class Schema

abstract class Schema implements PlaceholderInterface {
    
    /**
     * The database connection.
     *
     * @var \Drupal\Core\Database\Connection
     */
    protected $connection;
    
    /**
     * The placeholder counter.
     *
     * @var int
     */
    protected $placeholder = 0;
    
    /**
     * Definition of prefixInfo array structure.
     *
     * Rather than redefining DatabaseSchema::getPrefixInfo() for each driver,
     * by defining the defaultSchema variable only MySQL has to re-write the
     * method.
     *
     * @see DatabaseSchema::getPrefixInfo()
     *
     * @var string
     */
    protected $defaultSchema = 'public';
    
    /**
     * A unique identifier for this query object.
     *
     * @var string
     */
    protected $uniqueIdentifier;
    public function __construct($connection) {
        $this->uniqueIdentifier = uniqid('', TRUE);
        $this->connection = $connection;
    }
    
    /**
     * Implements the magic __clone function.
     */
    public function __clone() {
        $this->uniqueIdentifier = uniqid('', TRUE);
    }
    
    /**
     * {@inheritdoc}
     */
    public function uniqueIdentifier() {
        return $this->uniqueIdentifier;
    }
    
    /**
     * {@inheritdoc}
     */
    public function nextPlaceholder() {
        return $this->placeholder++;
    }
    
    /**
     * Get information about the table name and schema from the prefix.
     *
     * @param string $table
     *   Name of table to look prefix up for. Defaults to 'default' because that's
     *   default key for prefix.
     * @param bool $add_prefix
     *   Boolean that indicates whether the given table name should be prefixed.
     *
     * @return array
     *   A keyed array with information about the schema, table name and prefix.
     */
    protected function getPrefixInfo($table = 'default', $add_prefix = TRUE) {
        $info = [
            'schema' => $this->defaultSchema,
            'prefix' => $this->connection
                ->tablePrefix($table),
        ];
        if ($add_prefix) {
            $table = $info['prefix'] . $table;
        }
        // If the prefix contains a period in it, then that means the prefix also
        // contains a schema reference in which case we will change the schema key
        // to the value before the period in the prefix. Everything after the dot
        // will be prefixed onto the front of the table.
        if (($pos = strpos($table, '.')) !== FALSE) {
            // Grab everything before the period.
            $info['schema'] = substr($table, 0, $pos);
            // Grab everything after the dot.
            $info['table'] = substr($table, ++$pos);
        }
        else {
            $info['table'] = $table;
        }
        return $info;
    }
    
    /**
     * Create names for indexes, primary keys and constraints.
     *
     * This prevents using {} around non-table names like indexes and keys.
     */
    public function prefixNonTable($table) {
        $args = func_get_args();
        $info = $this->getPrefixInfo($table);
        $args[0] = $info['table'];
        return implode('_', $args);
    }
    
    /**
     * Build a condition to match a table name against a standard information_schema.
     *
     * The information_schema is a SQL standard that provides information about the
     * database server and the databases, schemas, tables, columns and users within
     * it. This makes information_schema a useful tool to use across the drupal
     * database drivers and is used by a few different functions. The function below
     * describes the conditions to be meet when querying information_schema.tables
     * for drupal tables or information associated with drupal tables. Even though
     * this is the standard method, not all databases follow standards and so this
     * method should be overwritten by a database driver if the database provider
     * uses alternate methods. Because information_schema.tables is used in a few
     * different functions, a database driver will only need to override this function
     * to make all the others work. For example see
     * core/includes/databases/mysql/schema.inc.
     *
     * @param $table_name
     *   The name of the table in question.
     * @param $operator
     *   The operator to apply on the 'table' part of the condition.
     * @param $add_prefix
     *   Boolean to indicate whether the table name needs to be prefixed.
     *
     * @return \Drupal\Core\Database\Query\Condition
     *   A Condition object.
     */
    protected function buildTableNameCondition($table_name, $operator = '=', $add_prefix = TRUE) {
        $info = $this->connection
            ->getConnectionOptions();
        // Retrieve the table name and schema
        $table_info = $this->getPrefixInfo($table_name, $add_prefix);
        $condition = $this->connection
            ->condition('AND');
        $condition->condition('table_catalog', $info['database']);
        $condition->condition('table_schema', $table_info['schema']);
        $condition->condition('table_name', $table_info['table'], $operator);
        return $condition;
    }
    
