<?php declare(strict_types=1);
/**
 * PrivateBin
 *
 * a zero-knowledge paste bin
 *
 * @link      https://github.com/PrivateBin/PrivateBin
 * @copyright 2012 Sébastien SAUVAGE (sebsauvage.net)
 * @license   https://www.opensource.org/licenses/zlib-license.php The zlib/libpng License
 */

namespace PrivateBin\Data;

use Exception;
use PDO;
use PDOException;
use PrivateBin\Controller;
use PrivateBin\Json;

/**
 * Database
 *
 * Model for database access, implemented as a singleton.
 */
class Database extends AbstractData
{
    /**
     * instance of database connection
     *
     * @access private
     * @var PDO
     */
    private $_db;

    /**
     * table prefix
     *
     * @access private
     * @var string
     */
    private $_prefix = '';

    /**
     * database type
     *
     * @access private
     * @var string
     */
    private $_type = '';

    /**
     * instantiates a new Database data backend
     *
     * @access public
     * @param  array $options
     * @throws Exception
     */
    public function __construct(array $options)
    {
        // set table prefix if given
        if (array_key_exists('tbl', $options)) {
            $this->_prefix = $options['tbl'];
        }

        // initialize the db connection with new options
        if (
            array_key_exists('dsn', $options) &&
            array_key_exists('usr', $options) &&
            array_key_exists('pwd', $options) &&
            array_key_exists('opt', $options)
        ) {
            // set default options
            $options['opt'][PDO::ATTR_ERRMODE]          = PDO::ERRMODE_EXCEPTION;
            $options['opt'][PDO::ATTR_EMULATE_PREPARES] = false;
            if (!array_key_exists(PDO::ATTR_PERSISTENT, $options['opt'])) {
                $options['opt'][PDO::ATTR_PERSISTENT] = true;
            }
            $db_tables_exist                            = true;

            // setup type and dabase connection
            $this->_type = strtolower(
                substr($options['dsn'], 0, strpos($options['dsn'], ':'))
            );
            // MySQL uses backticks to quote identifiers by default,
            // tell it to expect ANSI SQL double quotes
            if ($this->_type === 'mysql' && defined('PDO::MYSQL_ATTR_INIT_COMMAND')) {
                $options['opt'][PDO::MYSQL_ATTR_INIT_COMMAND] = "SET SESSION sql_mode='ANSI_QUOTES'";
            }
            $tableQuery = $this->_getTableQuery($this->_type);
            $this->_db  = new PDO(
                $options['dsn'],
                $options['usr'],
                $options['pwd'],
                $options['opt']
            );

            // check if the database contains the required tables
            $tables = $this->_db->query($tableQuery)->fetchAll(PDO::FETCH_COLUMN, 0);

            // create paste table if necessary
            if (!in_array($this->_sanitizeIdentifier('paste'), $tables)) {
                $this->_createPasteTable();
                $db_tables_exist = false;
            }

            // create comment table if necessary
            if (!in_array($this->_sanitizeIdentifier('comment'), $tables)) {
                $this->_createCommentTable();
                $db_tables_exist = false;
            }

            // create config table if necessary
            $db_version = Controller::VERSION;
            if (!in_array($this->_sanitizeIdentifier('config'), $tables)) {
                $this->_createConfigTable();
                // if we only needed to create the config table, the DB is older then 0.22
                if ($db_tables_exist) {
                    $db_version = '0.21';
                }
            } else {
                $db_version = $this->_getConfig('VERSION');
            }

            // update database structure if necessary
            if (version_compare($db_version, Controller::VERSION, '<')) {
                $this->_upgradeDatabase($db_version);
            }
        } else {
            throw new Exception(
                'Missing configuration for key dsn, usr, pwd or opt in the section model_options, please check your configuration file', 6
            );
        }
    }

