text: import itertools
  import os
  from collections.abc import Mapping, Sequence
  from copy import copy
  
  import sqlalchemy as sa
  from sqlalchemy.engine.url import make_url
  from sqlalchemy.exc import OperationalError, ProgrammingError
  
  from ..utils import starts_with
  from .orm import quote
  
  
  def escape_like(string, escape_char='*'):
      """
      Escape the string paremeter used in SQL LIKE expressions.
  
      ::
  
          from sqlalchemy_utils import escape_like
  
  
          query = session.query(User).filter(
              User.name.ilike(escape_like('John'))
          )
  
  
      :param string: a string to escape
      :param escape_char: escape character
      """
      return (
          string
          .replace(escape_char, escape_char * 2)
          .replace('%', escape_char + '%')
          .replace('_', escape_char + '_')
      )
  
  
  def json_sql(value, scalars_to_json=True):
      """
      Convert python data structures to PostgreSQL specific SQLAlchemy JSON
      constructs. This function is extremly useful if you need to build
      PostgreSQL JSON on python side.
  
      .. note::
  
          This function needs PostgreSQL >= 9.4
  
      Scalars are converted to to_json SQLAlchemy function objects
  
      ::
  
          json_sql(1)     # Equals SQL: to_json(1)
  
          json_sql('a')   # to_json('a')
  
  
      Mappings are converted to json_build_object constructs
  
      ::
  
          json_sql({'a': 'c', '2': 5})  # json_build_object('a', 'c', '2', 5)
  
  
      Sequences (other than strings) are converted to json_build_array constructs
  
      ::
  
          json_sql([1, 2, 3])  # json_build_array(1, 2, 3)
  
  
      You can also nest these data structures
  
      ::
  
          json_sql({'a': [1, 2, 3]})
          # json_build_object('a', json_build_array[1, 2, 3])
  
  
      :param value:
          value to be converted to SQLAlchemy PostgreSQL function constructs
      """
      scalar_convert = sa.text
      if scalars_to_json:
          def scalar_convert(a):
              return sa.func.to_json(sa.text(a))
  
      if isinstance(value, Mapping):
          return sa.func.json_build_object(
              *(
                  json_sql(v, scalars_to_json=False)
                  for v in itertools.chain(*value.items())
              )
          )
      elif isinstance(value, str):
          return scalar_convert("'{0}'".format(value))
      elif isinstance(value, Sequence):
          return sa.func.json_build_array(
              *(
                  json_sql(v, scalars_to_json=False)
                  for v in value
              )
          )
      elif isinstance(value, (int, float)):
          return scalar_convert(str(value))
      return value
  
  
  def jsonb_sql(value, scalars_to_jsonb=True):
      """
      Convert python data structures to PostgreSQL specific SQLAlchemy JSONB
      constructs. This function is extremly useful if you need to build
      PostgreSQL JSONB on python side.
  
      .. note::
  
          This function needs PostgreSQL >= 9.4
  
      Scalars are converted to to_jsonb SQLAlchemy function objects
  
      ::
  
          jsonb_sql(1)     # Equals SQL: to_jsonb(1)
  
          jsonb_sql('a')   # to_jsonb('a')
  
  
      Mappings are converted to jsonb_build_object constructs
  
      ::
  
          jsonb_sql({'a': 'c', '2': 5})  # jsonb_build_object('a', 'c', '2', 5)
  
  
      Sequences (other than strings) converted to jsonb_build_array constructs
  
      ::
  
          jsonb_sql([1, 2, 3])  # jsonb_build_array(1, 2, 3)
  
  
      You can also nest these data structures
  
      ::
  
          jsonb_sql({'a': [1, 2, 3]})
          # jsonb_build_object('a', jsonb_build_array[1, 2, 3])
  
  
      :param value:
          value to be converted to SQLAlchemy PostgreSQL function constructs
      :boolean jsonbb:
          Flag to alternatively convert the return with a to_jsonb construct
      """
      scalar_convert = sa.text
      if scalars_to_jsonb:
          def scalar_convert(a):
              return sa.func.to_jsonb(sa.text(a))
  
      if isinstance(value, Mapping):
          return sa.func.jsonb_build_object(
              *(
                  jsonb_sql(v, scalars_to_jsonb=False)
                  for v in itertools.chain(*value.items())
              )
          )
      elif isinstance(value, str):
          return scalar_convert("'{0}'".format(value))
      elif isinstance(value, Sequence):
          return sa.func.jsonb_build_array(
              *(
                  jsonb_sql(v, scalars_to_jsonb=False)
                  for v in value
              )
          )
      elif isinstance(value, (int, float)):
          return scalar_convert(str(value))
      return value
  
  
  def has_index(column_or_constraint):
      """
      Return whether or not given column or the columns of given foreign key
      constraint have an index. A column has an index if it has a single column
      index or it is the first column in compound column index.
  
