CDateFormatter

public function __construct($locale)
{
    if(is_string($locale))
        $this->_locale=CLocale::getInstance($locale);
    else
        $this->_locale=$locale;
}

public function format($pattern,$time)
{
    if($time===null)
        return null;

    if(is_string($time))
    {
        if(ctype_digit($time) || ($time{0}=='-' && ctype_digit(substr($time, 1))))
            $time=(int)$time;
        else
            $time=strtotime($time);
    }
    $date=CTimestamp::getDate($time,false,false);
    $tokens=$this->parseFormat($pattern);
    foreach($tokens as &$token)
    {
        if(is_array($token)) // a callback: method name, sub-pattern
            $token=$this->{$token[0]}($token[1],$date);
    }
    return implode('',$tokens);
}

public function formatDateTime($timestamp,$dateWidth='medium',$timeWidth='medium')
{
    if(!empty($dateWidth))
        $date=$this->format($this->_locale->getDateFormat($dateWidth),$timestamp);

    if(!empty($timeWidth))
        $time=$this->format($this->_locale->getTimeFormat($timeWidth),$timestamp);

    if(isset($date) && isset($time))
    {
        $dateTimePattern=$this->_locale->getDateTimeFormat();
        return strtr($dateTimePattern,array('{0}'=>$time,'{1}'=>$date));
    }
    elseif(isset($date))
        return $date;
    elseif(isset($time))
        return $time;
}

protected function formatDay($pattern,$date)
{
    $day=$date['mday'];
    if($pattern==='d')
        return $day;
    elseif($pattern==='dd')
        return str_pad($day,2,'0',STR_PAD_LEFT);
    else
        throw new CException(Yii::t('yii','The pattern for day of the month must be "d" or "dd".'));
}

protected function formatDayInMonth($pattern,$date)
{
    if($pattern==='F')
        return (int)(($date['mday']+6)/7);
    else
        throw new CException(Yii::t('yii','The pattern for day in month must be "F".'));
}

protected function formatDayInWeek($pattern,$date)
{
    $day=$date['wday'];
    switch($pattern)
    {
        case 'E':
        case 'EE':
        case 'EEE':
        case 'eee':
            return $this->_locale->getWeekDayName($day,'abbreviated');
        case 'EEEE':
        case 'eeee':
            return $this->_locale->getWeekDayName($day,'wide');
        case 'EEEEE':
        case 'eeeee':
            return $this->_locale->getWeekDayName($day,'narrow');
        case 'e':
        case 'ee':
        case 'c':
            return $day ? $day : 7;
        case 'ccc':
            return $this->_locale->getWeekDayName($day,'abbreviated',true);
        case 'cccc':
            return $this->_locale->getWeekDayName($day,'wide',true);
        case 'ccccc':
            return $this->_locale->getWeekDayName($day,'narrow',true);
        default:
            throw new CException(Yii::t('yii','The pattern for day of the week must be "E", "EE", "EEE", "EEEE", "EEEEE", "e", "ee", "eee", "eeee", "eeeee", "c", "cccc" or "ccccc".'));
    }
}

protected function formatDayInYear($pattern,$date)
{
    $day=$date['yday'];
    if(($n=strlen($pattern))<=3)
        return str_pad($day,$n,'0',STR_PAD_LEFT);
    else
        throw new CException(Yii::t('yii','The pattern for day in year must be "D", "DD" or "DDD".'));
}

protected function formatEra($pattern,$date)
{
    $era=$date['year']>0 ? 1 : 0;
    switch($pattern)
    {
        case 'G':
        case 'GG':
        case 'GGG':
            return $this->_locale->getEraName($era,'abbreviated');
        case 'GGGG':
            return $this->_locale->getEraName($era,'wide');
        case 'GGGGG':
            return $this->_locale->getEraName($era,'narrow');
        default:
            throw new CException(Yii::t('yii','The pattern for era must be "G", "GG", "GGG", "GGGG" or "GGGGG".'));
    }
}

protected function formatHour12($pattern,$date)
{
    $hour=$date['hours'];
    $hour=($hour==12|$hour==0)?12:($hour)%12;
    if($pattern==='h')
        return $hour;
    elseif($pattern==='hh')
        return str_pad($hour,2,'0',STR_PAD_LEFT);
    else
        throw new CException(Yii::t('yii','The pattern for 12 hour format must be "h" or "hh".'));
}

protected function formatHour24($pattern,$date)
{
    $hour=$date['hours'];
    if($pattern==='H')
        return $hour;
    elseif($pattern==='HH')
        return str_pad($hour,2,'0',STR_PAD_LEFT);
    else
        throw new CException(Yii::t('yii','The pattern for 24 hour format must be "H" or "HH".'));
}

protected function formatHourInDay($pattern,$date)
{
    $hour=$date['hours']==0?24:$date['hours'];
    if($pattern==='k')
        return $hour;
    elseif($pattern==='kk')
        return str_pad($hour,2,'0',STR_PAD_LEFT);
    else
        throw new CException(Yii::t('yii','The pattern for hour in day must be "k" or "kk".'));
}