    /**
     * Create a paste.
     *
     * @access public
     * @param  string $pasteid
     * @param  array  $paste
     * @return bool
     */
    public function create($pasteid, array &$paste)
    {
        $expire_date      = 0;
        $opendiscussion   = $burnafterreading = false;
        $attachment       = $attachmentname   = null;
        $meta             = $paste['meta'];
        $isVersion1       = array_key_exists('data', $paste);
        if (array_key_exists('expire_date', $meta)) {
            $expire_date = (int) $meta['expire_date'];
            unset($meta['expire_date']);
        }
        if (array_key_exists('opendiscussion', $meta)) {
            $opendiscussion = $meta['opendiscussion'];
            unset($meta['opendiscussion']);
        }
        if (array_key_exists('burnafterreading', $meta)) {
            $burnafterreading = $meta['burnafterreading'];
            unset($meta['burnafterreading']);
        }
        if ($isVersion1) {
            if (array_key_exists('attachment', $meta)) {
                $attachment = $meta['attachment'];
                unset($meta['attachment']);
            }
            if (array_key_exists('attachmentname', $meta)) {
                $attachmentname = $meta['attachmentname'];
                unset($meta['attachmentname']);
            }
        } else {
            $opendiscussion   = $paste['adata'][2];
            $burnafterreading = $paste['adata'][3];
        }
        try {
            return $this->_exec(
                'INSERT INTO "' . $this->_sanitizeIdentifier('paste') .
                '" VALUES(?,?,?,?,?,?,?,?)',
                array(
                    $pasteid,
                    $isVersion1 ? $paste['data'] : Json::encode($paste),
                    $expire_date,
                    (int) $opendiscussion,
                    (int) $burnafterreading,
                    Json::encode($meta),
                    $attachment,
                    $attachmentname,
                )
            );
        } catch (Exception $e) {
            error_log('Error while attempting to insert a paste into the database: ' . $e->getMessage() . PHP_EOL);
            return false;
        }
    }

    /**
     * Read a paste.
     *
     * @access public
     * @param  string $pasteid
     * @return array|false
     */
    public function read($pasteid)
    {
        try {
            $row = $this->_select(
                'SELECT * FROM "' . $this->_sanitizeIdentifier('paste') .
                '" WHERE "dataid" = ?', array($pasteid), true
            );
        } catch (Exception $e) {
            $row = false;
        }
        if ($row === false) {
            return false;
        }
        // create array
        $data       = Json::decode($row['data']);
        $isVersion2 = array_key_exists('v', $data) && $data['v'] >= 2;
        $paste      = $isVersion2 ? $data : array('data' => $row['data']);

        try {
            $row['meta'] = Json::decode($row['meta']);
        } catch (Exception $e) {
            $row['meta'] = array();
        }
        $row                        = self::upgradePreV1Format($row);
        $paste['meta']              = $row['meta'];
        $expire_date                = (int) $row['expiredate'];
        if ($expire_date > 0) {
            $paste['meta']['expire_date'] = $expire_date;
        }
        if ($isVersion2) {
            return $paste;
        }

        // support v1 attachments
        if (array_key_exists('attachment', $row) && !empty($row['attachment'])) {
            $paste['attachment'] = $row['attachment'];
            if (array_key_exists('attachmentname', $row) && !empty($row['attachmentname'])) {
                $paste['attachmentname'] = $row['attachmentname'];
            }
        }
        if ($row['opendiscussion']) {
            $paste['meta']['opendiscussion'] = true;
        }
        if ($row['burnafterreading']) {
            $paste['meta']['burnafterreading'] = true;
        }

        return $paste;
    }

    /**
     * Delete a paste and its discussion.
     *
     * @access public
     * @param  string $pasteid
     */
    public function delete($pasteid)
    {
        $this->_exec(
            'DELETE FROM "' . $this->_sanitizeIdentifier('paste') .
            '" WHERE "dataid" = ?', array($pasteid)
        );
        $this->_exec(
            'DELETE FROM "' . $this->_sanitizeIdentifier('comment') .
            '" WHERE "pasteid" = ?', array($pasteid)
        );
    }

    /**
     * Test if a paste exists.
     *
     * @access public
     * @param  string $pasteid
     * @return bool
     */
    public function exists($pasteid)
    {
        try {
            $row = $this->_select(
                'SELECT "dataid" FROM "' . $this->_sanitizeIdentifier('paste') .
                '" WHERE "dataid" = ?', array($pasteid), true
            );
        } catch (Exception $e) {
            return false;
        }
        return (bool) $row;
    }