    /**
     * Check if a table exists.
     *
     * @param $table
     *   The name of the table in drupal (no prefixing).
     *
     * @return bool
     *   TRUE if the given table exists, otherwise FALSE.
     */
    public function tableExists($table) {
        $condition = $this->buildTableNameCondition($table);
        $condition->compile($this->connection, $this);
        // Normally, we would heartily discourage the use of string
        // concatenation for conditionals like this however, we
        // couldn't use \Drupal::database()->select() here because it would prefix
        // information_schema.tables and the query would fail.
        // Don't use {} around information_schema.tables table.
        return (bool) $this->connection
            ->query("SELECT 1 FROM information_schema.tables WHERE " . (string) $condition, $condition->arguments())
            ->fetchField();
    }
    
    /**
     * Finds all tables that are like the specified base table name.
     *
     * @param string $table_expression
     *   A case-insensitive pattern against which table names are compared. Both
     *   '_' and '%' are treated like wildcards in MySQL 'LIKE' expressions, where
     *   '_' matches any single character and '%' matches an arbitrary number of
     *   characters (including zero characters). So 'foo%bar' matches table names
     *   like 'foobar', 'fooXBar', 'fooXBaR',  or 'fooXxBar'; whereas 'foo_bar'
     *   matches 'fooXBar' and 'fooXBaR' but not 'fooBar' or 'fooXxxBar'.
     *
     * @return array
     *   Both the keys and the values are the matching tables.
     */
    public function findTables($table_expression) {
        // Load all the tables up front in order to take into account per-table
        // prefixes. The actual matching is done at the bottom of the method.
        $condition = $this->buildTableNameCondition('%', 'LIKE');
        $condition->compile($this->connection, $this);
        $individually_prefixed_tables = $this->connection
            ->getUnprefixedTablesMap();
        $default_prefix = $this->connection
            ->tablePrefix();
        $default_prefix_length = strlen($default_prefix);
        $tables = [];
        // Normally, we would heartily discourage the use of string
        // concatenation for conditionals like this however, we
        // couldn't use \Drupal::database()->select() here because it would prefix
        // information_schema.tables and the query would fail.
        // Don't use {} around information_schema.tables table.
        $results = $this->connection
            ->query("SELECT table_name AS table_name FROM information_schema.tables WHERE " . (string) $condition, $condition->arguments());
        foreach ($results as $table) {
            // Take into account tables that have an individual prefix.
            if (isset($individually_prefixed_tables[$table->table_name])) {
                $prefix_length = strlen($this->connection
                    ->tablePrefix($individually_prefixed_tables[$table->table_name]));
            }
            elseif ($default_prefix && substr($table->table_name, 0, $default_prefix_length) !== $default_prefix) {
                // This table name does not start the default prefix, which means that
                // it is not managed by Drupal so it should be excluded from the result.
                continue;
            }
            else {
                $prefix_length = $default_prefix_length;
            }
            // Remove the prefix from the returned tables.
            $unprefixed_table_name = substr($table->table_name, $prefix_length);
            // The pattern can match a table which is the same as the prefix. That
            // will become an empty string when we remove the prefix, which will
            // probably surprise the caller, besides not being a prefixed table. So
            // remove it.
            if (!empty($unprefixed_table_name)) {
                $tables[$unprefixed_table_name] = $unprefixed_table_name;
            }
        }
        // Convert the table expression from its SQL LIKE syntax to a regular
        // expression and escape the delimiter that will be used for matching.
        $table_expression = str_replace([
            '%',
            '_',
        ], [
            '.*?',
            '.',
        ], preg_quote($table_expression, '/'));
        $tables = preg_grep('/^' . $table_expression . '$/i', $tables);
        return $tables;
    }
    
    /**
     * Check if a column exists in the given table.
     *
     * @param string $table
     *   The name of the table in drupal (no prefixing).
     * @param string $column
     *   The name of the column.
     *
     * @return bool
     *   TRUE if the given column exists, otherwise FALSE.
     */
    public function fieldExists($table, $column) {
        $condition = $this->buildTableNameCondition($table);
        $condition->condition('column_name', $column);
        $condition->compile($this->connection, $this);
        // Normally, we would heartily discourage the use of string
        // concatenation for conditionals like this however, we
        // couldn't use \Drupal::database()->select() here because it would prefix
        // information_schema.tables and the query would fail.
        // Don't use {} around information_schema.columns table.
        return (bool) $this->connection
            ->query("SELECT 1 FROM information_schema.columns WHERE " . (string) $condition, $condition->arguments())
            ->fetchField();
    }
    