      A foreign key constraint has an index if the constraint columns are the
      first columns in compound column index.
  
      :param column_or_constraint:
          SQLAlchemy Column object or SA ForeignKeyConstraint object
  
      .. versionadded: 0.26.2
  
      .. versionchanged: 0.30.18
          Added support for foreign key constaints.
  
      ::
  
          from sqlalchemy_utils import has_index
  
  
          class Article(Base):
              __tablename__ = 'article'
              id = sa.Column(sa.Integer, primary_key=True)
              title = sa.Column(sa.String(100))
              is_published = sa.Column(sa.Boolean, index=True)
              is_deleted = sa.Column(sa.Boolean)
              is_archived = sa.Column(sa.Boolean)
  
              __table_args__ = (
                  sa.Index('my_index', is_deleted, is_archived),
              )
  
  
          table = Article.__table__
  
          has_index(table.c.is_published) # True
          has_index(table.c.is_deleted)   # True
          has_index(table.c.is_archived)  # False
  
  
      Also supports primary key indexes
  
      ::
  
          from sqlalchemy_utils import has_index
  
  
          class ArticleTranslation(Base):
              __tablename__ = 'article_translation'
              id = sa.Column(sa.Integer, primary_key=True)
              locale = sa.Column(sa.String(10), primary_key=True)
              title = sa.Column(sa.String(100))
  
  
          table = ArticleTranslation.__table__
  
          has_index(table.c.locale)   # False
          has_index(table.c.id)       # True
  
  
      This function supports foreign key constraints as well
  
      ::
  
  
          class User(Base):
              __tablename__ = 'user'
              first_name = sa.Column(sa.Unicode(255), primary_key=True)
              last_name = sa.Column(sa.Unicode(255), primary_key=True)
  
          class Article(Base):
              __tablename__ = 'article'
              id = sa.Column(sa.Integer, primary_key=True)
              author_first_name = sa.Column(sa.Unicode(255))
              author_last_name = sa.Column(sa.Unicode(255))
              __table_args__ = (
                  sa.ForeignKeyConstraint(
                      [author_first_name, author_last_name],
                      [User.first_name, User.last_name]
                  ),
                  sa.Index(
                      'my_index',
                      author_first_name,
                      author_last_name
                  )
              )
  
          table = Article.__table__
          constraint = list(table.foreign_keys)[0].constraint
  
          has_index(constraint)  # True
      """
      table = column_or_constraint.table
      if not isinstance(table, sa.Table):
          raise TypeError(
              'Only columns belonging to Table objects are supported. Given '
              'column belongs to %r.' % table
          )
      primary_keys = table.primary_key.columns.values()
      if isinstance(column_or_constraint, sa.ForeignKeyConstraint):
          columns = list(column_or_constraint.columns.values())
      else:
          columns = [column_or_constraint]
  
      return (
          (primary_keys and starts_with(primary_keys, columns)) or
          any(
              starts_with(index.columns.values(), columns)
              for index in table.indexes
          )
      )
  
  
  def has_unique_index(column_or_constraint):
      """
      Return whether or not given column or given foreign key constraint has a
      unique index.
  
      A column has a unique index if it has a single column primary key index or
      it has a single column UniqueConstraint.
  
      A foreign key constraint has a unique index if the columns of the
      constraint are the same as the columns of table primary key or the coluns
      of any unique index or any unique constraint of the given table.
  
      :param column: SQLAlchemy Column object
  
      .. versionadded: 0.27.1
  
      .. versionchanged: 0.30.18
          Added support for foreign key constaints.
  
          Fixed support for unique indexes (previously only worked for unique
          constraints)
  
      ::
  
          from sqlalchemy_utils import has_unique_index
  
  
          class Article(Base):
              __tablename__ = 'article'
              id = sa.Column(sa.Integer, primary_key=True)
              title = sa.Column(sa.String(100))
              is_published = sa.Column(sa.Boolean, unique=True)
              is_deleted = sa.Column(sa.Boolean)
              is_archived = sa.Column(sa.Boolean)
  
  
          table = Article.__table__
  
          has_unique_index(table.c.is_published) # True
          has_unique_index(table.c.is_deleted)   # False
          has_unique_index(table.c.id)           # True
  
