text: import _thread
  import copy
  import threading
  import time
  import warnings
  from collections import deque
  from contextlib import contextmanager
  
  try:
      import zoneinfo
  except ImportError:
      from backports import zoneinfo
  
  from django.conf import settings
  from django.core.exceptions import ImproperlyConfigured
  from django.db import DEFAULT_DB_ALIAS, DatabaseError
  from django.db.backends import utils
  from django.db.backends.base.validation import BaseDatabaseValidation
  from django.db.backends.signals import connection_created
  from django.db.transaction import TransactionManagementError
  from django.db.utils import DatabaseErrorWrapper
  from django.utils import timezone
  from django.utils.asyncio import async_unsafe
  from django.utils.functional import cached_property
  
  NO_DB_ALIAS = "__no_db__"
  
  
  # RemovedInDjango50Warning
  def timezone_constructor(tzname):
      if settings.USE_DEPRECATED_PYTZ:
          import pytz
  
          return pytz.timezone(tzname)
      return zoneinfo.ZoneInfo(tzname)
  
  
  class BaseDatabaseWrapper:
      """Represent a database connection."""
  
      # Mapping of Field objects to their column types.
      data_types = {}
      # Mapping of Field objects to their SQL suffix such as AUTOINCREMENT.
      data_types_suffix = {}
      # Mapping of Field objects to their SQL for CHECK constraints.
      data_type_check_constraints = {}
      ops = None
      vendor = "unknown"
      display_name = "unknown"
      SchemaEditorClass = None
      # Classes instantiated in __init__().
      client_class = None
      creation_class = None
      features_class = None
      introspection_class = None
      ops_class = None
      validation_class = BaseDatabaseValidation
  
      queries_limit = 9000
  
      def __init__(self, settings_dict, alias=DEFAULT_DB_ALIAS):
          # Connection related attributes.
          # The underlying database connection.
          self.connection = None
          # `settings_dict` should be a dictionary containing keys such as
          # NAME, USER, etc. It's called `settings_dict` instead of `settings`
          # to disambiguate it from Django settings modules.
          self.settings_dict = settings_dict
          self.alias = alias
          # Query logging in debug mode or when explicitly enabled.
          self.queries_log = deque(maxlen=self.queries_limit)
          self.force_debug_cursor = False
  
          # Transaction related attributes.
          # Tracks if the connection is in autocommit mode. Per PEP 249, by
          # default, it isn't.
          self.autocommit = False
          # Tracks if the connection is in a transaction managed by 'atomic'.
          self.in_atomic_block = False
          # Increment to generate unique savepoint ids.
          self.savepoint_state = 0
          # List of savepoints created by 'atomic'.
          self.savepoint_ids = []
          # Stack of active 'atomic' blocks.
          self.atomic_blocks = []
          # Tracks if the outermost 'atomic' block should commit on exit,
          # ie. if autocommit was active on entry.
          self.commit_on_exit = True
          # Tracks if the transaction should be rolled back to the next
          # available savepoint because of an exception in an inner block.
          self.needs_rollback = False
  
          # Connection termination related attributes.
          self.close_at = None
          self.closed_in_transaction = False
          self.errors_occurred = False
          self.health_check_enabled = False
          self.health_check_done = False
  
          # Thread-safety related attributes.
          self._thread_sharing_lock = threading.Lock()
          self._thread_sharing_count = 0
          self._thread_ident = _thread.get_ident()
  
          # A list of no-argument functions to run when the transaction commits.
          # Each entry is an (sids, func) tuple, where sids is a set of the
          # active savepoint IDs when this function was registered.
          self.run_on_commit = []
  
          # Should we run the on-commit hooks the next time set_autocommit(True)
          # is called?
          self.run_commit_hooks_on_set_autocommit_on = False
  
          # A stack of wrappers to be invoked around execute()/executemany()
          # calls. Each entry is a function taking five arguments: execute, sql,
          # params, many, and context. It's the function's responsibility to
          # call execute(sql, params, many, context).
          self.execute_wrappers = []
  
          self.client = self.client_class(self)
          self.creation = self.creation_class(self)
          self.features = self.features_class(self)
          self.introspection = self.introspection_class(self)
          self.ops = self.ops_class(self)
          self.validation = self.validation_class(self)
  
      def __repr__(self):
          return (
              f"<{self.__class__.__qualname__} "
              f"vendor={self.vendor!r} alias={self.alias!r}>"
          )
  
      def ensure_timezone(self):
          """
          Ensure the connection's timezone is set to `self.timezone_name` and
          return whether it changed or not.
          """
          return False
  
      @cached_property
      def timezone(self):
          """
          Return a tzinfo of the database connection time zone.
  
