class Schema

class Schema extends DatabaseSchema {
    
    /**
     * Override DatabaseSchema::$defaultSchema.
     *
     * @var string
     */
    protected $defaultSchema = 'main';
    
    /**
     * {@inheritdoc}
     */
    public function tableExists($table) {
        $info = $this->getPrefixInfo($table);
        // Don't use {} around sqlite_master table.
        return (bool) $this->connection
            ->query('SELECT 1 FROM ' . $info['schema'] . '.sqlite_master WHERE type = :type AND name = :name', [
            ':type' => 'table',
            ':name' => $info['table'],
        ])
            ->fetchField();
    }
    
    /**
     * {@inheritdoc}
     */
    public function fieldExists($table, $column) {
        $schema = $this->introspectSchema($table);
        return !empty($schema['fields'][$column]);
    }
    
    /**
     * Generate SQL to create a new table from a Drupal schema definition.
     *
     * @param $name
     *   The name of the table to create.
     * @param $table
     *   A Schema API table definition array.
     *
     * @return array
     *   An array of SQL statements to create the table.
     */
    public function createTableSql($name, $table) {
        if (!empty($table['primary key']) && is_array($table['primary key'])) {
            $this->ensureNotNullPrimaryKey($table['primary key'], $table['fields']);
        }
        $sql = [];
        $sql[] = "CREATE TABLE {" . $name . "} (\n" . $this->createColumnsSql($name, $table) . "\n)\n";
        return array_merge($sql, $this->createIndexSql($name, $table));
    }
    
    /**
     * Build the SQL expression for indexes.
     */
    protected function createIndexSql($tablename, $schema) {
        $sql = [];
        $info = $this->getPrefixInfo($tablename);
        if (!empty($schema['unique keys'])) {
            foreach ($schema['unique keys'] as $key => $fields) {
                $sql[] = 'CREATE UNIQUE INDEX ' . $info['schema'] . '.' . $info['table'] . '_' . $key . ' ON ' . $info['table'] . ' (' . $this->createKeySql($fields) . ")\n";
            }
        }
        if (!empty($schema['indexes'])) {
            foreach ($schema['indexes'] as $key => $fields) {
                $sql[] = 'CREATE INDEX ' . $info['schema'] . '.' . $info['table'] . '_' . $key . ' ON ' . $info['table'] . ' (' . $this->createKeySql($fields) . ")\n";
            }
        }
        return $sql;
    }
    
    /**
     * Build the SQL expression for creating columns.
     */
    protected function createColumnsSql($tablename, $schema) {
        $sql_array = [];
        // Add the SQL statement for each field.
        foreach ($schema['fields'] as $name => $field) {
            if (isset($field['type']) && $field['type'] == 'serial') {
                if (isset($schema['primary key']) && ($key = array_search($name, $schema['primary key'])) !== FALSE) {
                    unset($schema['primary key'][$key]);
                }
            }
            $sql_array[] = $this->createFieldSql($name, $this->processField($field));
        }
        // Process keys.
        if (!empty($schema['primary key'])) {
            $sql_array[] = " PRIMARY KEY (" . $this->createKeySql($schema['primary key']) . ")";
        }
        return implode(", \n", $sql_array);
    }
    
    /**
     * Build the SQL expression for keys.
     */
    protected function createKeySql($fields) {
        $return = [];
        foreach ($fields as $field) {
            if (is_array($field)) {
                $return[] = $field[0];
            }
            else {
                $return[] = $field;
            }
        }
        return implode(', ', $return);
    }
    
    /**
     * Set database-engine specific properties for a field.
     *
     * @param $field
     *   A field description array, as specified in the schema documentation.
     */
    protected function processField($field) {
        if (!isset($field['size'])) {
            $field['size'] = 'normal';
        }
        // Set the correct database-engine specific datatype.
        // In case one is already provided, force it to uppercase.
        if (isset($field['sqlite_type'])) {
            $field['sqlite_type'] = mb_strtoupper($field['sqlite_type']);
        }
        else {
            $map = $this->getFieldTypeMap();
            $field['sqlite_type'] = $map[$field['type'] . ':' . $field['size']];
            // Numeric fields with a specified scale have to be stored as floats.
            if ($field['sqlite_type'] === 'NUMERIC' && isset($field['scale'])) {
                $field['sqlite_type'] = 'FLOAT';
            }
        }
        if (isset($field['type']) && $field['type'] == 'serial') {
            $field['auto_increment'] = TRUE;
        }
        return $field;
    }
    
