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header(last_modified());

function last_modified() {
  $file = './lastmod.json';
	$current_date = gmdate("Ymd");
	if (file_exists($file)) {
		$json = file_get_contents($file);
		$lm_dates = json_decode($json);
		/**
		http://sitename.ru/
		http://sitename.ru/ishop/70
		http://sitename.ru/site/4
		http://sitename.ru/site/7
		http://sitename.ru/site/8
		 */
		$reg_exp = '/^(\/(ishop\/70|site\/(4|7|8))?)$/';

		if (preg_match($reg_exp, $_SERVER['REQUEST_URI'])) {
			$type = 'daily';
			$num_of_days = 1;
		} else {
			$type = 'weekly';
			$num_of_days = 7;
		}
		$date = $lm_dates->$type->date;
		if (($current_date - $date) >= $num_of_days) {
			$lm = "Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT";
			$lm_dates->$type->date   = $current_date;
			$lm_dates->$type->string = $lm;
			file_put_contents($file, json_encode($lm_dates));
		} else {
			$lm = $lm_dates->$type->string;
		}
	} else {
		$lm = "Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT";
		$dates = array(
			'daily'  => array('date' => $current_date, 'string' => $lm),
			'weekly' => array('date' => $current_date, 'string' => $lm)
		);
		file_put_contents($file,  json_encode($dates));
	}

	return $lm;
}