class Log

class Log {
    
    /**
     * Cache of logged queries. This will only be used if the query logger is enabled.
     *
     * The structure for the logging array is as follows:
     *
     * array(
     *   $logging_key = array(
     *     array('query' => '', 'args' => array(), 'caller' => '', 'target' => '', 'time' => 0, 'start' => 0),
     *     array('query' => '', 'args' => array(), 'caller' => '', 'target' => '', 'time' => 0, 'start' => 0),
     *   ),
     * );
     *
     * @var array
     */
    protected $queryLog = [];
    
    /**
     * The connection key for which this object is logging.
     *
     * @var string
     */
    protected $connectionKey = 'default';
    
    /**
     * Constructor.
     *
     * @param $key
     *   The database connection key for which to enable logging.
     */
    public function __construct($key = 'default') {
        $this->connectionKey = $key;
    }
    
    /**
     * Begin logging queries to the specified connection and logging key.
     *
     * If the specified logging key is already running this method does nothing.
     *
     * @param $logging_key
     *   The identification key for this log request. By specifying different
     *   logging keys we are able to start and stop multiple logging runs
     *   simultaneously without them colliding.
     */
    public function start($logging_key) {
        if (empty($this->queryLog[$logging_key])) {
            $this->clear($logging_key);
        }
    }
    
    /**
     * Retrieve the query log for the specified logging key so far.
     *
     * @param $logging_key
     *   The logging key to fetch.
     *
     * @return array
     *   An indexed array of all query records for this logging key.
     */
    public function get($logging_key) {
        return $this->queryLog[$logging_key];
    }
    
    /**
     * Empty the query log for the specified logging key.
     *
     * This method does not stop logging, it simply clears the log. To stop
     * logging, use the end() method.
     *
     * @param $logging_key
     *   The logging key to empty.
     */
    public function clear($logging_key) {
        $this->queryLog[$logging_key] = [];
    }
    
    /**
     * Stop logging for the specified logging key.
     *
     * @param $logging_key
     *   The logging key to stop.
     */
    public function end($logging_key) {
        unset($this->queryLog[$logging_key]);
    }
    
    /**
     * Log a query to all active logging keys, from a statement execution event.
     *
     * @param \Drupal\Core\Database\Event\StatementExecutionEndEvent $event
     *   The statement execution event.
     */
    public function logFromEvent(StatementExecutionEndEvent $event) : void {
        foreach (array_keys($this->queryLog) as $key) {
            $this->queryLog[$key][] = [
                'query' => $event->queryString,
                'args' => $event->args,
                'target' => $event->target,
                'caller' => $event->caller,
                'time' => $event->getElapsedTime(),
                'start' => $event->startTime,
            ];
        }
    }

}