<?php

/**
 * ownCloud - Encryption stream wrapper
 *
 * @copyright (C) 2015 ownCloud, Inc.
 *
 * @author Bjoern Schiessle <schiessle@owncloud.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU AFFERO GENERAL PUBLIC LICENSE
 * License as published by the Free Software Foundation; either
 * version 3 of the License, or any later version.
 *
 * This library 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 AFFERO GENERAL PUBLIC LICENSE for more details.
 *
 * You should have received a copy of the GNU Affero General Public
 * License along with this library.  If not, see <http://www.gnu.org/licenses/>.
 */

namespace OC\Files\Stream;

use Icewind\Streams\Wrapper;
use OC\Encryption\Exceptions\EncryptionHeaderKeyExistsException;

class Encryption extends Wrapper {

	/** @var \OC\Encryption\Util */
	protected $util;

	/** @var \OCP\Encryption\IEncryptionModule */
	protected $encryptionModule;

	/** @var \OC\Files\Storage\Storage */
	protected $storage;

	/** @var \OC\Files\Storage\Wrapper\Encryption */
	protected $encryptionStorage;

	/** @var string */
	protected $internalPath;

	/** @var integer */
	protected $size;

	/** @var integer */
	protected $position;

	/** @var integer */
	protected $unencryptedSize;

	/** @var integer */
	protected $unencryptedBlockSize;

	/** @var array */
	protected $header;

	/** @var string */
	protected $fullPath;

	/**
	 * header data returned by the encryption module, will be written to the file
	 * in case of a write operation
	 *
	 * @var array
	 */
	protected $newHeader;

	/**
	 * user who perform the read/write operation null for public access
	 *
	 *  @var string
	 */
	protected $uid;

	/** @var bool */
	protected $readOnly;

	/** @var array */
	protected $expectedContextProperties;

	public function __construct() {
		$this->expectedContextProperties = array(
			'source',
			'storage',
			'internalPath',
			'fullPath',
			'encryptionModule',
			'header',
			'uid',
			'util',
			'size',
			'unencryptedSize',
			'encryptionStorage'
		);
	}


	/**
	 * Wraps a stream with the provided callbacks
	 *
	 * @param resource $source
	 * @param string $internalPath relative to mount point
	 * @param string $fullPath relative to data/
	 * @param array $header
	 * @param sting $uid
	 * @param \OCP\Encryption\IEncryptionModule $encryptionModule
	 * @param \OC\Files\Storage\Storage $storage
	 * @param OC\Files\Storage\Wrapper\Encryption $encStorage
	 * @param \OC\Encryption\Util $util
	 * @param string $mode
	 * @param int $size
	 * @param int $unencryptedSize
	 * @return resource
	 *
	 * @throws \BadMethodCallException
	 */
	public static function wrap($source, $internalPath, $fullPath, array $header,
		$uid, \OCP\Encryption\IEncryptionModule $encryptionModule,
		\OC\Files\Storage\Storage $storage, \OC\Files\Storage\Wrapper\Encryption $encStorage,
		\OC\Encryption\Util $util, $mode, $size, $unencryptedSize) {

		$context = stream_context_create(array(
			'ocencryption' => array(
				'source' => $source,
				'storage' => $storage,
				'internalPath' => $internalPath,
				'fullPath' => $fullPath,
				'encryptionModule' => $encryptionModule,
				'header' => $header,
				'uid' => $uid,
				'util' => $util,
				'size' => $size,
				'unencryptedSize' => $unencryptedSize,
				'encryptionStorage' => $encStorage
			)
		));

		return self::wrapSource($source, $mode, $context, 'ocencryption', 'OC\Files\Stream\Encryption');
	}

	/**
	 * add stream wrapper
	 *
	 * @param resource $source
	 * @param string $mode
	 * @param array $context
	 * @param string $protocol
	 * @param string $class
	 * @return resource
	 * @throws \BadMethodCallException
	 */
	protected static function wrapSource($source, $mode, $context, $protocol, $class) {
		try {
			stream_wrapper_register($protocol, $class);
			if (@rewinddir($source) === false) {
				$wrapped = fopen($protocol . '://', $mode, false, $context);
			} else {
				$wrapped = opendir($protocol . '://', $context);
			}
		} catch (\BadMethodCallException $e) {
			stream_wrapper_unregister($protocol);
			throw $e;
		}
		stream_wrapper_unregister($protocol);
		return $wrapped;
	}

	/**
	 * Load the source from the stream context and return the context options
	 *
	 * @param string $name
	 * @return array
	 * @throws \BadMethodCallException
	 */
	protected function loadContext($name) {
		$context = parent::loadContext($name);

		foreach ($this->expectedContextProperties as $property) {
			if (isset($context[$property])) {
				$this->{$property} = $context[$property];
			} else {
				throw new \BadMethodCallException('Invalid context, "' . $property . '" options not set');
			}
		}
		return $context;

	}

	public function stream_open($path, $mode, $options, &$opened_path) {
		$this->loadContext('ocencryption');

		$this->position = 0;
		$this->unencryptedBlockSize = $this->encryptionModule->getUnencryptedBlockSize();

		if (
			$mode === 'w'
			|| $mode === 'w+'
			|| $mode === 'wb'
			|| $mode === 'wb+'
		) {
			// We're writing a new file so start write counter with 0 bytes
			// TODO can we remove this completely?
			//$this->unencryptedSize = 0;
			//$this->size = 0;
			$this->readOnly = false;
		} else {
			$this->readOnly = true;
		}