          This is only used when time zone support is enabled. When a datetime is
          read from the database, it is always returned in this time zone.
  
          When the database backend supports time zones, it doesn't matter which
          time zone Django uses, as long as aware datetimes are used everywhere.
          Other users connecting to the database can choose their own time zone.
  
          When the database backend doesn't support time zones, the time zone
          Django uses may be constrained by the requirements of other users of
          the database.
          """
          if not settings.USE_TZ:
              return None
          elif self.settings_dict["TIME_ZONE"] is None:
              return timezone.utc
          else:
              return timezone_constructor(self.settings_dict["TIME_ZONE"])
  
      @cached_property
      def timezone_name(self):
          """
          Name of the time zone of the database connection.
          """
          if not settings.USE_TZ:
              return settings.TIME_ZONE
          elif self.settings_dict["TIME_ZONE"] is None:
              return "UTC"
          else:
              return self.settings_dict["TIME_ZONE"]
  
      @property
      def queries_logged(self):
          return self.force_debug_cursor or settings.DEBUG
  
      @property
      def queries(self):
          if len(self.queries_log) == self.queries_log.maxlen:
              warnings.warn(
                  "Limit for query logging exceeded, only the last {} queries "
                  "will be returned.".format(self.queries_log.maxlen)
              )
          return list(self.queries_log)
  
      # ##### Backend-specific methods for creating connections and cursors #####
  
      def get_connection_params(self):
          """Return a dict of parameters suitable for get_new_connection."""
          raise NotImplementedError(
              "subclasses of BaseDatabaseWrapper may require a get_connection_params() "
              "method"
          )
  
      def get_new_connection(self, conn_params):
          """Open a connection to the database."""
          raise NotImplementedError(
              "subclasses of BaseDatabaseWrapper may require a get_new_connection() "
              "method"
          )
  
      def init_connection_state(self):
          """Initialize the database connection settings."""
          raise NotImplementedError(
              "subclasses of BaseDatabaseWrapper may require an init_connection_state() "
              "method"
          )
  
      def create_cursor(self, name=None):
          """Create a cursor. Assume that a connection is established."""
          raise NotImplementedError(
              "subclasses of BaseDatabaseWrapper may require a create_cursor() method"
          )
  
      # ##### Backend-specific methods for creating connections #####
  
      @async_unsafe
      def connect(self):
          """Connect to the database. Assume that the connection is closed."""
          # Check for invalid configurations.
          self.check_settings()
          # In case the previous connection was closed while in an atomic block
          self.in_atomic_block = False
          self.savepoint_ids = []
          self.atomic_blocks = []
          self.needs_rollback = False
          # Reset parameters defining when to close/health-check the connection.
          self.health_check_enabled = self.settings_dict["CONN_HEALTH_CHECKS"]
          max_age = self.settings_dict["CONN_MAX_AGE"]
          self.close_at = None if max_age is None else time.monotonic() + max_age
          self.closed_in_transaction = False
          self.errors_occurred = False
          # New connections are healthy.
          self.health_check_done = True
          # Establish the connection
          conn_params = self.get_connection_params()
          self.connection = self.get_new_connection(conn_params)
          self.set_autocommit(self.settings_dict["AUTOCOMMIT"])
          self.init_connection_state()
          connection_created.send(sender=self.__class__, connection=self)
  
          self.run_on_commit = []
  
      def check_settings(self):
          if self.settings_dict["TIME_ZONE"] is not None and not settings.USE_TZ:
              raise ImproperlyConfigured(
                  "Connection '%s' cannot set TIME_ZONE because USE_TZ is False."
                  % self.alias
              )
  
      @async_unsafe
      def ensure_connection(self):
          """Guarantee that a connection to the database is established."""
          if self.connection is None:
              with self.wrap_database_errors:
                  self.connect()
  
      # ##### Backend-specific wrappers for PEP-249 connection methods #####
  
      def _prepare_cursor(self, cursor):
          """
          Validate the connection is usable and perform database cursor wrapping.
          """
          self.validate_thread_sharing()
          if self.queries_logged:
              wrapped_cursor = self.make_debug_cursor(cursor)
          else:
              wrapped_cursor = self.make_cursor(cursor)
          return wrapped_cursor
  
      def _cursor(self, name=None):
          self.close_if_health_check_failed()
          self.ensure_connection()
          with self.wrap_database_errors:
              return self._prepare_cursor(self.create_cursor(name))
  
      def _commit(self):
          if self.connection is not None:
              with self.wrap_database_errors:
                  return self.connection.commit()
  
      def _rollback(self):
          if self.connection is not None:
              with self.wrap_database_errors:
                  return self.connection.rollback()
  
      def _close(self):
          if self.connection is not None:
              with self.wrap_database_errors:
                  return self.connection.close()
  
