<?php
/**
 * MediaWiki session
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 * http://www.gnu.org/copyleft/gpl.html
 *
 * @file
 * @ingroup Session
 */

namespace MediaWiki\Session;

use Psr\Log\LoggerInterface;
use User;
use WebRequest;

/**
 * Manages data for an an authenticated session
 *
 * A Session represents the fact that the current HTTP request is part of a
 * session. There are two broad types of Sessions, based on whether they
 * return true or false from self::canSetUser():
 * * When true (mutable), the Session identifies multiple requests as part of
 *   a session generically, with no tie to a particular user.
 * * When false (immutable), the Session identifies multiple requests as part
 *   of a session by identifying and authenticating the request itself as
 *   belonging to a particular user.
 *
 * The Session object also serves as a replacement for PHP's $_SESSION,
 * managing access to per-session data.
 *
 * @ingroup Session
 * @since 1.27
 */
final class Session implements \Countable, \Iterator, \ArrayAccess {
	/** @var null|string[] Encryption algorithm to use */
	private static $encryptionAlgorithm = null;

	/** @var SessionBackend Session backend */
	private $backend;

	/** @var int Session index */
	private $index;

	/** @var LoggerInterface */
	private $logger;

	/**
	 * @param SessionBackend $backend
	 * @param int $index
	 * @param LoggerInterface $logger
	 */
	public function __construct( SessionBackend $backend, $index, LoggerInterface $logger ) {
		$this->backend = $backend;
		$this->index = $index;
		$this->logger = $logger;
	}

	public function __destruct() {
		$this->backend->deregisterSession( $this->index );
	}

	/**
	 * Returns the session ID
	 * @return string
	 */
	public function getId() {
		return $this->backend->getId();
	}

	/**
	 * Returns the SessionId object
	 * @private For internal use by WebRequest
	 * @return SessionId
	 */
	public function getSessionId() {
		return $this->backend->getSessionId();
	}

	/**
	 * Changes the session ID
	 * @return string New ID (might be the same as the old)
	 */
	public function resetId() {
		return $this->backend->resetId();
	}

	/**
	 * Fetch the SessionProvider for this session
	 * @return SessionProviderInterface
	 */
	public function getProvider() {
		return $this->backend->getProvider();
	}

	/**
	 * Indicate whether this session is persisted across requests
	 *
	 * For example, if cookies are set.
	 *
	 * @return bool
	 */
	public function isPersistent() {
		return $this->backend->isPersistent();
	}

	/**
	 * Make this session persisted across requests
	 *
	 * If the session is already persistent, equivalent to calling
	 * $this->renew().
	 */
	public function persist() {
		$this->backend->persist();
	}

	/**
	 * Make this session not be persisted across requests
	 *
	 * This will remove persistence information (e.g. delete cookies)
	 * from the associated WebRequest(s), and delete session data in the
	 * backend. The session data will still be available via get() until
	 * the end of the request.
	 */
	public function unpersist() {
		$this->backend->unpersist();
	}

	/**
	 * Indicate whether the user should be remembered independently of the
	 * session ID.
	 * @return bool
	 */
	public function shouldRememberUser() {
		return $this->backend->shouldRememberUser();
	}

	/**
	 * Set whether the user should be remembered independently of the session
	 * ID.
	 * @param bool $remember
	 */
	public function setRememberUser( $remember ) {
		$this->backend->setRememberUser( $remember );
	}

	/**
	 * Returns the request associated with this session
	 * @return WebRequest
	 */
	public function getRequest() {
		return $this->backend->getRequest( $this->index );
	}

	/**
	 * Returns the authenticated user for this session
	 * @return User
	 */
	public function getUser() {
		return $this->backend->getUser();
	}

	/**
	 * Fetch the rights allowed the user when this session is active.
	 * @return null|string[] Allowed user rights, or null to allow all.
	 */
	public function getAllowedUserRights() {
		return $this->backend->getAllowedUserRights();
	}

	/**
	 * Indicate whether the session user info can be changed
	 * @return bool
	 */
	public function canSetUser() {
		return $this->backend->canSetUser();
	}

