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<?php

namespace Aws\DynamoDb;

/**

 * Provides an interface for using Amazon DynamoDB as a session store by hooking

 * into PHP's session handler hooks. Once registered, You may use the native

 * `$_SESSION` superglobal and session functions, and the sessions will be

 * stored automatically in DynamoDB. DynamoDB is a great session storage

 * solution due to its speed, scalability, and fault tolerance.

 *

 * For maximum performance, we recommend that you keep the size of your sessions

 * small. Locking is disabled by default, since it can drive up latencies and

 * costs under high traffic. Only turn it on if you need it.

 *

 * By far, the most expensive operation is garbage collection. Therefore, we

 * encourage you to carefully consider your session garbage collection strategy.

 * Note: the DynamoDB Session Handler does not allow garbage collection to be

 * triggered randomly. You must run garbage collection manually or through other

 * automated means using a cron job or similar scheduling technique.

 */

class SessionHandler implements \SessionHandlerInterface

{

    /** @var SessionConnectionInterface Session save logic.*/

    private $connection;

    /** @var string Session save path. */

    private $savePath;

    /** @var string Session name. */

    private $sessionName;

    /** @var string The last known session ID */

    private $openSessionId = '';

    /** @var string Stores serialized data for tracking changes. */

    private $dataRead = '';

    /** @var bool Keeps track of whether the session has been written. */

    private $sessionWritten = false;

    /**

     * Creates a new DynamoDB Session Handler.

     *

     * The configuration array accepts the following array keys and values:

     * - table_name:                    Name of table to store the sessions.

     * - hash_key:                      Name of hash key in table. Default: "id".

     * - data_attribute:                Name of the data attribute in table. Default: "data".

     * - session_lifetime:              Lifetime of inactive sessions expiration.

     * - session_lifetime_attribute:    Name of the session life time attribute in table. Default: "expires".

     * - consistent_read:               Whether or not to use consistent reads.

     * - batch_config:                  Batch options used for garbage collection.

     * - locking:                       Whether or not to use session locking.

     * - max_lock_wait_time:            Max time (s) to wait for lock acquisition.

     * - min_lock_retry_microtime:      Min time (µs) to wait between lock attempts.

     * - max_lock_retry_microtime:      Max time (µs) to wait between lock attempts.

     *

     * You can find the full list of parameters and defaults within the trait

     * Aws\DynamoDb\SessionConnectionConfigTrait

     *

     * @param DynamoDbClient $client Client for doing DynamoDB operations

     * @param array          $config Configuration for the Session Handler

     *

     * @return SessionHandler

     */

    public static function fromClient(DynamoDbClient $client, array $config = [])

    {

        $config += ['locking' => false];

        if ($config['locking']) {

            $connection = new LockingSessionConnection($client, $config);

        } else {

            $connection = new StandardSessionConnection($client, $config);

        }

        return new static($connection);

    }

    /**

     * @param SessionConnectionInterface $connection

     */

    public function __construct(SessionConnectionInterface $connection)

    {

        $this->connection = $connection;

    }

    /**

     * Register the DynamoDB session handler.

     *

     * @return bool Whether or not the handler was registered.

     * @codeCoverageIgnore

     */

    public function register()

    {

         return session_set_save_handler($this, true);

    }

    /**

     * Open a session for writing. Triggered by session_start().

     *

     * @param string $savePath    Session save path.

     * @param string $sessionName Session name.

     *

     * @return bool Whether or not the operation succeeded.

     */

     #[\ReturnTypeWillChange]

    public function open($savePath, $sessionName)

    {

        $this->savePath = $savePath;

        $this->sessionName = $sessionName;

        return true;

    }

    /**

     * Close a session from writing.

     *

     * @return bool Success

     */

     #[\ReturnTypeWillChange]

    public function close()

    {

        $id = session_id();

        // Make sure the session is unlocked and the expiration time is updated,

        // even if the write did not occur

        if ($this->openSessionId !== $id || !$this->sessionWritten) {

            $result = $this->connection->write($this->formatId($id), '', false);

            $this->sessionWritten = (bool) $result;

        }

        return $this->sessionWritten;

    }

    /**

     * Read a session stored in DynamoDB.

     *

     * @param string $id Session ID.

     *

     * @return string Session data.

     */

     #[\ReturnTypeWillChange]

    public function read($id)

    {

        $this->openSessionId = $id;

        // PHP expects an empty string to be returned from this method if no

        // data is retrieved

        $this->dataRead = '';

        // Get session data using the selected locking strategy

        $item = $this->connection->read($this->formatId($id));

        $dataAttribute = $this->connection->getDataAttribute();

        $sessionLifetimeAttribute = $this->connection->getSessionLifetimeAttribute();

        // Return the data if it is not expired. If it is expired, remove it

        if (isset($item[$sessionLifetimeAttribute]) && isset($item[$dataAttribute])) {

            $this->dataRead = $item[$dataAttribute];

            if ($item[$sessionLifetimeAttribute] <= time()) {

                $this->dataRead = '';

                $this->destroy($id);

            }

        }

        return $this->dataRead;

    }

    /**

     * Write a session to DynamoDB.

     *

     * @param string $id   Session ID.

     * @param string $data Serialized session data to write.

     *

     * @return bool Whether or not the operation succeeded.

     */

     #[\ReturnTypeWillChange]

    public function write($id, $data)

    {

        $changed = $id !== $this->openSessionId

            || $data !== $this->dataRead;

        $this->openSessionId = $id;

        // Write the session data using the selected locking strategy

        $this->sessionWritten = $this->connection

            ->write($this->formatId($id), $data, $changed);

        return $this->sessionWritten;

    }

    /**

     * Delete a session stored in DynamoDB.

     *

     * @param string $id Session ID.

     *

     * @return bool Whether or not the operation succeeded.

     */

     #[\ReturnTypeWillChange]

    public function destroy($id)

    {

        $this->openSessionId = $id;

        // Delete the session data using the selected locking strategy

        $this->sessionWritten

            = $this->connection->delete($this->formatId($id));

        return $this->sessionWritten;

    }

    /**

     * Satisfies the session handler interface, but does nothing. To do garbage

     * collection, you must manually call the garbageCollect() method.

     *

     * @param int $maxLifetime Ignored.

     *

     * @return bool Whether or not the operation succeeded.

     * @codeCoverageIgnore

     */

     #[\ReturnTypeWillChange]

    public function gc($maxLifetime)

    {

        // Garbage collection for a DynamoDB table must be triggered manually.

        return true;

    }

    /**

     * Triggers garbage collection on expired sessions.

     * @codeCoverageIgnore

     */

    public function garbageCollect()

    {

        $this->connection->deleteExpired();

    }

    /**

     * Prepend the session ID with the session name.

     *

     * @param string $id The session ID.

     *

     * @return string Prepared session ID.

     */

    private function formatId($id)

    {

        return trim($this->sessionName . '_' . $id, '_');

    }

}