    /**
     * Create a comment in a paste.
     *
     * @access public
     * @param  string $pasteid
     * @param  string $parentid
     * @param  string $commentid
     * @param  array  $comment
     * @return bool
     */
    public function createComment($pasteid, $parentid, $commentid, array &$comment)
    {
        if (array_key_exists('data', $comment)) {
            $version = 1;
            $data    = $comment['data'];
        } else {
            try {
                $version = 2;
                $data    = Json::encode($comment);
            } catch (Exception $e) {
                return false;
            }
        }
        list($createdKey, $iconKey) = $this->_getVersionedKeys($version);
        $meta                       = $comment['meta'];
        unset($comment['meta']);
        foreach (array('nickname', $iconKey) as $key) {
            if (!array_key_exists($key, $meta)) {
                $meta[$key] = null;
            }
        }
        try {
            return $this->_exec(
                'INSERT INTO "' . $this->_sanitizeIdentifier('comment') .
                '" VALUES(?,?,?,?,?,?,?)',
                array(
                    $commentid,
                    $pasteid,
                    $parentid,
                    $data,
                    $meta['nickname'],
                    $meta[$iconKey],
                    $meta[$createdKey],
                )
            );
        } catch (Exception $e) {
            error_log('Error while attempting to insert a comment into the database: ' . $e->getMessage() . PHP_EOL);
            return false;
        }
    }

    /**
     * Read all comments of paste.
     *
     * @access public
     * @param  string $pasteid
     * @return array
     */
    public function readComments($pasteid)
    {
        $rows = $this->_select(
            'SELECT * FROM "' . $this->_sanitizeIdentifier('comment') .
            '" WHERE "pasteid" = ?', array($pasteid)
        );

        // create comment list
        $comments = array();
        if (is_array($rows) && count($rows)) {
            foreach ($rows as $row) {
                $i    = $this->getOpenSlot($comments, (int) $row['postdate']);
                $data = Json::decode($row['data']);
                if (array_key_exists('v', $data) && $data['v'] >= 2) {
                    $version      = 2;
                    $comments[$i] = $data;
                } else {
                    $version      = 1;
                    $comments[$i] = array('data' => $row['data']);
                }
                list($createdKey, $iconKey) = $this->_getVersionedKeys($version);
                $comments[$i]['id']         = $row['dataid'];
                $comments[$i]['parentid']   = $row['parentid'];
                $comments[$i]['meta']       = array($createdKey => (int) $row['postdate']);
                foreach (array('nickname' => 'nickname', 'vizhash' => $iconKey) as $rowKey => $commentKey) {
                    if (array_key_exists($rowKey, $row) && !empty($row[$rowKey])) {
                        $comments[$i]['meta'][$commentKey] = $row[$rowKey];
                    }
                }
            }
            ksort($comments);
        }
        return $comments;
    }

    /**
     * Test if a comment exists.
     *
     * @access public
     * @param  string $pasteid
     * @param  string $parentid
     * @param  string $commentid
     * @return bool
     */
    public function existsComment($pasteid, $parentid, $commentid)
    {
        try {
            return (bool) $this->_select(
                'SELECT "dataid" FROM "' . $this->_sanitizeIdentifier('comment') .
                '" WHERE "pasteid" = ? AND "parentid" = ? AND "dataid" = ?',
                array($pasteid, $parentid, $commentid), true
            );
        } catch (Exception $e) {
            return false;
        }
    }

    /**
     * Save a value.
     *
     * @access public
     * @param  string $value
     * @param  string $namespace
     * @param  string $key
     * @return bool
     */
    public function setValue($value, $namespace, $key = '')
    {
        if ($namespace === 'traffic_limiter') {
            $this->_last_cache[$key] = $value;
            try {
                $value = Json::encode($this->_last_cache);
            } catch (Exception $e) {
                return false;
            }
        }
        return $this->_exec(
            'UPDATE "' . $this->_sanitizeIdentifier('config') .
            '" SET "value" = ? WHERE "id" = ?',
            array($value, strtoupper($namespace))
        );
    }

