<?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */

namespace Symfony\Component\HttpFoundation\Session\Storage\Handler;

/**
 * Session handler using a PDO connection to read and write data.
 *
 * Session data is a binary string that can contain non-printable characters like the null byte.
 * For this reason this handler base64 encodes the data to be able to save it in a character column.
 *
 * This version of the PdoSessionHandler does NOT implement locking. So concurrent requests to the
 * same session can result in data loss due to race conditions.
 *
 * @author Fabien Potencier <fabien@symfony.com>
 * @author Michael Williams <michael.williams@funsational.com>
 * @author Tobias Schultze <http://tobion.de>
 */
class PdoSessionHandler implements \SessionHandlerInterface
{
    /**
     * @var \PDO PDO instance
     */
    private $pdo;

    /**
     * @var string Table name
     */
    private $table;

    /**
     * @var string Column for session id
     */
    private $idCol;

    /**
     * @var string Column for session data
     */
    private $dataCol;

    /**
     * @var string Column for timestamp
     */
    private $timeCol;

    /**
     * Constructor.
     *
     * List of available options:
     *  * db_table: The name of the table [required]
     *  * db_id_col: The column where to store the session id [default: sess_id]
     *  * db_data_col: The column where to store the session data [default: sess_data]
     *  * db_time_col: The column where to store the timestamp [default: sess_time]
     *
     * @param \PDO  $pdo       A \PDO instance
     * @param array $dbOptions An associative array of DB options
     *
     * @throws \InvalidArgumentException When "db_table" option is not provided
     */
    public function __construct(\PDO $pdo, array $dbOptions = array())
    {
        if (!array_key_exists('db_table', $dbOptions)) {
            throw new \InvalidArgumentException('You must provide the "db_table" option for a PdoSessionStorage.');
        }
        if (\PDO::ERRMODE_EXCEPTION !== $pdo->getAttribute(\PDO::ATTR_ERRMODE)) {
            throw new \InvalidArgumentException(sprintf('"%s" requires PDO error mode attribute be set to throw Exceptions (i.e. $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION))', __CLASS__));
        }
        $this->pdo = $pdo;
        $dbOptions = array_merge(array(
            'db_id_col' => 'sess_id',
            'db_data_col' => 'sess_data',
            'db_time_col' => 'sess_time',
        ), $dbOptions);

        $this->table = $dbOptions['db_table'];
        $this->idCol = $dbOptions['db_id_col'];
        $this->dataCol = $dbOptions['db_data_col'];
        $this->timeCol = $dbOptions['db_time_col'];
    }

    /**
     * {@inheritdoc}
     */
    public function open($savePath, $sessionName)
    {
        return true;
    }

    /**
     * {@inheritdoc}
     */
    public function close()
    {
        return true;
    }

    /**
     * {@inheritdoc}
     */
    public function destroy($sessionId)
    {
        // delete the record associated with this id
        $sql = "DELETE FROM $this->table WHERE $this->idCol = :id";

        try {
            $stmt = $this->pdo->prepare($sql);
            $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
            $stmt->execute();
        } catch (\PDOException $e) {
            throw new \RuntimeException(sprintf('PDOException was thrown when trying to delete a session: %s', $e->getMessage()), 0, $e);
        }

        return true;
    }

    /**
     * {@inheritdoc}
     */
    public function gc($maxlifetime)
    {
        // delete the session records that have expired
        $sql = "DELETE FROM $this->table WHERE $this->timeCol < :time";

        try {
            $stmt = $this->pdo->prepare($sql);
            $stmt->bindValue(':time', time() - $maxlifetime, \PDO::PARAM_INT);
            $stmt->execute();
        } catch (\PDOException $e) {
            throw new \RuntimeException(sprintf('PDOException was thrown when trying to delete expired sessions: %s', $e->getMessage()), 0, $e);
        }

        return true;
    }

    /**
     * {@inheritdoc}
     */
    public function read($sessionId)
    {
        $sql = "SELECT $this->dataCol FROM $this->table WHERE $this->idCol = :id";

        try {
            $stmt = $this->pdo->prepare($sql);
            $stmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
            $stmt->execute();