		$sharePath = $this->fullPath;
		if (!$this->storage->file_exists($this->internalPath)) {
			$sharePath = dirname($path);
		}

		$accessList = $this->util->getSharingUsersArray($sharePath);
		$this->newHeader = $this->encryptionModule->begin($this->fullPath, $this->uid, $this->header, $accessList);

		return true;

	}

	public function stream_read($count) {

		$result = '';

		// skip the header if we read the file from the beginning
		if ($this->position === 0 && !empty($this->header)) {
			parent::stream_read($this->util->getBlockSize());
		}

		while ($count > 0) {
			$remainingLength = $count;
			// update the cache of the current block
			$data = parent::stream_read($this->util->getBlockSize());
			$decrypted = $this->encryptionModule->decrypt($data);
			// determine the relative position in the current block
			$blockPosition = ($this->position % $this->unencryptedBlockSize);
			// if entire read inside current block then only position needs to be updated
			if ($remainingLength < ($this->unencryptedBlockSize - $blockPosition)) {
				$result .= substr($decrypted, $blockPosition, $remainingLength);
				$this->position += $remainingLength;
				$count = 0;
			// otherwise remainder of current block is fetched, the block is flushed and the position updated
			} else {
				$result .= substr($decrypted, $blockPosition);
				$this->position += ($this->unencryptedBlockSize - $blockPosition);
				$count -= ($this->unencryptedBlockSize - $blockPosition);
			}
		}
		return $result;

	}

	public function stream_write($data) {

		if ($this->position === 0) {
			$this->writeHeader();
		}

		$length = 0;
		// loop over $data to fit it in 6126 sized unencrypted blocks
		while (strlen($data) > 0) {
			$remainingLength = strlen($data);

			// read current block
			$currentBlock = parent::stream_read($this->util->getBlockSize());
			$decrypted = $this->encryptionModule->decrypt($currentBlock, $this->uid);

			// for seekable streams the pointer is moved back to the beginning of the encrypted block
			// flush will start writing there when the position moves to another block
			$positionInFile = floor($this->position / $this->unencryptedBlockSize) *
				$this->util->getBlockSize() + $this->util->getHeaderSize();
			$resultFseek = parent::stream_seek($positionInFile);

			// only allow writes on seekable streams, or at the end of the encrypted stream
			if ($resultFseek || $positionInFile === $this->size) {

				// determine the relative position in the current block
				$blockPosition = ($this->position % $this->unencryptedBlockSize);
				// check if $data fits in current block
				// if so, overwrite existing data (if any)
				// update position and liberate $data
				if ($remainingLength < ($this->unencryptedBlockSize - $blockPosition)) {
					$decrypted = substr($decrypted, 0, $blockPosition)
						. $data . substr($decrypted, $blockPosition + $remainingLength);
					$encrypted = $this->encryptionModule->encrypt($decrypted);
					parent::stream_write($encrypted);
					$this->position += $remainingLength;
					$length += $remainingLength;
					$data = '';
				// if $data doens't fit the current block, the fill the current block and reiterate
				// after the block is filled, it is flushed and $data is updatedxxx
				} else {
					$decrypted = substr($decrypted, 0, $blockPosition) .
						substr($data, 0, $this->unencryptedBlockSize - $blockPosition);
					$encrypted = $this->encryptionModule->encrypt($decrypted);
					parent::stream_write($encrypted);
					$this->position += ($this->unencryptedBlockSize - $blockPosition);
					$this->size = max($this->size, $this->stream_tell());
					$length += ($this->unencryptedBlockSize - $blockPosition);
					$data = substr($data, $this->unencryptedBlockSize - $blockPosition);
				}
			} else {
				$encrypted = $this->encryptionModule->encrypt($data);
				parent::stream_write($encrypted);
				$data = '';
			}
		}
		$this->unencryptedSize = max($this->unencryptedSize, $this->position);
		return $length;
	}

	public function stream_tell() {
		return $this->position;
	}

	public function stream_seek($offset, $whence = SEEK_SET) {

		$return = false;

		switch ($whence) {
			case SEEK_SET:
				if ($offset < $this->unencryptedSize && $offset >= 0) {
					$newPosition = $offset;
				}
				break;
			case SEEK_CUR:
				if ($offset >= 0) {
					$newPosition = $offset + $this->position;
				}
				break;
			case SEEK_END:
				if ($this->unencryptedSize + $offset >= 0) {
					$newPosition = $this->unencryptedSize + $offset;
				}
				break;
			default:
				return $return;
		}

		$newFilePosition = floor($newPosition / $this->unencryptedBlockSize)
			* $this->util->getBlockSize() + $this->util->getHeaderSize();

		if (parent::stream_seek($newFilePosition)) {
			$this->position = $newPosition;
			$return = true;
		}
		return $return;

	}

	public function stream_close() {
		$this->flush();
		return parent::stream_close();
	}

	/**
	 * tell encryption module that we are done and write remaining data to the file
	 */
	protected function flush() {
		$remainingData = $this->encryptionModule->end($this->fullPath);
		if ($this->readOnly === false) {
			if(!empty($remainingData)) {
				parent::stream_write($remainingData);
			}
			$this->encryptionStorage->updateUnencryptedSize($this->fullPath, $this->unencryptedSize);
		}
	}


	/**
	 * write header at beginning of encrypted file
	 *
	 * @throws EncryptionHeaderKeyExistsException if header key is already in use
	 */
	private function writeHeader() {
		$header = $this->util->createHeader($this->newHeader, $this->encryptionModule);
		parent::stream_write($header);
	}

}