text: # Copyright Contributors to the Amundsen project.
  # SPDX-License-Identifier: Apache-2.0
  
  import abc
  import logging
  from collections import namedtuple
  
  from pyhocon import ConfigFactory, ConfigTree
  from typing import Iterator, Union, Dict, Any
  
  from databuilder import Scoped
  from databuilder.extractor.base_extractor import Extractor
  from databuilder.extractor.sql_alchemy_extractor import SQLAlchemyExtractor
  from databuilder.models.table_metadata import TableMetadata, ColumnMetadata
  from itertools import groupby
  
  
  TableKey = namedtuple('TableKey', ['schema', 'table_name'])
  
  LOGGER = logging.getLogger(__name__)
  
  
  class BasePostgresMetadataExtractor(Extractor):
      """
      Extracts Postgres table and column metadata from underlying meta store database using SQLAlchemyExtractor
      """
  
      # CONFIG KEYS
      WHERE_CLAUSE_SUFFIX_KEY = 'where_clause_suffix'
      CLUSTER_KEY = 'cluster_key'
      USE_CATALOG_AS_CLUSTER_NAME = 'use_catalog_as_cluster_name'
      DATABASE_KEY = 'database_key'
  
      # Default values
      DEFAULT_CLUSTER_NAME = 'master'
  
      DEFAULT_CONFIG = ConfigFactory.from_dict(
          {WHERE_CLAUSE_SUFFIX_KEY: ' ', CLUSTER_KEY: DEFAULT_CLUSTER_NAME, USE_CATALOG_AS_CLUSTER_NAME: True}
      )
  
      @abc.abstractmethod
      def get_sql_statement(self, use_catalog_as_cluster_name: bool, where_clause_suffix: str) -> Any:
          """
          :return: Provides a record or None if no more to extract
          """
          return None
  
      def init(self, conf: ConfigTree) -> None:
          conf = conf.with_fallback(BasePostgresMetadataExtractor.DEFAULT_CONFIG)
          self._cluster = '{}'.format(conf.get_string(BasePostgresMetadataExtractor.CLUSTER_KEY))
  
          self._database = conf.get_string(BasePostgresMetadataExtractor.DATABASE_KEY, default='postgres')
  
          self.sql_stmt = self.get_sql_statement(
              use_catalog_as_cluster_name=conf.get_bool(BasePostgresMetadataExtractor.USE_CATALOG_AS_CLUSTER_NAME),
              where_clause_suffix=conf.get_string(BasePostgresMetadataExtractor.WHERE_CLAUSE_SUFFIX_KEY),
          )
  
          self._alchemy_extractor = SQLAlchemyExtractor()
          sql_alch_conf = Scoped.get_scoped_conf(conf, self._alchemy_extractor.get_scope())\
              .with_fallback(ConfigFactory.from_dict({SQLAlchemyExtractor.EXTRACT_SQL: self.sql_stmt}))
  
          self.sql_stmt = sql_alch_conf.get_string(SQLAlchemyExtractor.EXTRACT_SQL)
  
          LOGGER.info('SQL for postgres metadata: {}'.format(self.sql_stmt))
  
          self._alchemy_extractor.init(sql_alch_conf)
          self._extract_iter: Union[None, Iterator] = None
  
      def extract(self) -> Union[TableMetadata, None]:
          if not self._extract_iter:
              self._extract_iter = self._get_extract_iter()
          try:
              return next(self._extract_iter)
          except StopIteration:
              return None
  
      def _get_extract_iter(self) -> Iterator[TableMetadata]:
          """
          Using itertools.groupby and raw level iterator, it groups to table and yields TableMetadata
          :return:
          """
          for key, group in groupby(self._get_raw_extract_iter(), self._get_table_key):
              columns = []
  
              for row in group:
                  last_row = row
                  columns.append(ColumnMetadata(row['col_name'], row['col_description'],
                                                row['col_type'], row['col_sort_order']))
  
              yield TableMetadata(self._database, last_row['cluster'],
                                  last_row['schema'],
                                  last_row['name'],
                                  last_row['description'],
                                  columns)
  
      def _get_raw_extract_iter(self) -> Iterator[Dict[str, Any]]:
          """
          Provides iterator of result row from SQLAlchemy extractor
          :return:
          """
          row = self._alchemy_extractor.extract()
          while row:
              yield row
              row = self._alchemy_extractor.extract()
  
      def _get_table_key(self, row: Dict[str, Any]) -> Union[TableKey, None]:
          """
          Table key consists of schema and table name
          :param row:
          :return:
          """
          if row:
              return TableKey(schema=row['schema'], table_name=row['name'])
  
          return None
  