    /**
     * Create an SQL string for a field to be used in table creation or alteration.
     *
     * Before passing a field out of a schema definition into this function it has
     * to be processed by self::processField().
     *
     * @param $name
     *   Name of the field.
     * @param $spec
     *   The field specification, as per the schema data structure format.
     */
    protected function createFieldSql($name, $spec) {
        $name = $this->connection
            ->escapeField($name);
        if (!empty($spec['auto_increment'])) {
            $sql = $name . " INTEGER PRIMARY KEY AUTOINCREMENT";
            if (!empty($spec['unsigned'])) {
                $sql .= ' CHECK (' . $name . '>= 0)';
            }
        }
        else {
            $sql = $name . ' ' . $spec['sqlite_type'];
            if (in_array($spec['sqlite_type'], [
                'VARCHAR',
                'TEXT',
            ])) {
                if (isset($spec['length'])) {
                    $sql .= '(' . $spec['length'] . ')';
                }
                if (isset($spec['binary']) && $spec['binary'] === FALSE) {
                    $sql .= ' COLLATE NOCASE_UTF8';
                }
            }
            if (isset($spec['not null'])) {
                if ($spec['not null']) {
                    $sql .= ' NOT NULL';
                }
                else {
                    $sql .= ' NULL';
                }
            }
            if (!empty($spec['unsigned'])) {
                $sql .= ' CHECK (' . $name . '>= 0)';
            }
            if (isset($spec['default'])) {
                if (is_string($spec['default'])) {
                    $spec['default'] = $this->connection
                        ->quote($spec['default']);
                }
                $sql .= ' DEFAULT ' . $spec['default'];
            }
            if (empty($spec['not null']) && !isset($spec['default'])) {
                $sql .= ' DEFAULT NULL';
            }
        }
        return $sql;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getFieldTypeMap() {
        // Put :normal last so it gets preserved by array_flip. This makes
        // it much easier for modules (such as schema.module) to map
        // database types back into schema types.
        // $map does not use drupal_static as its value never changes.
        static $map = [
            'varchar_ascii:normal' => 'VARCHAR',
            'varchar:normal' => 'VARCHAR',
            'char:normal' => 'CHAR',
            'text:tiny' => 'TEXT',
            'text:small' => 'TEXT',
            'text:medium' => 'TEXT',
            'text:big' => 'TEXT',
            'text:normal' => 'TEXT',
            'serial:tiny' => 'INTEGER',
            'serial:small' => 'INTEGER',
            'serial:medium' => 'INTEGER',
            'serial:big' => 'INTEGER',
            'serial:normal' => 'INTEGER',
            'int:tiny' => 'INTEGER',
            'int:small' => 'INTEGER',
            'int:medium' => 'INTEGER',
            'int:big' => 'INTEGER',
            'int:normal' => 'INTEGER',
            'float:tiny' => 'FLOAT',
            'float:small' => 'FLOAT',
            'float:medium' => 'FLOAT',
            'float:big' => 'FLOAT',
            'float:normal' => 'FLOAT',
            'numeric:normal' => 'NUMERIC',
            'blob:big' => 'BLOB',
            'blob:normal' => 'BLOB',
        ];
        return $map;
    }
    