            // We use fetchAll instead of fetchColumn to make sure the DB cursor gets closed
            $sessionRows = $stmt->fetchAll(\PDO::FETCH_NUM);

            if ($sessionRows) {
                return base64_decode($sessionRows[0][0]);
            }

            return '';
        } catch (\PDOException $e) {
            throw new \RuntimeException(sprintf('PDOException was thrown when trying to read the session data: %s', $e->getMessage()), 0, $e);
        }
    }

    /**
     * {@inheritdoc}
     */
    public function write($sessionId, $data)
    {
        $encoded = base64_encode($data);

        try {
            // We use a single MERGE SQL query when supported by the database.
            $mergeSql = $this->getMergeSql();

            if (null !== $mergeSql) {
                $mergeStmt = $this->pdo->prepare($mergeSql);
                $mergeStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
                $mergeStmt->bindParam(':data', $encoded, \PDO::PARAM_STR);
                $mergeStmt->bindValue(':time', time(), \PDO::PARAM_INT);
                $mergeStmt->execute();

                return true;
            }

            $updateStmt = $this->pdo->prepare(
                "UPDATE $this->table SET $this->dataCol = :data, $this->timeCol = :time WHERE $this->idCol = :id"
            );
            $updateStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
            $updateStmt->bindParam(':data', $encoded, \PDO::PARAM_STR);
            $updateStmt->bindValue(':time', time(), \PDO::PARAM_INT);
            $updateStmt->execute();

            // When MERGE is not supported, like in Postgres, we have to use this approach that can result in
            // duplicate key errors when the same session is written simultaneously. We can just catch such an
            // error and re-execute the update. This is similar to a serializable transaction with retry logic
            // on serialization failures but without the overhead and without possible false positives due to
            // longer gap locking.
            if (!$updateStmt->rowCount()) {
                try {
                    $insertStmt = $this->pdo->prepare(
                        "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time)"
                    );
                    $insertStmt->bindParam(':id', $sessionId, \PDO::PARAM_STR);
                    $insertStmt->bindParam(':data', $encoded, \PDO::PARAM_STR);
                    $insertStmt->bindValue(':time', time(), \PDO::PARAM_INT);
                    $insertStmt->execute();
                } catch (\PDOException $e) {
                    // Handle integrity violation SQLSTATE 23000 (or a subclass like 23505 in Postgres) for duplicate keys
                    if (0 === strpos($e->getCode(), '23')) {
                        $updateStmt->execute();
                    } else {
                        throw $e;
                    }
                }
            }
        } catch (\PDOException $e) {
            throw new \RuntimeException(sprintf('PDOException was thrown when trying to write the session data: %s', $e->getMessage()), 0, $e);
        }

        return true;
    }

    /**
     * Returns a merge/upsert (i.e. insert or update) SQL query when supported by the database.
     *
     * @return string|null The SQL string or null when not supported
     */
    private function getMergeSql()
    {
        $driver = $this->pdo->getAttribute(\PDO::ATTR_DRIVER_NAME);

        switch ($driver) {
            case 'mysql':
                return "INSERT INTO $this->table ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time) ".
                    "ON DUPLICATE KEY UPDATE $this->dataCol = VALUES($this->dataCol), $this->timeCol = VALUES($this->timeCol)";
            case 'oci':
                // DUAL is Oracle specific dummy table
                return "MERGE INTO $this->table USING DUAL ON ($this->idCol = :id) ".
                    "WHEN NOT MATCHED THEN INSERT ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time) ".
                    "WHEN MATCHED THEN UPDATE SET $this->dataCol = :data, $this->timeCol = :time";
            case 'sqlsrv' === $driver && version_compare($this->pdo->getAttribute(\PDO::ATTR_SERVER_VERSION), '10', '>='):
                // MERGE is only available since SQL Server 2008 and must be terminated by semicolon
                // It also requires HOLDLOCK according to http://weblogs.sqlteam.com/dang/archive/2009/01/31/UPSERT-Race-Condition-With-MERGE.aspx
                return "MERGE INTO $this->table WITH (HOLDLOCK) USING (SELECT 1 AS dummy) AS src ON ($this->idCol = :id) ".
                    "WHEN NOT MATCHED THEN INSERT ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time) ".
                    "WHEN MATCHED THEN UPDATE SET $this->dataCol = :data, $this->timeCol = :time;";
            case 'sqlite':
                return "INSERT OR REPLACE INTO $this->table ($this->idCol, $this->dataCol, $this->timeCol) VALUES (:id, :data, :time)";
        }
    }
}
