function validateDate()
{
	var date = document.getElementById( 'date' ).value;

	if( date == '' )
	{
		return true;
	}

	var dates = date.split( '/' );
	var year  = dates[ 0 ];
	var month = dates[ 1 ];
	var day   = dates[ 2 ];

	if( !checkDate( year, month, day ) )
	{
		alert( '納品希望日 が正しく指定されていません。' );
		return false;
	}

	var	today = new Date();
	today.setHours( 0 );
	today.setMinutes( 0 );
	today.setSeconds( 0 );
	today.setMilliseconds( 0 );

	var target_date = new Date( year, month - 1, day );
	var	enable_date = computeDate( today, 23 );

	if( target_date.getTime() < enable_date.getTime() )
	{
		alert( 'エラー: 納品希望日は、' + enable_date.getFullYear() + '年' + parseInt( enable_date.getMonth() + 1 ) + '月' + enable_date.getDate() + '日以降から選択可能です。' );
		return false;
	}

	return true;
}

function computeDate( dt, addDays )
{
	var baseSec   = dt.getTime();
	var addSec    = addDays * 60 * 60 * 24 * 1000;
	var targetSec = baseSec + addSec;

	dt.setTime( targetSec );

	return dt;
}

function checkDate( year, month, day )
{
	var dt = new Date( year, month - 1, day );

	if( dt == null || dt.getFullYear() != year || dt.getMonth() + 1 != month || dt.getDate() != day )
	{
		return false;
	}

	return true;
}