    /**
     * Load a value.
     *
     * @access public
     * @param  string $namespace
     * @param  string $key
     * @return string
     */
    public function getValue($namespace, $key = '')
    {
        $configKey = strtoupper($namespace);
        $value     = $this->_getConfig($configKey);
        if ($value === '') {
            // initialize the row, so that setValue can rely on UPDATE queries
            $this->_exec(
                'INSERT INTO "' . $this->_sanitizeIdentifier('config') .
                '" VALUES(?,?)',
                array($configKey, '')
            );

            // migrate filesystem based salt into database
            $file = 'data' . DIRECTORY_SEPARATOR . 'salt.php';
            if ($namespace === 'salt' && is_readable($file)) {
                $fs    = new Filesystem(array('dir' => 'data'));
                $value = $fs->getValue('salt');
                $this->setValue($value, 'salt');
                @unlink($file);
                return $value;
            }
        }
        if ($value && $namespace === 'traffic_limiter') {
            try {
                $this->_last_cache = Json::decode($value);
            } catch (Exception $e) {
                $this->_last_cache = array();
            }
            if (array_key_exists($key, $this->_last_cache)) {
                return $this->_last_cache[$key];
            }
        }
        return (string) $value;
    }

    /**
     * Returns up to batch size number of paste ids that have expired
     *
     * @access private
     * @param  int $batchsize
     * @return array
     */
    protected function _getExpiredPastes($batchsize)
    {
        $statement = $this->_db->prepare(
            'SELECT "dataid" FROM "' . $this->_sanitizeIdentifier('paste') .
            '" WHERE "expiredate" < ? AND "expiredate" != ? ' .
            ($this->_type === 'oci' ? 'FETCH NEXT ? ROWS ONLY' : 'LIMIT ?')
        );
        $statement->execute(array(time(), 0, $batchsize));
        return $statement->fetchAll(PDO::FETCH_COLUMN, 0);
    }

    /**
     * @inheritDoc
     */
    public function getAllPastes()
    {
        return $this->_db->query(
            'SELECT "dataid" FROM "' . $this->_sanitizeIdentifier('paste') . '"'
        )->fetchAll(PDO::FETCH_COLUMN, 0);
    }

    /**
     * execute a statement
     *
     * @access private
     * @param  string $sql
     * @param  array $params
     * @throws PDOException
     * @return bool
     */
    private function _exec($sql, array $params)
    {
        $statement = $this->_db->prepare($sql);
        $position  = 1;
        foreach ($params as &$parameter) {
            if (is_int($parameter)) {
                $statement->bindParam($position, $parameter, PDO::PARAM_INT);
            } elseif (is_string($parameter) && strlen($parameter) >= 4000) {
                $statement->bindParam($position, $parameter, PDO::PARAM_STR, strlen($parameter));
            } else {
                $statement->bindParam($position, $parameter);
            }
            ++$position;
        }
        $result = $statement->execute();
        $statement->closeCursor();
        return $result;
    }

    /**
     * run a select statement
     *
     * @access private
     * @param  string $sql
     * @param  array $params
     * @param  bool $firstOnly if only the first row should be returned
     * @throws PDOException
     * @return array|false
     */
    private function _select($sql, array $params, $firstOnly = false)
    {
        $statement = $this->_db->prepare($sql);
        $statement->execute($params);
        if ($firstOnly) {
            $result = $statement->fetch(PDO::FETCH_ASSOC);
        } elseif ($this->_type === 'oci') {
            // workaround for https://bugs.php.net/bug.php?id=46728
            $result = array();
            while ($row = $statement->fetch(PDO::FETCH_ASSOC)) {
                $result[] = array_map('PrivateBin\Data\Database::_sanitizeClob', $row);
            }
        } else {
            $result = $statement->fetchAll(PDO::FETCH_ASSOC);
        }
        $statement->closeCursor();
        if ($this->_type === 'oci' && is_array($result)) {
            // returned CLOB values are streams, convert these into strings
            $result = $firstOnly ?
                array_map('PrivateBin\Data\Database::_sanitizeClob', $result) :
                $result;
        }
        return $result;
    }