    /**
     * {@inheritdoc}
     */
    public function renameTable($table, $new_name) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("Cannot rename '{$table}' to '{$new_name}': table '{$table}' doesn't exist.");
        }
        if ($this->tableExists($new_name)) {
            throw new SchemaObjectExistsException("Cannot rename '{$table}' to '{$new_name}': table '{$new_name}' already exists.");
        }
        $schema = $this->introspectSchema($table);
        // SQLite doesn't allow you to rename tables outside of the current
        // database. So the syntax '... RENAME TO database.table' would fail.
        // So we must determine the full table name here rather than surrounding
        // the table with curly braces in case the db_prefix contains a reference
        // to a database outside of our existing database.
        $info = $this->getPrefixInfo($new_name);
        $this->connection
            ->query('ALTER TABLE {' . $table . '} RENAME TO ' . $info['table']);
        // Drop the indexes, there is no RENAME INDEX command in SQLite.
        if (!empty($schema['unique keys'])) {
            foreach ($schema['unique keys'] as $key => $fields) {
                $this->dropIndex($table, $key);
            }
        }
        if (!empty($schema['indexes'])) {
            foreach ($schema['indexes'] as $index => $fields) {
                $this->dropIndex($table, $index);
            }
        }
        // Recreate the indexes.
        $statements = $this->createIndexSql($new_name, $schema);
        foreach ($statements as $statement) {
            $this->connection
                ->query($statement);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function dropTable($table) {
        if (!$this->tableExists($table)) {
            return FALSE;
        }
        $this->connection->tableDropped = TRUE;
        $this->connection
            ->query('DROP TABLE {' . $table . '}');
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addField($table, $field, $specification, $keys_new = []) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("Cannot add field '{$table}.{$field}': table doesn't exist.");
        }
        if ($this->fieldExists($table, $field)) {
            throw new SchemaObjectExistsException("Cannot add field '{$table}.{$field}': field already exists.");
        }
        if (isset($keys_new['primary key']) && in_array($field, $keys_new['primary key'], TRUE)) {
            $this->ensureNotNullPrimaryKey($keys_new['primary key'], [
                $field => $specification,
            ]);
        }
        // SQLite doesn't have a full-featured ALTER TABLE statement. It only
        // supports adding new fields to a table, in some simple cases. In most
        // cases, we have to create a new table and copy the data over.
        if (empty($keys_new) && (empty($specification['not null']) || isset($specification['default']))) {
            // When we don't have to create new keys and we are not creating a
            // NOT NULL column without a default value, we can use the quicker version.
            $query = 'ALTER TABLE {' . $table . '} ADD ' . $this->createFieldSql($field, $this->processField($specification));
            $this->connection
                ->query($query);
            // Apply the initial value if set.
            if (isset($specification['initial_from_field'])) {
                if (isset($specification['initial'])) {
                    $expression = 'COALESCE(' . $specification['initial_from_field'] . ', :default_initial_value)';
                    $arguments = [
                        ':default_initial_value' => $specification['initial'],
                    ];
                }
                else {
                    $expression = $specification['initial_from_field'];
                    $arguments = [];
                }
                $this->connection
                    ->update($table)
                    ->expression($field, $expression, $arguments)
                    ->execute();
            }
            elseif (isset($specification['initial'])) {
                $this->connection
                    ->update($table)
                    ->fields([
                    $field => $specification['initial'],
                ])
                    ->execute();
            }
        }
        else {
            // We cannot add the field directly. Use the slower table alteration
            // method, starting from the old schema.
            $old_schema = $this->introspectSchema($table);
            $new_schema = $old_schema;
            // Add the new field.
            $new_schema['fields'][$field] = $specification;
            // Build the mapping between the old fields and the new fields.
            $mapping = [];
            if (isset($specification['initial_from_field'])) {
                // If we have an initial value, copy it over.
                if (isset($specification['initial'])) {
                    $expression = 'COALESCE(' . $specification['initial_from_field'] . ', :default_initial_value)';
                    $arguments = [
                        ':default_initial_value' => $specification['initial'],
                    ];
                }
                else {
                    $expression = $specification['initial_from_field'];
                    $arguments = [];
                }
                $mapping[$field] = [
                    'expression' => $expression,
                    'arguments' => $arguments,
                ];
            }
            elseif (isset($specification['initial'])) {
                // If we have an initial value, copy it over.
                $mapping[$field] = [
                    'expression' => ':newfieldinitial',
                    'arguments' => [
                        ':newfieldinitial' => $specification['initial'],
                    ],
                ];
            }
            else {
                // Else use the default of the field.
                $mapping[$field] = NULL;
            }
            // Add the new indexes.
            $new_schema = array_merge($new_schema, $keys_new);
            $this->alterTable($table, $old_schema, $new_schema, $mapping);
        }
    }
    