    /**
     * Returns a mapping of Drupal schema field names to DB-native field types.
     *
     * Because different field types do not map 1:1 between databases, Drupal has
     * its own normalized field type names. This function returns a driver-specific
     * mapping table from Drupal names to the native names for each database.
     *
     * @return array
     *   An array of Schema API field types to driver-specific field types.
     */
    public abstract function getFieldTypeMap();
    
    /**
     * Rename a table.
     *
     * @param $table
     *   The table to be renamed.
     * @param $new_name
     *   The new name for the table.
     *
     * @throws \Drupal\Core\Database\SchemaObjectDoesNotExistException
     *   If the specified table doesn't exist.
     * @throws \Drupal\Core\Database\SchemaObjectExistsException
     *   If a table with the specified new name already exists.
     */
    public abstract function renameTable($table, $new_name);
    
    /**
     * Drop a table.
     *
     * @param $table
     *   The table to be dropped.
     *
     * @return bool
     *   TRUE if the table was successfully dropped, FALSE if there was no table
     *   by that name to begin with.
     */
    public abstract function dropTable($table);
    
    /**
     * Add a new field to a table.
     *
     * @param $table
     *   Name of the table to be altered.
     * @param $field
     *   Name of the field to be added.
     * @param $spec
     *   The field specification array, as taken from a schema definition.
     *   The specification may also contain the key 'initial', the newly
     *   created field will be set to the value of the key in all rows.
     *   This is most useful for creating NOT NULL columns with no default
     *   value in existing tables.
     *   Alternatively, the 'initial_from_field' key may be used, which will
     *   auto-populate the new field with values from the specified field.
     * @param $keys_new
     *   (optional) Keys and indexes specification to be created on the
     *   table along with adding the field. The format is the same as a
     *   table specification but without the 'fields' element. If you are
     *   adding a type 'serial' field, you MUST specify at least one key
     *   or index including it in this array. See ::changeField() for more
     *   explanation why.
     *
     * @throws \Drupal\Core\Database\SchemaObjectDoesNotExistException
     *   If the specified table doesn't exist.
     * @throws \Drupal\Core\Database\SchemaObjectExistsException
     *   If the specified table already has a field by that name.
     */
    public abstract function addField($table, $field, $spec, $keys_new = []);
    
    /**
     * Drop a field.
     *
     * @param $table
     *   The table to be altered.
     * @param $field
     *   The field to be dropped.
     *
     * @return bool
     *   TRUE if the field was successfully dropped, FALSE if there was no field
     *   by that name to begin with.
     */
    public abstract function dropField($table, $field);
    
    /**
     * Checks if an index exists in the given table.
     *
     * @param $table
     *   The name of the table in drupal (no prefixing).
     * @param $name
     *   The name of the index in drupal (no prefixing).
     *
     * @return bool
     *   TRUE if the given index exists, otherwise FALSE.
     */
    public abstract function indexExists($table, $name);
    
    /**
     * Add a primary key.
     *
     * @param $table
     *   The table to be altered.
     * @param $fields
     *   Fields for the primary key.
     *
     * @throws \Drupal\Core\Database\SchemaObjectDoesNotExistException
     *   If the specified table doesn't exist.
     * @throws \Drupal\Core\Database\SchemaObjectExistsException
     *   If the specified table already has a primary key.
     */
    public abstract function addPrimaryKey($table, $fields);
    
    /**
     * Drop the primary key.
     *
     * @param $table
     *   The table to be altered.
     *
     * @return bool
     *   TRUE if the primary key was successfully dropped, FALSE if there was no
     *   primary key on this table to begin with.
     */
    public abstract function dropPrimaryKey($table);
    
    /**
     * Finds the primary key columns of a table, from the database.
     *
     * @param string $table
     *   The name of the table.
     *
     * @return string[]|false
     *   A simple array with the names of the columns composing the table's
     *   primary key, or FALSE if the table does not exist.
     *
     * @throws \RuntimeException
     *   If the driver does not override this method.
     */
    protected function findPrimaryKeyColumns($table) {
        if (!$this->tableExists($table)) {
            return FALSE;
        }
        throw new \RuntimeException("The '" . $this->connection
            ->driver() . "' database driver does not implement " . __METHOD__);
    }
    
    /**
     * Add a unique key.
     *
     * @param $table
     *   The table to be altered.
     * @param $name
     *   The name of the key.
     * @param $fields
     *   An array of field names.
     *
     * @throws \Drupal\Core\Database\SchemaObjectDoesNotExistException
     *   If the specified table doesn't exist.
     * @throws \Drupal\Core\Database\SchemaObjectExistsException
     *   If the specified table already has a key by that name.
     */
    public abstract function addUniqueKey($table, $name, $fields);
    
