/**
 * Returns a formatted string that represents a date in user time
 * <b>WARNING: note that the format is for strftime(), not date().</b>
 * Because of a bug in most Windows time libraries, we can't use
 * the nicer %e, so we have to use %d which has leading zeroes.
 * A lot of the fuss in the function is just getting rid of these leading
 * zeroes as efficiently as possible.
 *
 * If parameter fixday = true (default), then take off leading
 * zero from %d, else mantain it.
 *
 * @param int $date timestamp in GMT
 * @param string $format strftime format
 *     If empty (default) then 'strftimedaydatetime' from the language pack 
 *     will be used
 * @param float $timezone
 * @param bool $fixday 
 *     If true (default) then the leading zero from %d is removed, 
 *     otherwise the leading zero is mantained.
 *     Can be overridden by setting $CFG->nofixday to true in config.php
 * @param bool $fixmonth 
 *     If true (default) then the leading zero from %m is removed, 
 *     otherwise the leading zero is mantained.
 *     Can be overridden by setting $CFG->nofixmonth to true in config.php
 * @return string
 */
function userdate($date, $format='', $timezone=99, $fixday = true, $fixmonth = true) {
    global $CFG;

    if (empty($format)) {
        $format = get_string('strftimedaydatetime');
    }

    // variables required for fixing dates in some multibyte language packs on Windows servers
    static $endchar = '';
    static $textlib = false;
    static $localewin = null;

    // set up date fixing variables if they are required for this language pack
    if (is_null($localewin)) {
        $localewin = new stdClass();
        if ($CFG->ostype=='WINDOWS') {
            $localewin->charset = get_string('localewincharset');
            $localewin->charsetdaymonth = get_string('localewincharsetdaymonth');
        } else {
            $localewin->charset = false;
            $localewin->charsetdaymonth = false;
        }
        if ($localewin->charsetdaymonth) {
            // $endchar helps strftime() to detect the end of the format string
            // when the last character would otherwise be a multibyte character
            $endchar = ' '; 
        }
        if ($localewin->charset || $localewin->charsetdaymonth) {
            $textlib = textlib_get_instance();
        }
    }

    // assemble an array of fixes to be applied during date formatting
    $fix = array();
    if (empty($CFG->nofixday) && $fixday) {
        $fix['%d'] = 'dd'; // two-digit day number (01 - 31)
    }
    if (empty($CFG->nofixmonth) && $fixmonth) {
        $fix['%m'] = 'mm'; // two-digit month number (01 - 12)
    }
    if ($localewin->charsetdaymonth) {
        $fix['%A'] = 'AA'; //  full weekday name
        $fix['%a'] = 'aa'; // abbreviated weekday name
        $fix['%B'] = 'BB'; // full month name
        $fix['%b'] = 'bb'; // abbreviated month name
        $fix['%p'] = 'pp'; // 'am' or 'pm' (or the corresponding strings for the current locale)
    }

    // modify format string for each relevant fix (unnecessary fixes are discarded)
    foreach ($fix as $fmt=>$str) {
        if (strpos($format, $fmt)===false) {
            unset($fix[$fmt]);
        } else {
            $format = str_replace($fmt, $str, $format);
        }
    }

    // adjust date for this time zone
    $date += dst_offset_on($date);
    $timezone = get_user_timezone_offset($timezone);

    // define date formatting function 
    if (abs($timezone) > 13) {   /// Server time
        $strftime = 'strftime';
    } else {
        $strftime = 'gmstrftime';
        $date += (int)($timezone * 3600);
    }

    // format the date using the modified $format string 
    $datestring = $strftime($format.$endchar, $date);

    // if necessary, remove $endchar from the end of $datestring
    if ($endchar) {
        $datestring = substr($datestring, 0, -1);
    }

    // apply relevant fixes for this format string
    foreach ($fix as $fmt=>$str) {
        switch ($fmt) {
            case '%d':
            case '%m':
                $replace = $strftime($fmt, $date);
                if (substr($replace, 0, 1)==='0') {
                    $replace = substr($replace, 1); // remove leading zero
                }
                $datestring = str_replace($str, $replace, $datestring);
                break;
            case '%A':
            case '%a':
            case '%B':
            case '%b':
            case '%p':
                $replace = $textlib->convert($strftime($fmt, $date), $localewin->charsetdaymonth, 'utf-8');
                $datestring = str_replace($str, $replace, $datestring);
                break;
        }
    }

    // If we are running under Windows convert from windows encoding to UTF-8
    // (because it's impossible to specify UTF-8 to fetch locale info in Win32)
    if ($localewin->charset) {
        $datestring = $textlib->convert($datestring, $localewin->charset, 'utf-8');
    }

    return $datestring;
}