    /**
     * Create a table with a new schema containing the old content.
     *
     * As SQLite does not support ALTER TABLE (with a few exceptions) it is
     * necessary to create a new table and copy over the old content.
     *
     * @param $table
     *   Name of the table to be altered.
     * @param $old_schema
     *   The old schema array for the table.
     * @param $new_schema
     *   The new schema array for the table.
     * @param $mapping
     *   An optional mapping between the fields of the old specification and the
     *   fields of the new specification. An associative array, whose keys are
     *   the fields of the new table, and values can take two possible forms:
     *     - a simple string, which is interpreted as the name of a field of the
     *       old table,
     *     - an associative array with two keys 'expression' and 'arguments',
     *       that will be used as an expression field.
     */
    protected function alterTable($table, $old_schema, $new_schema, array $mapping = []) {
        $i = 0;
        do {
            $new_table = $table . '_' . $i++;
        } while ($this->tableExists($new_table));
        $this->createTable($new_table, $new_schema);
        // Build a SQL query to migrate the data from the old table to the new.
        $select = $this->connection
            ->select($table);
        // Complete the mapping.
        $possible_keys = array_keys($new_schema['fields']);
        $mapping += array_combine($possible_keys, $possible_keys);
        // Now add the fields.
        foreach ($mapping as $field_alias => $field_source) {
            // Just ignore this field (ie. use its default value).
            if (!isset($field_source)) {
                continue;
            }
            if (is_array($field_source)) {
                $select->addExpression($field_source['expression'], $field_alias, $field_source['arguments']);
            }
            else {
                $select->addField($table, $field_source, $field_alias);
            }
        }
        // Execute the data migration query.
        $this->connection
            ->insert($new_table)
            ->from($select)
            ->execute();
        $old_count = $this->connection
            ->query('SELECT COUNT(*) FROM {' . $table . '}')
            ->fetchField();
        $new_count = $this->connection
            ->query('SELECT COUNT(*) FROM {' . $new_table . '}')
            ->fetchField();
        if ($old_count == $new_count) {
            $this->dropTable($table);
            $this->renameTable($new_table, $table);
        }
    }
    
    /**
     * Find out the schema of a table.
     *
     * This function uses introspection methods provided by the database to
     * create a schema array. This is useful, for example, during update when
     * the old schema is not available.
     *
     * @param $table
     *   Name of the table.
     *
     * @return array
     *   An array representing the schema.
     *
     * @throws \Exception
     *   If a column of the table could not be parsed.
     */
    protected function introspectSchema($table) {
        $mapped_fields = array_flip($this->getFieldTypeMap());
        $schema = [
            'fields' => [],
            'primary key' => [],
            'unique keys' => [],
            'indexes' => [],
        ];
        $info = $this->getPrefixInfo($table);
        $result = $this->connection
            ->query('PRAGMA ' . $info['schema'] . '.table_info(' . $info['table'] . ')');
        foreach ($result as $row) {
            if (preg_match('/^([^(]+)\\((.*)\\)$/', $row->type, $matches)) {
                $type = $matches[1];
                $length = $matches[2];
            }
            else {
                $type = $row->type;
                $length = NULL;
            }
            if (isset($mapped_fields[$type])) {
                [
                    $type,
                    $size,
                ] = explode(':', $mapped_fields[$type]);
                $schema['fields'][$row->name] = [
                    'type' => $type,
                    'size' => $size,
                    'not null' => !empty($row->notnull) || $row->pk !== "0",
                ];
                if ($length) {
                    $schema['fields'][$row->name]['length'] = $length;
                }
                // Convert the default into a properly typed value.
                if ($row->dflt_value === 'NULL') {
                    $schema['fields'][$row->name]['default'] = NULL;
                }
                elseif (is_string($row->dflt_value) && $row->dflt_value[0] === '\'') {
                    // Remove the wrapping single quotes. And replace duplicate single
                    // quotes with a single quote.
                    $schema['fields'][$row->name]['default'] = str_replace("''", "'", substr($row->dflt_value, 1, -1));
                }
                elseif (is_numeric($row->dflt_value)) {
                    // Adding 0 to a string will cause PHP to convert it to a float or
                    // an integer depending on what the string is. For example:
                    // - '1' + 0 = 1
                    // - '1.0' + 0 = 1.0
                    $schema['fields'][$row->name]['default'] = $row->dflt_value + 0;
                }
                else {
                    $schema['fields'][$row->name]['default'] = $row->dflt_value;
                }
                // $row->pk contains a number that reflects the primary key order. We
                // use that as the key and sort (by key) below to return the primary key
                // in the same order that it is stored in.
                if ($row->pk) {
                    $schema['primary key'][$row->pk] = $row->name;
                }
            }
            else {
                throw new \Exception("Unable to parse the column type " . $row->type);
            }
        }
        ksort($schema['primary key']);
        // Re-key the array because $row->pk starts counting at 1.
        $schema['primary key'] = array_values($schema['primary key']);
        $indexes = [];
        $result = $this->connection
            ->query('PRAGMA ' . $info['schema'] . '.index_list(' . $info['table'] . ')');
        foreach ($result as $row) {
            if (strpos($row->name, 'sqlite_autoindex_') !== 0) {
                $indexes[] = [
                    'schema_key' => $row->unique ? 'unique keys' : 'indexes',
                    'name' => $row->name,
                ];
            }
        }
        foreach ($indexes as $index) {
            $name = $index['name'];
            // Get index name without prefix.
            $index_name = substr($name, strlen($info['table']) + 1);
            $result = $this->connection
                ->query('PRAGMA ' . $info['schema'] . '.index_info(' . $name . ')');
            foreach ($result as $row) {
                $schema[$index['schema_key']][$index_name][] = $row->name;
            }
        }
        return $schema;
    }
    
