databricks
diff --git a/‎src/databricks/sql/backend/databricks_client.py
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+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+from typing import Dict, List, Optional, Any, Union, TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from databricks.sql.client import Cursor
+    from databricks.sql.result_set import ResultSet
+
+from databricks.sql.thrift_api.TCLIService import ttypes
+from databricks.sql.backend.types import SessionId, CommandId, CommandState
+
+
+class DatabricksClient(ABC):
+    """
+    Abstract client interface for interacting with Databricks SQL services.
+
+    Implementations of this class are responsible for:
+    - Managing connections to Databricks SQL services
+    - Executing SQL queries and commands
+    - Retrieving query results
+    - Fetching metadata about catalogs, schemas, tables, and columns
+    """
+
+    # == Connection and Session Management ==
+    @abstractmethod
+    def open_session(
+        self,
+        session_configuration: Optional[Dict[str, Any]],
+        catalog: Optional[str],
+        schema: Optional[str],
+    ) -> SessionId:
+        """
+        Opens a new session with the Databricks SQL service.
+
+        This method establishes a new session with the server and returns a session
+        identifier that can be used for subsequent operations.
+
+        Args:
+            session_configuration: Optional dictionary of configuration parameters for the session
+            catalog: Optional catalog name to use as the initial catalog for the session
+            schema: Optional schema name to use as the initial schema for the session
+
+        Returns:
+            SessionId: A session identifier object that can be used for subsequent operations
+
+        Raises:
+            Error: If the session configuration is invalid
+            OperationalError: If there's an error establishing the session
+            InvalidServerResponseError: If the server response is invalid or unexpected
+        """
+        pass
+
+    @abstractmethod
+    def close_session(self, session_id: SessionId) -> None:
+        """
+        Closes an existing session with the Databricks SQL service.
+
+        This method terminates the session identified by the given session ID and
+        releases any resources associated with it.
+
+        Args:
+            session_id: The session identifier returned by open_session()
+
+        Raises:
+            ValueError: If the session ID is invalid
+            OperationalError: If there's an error closing the session
+        """
+        pass
+
+    # == Query Execution, Command Management ==
+    @abstractmethod
+    def execute_command(
+        self,
+        operation: str,
+        session_id: SessionId,
+        max_rows: int,
+        max_bytes: int,
+        lz4_compression: bool,
+        cursor: Cursor,
+        use_cloud_fetch: bool,
+        parameters: List[ttypes.TSparkParameter],
+        async_op: bool,
+        enforce_embedded_schema_correctness: bool,
+    ) -> Union[ResultSet, None]:
+        """
+        Executes a SQL command or query within the specified session.
+
+        This method sends a SQL command to the server for execution and handles
+        the response. It can operate in both synchronous and asynchronous modes.
+
+        Args:
+            operation: The SQL command or query to execute
+            session_id: The session identifier in which to execute the command
+            max_rows: Maximum number of rows to fetch in a single fetch batch
+            max_bytes: Maximum number of bytes to fetch in a single fetch batch
+            lz4_compression: Whether to use LZ4 compression for result data
+            cursor: The cursor object that will handle the results. The command id is set in this cursor.
+            use_cloud_fetch: Whether to use cloud fetch for retrieving large result sets
+            parameters: List of parameters to bind to the query
+            async_op: Whether to execute the command asynchronously
+            enforce_embedded_schema_correctness: Whether to enforce schema correctness
+
+        Returns:
+            If async_op is False, returns a ResultSet object containing the
+            query results and metadata. If async_op is True, returns None and the
+            results must be fetched later using get_execution_result().
+
+        Raises:
+            ValueError: If the session ID is invalid
+            OperationalError: If there's an error executing the command
+            ServerOperationError: If the server encounters an error during execution
+        """
+        pass
+
+    @abstractmethod
+    def cancel_command(self, command_id: CommandId) -> None:
+        """
+        Cancels a running command or query.
+
+        This method attempts to cancel a command that is currently being executed.
+        It can be called from a different thread than the one executing the command.
+
+        Args:
+            command_id: The command identifier to cancel
+
+        Raises:
+            ValueError: If the command ID is invalid
+            OperationalError: If there's an error canceling the command
+        """
+        pass
+
+    @abstractmethod
+    def close_command(self, command_id: CommandId) -> None:
+        """
+        Closes a command and releases associated resources.
+
+        This method informs the server that the client is done with the command
+        and any resources associated with it can be released.
+
+        Args:
+            command_id: The command identifier to close
+
+        Raises:
+            ValueError: If the command ID is invalid
+            OperationalError: If there's an error closing the command
+        """
+        pass
+
+    @abstractmethod
+    def get_query_state(self, command_id: CommandId) -> CommandState:
+        """
+        Gets the current state of a query or command.
+
+        This method retrieves the current execution state of a command from the server.
