fields around
		$newdatesplit[0]=$datesplit[2]; // Move Year to first field
		$newdatesplit[1]=$datesplit[0]; // Move Month to second field
		$newdatesplit[2]=$datesplit[1]; // Move Day to third field
		$datesplit=$newdatesplit;
	} elseif (strlen($datesplit[0])==4) { // The year is first listed - do nothing
		// nothing to be done
	} else { // Date entered is not valid; could not find year field
		$date_err="Error: Date not valid. No Year field found (Year must be 4 digits)";
		return $date_err;
	}
	
	// Main validation code

    if ($datesplit[1]>12) { // No valid month field
    	$date_err="Error: Invalid Month field (".$datesplit[1].") ";
		return $date_err;
    } else {
       switch ($datesplit[1]) { // Check number of days in a month
           case 4:
           case 6:
           case 9:
           case 11:
                if ($datesplit[2]>30) {
    				$date_err="Error: Invalid # of days (".$datesplit[2].") for month ".$datesplit[1]." and year ".$datesplit[0];
					return $date_err;
                }
				break;
           case 2: // February Check
		   		if (($datesplit[0]/4)==(floor($datesplit[0]/4))) {
					if (($datesplit[0]/100)==(floor($datesplit[0]/100))) {
						if (($datesplit[0]==1600) or ($datesplit[0]==2000) or ($datesplit[0]==2400)) {
							if ($datesplit[2]>29) {
			    				$date_err="Error: Invalid # of days (".$datesplit[2].") for month ".$datesplit[1]." and year ".$datesplit[0];
								return $date_err;
							}
						} else {
							if ($datesplit[2]>28) {
			    				$date_err="Error: Invalid # of days (".$datesplit[2].") for month ".$datesplit[1]." and year ".$datesplit[0];
								return $date_err;
							}
						}
					} else {
						if ($datesplit[2]>29) {
			    			$date_err="Error: Invalid # of days (".$datesplit[2].") for month ".$datesplit[1]." and year ".$datesplit[0];
							return $date_err;
						}
					}
				} else {
					if ($datesplit[2]>28) {
	    				$date_err="Error: Invalid # of days (".$datesplit[2].") for month ".$datesplit[1]." and year ".$datesplit[0];
						return $date_err;
    	            }
        		}
				break;
		   default:
                if ($datesplit[2]>31) {
    				$date_err="Error: Invalid # of days (".$datesplit[2].") for month ".$datesplit[1]." and year ".$datesplit[0];
					return $date_err;
                }
        }
      }
		  // Add leading zero if month or day field is only one character
	  if (strlen($datesplit[1])==1) {
	  	$datesplit[1]="0".$datesplit[1];
	  }
	  if (strlen($datesplit[2])==1) {
	  	$datesplit[2]="0".$datesplit[2];
	  }
	  
      // Create date field in MySQL format
	  $newdate=$datesplit[0]."-".$datesplit[1]."-".$datesplit[2];
	  return $newdate;	
	  
} // End date_validate function
?>