	/**
	 * Set a new user for this session
	 * @note This should only be called when the user has been authenticated
	 * @param User $user User to set on the session.
	 *   This may become a "UserValue" in the future, or User may be refactored
	 *   into such.
	 */
	public function setUser( $user ) {
		$this->backend->setUser( $user );
	}

	/**
	 * Get a suggested username for the login form
	 * @return string|null
	 */
	public function suggestLoginUsername() {
		return $this->backend->suggestLoginUsername( $this->index );
	}

	/**
	 * Whether HTTPS should be forced
	 * @return bool
	 */
	public function shouldForceHTTPS() {
		return $this->backend->shouldForceHTTPS();
	}

	/**
	 * Set whether HTTPS should be forced
	 * @param bool $force
	 */
	public function setForceHTTPS( $force ) {
		$this->backend->setForceHTTPS( $force );
	}

	/**
	 * Fetch the "logged out" timestamp
	 * @return int
	 */
	public function getLoggedOutTimestamp() {
		return $this->backend->getLoggedOutTimestamp();
	}

	/**
	 * Set the "logged out" timestamp
	 * @param int $ts
	 */
	public function setLoggedOutTimestamp( $ts ) {
		$this->backend->setLoggedOutTimestamp( $ts );
	}

	/**
	 * Fetch provider metadata
	 * @protected For use by SessionProvider subclasses only
	 * @return mixed
	 */
	public function getProviderMetadata() {
		return $this->backend->getProviderMetadata();
	}

	/**
	 * Delete all session data and clear the user (if possible)
	 */
	public function clear() {
		$data = &$this->backend->getData();
		if ( $data ) {
			$data = [];
			$this->backend->dirty();
		}
		if ( $this->backend->canSetUser() ) {
			$this->backend->setUser( new User );
		}
		$this->backend->save();
	}

	/**
	 * Renew the session
	 *
	 * Resets the TTL in the backend store if the session is near expiring, and
	 * re-persists the session to any active WebRequests if persistent.
	 */
	public function renew() {
		$this->backend->renew();
	}

	/**
	 * Fetch a copy of this session attached to an alternative WebRequest
	 *
	 * Actions on the copy will affect this session too, and vice versa.
	 *
	 * @param WebRequest $request Any existing session associated with this
	 *  WebRequest object will be overwritten.
	 * @return Session
	 */
	public function sessionWithRequest( WebRequest $request ) {
		$request->setSessionId( $this->backend->getSessionId() );
		return $this->backend->getSession( $request );
	}

	/**
	 * Fetch a value from the session
	 * @param string|int $key
	 * @param mixed $default Returned if $this->exists( $key ) would be false
	 * @return mixed
	 */
	public function get( $key, $default = null ) {
		$data = &$this->backend->getData();
		return array_key_exists( $key, $data ) ? $data[$key] : $default;
	}

	/**
	 * Test if a value exists in the session
	 * @note Unlike isset(), null values are considered to exist.
	 * @param string|int $key
	 * @return bool
	 */
	public function exists( $key ) {
		$data = &$this->backend->getData();
		return array_key_exists( $key, $data );
	}

	/**
	 * Set a value in the session
	 * @param string|int $key
	 * @param mixed $value
	 */
	public function set( $key, $value ) {
		$data = &$this->backend->getData();
		if ( !array_key_exists( $key, $data ) || $data[$key] !== $value ) {
			$data[$key] = $value;
			$this->backend->dirty();
		}
	}

	/**
	 * Remove a value from the session
	 * @param string|int $key
	 */
	public function remove( $key ) {
		$data = &$this->backend->getData();
		if ( array_key_exists( $key, $data ) ) {
			unset( $data[$key] );
			$this->backend->dirty();
		}
	}