      # ##### Generic wrappers for PEP-249 connection methods #####
  
      @async_unsafe
      def cursor(self):
          """Create a cursor, opening a connection if necessary."""
          return self._cursor()
  
      @async_unsafe
      def commit(self):
          """Commit a transaction and reset the dirty flag."""
          self.validate_thread_sharing()
          self.validate_no_atomic_block()
          self._commit()
          # A successful commit means that the database connection works.
          self.errors_occurred = False
          self.run_commit_hooks_on_set_autocommit_on = True
  
      @async_unsafe
      def rollback(self):
          """Roll back a transaction and reset the dirty flag."""
          self.validate_thread_sharing()
          self.validate_no_atomic_block()
          self._rollback()
          # A successful rollback means that the database connection works.
          self.errors_occurred = False
          self.needs_rollback = False
          self.run_on_commit = []
  
      @async_unsafe
      def close(self):
          """Close the connection to the database."""
          self.validate_thread_sharing()
          self.run_on_commit = []
  
          # Don't call validate_no_atomic_block() to avoid making it difficult
          # to get rid of a connection in an invalid state. The next connect()
          # will reset the transaction state anyway.
          if self.closed_in_transaction or self.connection is None:
              return
          try:
              self._close()
          finally:
              if self.in_atomic_block:
                  self.closed_in_transaction = True
                  self.needs_rollback = True
              else:
                  self.connection = None
  
      # ##### Backend-specific savepoint management methods #####
  
      def _savepoint(self, sid):
          with self.cursor() as cursor:
              cursor.execute(self.ops.savepoint_create_sql(sid))
  
      def _savepoint_rollback(self, sid):
          with self.cursor() as cursor:
              cursor.execute(self.ops.savepoint_rollback_sql(sid))
  
      def _savepoint_commit(self, sid):
          with self.cursor() as cursor:
              cursor.execute(self.ops.savepoint_commit_sql(sid))
  
      def _savepoint_allowed(self):
          # Savepoints cannot be created outside a transaction
          return self.features.uses_savepoints and not self.get_autocommit()
  
      # ##### Generic savepoint management methods #####
  
      @async_unsafe
      def savepoint(self):
          """
          Create a savepoint inside the current transaction. Return an
          identifier for the savepoint that will be used for the subsequent
          rollback or commit. Do nothing if savepoints are not supported.
          """
          if not self._savepoint_allowed():
              return
  
          thread_ident = _thread.get_ident()
          tid = str(thread_ident).replace("-", "")
  
          self.savepoint_state += 1
          sid = "s%s_x%d" % (tid, self.savepoint_state)
  
          self.validate_thread_sharing()
          self._savepoint(sid)
  
          return sid
  
      @async_unsafe
      def savepoint_rollback(self, sid):
          """
          Roll back to a savepoint. Do nothing if savepoints are not supported.
          """
          if not self._savepoint_allowed():
              return
  
          self.validate_thread_sharing()
          self._savepoint_rollback(sid)
  
          # Remove any callbacks registered while this savepoint was active.
          self.run_on_commit = [
              (sids, func) for (sids, func) in self.run_on_commit if sid not in sids
          ]
  
      @async_unsafe
      def savepoint_commit(self, sid):
          """
          Release a savepoint. Do nothing if savepoints are not supported.
          """
          if not self._savepoint_allowed():
              return
  
          self.validate_thread_sharing()
          self._savepoint_commit(sid)
  
      @async_unsafe
      def clean_savepoints(self):
          """
          Reset the counter used to generate unique savepoint ids in this thread.
          """
          self.savepoint_state = 0
  
      # ##### Backend-specific transaction management methods #####
  
      def _set_autocommit(self, autocommit):
          """
          Backend-specific implementation to enable or disable autocommit.
          """
          raise NotImplementedError(
              "subclasses of BaseDatabaseWrapper may require a _set_autocommit() method"
          )
  
      # ##### Generic transaction management methods #####
  
      def get_autocommit(self):
          """Get the autocommit state."""
          self.ensure_connection()
          return self.autocommit
  
      def set_autocommit(
          self, autocommit, force_begin_transaction_with_broken_autocommit=False
      ):
          """
          Enable or disable autocommit.
  