    /**
     * Drop a unique key.
     *
     * @param $table
     *   The table to be altered.
     * @param $name
     *   The name of the key.
     *
     * @return bool
     *   TRUE if the key was successfully dropped, FALSE if there was no key by
     *   that name to begin with.
     */
    public abstract function dropUniqueKey($table, $name);
    
    /**
     * Add an index.
     *
     * @param $table
     *   The table to be altered.
     * @param $name
     *   The name of the index.
     * @param $fields
     *   An array of field names or field information; if field information is
     *   passed, it's an array whose first element is the field name and whose
     *   second is the maximum length in the index. For example, the following
     *   will use the full length of the `foo` field, but limit the `bar` field to
     *   4 characters:
     *   @code
     *     $fields = ['foo', ['bar', 4]];
     *   @endcode
     * @param array $spec
     *   The table specification for the table to be altered. This is used in
     *   order to be able to ensure that the index length is not too long.
     *   This schema definition can usually be obtained through hook_schema(), or
     *   in case the table was created by the Entity API, through the schema
     *   handler listed in the entity class definition. For reference, see
     *   SqlContentEntityStorageSchema::getDedicatedTableSchema() and
     *   SqlContentEntityStorageSchema::getSharedTableFieldSchema().
     *
     *   In order to prevent human error, it is recommended to pass in the
     *   complete table specification. However, in the edge case of the complete
     *   table specification not being available, we can pass in a partial table
     *   definition containing only the fields that apply to the index:
     *   @code
     *   $spec = [
     *     // Example partial specification for a table:
     *     'fields' => [
     *       'example_field' => [
     *         'description' => 'An example field',
     *         'type' => 'varchar',
     *         'length' => 32,
     *         'not null' => TRUE,
     *         'default' => '',
     *       ],
     *     ],
     *     'indexes' => [
     *       'table_example_field' => ['example_field'],
     *     ],
     *   ];
     *   @endcode
     *   Note that the above is a partial table definition and that we would
     *   usually pass a complete table definition as obtained through
     *   hook_schema() instead.
     *
     * @see schemaapi
     * @see hook_schema()
     *
     * @throws \Drupal\Core\Database\SchemaObjectDoesNotExistException
     *   If the specified table doesn't exist.
     * @throws \Drupal\Core\Database\SchemaObjectExistsException
     *   If the specified table already has an index by that name.
     *
     * @todo remove the $spec argument whenever schema introspection is added.
     */
    public abstract function addIndex($table, $name, $fields, array $spec);
    
    /**
     * Drop an index.
     *
     * @param $table
     *   The table to be altered.
     * @param $name
     *   The name of the index.
     *
     * @return bool
     *   TRUE if the index was successfully dropped, FALSE if there was no index
     *   by that name to begin with.
     */
    public abstract function dropIndex($table, $name);
    
    /**
     * Finds the columns for the primary key, unique keys and indexes of a table.
     *
     * @param string $table
     *   The name of the table.
     *
     * @return array
     *   A schema array with the following keys: 'primary key', 'unique keys' and
     *   'indexes', and values as arrays of database columns.
     *
     * @throws \Drupal\Core\Database\SchemaObjectDoesNotExistException
     *   If the specified table doesn't exist.
     * @throws \RuntimeException
     *   If the driver does not implement this method.
     */
    protected function introspectIndexSchema($table) {
        if (!$this->tableExists($table)) {
            throw new SchemaObjectDoesNotExistException("The table {$table} doesn't exist.");
        }
        throw new \RuntimeException("The '{$this->connection->driver()}' database driver does not implement " . __METHOD__);
    }
    
