class DB(object):
  def __init__(self, *, db_user=None, db_password=None, db_identifier=None, db_schema=None):
    self.db_user = db_user
    if not self.db_user: self.db_user = config.db_user
    self.db_password = db_password
    if not self.db_password: self.db_password = config.db_password
    self.db_identifier = db_identifier
    if not self.db_identifier: self.db_identifier = config.db_identifier
    self.db_schema = db_schema
    if not self.db_schema: self.db_schema = config.db_schema
    self.db = None

  def connect(self):
    if self.db: return
    os.environ["NLS_LANG"] = "Russian.AL32UTF8"
    self.db = cx_Oracle.connect(self.db_user+'/'+self.db_password+'@'+self.db_identifier)

    # for CLOB we need some magic
    # https://cx-oracle.readthedocs.io/en/latest/user_guide/lob_data.html
    def OutputTypeHandler(cursor, name, defaultType, size, precision, scale):
      if defaultType == cx_Oracle.DB_TYPE_CLOB:
        return cursor.var(cx_Oracle.DB_TYPE_LONG, arraysize=cursor.arraysize)
      if defaultType == cx_Oracle.DB_TYPE_BLOB:
        return cursor.var(cx_Oracle.DB_TYPE_LONG_RAW, arraysize=cursor.arraysize)
    self.db.outputtypehandler = OutputTypeHandler

    self.cc = self.db.cursor()

    self.execute("alter session set nls_date_format='dd.mm.yyyy hh24:mi:ss'")
    if self.db_schema: self.execute("alter session set current_schema=%s" % self.db_schema)

  def _execute(self, query, params):
    if params:
      self.cc.execute(query, params)
    else:
      self.cc.execute(query)
    return self.cc

  def execute(self, query, params=None):
    self.connect()
    try:
      self._execute(query, params)
    except (cx_Oracle.OperationalError, cx_Oracle.DatabaseError, cx_Oracle.InterfaceError):
      self.db = None
      self.connect()
      self._execute(query, params)
    return self.cc

  def commit(self):
    if self.db:
      self.db.commit()

  def disconnect(self):
    if self.db:
      self.db.disconnect()