          The usual way to start a transaction is to turn autocommit off.
          SQLite does not properly start a transaction when disabling
          autocommit. To avoid this buggy behavior and to actually enter a new
          transaction, an explicit BEGIN is required. Using
          force_begin_transaction_with_broken_autocommit=True will issue an
          explicit BEGIN with SQLite. This option will be ignored for other
          backends.
          """
          self.validate_no_atomic_block()
          self.close_if_health_check_failed()
          self.ensure_connection()
  
          start_transaction_under_autocommit = (
              force_begin_transaction_with_broken_autocommit
              and not autocommit
              and hasattr(self, "_start_transaction_under_autocommit")
          )
  
          if start_transaction_under_autocommit:
              self._start_transaction_under_autocommit()
          else:
              self._set_autocommit(autocommit)
  
          self.autocommit = autocommit
  
          if autocommit and self.run_commit_hooks_on_set_autocommit_on:
              self.run_and_clear_commit_hooks()
              self.run_commit_hooks_on_set_autocommit_on = False
  
      def get_rollback(self):
          """Get the "needs rollback" flag -- for *advanced use* only."""
          if not self.in_atomic_block:
              raise TransactionManagementError(
                  "The rollback flag doesn't work outside of an 'atomic' block."
              )
          return self.needs_rollback
  
      def set_rollback(self, rollback):
          """
          Set or unset the "needs rollback" flag -- for *advanced use* only.
          """
          if not self.in_atomic_block:
              raise TransactionManagementError(
                  "The rollback flag doesn't work outside of an 'atomic' block."
              )
          self.needs_rollback = rollback
  
      def validate_no_atomic_block(self):
          """Raise an error if an atomic block is active."""
          if self.in_atomic_block:
              raise TransactionManagementError(
                  "This is forbidden when an 'atomic' block is active."
              )
  
      def validate_no_broken_transaction(self):
          if self.needs_rollback:
              raise TransactionManagementError(
                  "An error occurred in the current transaction. You can't "
                  "execute queries until the end of the 'atomic' block."
              )
  
      # ##### Foreign key constraints checks handling #####
  
      @contextmanager
      def constraint_checks_disabled(self):
          """
          Disable foreign key constraint checking.
          """
          disabled = self.disable_constraint_checking()
          try:
              yield
          finally:
              if disabled:
                  self.enable_constraint_checking()
  
      def disable_constraint_checking(self):
          """
          Backends can implement as needed to temporarily disable foreign key
          constraint checking. Should return True if the constraints were
          disabled and will need to be reenabled.
          """
          return False
  
      def enable_constraint_checking(self):
          """
          Backends can implement as needed to re-enable foreign key constraint
          checking.
          """
          pass
  
      def check_constraints(self, table_names=None):
          """
          Backends can override this method if they can apply constraint
          checking (e.g. via "SET CONSTRAINTS ALL IMMEDIATE"). Should raise an
          IntegrityError if any invalid foreign key references are encountered.
          """
          pass
  
      # ##### Connection termination handling #####
  
      def is_usable(self):
          """
          Test if the database connection is usable.
  
          This method may assume that self.connection is not None.
  
          Actual implementations should take care not to raise exceptions
          as that may prevent Django from recycling unusable connections.
          """
          raise NotImplementedError(
              "subclasses of BaseDatabaseWrapper may require an is_usable() method"
          )
  
      def close_if_health_check_failed(self):
          """Close existing connection if it fails a health check."""
          if (
              self.connection is None
              or not self.health_check_enabled
              or self.health_check_done
          ):
              return
  
          if not self.is_usable():
              self.close()
          self.health_check_done = True
  
      def close_if_unusable_or_obsolete(self):
          """
          Close the current connection if unrecoverable errors have occurred
          or if it outlived its maximum age.
          """
          if self.connection is not None:
              self.health_check_done = False
              # If the application didn't restore the original autocommit setting,
              # don't take chances, drop the connection.
              if self.get_autocommit() != self.settings_dict["AUTOCOMMIT"]:
                  self.close()
                  return
  
              # If an exception other than DataError or IntegrityError occurred
              # since the last commit / rollback, check if the connection works.
              if self.errors_occurred:
                  if self.is_usable():
                      self.errors_occurred = False
                      self.health_check_done = True
                  else:
                      self.close()
                      return
  
              if self.close_at is not None and time.monotonic() >= self.close_at:
                  self.close()
                  return
  