    /**
     * Change a field definition.
     *
     * IMPORTANT NOTE: To maintain database portability, you have to explicitly
     * recreate all indices and primary keys that are using the changed field.
     *
     * That means that you have to drop all affected keys and indexes with
     * Schema::dropPrimaryKey(), Schema::dropUniqueKey(), or Schema::dropIndex()
     * before calling ::changeField().
     * To recreate the keys and indices, pass the key definitions as the
     * optional $keys_new argument directly to ::changeField().
     *
     * For example, suppose you have:
     * @code
     * $schema['foo'] = array(
     *   'fields' => array(
     *     'bar' => array('type' => 'int', 'not null' => TRUE)
     *   ),
     *   'primary key' => array('bar')
     * );
     * @endcode
     * and you want to change foo.bar to be type serial, leaving it as the
     * primary key. The correct sequence is:
     * @code
     * $injected_database->schema()->dropPrimaryKey('foo');
     * $injected_database->schema()->changeField('foo', 'bar', 'bar',
     *   array('type' => 'serial', 'not null' => TRUE),
     *   array('primary key' => array('bar')));
     * @endcode
     *
     * The reasons for this are due to the different database engines:
     *
     * On PostgreSQL, changing a field definition involves adding a new field
     * and dropping an old one which* causes any indices, primary keys and
     * sequences (from serial-type fields) that use the changed field to be dropped.
     *
     * On MySQL, all type 'serial' fields must be part of at least one key
     * or index as soon as they are created. You cannot use
     * Schema::addPrimaryKey, Schema::addUniqueKey(), or Schema::addIndex()
     * for this purpose because the ALTER TABLE command will fail to add
     * the column without a key or index specification.
     * The solution is to use the optional $keys_new argument to create the key
     * or index at the same time as field.
     *
     * You could use Schema::addPrimaryKey, Schema::addUniqueKey(), or
     * Schema::addIndex() in all cases unless you are converting a field to
     * be type serial. You can use the $keys_new argument in all cases.
     *
     * @param $table
     *   Name of the table.
     * @param $field
     *   Name of the field to change.
     * @param $field_new
     *   New name for the field (set to the same as $field if you don't want to change the name).
     * @param $spec
     *   The field specification for the new field.
     * @param $keys_new
     *   (optional) Keys and indexes specification to be created on the
     *   table along with changing the field. The format is the same as a
     *   table specification but without the 'fields' element.
     *
     * @throws \Drupal\Core\Database\SchemaObjectDoesNotExistException
     *   If the specified table or source field doesn't exist.
     * @throws \Drupal\Core\Database\SchemaObjectExistsException
     *   If the specified destination field already exists.
     */
    public abstract function changeField($table, $field, $field_new, $spec, $keys_new = []);
    
    /**
     * Create a new table from a Drupal table definition.
     *
     * @param $name
     *   The name of the table to create.
     * @param $table
     *   A Schema API table definition array.
     *
     * @throws \Drupal\Core\Database\SchemaObjectExistsException
     *   If the specified table already exists.
     */
    public function createTable($name, $table) {
        if ($this->tableExists($name)) {
            throw new SchemaObjectExistsException("Table '{$name}' already exists.");
        }
        $statements = $this->createTableSql($name, $table);
        foreach ($statements as $statement) {
            $this->connection
                ->query($statement);
        }
    }
    
    /**
     * Return an array of field names from an array of key/index column specifiers.
     *
     * This is usually an identity function but if a key/index uses a column prefix
     * specification, this function extracts just the name.
     *
     * @param $fields
     *   An array of key/index column specifiers.
     *
     * @return array
     *   An array of field names.
     */
    public function fieldNames($fields) {
        $return = [];
        foreach ($fields as $field) {
            if (is_array($field)) {
                $return[] = $field[0];
            }
            else {
                $return[] = $field;
            }
        }
        return $return;
    }
    
    /**
     * Prepare a table or column comment for database query.
     *
     * @param $comment
     *   The comment string to prepare.
     * @param $length
     *   Optional upper limit on the returned string length.
     *
     * @return string
     *   The prepared comment.
     */
    public function prepareComment($comment, $length = NULL) {
        // Remove semicolons to avoid triggering multi-statement check.
        $comment = strtr($comment, [
            ';' => '.',
        ]);
        return $this->connection
            ->quote($comment);
    }
    
    /**
     * Escapes a value to be used as the default value on a column.
     *
     * @param mixed $value
     *   The value to be escaped (int, float, null or string).
     *
     * @return string|int|float
     *   The escaped value.
     */
    protected function escapeDefaultValue($value) {
        if (is_null($value)) {
            return 'NULL';
        }
        return is_string($value) ? $this->connection
            ->quote($value) : $value;
    }
    
    /**
     * Ensures that all the primary key fields are correctly defined.
     *
     * @param array $primary_key
     *   An array containing the fields that will form the primary key of a table.
     * @param array $fields
     *   An array containing the field specifications of the table, as per the
     *   schema data structure format.
     *
     * @throws \Drupal\Core\Database\SchemaException
     *   Thrown if any primary key field specification does not exist or if they
     *   do not define 'not null' as TRUE.
     */
    protected function ensureNotNullPrimaryKey(array $primary_key, array $fields) {
        foreach (array_intersect($primary_key, array_keys($fields)) as $field_name) {
            if (!isset($fields[$field_name]['not null']) || $fields[$field_name]['not null'] !== TRUE) {
                throw new SchemaException("The '{$field_name}' field specification does not define 'not null' as TRUE.");
            }
        }
    }

}