import logging

from sqlalchemy.types import TypeDecorator, Text
from sqlalchemy.dialects.mysql import TEXT as MySQLText, LONGTEXT


logger = logging.getLogger(__name__)


class UTF8LongText(TypeDecorator):
  """ Platform-independent UTF-8 LONGTEXT type.

  Uses MySQL's LongText with charset utf8mb4, otherwise uses TEXT, because
  other engines default to UTF-8 and have longer TEXT fields.
  """
  impl = Text

  def load_dialect_impl(self, dialect):
    if dialect.name == 'mysql':
      return dialect.type_descriptor(LONGTEXT(charset='utf8mb4', collation='utf8mb4_unicode_ci'))
    else:
      return dialect.type_descriptor(Text())