      # ##### Thread safety handling #####
  
      @property
      def allow_thread_sharing(self):
          with self._thread_sharing_lock:
              return self._thread_sharing_count > 0
  
      def inc_thread_sharing(self):
          with self._thread_sharing_lock:
              self._thread_sharing_count += 1
  
      def dec_thread_sharing(self):
          with self._thread_sharing_lock:
              if self._thread_sharing_count <= 0:
                  raise RuntimeError(
                      "Cannot decrement the thread sharing count below zero."
                  )
              self._thread_sharing_count -= 1
  
      def validate_thread_sharing(self):
          """
          Validate that the connection isn't accessed by another thread than the
          one which originally created it, unless the connection was explicitly
          authorized to be shared between threads (via the `inc_thread_sharing()`
          method). Raise an exception if the validation fails.
          """
          if not (self.allow_thread_sharing or self._thread_ident == _thread.get_ident()):
              raise DatabaseError(
                  "DatabaseWrapper objects created in a "
                  "thread can only be used in that same thread. The object "
                  "with alias '%s' was created in thread id %s and this is "
                  "thread id %s." % (self.alias, self._thread_ident, _thread.get_ident())
              )
  
      # ##### Miscellaneous #####
  
      def prepare_database(self):
          """
          Hook to do any database check or preparation, generally called before
          migrating a project or an app.
          """
          pass
  
      @cached_property
      def wrap_database_errors(self):
          """
          Context manager and decorator that re-throws backend-specific database
          exceptions using Django's common wrappers.
          """
          return DatabaseErrorWrapper(self)
  
      def chunked_cursor(self):
          """
          Return a cursor that tries to avoid caching in the database (if
          supported by the database), otherwise return a regular cursor.
          """
          return self.cursor()
  
      def make_debug_cursor(self, cursor):
          """Create a cursor that logs all queries in self.queries_log."""
          return utils.CursorDebugWrapper(cursor, self)
  
      def make_cursor(self, cursor):
          """Create a cursor without debug logging."""
          return utils.CursorWrapper(cursor, self)
  
      @contextmanager
      def temporary_connection(self):
          """
          Context manager that ensures that a connection is established, and
          if it opened one, closes it to avoid leaving a dangling connection.
          This is useful for operations outside of the request-response cycle.
  
          Provide a cursor: with self.temporary_connection() as cursor: ...
          """
          must_close = self.connection is None
          try:
              with self.cursor() as cursor:
                  yield cursor
          finally:
              if must_close:
                  self.close()
  
      @contextmanager
      def _nodb_cursor(self):
          """
          Return a cursor from an alternative connection to be used when there is
          no need to access the main database, specifically for test db
          creation/deletion. This also prevents the production database from
          being exposed to potential child threads while (or after) the test
          database is destroyed. Refs #10868, #17786, #16969.
          """
          conn = self.__class__({**self.settings_dict, "NAME": None}, alias=NO_DB_ALIAS)
          try:
              with conn.cursor() as cursor:
                  yield cursor
          finally:
              conn.close()
  
      def schema_editor(self, *args, **kwargs):
          """
          Return a new instance of this backend's SchemaEditor.
          """
          if self.SchemaEditorClass is None:
              raise NotImplementedError(
                  "The SchemaEditorClass attribute of this database wrapper is still None"
              )
          return self.SchemaEditorClass(self, *args, **kwargs)
  
      def on_commit(self, func):
          if not callable(func):
              raise TypeError("on_commit()'s callback must be a callable.")
          if self.in_atomic_block:
              # Transaction in progress; save for execution on commit.
              self.run_on_commit.append((set(self.savepoint_ids), func))
          elif not self.get_autocommit():
              raise TransactionManagementError(
                  "on_commit() cannot be used in manual transaction management"
              )
          else:
              # No transaction in progress and in autocommit mode; execute
              # immediately.
              func()
  
      def run_and_clear_commit_hooks(self):
          self.validate_no_atomic_block()
          current_run_on_commit = self.run_on_commit
          self.run_on_commit = []
          while current_run_on_commit:
              sids, func = current_run_on_commit.pop(0)
              func()
  
      @contextmanager
      def execute_wrapper(self, wrapper):
          """
          Return a context manager under which the wrapper is applied to suitable
          database query executions.
          """
          self.execute_wrappers.append(wrapper)
          try:
              yield
          finally:
              self.execute_wrappers.pop()
  
      def copy(self, alias=None):
          """
          Return a copy of this connection.
  
          For tests that require two connections to the same database.
          """
          settings_dict = copy.deepcopy(self.settings_dict)
          if alias is None:
              alias = self.alias
          return type(self)(settings_dict, alias)
  