<?PHP
/**
 * Gathers wrappers for handling basic security operations.
 */
declare(strict_types = 1);

/**
 * Class providing static functions with basic security operations.
 */
final class MD_STD_SEC {
    /**
     * Function for retrieving the anti-csrf token or generating it if need be.
     *
     * @return string
     */
    public static function getAntiCsrfToken():string {

        if (empty($_SESSION['csrf-token'])) {
            $_SESSION['csrf-token'] = bin2hex(random_bytes(32));
        }

        return $_SESSION['csrf-token'];

    }

    /**
     * Function for validating anti-csrf tokens. Each anti-csrf token is removed
     * after use.
     *
     * @return boolean
     */
    public static function validateAntiCsrfToken():bool {

        $validity = false;
        if (!empty($_POST['csrf-token'])
            && !empty($_SESSION['csrf-token'])
            && hash_equals($_SESSION['csrf-token'], $_POST['csrf-token']) === true
        ) {
            $validity = true;
        }
        $_SESSION['csrf-token'] = null; unset($_SESSION['csrf-token']);

        return $validity;

    }

    const BRUTE_FORCE_DELAY_DEFAULT = 2000; // 2000 microseconds = 2 milliseconds
    const BRUTE_FORCE_DELAY_MULTIPLIER_COMMON   = 1.08;
    const BRUTE_FORCE_DELAY_MULTIPLIER_PER_USER = 1.8;
    const BRUTE_FORCE_DELAY_MULTIPLIER_PER_IP = 4;

    /**
     * Prevent brute force attacks by delaying the login .
     *
     * @param string $tool_name Identifier of the login.
     * @param string $username  Username to look for.
     *
     * @return boolean
     */
    public static function preventBruteForce(string $tool_name, string $username):bool {

        // Unstable but working way to get the user's IP. If the IP is falsified,
        // this can't be found out anyway and security is established by _common.
        $ip = \strval($_SERVER['REMOTE_ADDR'] ?: ($_SERVER['HTTP_X_FORWARDED_FOR'] ?: $_SERVER['HTTP_CLIENT_IP']));

        // Set name of log file
        $logfile_common = \sys_get_temp_dir() . "/logins_{$tool_name}.json";

        // Ensure the log files exist
        if (!\file_exists($logfile_common)) \file_put_contents($logfile_common, "[]");

        // Hash entered username and IP to prevent malicious strings from
        // entering the system.
        $hash_user = \md5($username);
        $hash_ip   = \md5($ip);

        // Delete the log files if they are too old
        $loginLog = \json_decode(MD_STD::file_get_contents($logfile_common), \true) ?: [];

        // Ensure the counters exist and aren't old than 600 seconds / 10 minutes
        if (empty($loginLog['common']) || \time() - $loginLog['common']['time'] > 600) {
            $loginLog['common'] = ["count" => 0, "time" => \time()];
        }
        if (empty($loginLog['usr'][$hash_user]) || \time() - $loginLog['usr'][$hash_user]['time'] > 600) {
            $loginLog['usr'][$hash_user] = ["count" => 0, "time" => \time()];
        }
        if (empty($loginLog['ip'][$hash_ip]) || \time() - $loginLog['ip'][$hash_ip]['time'] > 600) {
            $loginLog['ip'][$hash_ip] = ["count" => 0, "time" => \time()];
        }

        // Increase counters and update timers
        $loginLog['common']['count']++;
        $loginLog['common']['time'] = \time();
        $loginLog['usr'][$hash_user]['count']++;
        $loginLog['usr'][$hash_user]['time'] = \time();
        $loginLog['ip'][$hash_ip]['count']++;
        $loginLog['ip'][$hash_ip]['time'] = \time();

        // Update the log file
        \file_put_contents($logfile_common, \json_encode($loginLog));

        // Translate counters into delay multipliers
        $delay_multiplier_common = $loginLog['common']['count'];
        $delay_multiplier_per_user = $loginLog['usr'][$hash_user]['count'];
        $delay_multiplier_per_ip = $loginLog['ip'][$hash_ip]['count'];

        // Calculate delay
        $delay_micoseconds = \intval(self::BRUTE_FORCE_DELAY_DEFAULT *
            (self::BRUTE_FORCE_DELAY_MULTIPLIER_COMMON ** $delay_multiplier_common) *
            (self::BRUTE_FORCE_DELAY_MULTIPLIER_PER_USER ** $delay_multiplier_per_user) *
            (self::BRUTE_FORCE_DELAY_MULTIPLIER_PER_IP ** $delay_multiplier_per_ip));

        $max_execution_microseconds = \abs((int)\ini_get("max_execution_time")) * 1000000;

        // Sleep
        \usleep(min($delay_micoseconds, \abs($max_execution_microseconds - 1000000)));

        if ($delay_micoseconds > \abs($max_execution_microseconds - 1000000)) {
            return false;
        }

        return true;

    }

    /**
     * Send CSP headers.
     *
     * @param array{default-src: string, connect-src: string, script-src: string, img-src: string, media-src: string, style-src: string, frame-src: string, object-src: string, base-uri: string, form-action: string, frame-ancestors?: string} $directives      Directives to send. Font source is always set to 'self', and hence excluded.
     * @param string                                                                                                                                                                                                                             $frame_ancestors Frame ancestors directive. Default is to not set it.
     *
     * @return void
     */
    public static function sendContentSecurityPolicy(array $directives, string $frame_ancestors = ""):void {

        $policy = 'Content-Security-Policy: default-src ' . $directives['default-src'] . '; connect-src ' . $directives['connect-src'] . '; script-src ' . $directives['script-src'] . '; img-src ' . $directives['img-src'] . '; media-src ' . $directives['media-src'] . '; style-src ' . $directives['style-src'] . '; font-src \'self\'; frame-src ' . $directives['frame-src'] . '; object-src ' . $directives['object-src'] . '; base-uri ' . $directives['base-uri'] . '; form-action ' . $directives['form-action'] . '; manifest-src \'self\';';

        if (!empty($frame_ancestors)) {
            $policy .= ' frame-ancestors ' . $frame_ancestors . ';';
        }

        header($policy);

    }
}