protected function formatHourInPeriod($pattern,$date)
{
    $hour=$date['hours']%12;
    if($pattern==='K')
        return $hour;
    elseif($pattern==='KK')
        return str_pad($hour,2,'0',STR_PAD_LEFT);
    else
        throw new CException(Yii::t('yii','The pattern for hour in AM/PM must be "K" or "KK".'));
}

protected function formatMinutes($pattern,$date)
{
    $minutes=$date['minutes'];
    if($pattern==='m')
        return $minutes;
    elseif($pattern==='mm')
        return str_pad($minutes,2,'0',STR_PAD_LEFT);
    else
        throw new CException(Yii::t('yii','The pattern for minutes must be "m" or "mm".'));
}

protected function formatMonth($pattern,$date)
{
    $month=$date['mon'];
    switch($pattern)
    {
        case 'M':
            return $month;
        case 'MM':
            return str_pad($month,2,'0',STR_PAD_LEFT);
        case 'MMM':
            return $this->_locale->getMonthName($month,'abbreviated');
        case 'MMMM':
            return $this->_locale->getMonthName($month,'wide');
        case 'MMMMM':
            return $this->_locale->getMonthName($month,'narrow');
        case 'L':
            return $month;
        case 'LL':
            return str_pad($month,2,'0',STR_PAD_LEFT);
        case 'LLL':
            return $this->_locale->getMonthName($month,'abbreviated', true);
        case 'LLLL':
            return $this->_locale->getMonthName($month,'wide', true);
        case 'LLLLL':
            return $this->_locale->getMonthName($month,'narrow', true);
        default:
            throw new CException(Yii::t('yii','The pattern for month must be "M", "MM", "MMM", "MMMM", "L", "LL", "LLL" or "LLLL".'));
    }
}

protected function formatPeriod($pattern,$date)
{
    if($pattern==='a')
    {
        if(intval($date['hours']/12))
            return $this->_locale->getPMName();
        else
            return $this->_locale->getAMName();
    }
    else
        throw new CException(Yii::t('yii','The pattern for AM/PM marker must be "a".'));
}

protected function formatSeconds($pattern,$date)
{
    $seconds=$date['seconds'];
    if($pattern==='s')
        return $seconds;
    elseif($pattern==='ss')
        return str_pad($seconds,2,'0',STR_PAD_LEFT);
    else
        throw new CException(Yii::t('yii','The pattern for seconds must be "s" or "ss".'));
}

protected function formatTimeZone($pattern,$date)
{
    if($pattern[0]==='z' || $pattern[0]==='v')
        return @date('T', @mktime($date['hours'], $date['minutes'], $date['seconds'], $date['mon'], $date['mday'], $date['year']));
    elseif($pattern[0]==='Z')
        return @date('P', @mktime($date['hours'], $date['minutes'], $date['seconds'], $date['mon'], $date['mday'], $date['year']));
    else
        throw new CException(Yii::t('yii','The pattern for time zone must be "z" or "v".'));
}

protected function formatWeekInMonth($pattern,$date)
{
    if($pattern==='W')
    {
        $weekDay=date('N',mktime(0,0,0,$date['mon'],1,$date['year']));
        return floor(($weekDay+$date['mday']-2)/7)+1;
    }
    else
        throw new CException(Yii::t('yii','The pattern for week in month must be "W".'));
}

protected function formatWeekInYear($pattern,$date)
{
    if($pattern==='w')
        return @date('W',@mktime(0,0,0,$date['mon'],$date['mday'],$date['year']));
    else
        throw new CException(Yii::t('yii','The pattern for week in year must be "w".'));
}

protected function formatYear($pattern,$date)
{
    $year=$date['year'];
    if($pattern==='yy')
        return str_pad($year%100,2,'0',STR_PAD_LEFT);
    else
        return str_pad($year,strlen($pattern),'0',STR_PAD_LEFT);
}

protected function parseFormat($pattern)
{
    static $formats=array();  // cache
    if(isset($formats[$pattern]))
        return $formats[$pattern];
    $tokens=array();
    $n=strlen($pattern);
    $isLiteral=false;
    $literal='';
    for($i=0;$i<$n;++$i)
    {
        $c=$pattern[$i];
        if($c==="'")
        {
            if($i<$n-1 && $pattern[$i+1]==="'")
            {
                $tokens[]="'";
                $i++;
            }
            elseif($isLiteral)
            {
                $tokens[]=$literal;
                $literal='';
                $isLiteral=false;
            }
            else
            {
                $isLiteral=true;
                $literal='';
            }
        }
        elseif($isLiteral)
            $literal.=$c;
        else
        {
            for($j=$i+1;$j<$n;++$j)
            {
                if($pattern[$j]!==$c)
                    break;
            }
            $p=str_repeat($c,$j-$i);
            if(isset(self::$_formatters[$c]))
                $tokens[]=array(self::$_formatters[$c],$p);
            else
                $tokens[]=$p;
            $i=$j-1;
        }
    }
    if($literal!=='')
        $tokens[]=$literal;

    return $formats[$pattern]=$tokens;
}