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.
     *
     * @param \Drupal\Core\Database\StatementInterface $statement
     *   The prepared statement object to log.
     * @param array $args
     *   The arguments passed to the statement object.
     * @param float $time
     *   The time the query took to execute as a float (in seconds with
     *   microsecond precision).
     * @param float $start
     *   The time the query started as a float (in seconds since the Unix epoch
     *   with microsecond precision).
     */
    public function log(StatementInterface $statement, $args, $time, float $start = NULL) {
        foreach (array_keys($this->queryLog) as $key) {
            // @todo Remove the method_exists check for getConnectionTarget in
            //   Drupal 10.
            // @see https://www.drupal.org/project/drupal/issues/3210310
            $this->queryLog[$key][] = [
                'query' => $statement->getQueryString(),
                'args' => $args,
                'target' => method_exists($statement, 'getConnectionTarget') ? $statement->getConnectionTarget() : $statement->dbh
                    ->getTarget(),
                'caller' => $this->findCaller(),
                'time' => $time,
                'start' => $start,
            ];
        }
    }
    
    /**
     * Determine the routine that called this query.
     *
     * Traversing the call stack from the very first call made during the
     * request, we define "the routine that called this query" as the last entry
     * in the call stack that is not any method called from the namespace of the
     * database driver, is not inside the Drupal\Core\Database namespace and does
     * have a file (which excludes call_user_func_array(), anonymous functions
     * and similar). That makes the climbing logic very simple, and handles the
     * variable stack depth caused by the query builders.
     *
     * See the @link http://php.net/debug_backtrace debug_backtrace() @endlink
     * function.
     *
     * @return array|null
     *   This method returns a stack trace entry similar to that generated by
     *   debug_backtrace(). However, it flattens the trace entry and the trace
     *   entry before it so that we get the function and args of the function that
     *   called into the database system, not the function and args of the
     *   database call itself.
     */
    public function findCaller() {
        $driver_namespace = Database::getConnectionInfo($this->connectionKey)['default']['namespace'];
        $stack = static::removeDatabaseEntries($this->getDebugBacktrace(), $driver_namespace);
        // Return the first function call whose stack entry has a 'file' key, that
        // is, it is not a callback or a closure.
        for ($i = 0; $i < count($stack); $i++) {
            if (!empty($stack[$i]['file'])) {
                return [
                    'file' => $stack[$i]['file'],
                    'line' => $stack[$i]['line'],
                    'function' => $stack[$i + 1]['function'],
                    'class' => $stack[$i + 1]['class'] ?? NULL,
                    'type' => $stack[$i + 1]['type'] ?? NULL,
                    'args' => $stack[$i + 1]['args'] ?? [],
                ];
            }
        }
    }
    
    /**
     * Removes database related calls from a backtrace array.
     *
     * @param array $backtrace
     *   A standard PHP backtrace. Passed by reference.
     * @param string $driver_namespace
     *   The PHP namespace of the database driver.
     *
     * @return array
     *   The cleaned backtrace array.
     */
    public static function removeDatabaseEntries(array $backtrace, string $driver_namespace) : array {
        // Starting from the very first entry processed during the request, find
        // the first function call that can be identified as a call to a
        // method/function in the database layer.
        for ($n = count($backtrace) - 1; $n >= 0; $n--) {
            // If the call was made from a function, 'class' will be empty. We give
            // it a default empty string value in that case.
            $class = $backtrace[$n]['class'] ?? '';
            if (strpos($class, __NAMESPACE__, 0) === 0 || strpos($class, $driver_namespace, 0) === 0) {
                break;
            }
        }
        return array_values(array_slice($backtrace, $n));
    }
    
    /**
     * Gets the debug backtrace.
     *
     * Wraps the debug_backtrace function to allow mocking results in PHPUnit
     * tests.
     *
     * @return array[]
     *   The debug backtrace.
     */
    protected function getDebugBacktrace() {
        return debug_backtrace();
    }

}