	/**
	 * Fetch a CSRF token from the session
	 *
	 * Note that this does not persist the session, which you'll probably want
	 * to do if you want the token to actually be useful.
	 *
	 * @param string|string[] $salt Token salt
	 * @param string $key Token key
	 * @return Token
	 */
	public function getToken( $salt = '', $key = 'default' ) {
		$new = false;
		$secrets = $this->get( 'wsTokenSecrets' );
		if ( !is_array( $secrets ) ) {
			$secrets = [];
		}
		if ( isset( $secrets[$key] ) && is_string( $secrets[$key] ) ) {
			$secret = $secrets[$key];
		} else {
			$secret = \MWCryptRand::generateHex( 32 );
			$secrets[$key] = $secret;
			$this->set( 'wsTokenSecrets', $secrets );
			$new = true;
		}
		if ( is_array( $salt ) ) {
			$salt = implode( '|', $salt );
		}
		return new Token( $secret, (string)$salt, $new );
	}

	/**
	 * Remove a CSRF token from the session
	 *
	 * The next call to self::getToken() with $key will generate a new secret.
	 *
	 * @param string $key Token key
	 */
	public function resetToken( $key = 'default' ) {
		$secrets = $this->get( 'wsTokenSecrets' );
		if ( is_array( $secrets ) && isset( $secrets[$key] ) ) {
			unset( $secrets[$key] );
			$this->set( 'wsTokenSecrets', $secrets );
		}
	}

	/**
	 * Remove all CSRF tokens from the session
	 */
	public function resetAllTokens() {
		$this->remove( 'wsTokenSecrets' );
	}

	/**
	 * Fetch the secret keys for self::setSecret() and self::getSecret().
	 * @return string[] Encryption key, HMAC key
	 */
	private function getSecretKeys() {
		global $wgSessionSecret, $wgSecretKey, $wgSessionPbkdf2Iterations;

		$wikiSecret = $wgSessionSecret ?: $wgSecretKey;
		$userSecret = $this->get( 'wsSessionSecret', null );
		if ( $userSecret === null ) {
			$userSecret = \MWCryptRand::generateHex( 32 );
			$this->set( 'wsSessionSecret', $userSecret );
		}
		$iterations = $this->get( 'wsSessionPbkdf2Iterations', null );
		if ( $iterations === null ) {
			$iterations = $wgSessionPbkdf2Iterations;
			$this->set( 'wsSessionPbkdf2Iterations', $iterations );
		}

		$keymats = hash_pbkdf2( 'sha256', $wikiSecret, $userSecret, $iterations, 64, true );
		return [
			substr( $keymats, 0, 32 ),
			substr( $keymats, 32, 32 ),
		];
	}

	/**
	 * Decide what type of encryption to use, based on system capabilities.
	 * @return array
	 */
	private static function getEncryptionAlgorithm() {
		global $wgSessionInsecureSecrets;

		if ( self::$encryptionAlgorithm === null ) {
			if ( function_exists( 'openssl_encrypt' ) ) {
				$methods = openssl_get_cipher_methods();
				if ( in_array( 'aes-256-ctr', $methods, true ) ) {
					self::$encryptionAlgorithm = [ 'openssl', 'aes-256-ctr' ];
					return self::$encryptionAlgorithm;
				}
				if ( in_array( 'aes-256-cbc', $methods, true ) ) {
					self::$encryptionAlgorithm = [ 'openssl', 'aes-256-cbc' ];
					return self::$encryptionAlgorithm;
				}
			}

			if ( function_exists( 'mcrypt_encrypt' )
				&& in_array( 'rijndael-128', mcrypt_list_algorithms(), true )
			) {
				$modes = mcrypt_list_modes();
				if ( in_array( 'ctr', $modes, true ) ) {
					self::$encryptionAlgorithm = [ 'mcrypt', 'rijndael-128', 'ctr' ];
					return self::$encryptionAlgorithm;
				}
				if ( in_array( 'cbc', $modes, true ) ) {
					self::$encryptionAlgorithm = [ 'mcrypt', 'rijndael-128', 'cbc' ];
					return self::$encryptionAlgorithm;
				}
			}

			if ( $wgSessionInsecureSecrets ) {
				// @todo: import a pure-PHP library for AES instead of this
				self::$encryptionAlgorithm = [ 'insecure' ];
				return self::$encryptionAlgorithm;
			}