    /**
     * get version dependent key names
     *
     * @access private
     * @param  int $version
     * @return array
     */
    private function _getVersionedKeys($version)
    {
        if ($version === 1) {
            return array('postdate', 'vizhash');
        }
        return array('created', 'icon');
    }

    /**
     * get table list query, depending on the database type
     *
     * @access private
     * @param  string $type
     * @throws Exception
     * @return string
     */
    private function _getTableQuery($type)
    {
        switch ($type) {
            case 'ibm':
                $sql = 'SELECT "tabname" FROM "SYSCAT"."TABLES"';
                break;
            case 'informix':
                $sql = 'SELECT "tabname" FROM "systables"';
                break;
            case 'mssql':
                // U: tables created by the user
                $sql = 'SELECT "name" FROM "sysobjects" '
                     . 'WHERE "type" = \'U\' ORDER BY "name"';
                break;
            case 'mysql':
                $sql = 'SHOW TABLES';
                break;
            case 'oci':
                $sql = 'SELECT table_name FROM all_tables';
                break;
            case 'pgsql':
                $sql = 'SELECT "tablename" FROM "pg_catalog"."pg_tables" '
                     . 'WHERE "schemaname" NOT IN (\'pg_catalog\', \'information_schema\')';
                break;
            case 'sqlite':
                $sql = 'SELECT "name" FROM "sqlite_master" WHERE "type"=\'table\' '
                     . 'UNION ALL SELECT "name" FROM "sqlite_temp_master" '
                     . 'WHERE "type"=\'table\' ORDER BY "name"';
                break;
            default:
                throw new Exception(
                    "PDO type $type is currently not supported.", 5
                );
        }
        return $sql;
    }

    /**
     * get a value by key from the config table
     *
     * @access private
     * @param  string $key
     * @return string
     */
    private function _getConfig($key)
    {
        try {
            $row = $this->_select(
                'SELECT "value" FROM "' . $this->_sanitizeIdentifier('config') .
                '" WHERE "id" = ?', array($key), true
            );
        } catch (PDOException $e) {
            return '';
        }
        return $row ? $row['value'] : '';
    }

    /**
     * get the primary key clauses, depending on the database driver
     *
     * @access private
     * @param  string $key
     * @return array
     */
    private function _getPrimaryKeyClauses($key = 'dataid')
    {
        $main_key = $after_key = '';
        switch ($this->_type) {
            case 'mysql':
            case 'oci':
                $after_key = ", PRIMARY KEY (\"$key\")";
                break;
            default:
                $main_key = ' PRIMARY KEY';
                break;
        }
        return array($main_key, $after_key);
    }

    /**
     * get the data type, depending on the database driver
     *
     * PostgreSQL and OCI uses a different API for BLOBs then SQL, hence we use TEXT and CLOB
     *
     * @access private
     * @return string
     */
    private function _getDataType()
    {
        switch ($this->_type) {
            case 'oci':
                return 'CLOB';
            case 'pgsql':
                return 'TEXT';
            default:
                return 'BLOB';
        }
    }

    /**
     * get the attachment type, depending on the database driver
     *
     * PostgreSQL and OCI use different APIs for BLOBs then SQL, hence we use TEXT and CLOB
     *
     * @access private
     * @return string
     */
    private function _getAttachmentType()
    {
        switch ($this->_type) {
            case 'oci':
                return 'CLOB';
            case 'pgsql':
                return 'TEXT';
            default:
                return 'MEDIUMBLOB';
        }
    }

    /**
     * get the meta type, depending on the database driver
     *
     * OCI doesn't accept TEXT so it has to be VARCHAR2(4000)
     *
     * @access private
     * @return string
     */
    private function _getMetaType()
    {
        switch ($this->_type) {
            case 'oci':
                return 'VARCHAR2(4000)';
            default:
                return 'TEXT';
        }
    }