  
      This function supports foreign key constraints as well
  
      ::
  
  
          class User(Base):
              __tablename__ = 'user'
              first_name = sa.Column(sa.Unicode(255), primary_key=True)
              last_name = sa.Column(sa.Unicode(255), primary_key=True)
  
          class Article(Base):
              __tablename__ = 'article'
              id = sa.Column(sa.Integer, primary_key=True)
              author_first_name = sa.Column(sa.Unicode(255))
              author_last_name = sa.Column(sa.Unicode(255))
              __table_args__ = (
                  sa.ForeignKeyConstraint(
                      [author_first_name, author_last_name],
                      [User.first_name, User.last_name]
                  ),
                  sa.Index(
                      'my_index',
                      author_first_name,
                      author_last_name,
                      unique=True
                  )
              )
  
          table = Article.__table__
          constraint = list(table.foreign_keys)[0].constraint
  
          has_unique_index(constraint)  # True
  
  
      :raises TypeError: if given column does not belong to a Table object
      """
      table = column_or_constraint.table
      if not isinstance(table, sa.Table):
          raise TypeError(
              'Only columns belonging to Table objects are supported. Given '
              'column belongs to %r.' % table
          )
      primary_keys = list(table.primary_key.columns.values())
      if isinstance(column_or_constraint, sa.ForeignKeyConstraint):
          columns = list(column_or_constraint.columns.values())
      else:
          columns = [column_or_constraint]
  
      return (
          (columns == primary_keys) or
          any(
              columns == list(constraint.columns.values())
              for constraint in table.constraints
              if isinstance(constraint, sa.sql.schema.UniqueConstraint)
          ) or
          any(
              columns == list(index.columns.values())
              for index in table.indexes
              if index.unique
          )
      )
  
  
  def is_auto_assigned_date_column(column):
      """
      Returns whether or not given SQLAlchemy Column object's is auto assigned
      DateTime or Date.
  
      :param column: SQLAlchemy Column object
      """
      return (
          (
              isinstance(column.type, sa.DateTime) or
              isinstance(column.type, sa.Date)
          ) and
          (
              column.default or
              column.server_default or
              column.onupdate or
              column.server_onupdate
          )
      )
  
  
  def database_exists(url):
      """Check if a database exists.
  
      :param url: A SQLAlchemy engine URL.
  
      Performs backend-specific testing to quickly determine if a database
      exists on the server. ::
  
          database_exists('postgresql://postgres@localhost/name')  #=> False
          create_database('postgresql://postgres@localhost/name')
          database_exists('postgresql://postgres@localhost/name')  #=> True
  
      Supports checking against a constructed URL as well. ::
  
          engine = create_engine('postgresql://postgres@localhost/name')
          database_exists(engine.url)  #=> False
          create_database(engine.url)
          database_exists(engine.url)  #=> True
  
      """
  
      def get_scalar_result(engine, sql):
          result_proxy = engine.execute(sql)
          result = result_proxy.scalar()
          result_proxy.close()
          engine.dispose()
          return result
  
      def sqlite_file_exists(database):
          if not os.path.isfile(database) or os.path.getsize(database) < 100:
              return False
  
          with open(database, 'rb') as f:
              header = f.read(100)
  
          return header[:16] == b'SQLite format 3\x00'
  
      url = copy(make_url(url))
      database, url.database = url.database, None
      engine = sa.create_engine(url)
  
      if engine.dialect.name == 'postgresql':
          text = "SELECT 1 FROM pg_database WHERE datname='%s'" % database
          return bool(get_scalar_result(engine, text))
  
      elif engine.dialect.name == 'mysql':
          text = ("SELECT SCHEMA_NAME FROM INFORMATION_SCHEMA.SCHEMATA "
                  "WHERE SCHEMA_NAME = '%s'" % database)
          return bool(get_scalar_result(engine, text))
  
      elif engine.dialect.name == 'sqlite':
          if database:
              return database == ':memory:' or sqlite_file_exists(database)
          else:
              # The default SQLAlchemy database is in memory,
              # and :memory is not required, thus we should support that use-case
              return True
  
      else:
          engine.dispose()
          engine = None
          text = 'SELECT 1'
          try:
              url.database = database
              engine = sa.create_engine(url)
              result = engine.execute(text)
              result.close()
              return True
  
          except (ProgrammingError, OperationalError):
              return False
          finally:
              if engine is not None:
                  engine.dispose()
  
  
  def create_database(url, encoding='utf8', template=None):
      """Issue the appropriate CREATE DATABASE statement.
  
      :param url: A SQLAlchemy engine URL.
      :param encoding: The encoding to create the database as.
      :param template:
          The name of the template from which to create the new database. At the
          moment only supported by PostgreSQL driver.
  