			throw new \BadMethodCallException(
				'Encryption is not available. You really should install the PHP OpenSSL extension, ' .
				'or failing that the mcrypt extension. But if you really can\'t and you\'re willing ' .
				'to accept insecure storage of sensitive session data, set ' .
				'$wgSessionInsecureSecrets = true in LocalSettings.php to make this exception go away.'
			);
		}

		return self::$encryptionAlgorithm;
	}

	/**
	 * Set a value in the session, encrypted
	 *
	 * This relies on the secrecy of $wgSecretKey (by default), or $wgSessionSecret.
	 *
	 * @param string|int $key
	 * @param mixed $value
	 */
	public function setSecret( $key, $value ) {
		list( $encKey, $hmacKey ) = $this->getSecretKeys();
		$serialized = serialize( $value );

		// The code for encryption (with OpenSSL) and sealing is taken from
		// Chris Steipp's OATHAuthUtils class in Extension::OATHAuth.

		// Encrypt
		// @todo: import a pure-PHP library for AES instead of doing $wgSessionInsecureSecrets
		$iv = \MWCryptRand::generate( 16, true );
		$algorithm = self::getEncryptionAlgorithm();
		switch ( $algorithm[0] ) {
			case 'openssl':
				$ciphertext = openssl_encrypt( $serialized, $algorithm[1], $encKey, OPENSSL_RAW_DATA, $iv );
				if ( $ciphertext === false ) {
					throw new \UnexpectedValueException( 'Encryption failed: ' . openssl_error_string() );
				}
				break;
			case 'mcrypt':
				// PKCS7 padding
				$blocksize = mcrypt_get_block_size( $algorithm[1], $algorithm[2] );
				$pad = $blocksize - ( strlen( $serialized ) % $blocksize );
				$serialized .= str_repeat( chr( $pad ), $pad );

				$ciphertext = mcrypt_encrypt( $algorithm[1], $encKey, $serialized, $algorithm[2], $iv );
				if ( $ciphertext === false ) {
					throw new \UnexpectedValueException( 'Encryption failed' );
				}
				break;
			case 'insecure':
				$ex = new \Exception( 'No encryption is available, storing data as plain text' );
				$this->logger->warning( $ex->getMessage(), [ 'exception' => $ex ] );
				$ciphertext = $serialized;
				break;
			default:
				throw new \LogicException( 'invalid algorithm' );
		}

		// Seal
		$sealed = base64_encode( $iv ) . '.' . base64_encode( $ciphertext );
		$hmac = hash_hmac( 'sha256', $sealed, $hmacKey, true );
		$encrypted = base64_encode( $hmac ) . '.' . $sealed;

		// Store
		$this->set( $key, $encrypted );
	}

	/**
	 * Fetch a value from the session that was set with self::setSecret()
	 * @param string|int $key
	 * @param mixed $default Returned if $this->exists( $key ) would be false or decryption fails
	 * @return mixed
	 */
	public function getSecret( $key, $default = null ) {
		// Fetch
		$encrypted = $this->get( $key, null );
		if ( $encrypted === null ) {
			return $default;
		}

		// The code for unsealing, checking, and decrypting (with OpenSSL) is
		// taken from Chris Steipp's OATHAuthUtils class in
		// Extension::OATHAuth.

		// Unseal and check
		$pieces = explode( '.', $encrypted );
		if ( count( $pieces ) !== 3 ) {
			$ex = new \Exception( 'Invalid sealed-secret format' );
			$this->logger->warning( $ex->getMessage(), [ 'exception' => $ex ] );
			return $default;
		}
		list( $hmac, $iv, $ciphertext ) = $pieces;
		list( $encKey, $hmacKey ) = $this->getSecretKeys();
		$integCalc = hash_hmac( 'sha256', $iv . '.' . $ciphertext, $hmacKey, true );
		if ( !hash_equals( $integCalc, base64_decode( $hmac ) ) ) {
			$ex = new \Exception( 'Sealed secret has been tampered with, aborting.' );
			$this->logger->warning( $ex->getMessage(), [ 'exception' => $ex ] );
			return $default;
		}