    /**
     * create the paste table
     *
     * @access private
     */
    private function _createPasteTable()
    {
        list($main_key, $after_key) = $this->_getPrimaryKeyClauses();
        $dataType                   = $this->_getDataType();
        $attachmentType             = $this->_getAttachmentType();
        $metaType                   = $this->_getMetaType();
        $this->_db->exec(
            'CREATE TABLE "' . $this->_sanitizeIdentifier('paste') . '" ( ' .
            "\"dataid\" CHAR(16) NOT NULL$main_key, " .
            "\"data\" $attachmentType, " .
            '"expiredate" INT, ' .
            '"opendiscussion" INT, ' .
            '"burnafterreading" INT, ' .
            "\"meta\" $metaType, " .
            "\"attachment\" $attachmentType, " .
            "\"attachmentname\" $dataType$after_key )"
        );
    }

    /**
     * create the paste table
     *
     * @access private
     */
    private function _createCommentTable()
    {
        list($main_key, $after_key) = $this->_getPrimaryKeyClauses();
        $dataType                   = $this->_getDataType();
        $this->_db->exec(
            'CREATE TABLE "' . $this->_sanitizeIdentifier('comment') . '" ( ' .
            "\"dataid\" CHAR(16) NOT NULL$main_key, " .
            '"pasteid" CHAR(16), ' .
            '"parentid" CHAR(16), ' .
            "\"data\" $dataType, " .
            "\"nickname\" $dataType, " .
            "\"vizhash\" $dataType, " .
            "\"postdate\" INT$after_key )"
        );
        if ($this->_type === 'oci') {
            $this->_db->exec(
                'declare
                    already_exists  exception;
                    columns_indexed exception;
                    pragma exception_init( already_exists, -955 );
                    pragma exception_init(columns_indexed, -1408);
                begin
                    execute immediate \'create index "comment_parent" on "' . $this->_sanitizeIdentifier('comment') . '" ("pasteid")\';
                exception
                    when already_exists or columns_indexed then
                    NULL;
                end;'
            );
        } else {
            // CREATE INDEX IF NOT EXISTS not supported as of Oracle MySQL <= 8.0
            $this->_db->exec(
                'CREATE INDEX "' .
                $this->_sanitizeIdentifier('comment_parent') . '" ON "' .
                $this->_sanitizeIdentifier('comment') . '" ("pasteid")'
            );
        }
    }

    /**
     * create the paste table
     *
     * @access private
     */
    private function _createConfigTable()
    {
        list($main_key, $after_key) = $this->_getPrimaryKeyClauses('id');
        $charType                   = $this->_type === 'oci' ? 'VARCHAR2(16)' : 'CHAR(16)';
        $textType                   = $this->_getMetaType();
        $this->_db->exec(
            'CREATE TABLE "' . $this->_sanitizeIdentifier('config') .
            "\" ( \"id\" $charType NOT NULL$main_key, \"value\" $textType$after_key )"
        );
        $this->_exec(
            'INSERT INTO "' . $this->_sanitizeIdentifier('config') .
            '" VALUES(?,?)',
            array('VERSION', Controller::VERSION)
        );
    }

    /**
     * sanitizes CLOB values used with OCI
     *
     * From: https://stackoverflow.com/questions/36200534/pdo-oci-into-a-clob-field
     *
     * @access public
     * @static
     * @param  int|string|resource $value
     * @return int|string
     */
    public static function _sanitizeClob($value)
    {
        if (is_resource($value)) {
            $value = stream_get_contents($value);
        }
        return $value;
    }

    /**
     * sanitizes identifiers
     *
     * @access private
     * @param  string $identifier
     * @return string
     */
    private function _sanitizeIdentifier($identifier)
    {
        return preg_replace('/[^A-Za-z0-9_]+/', '', $this->_prefix . $identifier);
    }