      To create a database, you can pass a simple URL that would have
      been passed to ``create_engine``. ::
  
          create_database('postgresql://postgres@localhost/name')
  
      You may also pass the url from an existing engine. ::
  
          create_database(engine.url)
  
      Has full support for mysql, postgres, and sqlite. In theory,
      other database engines should be supported.
      """
  
      url = copy(make_url(url))
  
      database = url.database
  
      if url.drivername.startswith('postgres'):
          url.database = 'postgres'
      elif url.drivername.startswith('mssql'):
          url.database = 'master'
      elif not url.drivername.startswith('sqlite'):
          url.database = None
  
      if url.drivername == 'mssql+pyodbc':
          engine = sa.create_engine(url, connect_args={'autocommit': True})
      elif url.drivername == 'postgresql+pg8000':
          engine = sa.create_engine(url, isolation_level='AUTOCOMMIT')
      else:
          engine = sa.create_engine(url)
      result_proxy = None
  
      if engine.dialect.name == 'postgresql':
          if not template:
              template = 'template1'
  
          text = "CREATE DATABASE {0} ENCODING '{1}' TEMPLATE {2}".format(
              quote(engine, database),
              encoding,
              quote(engine, template)
          )
  
          if engine.driver == 'psycopg2cffi':
              connection = engine.connect()
              connection.connection.set_session(autocommit=True)
              connection.execute(text)
          else:
              if engine.driver == 'psycopg2':
                  from psycopg2.extensions import ISOLATION_LEVEL_AUTOCOMMIT
                  engine.raw_connection().set_isolation_level(
                      ISOLATION_LEVEL_AUTOCOMMIT
                  )
  
              result_proxy = engine.execute(text)
  
      elif engine.dialect.name == 'mysql':
          text = "CREATE DATABASE {0} CHARACTER SET = '{1}'".format(
              quote(engine, database),
              encoding
          )
          result_proxy = engine.execute(text)
  
      elif engine.dialect.name == 'sqlite' and database != ':memory:':
          if database:
              engine.execute("CREATE TABLE DB(id int);")
              engine.execute("DROP TABLE DB;")
  
      else:
          text = 'CREATE DATABASE {0}'.format(quote(engine, database))
          result_proxy = engine.execute(text)
  
      if result_proxy is not None:
          result_proxy.close()
      engine.dispose()
  
  
  def drop_database(url):
      """Issue the appropriate DROP DATABASE statement.
  
      :param url: A SQLAlchemy engine URL.
  
      Works similar to the :ref:`create_database` method in that both url text
      and a constructed url are accepted. ::
  
          drop_database('postgresql://postgres@localhost/name')
          drop_database(engine.url)
  
      """
  
      url = copy(make_url(url))
  
      database = url.database
  
      if url.drivername.startswith('postgres'):
          url.database = 'postgres'
      elif url.drivername.startswith('mssql'):
          url.database = 'master'
      elif not url.drivername.startswith('sqlite'):
          url.database = None
  
      if url.drivername == 'mssql+pyodbc':
          engine = sa.create_engine(url, connect_args={'autocommit': True})
      elif url.drivername == 'postgresql+pg8000':
          engine = sa.create_engine(url, isolation_level='AUTOCOMMIT')
      else:
          engine = sa.create_engine(url)
      conn_resource = None
  
      if engine.dialect.name == 'sqlite' and database != ':memory:':
          if database:
              os.remove(database)
  
      elif (
                  engine.dialect.name == 'postgresql' and
                  engine.driver in {'psycopg2', 'psycopg2cffi'}
      ):
          if engine.driver == 'psycopg2':
              from psycopg2.extensions import ISOLATION_LEVEL_AUTOCOMMIT
              connection = engine.connect()
              connection.connection.set_isolation_level(
                  ISOLATION_LEVEL_AUTOCOMMIT
              )
          else:
              connection = engine.connect()
              connection.connection.set_session(autocommit=True)
  
          # Disconnect all users from the database we are dropping.
          version = connection.dialect.server_version_info
          pid_column = (
              'pid' if (version >= (9, 2)) else 'procpid'
          )
          text = '''
          SELECT pg_terminate_backend(pg_stat_activity.%(pid_column)s)
          FROM pg_stat_activity
          WHERE pg_stat_activity.datname = '%(database)s'
            AND %(pid_column)s <> pg_backend_pid();
          ''' % {'pid_column': pid_column, 'database': database}
          connection.execute(text)
  
          # Drop the database.
          text = 'DROP DATABASE {0}'.format(quote(connection, database))
          connection.execute(text)
          conn_resource = connection
      else:
          text = 'DROP DATABASE {0}'.format(quote(engine, database))
          conn_resource = engine.execute(text)
  
      if conn_resource is not None:
          conn_resource.close()
      engine.dispose()
  