		// Decrypt
		$algorithm = self::getEncryptionAlgorithm();
		switch ( $algorithm[0] ) {
			case 'openssl':
				$serialized = openssl_decrypt( base64_decode( $ciphertext ), $algorithm[1], $encKey,
					OPENSSL_RAW_DATA, base64_decode( $iv ) );
				if ( $serialized === false ) {
					$ex = new \Exception( 'Decyption failed: ' . openssl_error_string() );
					$this->logger->debug( $ex->getMessage(), [ 'exception' => $ex ] );
					return $default;
				}
				break;
			case 'mcrypt':
				$serialized = mcrypt_decrypt( $algorithm[1], $encKey, base64_decode( $ciphertext ),
					$algorithm[2], base64_decode( $iv ) );
				if ( $serialized === false ) {
					$ex = new \Exception( 'Decyption failed' );
					$this->logger->debug( $ex->getMessage(), [ 'exception' => $ex ] );
					return $default;
				}

				// Remove PKCS7 padding
				$pad = ord( substr( $serialized, -1 ) );
				$serialized = substr( $serialized, 0, -$pad );
				break;
			case 'insecure':
				$ex = new \Exception(
					'No encryption is available, retrieving data that was stored as plain text'
				);
				$this->logger->warning( $ex->getMessage(), [ 'exception' => $ex ] );
				$serialized = base64_decode( $ciphertext );
				break;
			default:
				throw new \LogicException( 'invalid algorithm' );
		}

		$value = unserialize( $serialized );
		if ( $value === false && $serialized !== serialize( false ) ) {
			$value = $default;
		}
		return $value;
	}

	/**
	 * Delay automatic saving while multiple updates are being made
	 *
	 * Calls to save() or clear() will not be delayed.
	 *
	 * @return \Wikimedia\ScopedCallback When this goes out of scope, a save will be triggered
	 */
	public function delaySave() {
		return $this->backend->delaySave();
	}

	/**
	 * Save the session
	 *
	 * This will update the backend data and might re-persist the session
	 * if needed.
	 */
	public function save() {
		$this->backend->save();
	}

	/**
	 * @name Interface methods
	 * @{
	 */

	/** @inheritDoc */
	public function count() {
		$data = &$this->backend->getData();
		return count( $data );
	}

	/** @inheritDoc */
	public function current() {
		$data = &$this->backend->getData();
		return current( $data );
	}

	/** @inheritDoc */
	public function key() {
		$data = &$this->backend->getData();
		return key( $data );
	}

	/** @inheritDoc */
	public function next() {
		$data = &$this->backend->getData();
		next( $data );
	}

	/** @inheritDoc */
	public function rewind() {
		$data = &$this->backend->getData();
		reset( $data );
	}

	/** @inheritDoc */
	public function valid() {
		$data = &$this->backend->getData();
		return key( $data ) !== null;
	}

	/**
	 * @note Despite the name, this seems to be intended to implement isset()
	 *  rather than array_key_exists(). So do that.
	 * @inheritDoc
	 */
	public function offsetExists( $offset ) {
		$data = &$this->backend->getData();
		return isset( $data[$offset] );
	}

	/**
	 * @note This supports indirect modifications but can't mark the session
	 *  dirty when those happen. SessionBackend::save() checks the hash of the
	 *  data to detect such changes.
	 * @note Accessing a nonexistent key via this mechanism causes that key to
	 *  be created with a null value, and does not raise a PHP warning.
	 * @inheritDoc
	 */
	public function &offsetGet( $offset ) {
		$data = &$this->backend->getData();
		if ( !array_key_exists( $offset, $data ) ) {
			$ex = new \Exception( "Undefined index (auto-adds to session with a null value): $offset" );
			$this->logger->debug( $ex->getMessage(), [ 'exception' => $ex ] );
		}
		return $data[$offset];
	}

	/** @inheritDoc */
	public function offsetSet( $offset, $value ) {
		$this->set( $offset, $value );
	}

	/** @inheritDoc */
	public function offsetUnset( $offset ) {
		$this->remove( $offset );
	}

	/**@}*/

}