    /**
     * {@inheritdoc}
     */
    public function dropField($table, $field) {
        if (!$this->fieldExists($table, $field)) {
            return FALSE;
        }
        $old_schema = $this->introspectSchema($table);
        $new_schema = $old_schema;
        unset($new_schema['fields'][$field]);
        // Drop the primary key if the field to drop is part of it. This is
        // consistent with the behavior on PostgreSQL.
        // @see \Drupal\mysql\Driver\Database\mysql\Schema::dropField()
        if (isset($new_schema['primary key']) && in_array($field, $new_schema['primary key'], TRUE)) {
            unset($new_schema['primary key']);
        }
        // Handle possible index changes.
        foreach ($new_schema['indexes'] as $index => $fields) {
            foreach ($fields as $key => $field_name) {
                if ($field_name == $field) {
                    unset($new_schema['indexes'][$index][$key]);
                }
            }
            // If this index has no more fields then remove it.
            if (empty($new_schema['indexes'][$index])) {
                unset($new_schema['indexes'][$index]);
            }
        }
        $this->alterTable($table, $old_schema, $new_schema);
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function changeField($table, $field, $field_new, $spec, $keys_new = []) {
        if (!$this->fieldExists($table, $field)) {
            throw new SchemaObjectDoesNotExistException("Cannot change the definition of field '{$table}.{$field}': field doesn't exist.");
        }
        if ($field != $field_new && $this->fieldExists($table, $field_new)) {
            throw new SchemaObjectExistsException("Cannot rename field '{$table}.{$field}' to '{$field_new}': target field already exists.");
        }
        if (isset($keys_new['primary key']) && in_array($field_new, $keys_new['primary key'], TRUE)) {
            $this->ensureNotNullPrimaryKey($keys_new['primary key'], [
                $field_new => $spec,
            ]);
        }
        $old_schema = $this->introspectSchema($table);
        $new_schema = $old_schema;
        // Map the old field to the new field.
        if ($field != $field_new) {
            $mapping[$field_new] = $field;
        }
        else {
            $mapping = [];
        }
        // Remove the previous definition and swap in the new one.
        unset($new_schema['fields'][$field]);
        $new_schema['fields'][$field_new] = $spec;
        // Map the former indexes to the new column name.
        $new_schema['primary key'] = $this->mapKeyDefinition($new_schema['primary key'], $mapping);
        foreach ([
            'unique keys',
            'indexes',
        ] as $k) {
            foreach ($new_schema[$k] as &$key_definition) {
                $key_definition = $this->mapKeyDefinition($key_definition, $mapping);
            }
        }
        // Add in the keys from $keys_new.
        if (isset($keys_new['primary key'])) {
            $new_schema['primary key'] = $keys_new['primary key'];
        }
        foreach ([
            'unique keys',
            'indexes',
        ] as $k) {
            if (!empty($keys_new[$k])) {
                $new_schema[$k] = $keys_new[$k] + $new_schema[$k];
            }
        }
        $this->alterTable($table, $old_schema, $new_schema, $mapping);
    }
    