    /**
     * upgrade the database schema from an old version
     *
     * @access private
     * @param  string $oldversion
     */
    private function _upgradeDatabase($oldversion)
    {
        $dataType       = $this->_getDataType();
        $attachmentType = $this->_getAttachmentType();
        if (version_compare($oldversion, '0.21', '<=')) {
            // create the meta column if necessary (pre 0.21 change)
            try {
                $this->_db->exec(
                    'SELECT "meta" FROM "' . $this->_sanitizeIdentifier('paste') . '" ' .
                    ($this->_type === 'oci' ? 'FETCH NEXT 1 ROWS ONLY' : 'LIMIT 1')
                );
            } catch (PDOException $e) {
                $this->_db->exec('ALTER TABLE "' . $this->_sanitizeIdentifier('paste') . '" ADD COLUMN "meta" TEXT');
            }
            // SQLite only allows one ALTER statement at a time...
            $this->_db->exec(
                'ALTER TABLE "' . $this->_sanitizeIdentifier('paste') .
                "\" ADD COLUMN \"attachment\" $attachmentType"
            );
            $this->_db->exec(
                'ALTER TABLE "' . $this->_sanitizeIdentifier('paste') . "\" ADD COLUMN \"attachmentname\" $dataType"
            );
            // SQLite doesn't support MODIFY, but it allows TEXT of similar
            // size as BLOB, so there is no need to change it there
            if ($this->_type !== 'sqlite') {
                $this->_db->exec(
                    'ALTER TABLE "' . $this->_sanitizeIdentifier('paste') .
                    "\" ADD PRIMARY KEY (\"dataid\"), MODIFY COLUMN \"data\" $dataType"
                );
                $this->_db->exec(
                    'ALTER TABLE "' . $this->_sanitizeIdentifier('comment') .
                    "\" ADD PRIMARY KEY (\"dataid\"), MODIFY COLUMN \"data\" $dataType, " .
                    "MODIFY COLUMN \"nickname\" $dataType, MODIFY COLUMN \"vizhash\" $dataType"
                );
            } else {
                $this->_db->exec(
                    'CREATE UNIQUE INDEX IF NOT EXISTS "' .
                    $this->_sanitizeIdentifier('paste_dataid') . '" ON "' .
                    $this->_sanitizeIdentifier('paste') . '" ("dataid")'
                );
                $this->_db->exec(
                    'CREATE UNIQUE INDEX IF NOT EXISTS "' .
                    $this->_sanitizeIdentifier('comment_dataid') . '" ON "' .
                    $this->_sanitizeIdentifier('comment') . '" ("dataid")'
                );
            }
            // CREATE INDEX IF NOT EXISTS not supported as of Oracle MySQL <= 8.0
            $this->_db->exec(
                'CREATE INDEX "' .
                $this->_sanitizeIdentifier('comment_parent') . '" ON "' .
                $this->_sanitizeIdentifier('comment') . '" ("pasteid")'
            );
        }
        if (version_compare($oldversion, '1.3', '<=')) {
            // SQLite doesn't support MODIFY, but it allows TEXT of similar
            // size as BLOB and PostgreSQL uses TEXT, so there is no need
            // to change it there
            if ($this->_type !== 'sqlite' && $this->_type !== 'pgsql') {
                $this->_db->exec(
                    'ALTER TABLE "' . $this->_sanitizeIdentifier('paste') .
                    "\" MODIFY COLUMN \"data\" $attachmentType"
                );
            }
        }
        if (version_compare($oldversion, '1.7.1', '<=')) {
            $supportsDropColumn = true;
            if ($this->_type === 'sqlite') {
                try {
                    $row                = $this->_select('SELECT sqlite_version() AS "v"', array(), true);
                    $supportsDropColumn = version_compare($row['v'], '3.35.0', '>=');
                    if (!$supportsDropColumn) {
                        error_log('Error: the available SQLite version (' . $row['v'] . ') does not support dropping columns. SQLite version 3.35.0 or later is necessary. The migration will not be fully complete, and you will need to delete the "postdate" column of the "paste" table yourself!');
                    }
                } catch (PDOException $e) {
                    $supportsDropColumn = false;
                    error_log('Error while checking the SQLite version. The migration will not be fully complete, and you will need to delete the "postdate" column of the "paste" table yourself!');
                }
            }
            if ($supportsDropColumn) {
                $this->_db->exec(
                    'ALTER TABLE "' . $this->_sanitizeIdentifier('paste') .
                    '" DROP COLUMN "postdate"'
                );
            }
        }
        $this->_exec(
            'UPDATE "' . $this->_sanitizeIdentifier('config') .
            '" SET "value" = ? WHERE "id" = ?',
            array(Controller::VERSION, 'VERSION')
        );
    }
}