    /**
     * Utility method: rename columns in an index definition according to a new mapping.
     *
     * @param $key_definition
     *   The key definition.
     * @param $mapping
     *   The new mapping.
     */
    protected function mapKeyDefinition(array $key_definition, array $mapping) {
        foreach ($key_definition as &$field) {
            // The key definition can be an array($field, $length).
            if (is_array($field)) {
                $field =& $field[0];
            }
            $mapped_field = array_search($field, $mapping, TRUE);
            if ($mapped_field !== FALSE) {
                $field = $mapped_field;
            }
        }
        return $key_definition;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addIndex($table, $name, $fields, array $spec) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("Cannot add index '{$name}' to table '{$table}': table doesn't exist.");
        }
        if ($this->indexExists($table, $name)) {
            throw new SchemaObjectExistsException("Cannot add index '{$name}' to table '{$table}': index already exists.");
        }
        $schema['indexes'][$name] = $fields;
        $statements = $this->createIndexSql($table, $schema);
        foreach ($statements as $statement) {
            $this->connection
                ->query($statement);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function indexExists($table, $name) {
        $info = $this->getPrefixInfo($table);
        return $this->connection
            ->query('PRAGMA ' . $info['schema'] . '.index_info(' . $info['table'] . '_' . $name . ')')
            ->fetchField() != '';
    }
    
    /**
     * {@inheritdoc}
     */
    public function dropIndex($table, $name) {
        if (!$this->indexExists($table, $name)) {
            return FALSE;
        }
        $info = $this->getPrefixInfo($table);
        $this->connection
            ->query('DROP INDEX ' . $info['schema'] . '.' . $info['table'] . '_' . $name);
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addUniqueKey($table, $name, $fields) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("Cannot add unique key '{$name}' to table '{$table}': table doesn't exist.");
        }
        if ($this->indexExists($table, $name)) {
            throw new SchemaObjectExistsException("Cannot add unique key '{$name}' to table '{$table}': unique key already exists.");
        }
        $schema['unique keys'][$name] = $fields;
        $statements = $this->createIndexSql($table, $schema);
        foreach ($statements as $statement) {
            $this->connection
                ->query($statement);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function dropUniqueKey($table, $name) {
        if (!$this->indexExists($table, $name)) {
            return FALSE;
        }
        $info = $this->getPrefixInfo($table);
        $this->connection
            ->query('DROP INDEX ' . $info['schema'] . '.' . $info['table'] . '_' . $name);
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addPrimaryKey($table, $fields) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("Cannot add primary key to table '{$table}': table doesn't exist.");
        }
        $old_schema = $this->introspectSchema($table);
        $new_schema = $old_schema;
        if (!empty($new_schema['primary key'])) {
            throw new SchemaObjectExistsException("Cannot add primary key to table '{$table}': primary key already exists.");
        }
        $new_schema['primary key'] = $fields;
        $this->ensureNotNullPrimaryKey($new_schema['primary key'], $new_schema['fields']);
        $this->alterTable($table, $old_schema, $new_schema);
    }
    
    /**
     * {@inheritdoc}
     */
    public function dropPrimaryKey($table) {
        $old_schema = $this->introspectSchema($table);
        $new_schema = $old_schema;
        if (empty($new_schema['primary key'])) {
            return FALSE;
        }
        unset($new_schema['primary key']);
        $this->alterTable($table, $old_schema, $new_schema);
        return TRUE;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function findPrimaryKeyColumns($table) {
        if (!$this->tableExists($table)) {
            return FALSE;
        }
        $schema = $this->introspectSchema($table);
        return $schema['primary key'];
    }
    
    /**
     * {@inheritdoc}
     */
    protected function introspectIndexSchema($table) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("The table {$table} doesn't exist.");
        }
        $schema = $this->introspectSchema($table);
        unset($schema['fields']);
        return $schema;
    }
    
    /**
     * {@inheritdoc}
     */
    public function findTables($table_expression) {
        $tables = [];
        // The SQLite implementation doesn't need to use the same filtering strategy
        // as the parent one because individually prefixed tables live in their own
        // schema (database), which means that neither the main database nor any
        // attached one will contain a prefixed table name, so we just need to loop
        // over all known schemas and filter by the user-supplied table expression.
        $attached_dbs = $this->connection
            ->getAttachedDatabases();
        foreach ($attached_dbs as $schema) {
            // Can't use query placeholders for the schema because the query would
            // have to be :prefixsqlite_master, which does not work. We also need to
            // ignore the internal SQLite tables.
            $result = $this->connection
                ->query("SELECT name FROM " . $schema . ".sqlite_master WHERE type = :type AND name LIKE :table_name AND name NOT LIKE :pattern", [
                ':type' => 'table',
                ':table_name' => $table_expression,
                ':pattern' => 'sqlite_%',
            ]);
            $tables += $result->fetchAllKeyed(0, 0);
        }
        return $tables;
    }

}