+
+        Args:
+            command_id: The command identifier to check
+
+        Returns:
+            CommandState: The current state of the command
+
+        Raises:
+            ValueError: If the command ID is invalid
+            OperationalError: If there's an error retrieving the state
+            ServerOperationError: If the command is in an error state
+            DatabaseError: If the command has been closed unexpectedly
+        """
+        pass
+
+    @abstractmethod
+    def get_execution_result(
+        self,
+        command_id: CommandId,
+        cursor: Cursor,
+    ) -> ResultSet:
+        """
+        Retrieves the results of a previously executed command.
+
+        This method fetches the results of a command that was executed asynchronously
+        or retrieves additional results from a command that has more rows available.
+
+        Args:
+            command_id: The command identifier for which to retrieve results
+            cursor: The cursor object that will handle the results
+
+        Returns:
+            ResultSet: An object containing the query results and metadata
+
+        Raises:
+            ValueError: If the command ID is invalid
+            OperationalError: If there's an error retrieving the results
+        """
+        pass
+
+    # == Metadata Operations ==
+    @abstractmethod
+    def get_catalogs(
+        self,
+        session_id: SessionId,
+        max_rows: int,
+        max_bytes: int,
+        cursor: Cursor,
+    ) -> ResultSet:
+        """
+        Retrieves a list of available catalogs.
+
+        This method fetches metadata about all catalogs available in the current
+        session's context.
+
+        Args:
+            session_id: The session identifier
+            max_rows: Maximum number of rows to fetch in a single batch
+            max_bytes: Maximum number of bytes to fetch in a single batch
+            cursor: The cursor object that will handle the results
+
+        Returns:
+            ResultSet: An object containing the catalog metadata
+
+        Raises:
+            ValueError: If the session ID is invalid
+            OperationalError: If there's an error retrieving the catalogs
+        """
+        pass
+
+    @abstractmethod
+    def get_schemas(
+        self,
+        session_id: SessionId,
+        max_rows: int,
+        max_bytes: int,
+        cursor: Cursor,
+        catalog_name: Optional[str] = None,
+        schema_name: Optional[str] = None,
+    ) -> ResultSet:
+        """
+        Retrieves a list of schemas, optionally filtered by catalog and schema name patterns.
+
+        This method fetches metadata about schemas available in the specified catalog
+        or all catalogs if no catalog is specified.
+
+        Args:
+            session_id: The session identifier
+            max_rows: Maximum number of rows to fetch in a single batch
+            max_bytes: Maximum number of bytes to fetch in a single batch
+            cursor: The cursor object that will handle the results
+            catalog_name: Optional catalog name pattern to filter by
+            schema_name: Optional schema name pattern to filter by
+
+        Returns:
+            ResultSet: An object containing the schema metadata
+
+        Raises:
+            ValueError: If the session ID is invalid
+            OperationalError: If there's an error retrieving the schemas
+        """
+        pass
+
+    @abstractmethod
+    def get_tables(
+        self,
+        session_id: SessionId,
+        max_rows: int,
+        max_bytes: int,
+        cursor: Cursor,
+        catalog_name: Optional[str] = None,
+        schema_name: Optional[str] = None,
+        table_name: Optional[str] = None,
+        table_types: Optional[List[str]] = None,
+    ) -> ResultSet:
+        """
+        Retrieves a list of tables, optionally filtered by catalog, schema, table name, and table types.
+
+        This method fetches metadata about tables available in the specified catalog
+        and schema, or all catalogs and schemas if not specified.
+
+        Args:
+            session_id: The session identifier
+            max_rows: Maximum number of rows to fetch in a single batch
+            max_bytes: Maximum number of bytes to fetch in a single batch
+            cursor: The cursor object that will handle the results
+            catalog_name: Optional catalog name pattern to filter by
+                if catalog_name is None, we fetch across all catalogs
+            schema_name: Optional schema name pattern to filter by
+                if schema_name is None, we fetch across all schemas
+            table_name: Optional table name pattern to filter by
+            table_types: Optional list of table types to filter by (e.g., ['TABLE', 'VIEW'])
+
+        Returns:
+            ResultSet: An object containing the table metadata
+
+        Raises:
+            ValueError: If the session ID is invalid
+            OperationalError: If there's an error retrieving the tables
+        """
+        pass
+
+    @abstractmethod
+    def get_columns(
+        self,
+        session_id: SessionId,
+        max_rows: int,
+        max_bytes: int,
+        cursor: Cursor,
+        catalog_name: Optional[str] = None,
+        schema_name: Optional[str] = None,
+        table_name: Optional[str] = None,
+        column_name: Optional[str] = None,
+    ) -> ResultSet:
+        """
+        Retrieves a list of columns, optionally filtered by catalog, schema, table, and column name patterns.
+
+        This method fetches metadata about columns available in the specified table,
+        or all tables if not specified.
+
+        Args:
+            session_id: The session identifier
+            max_rows: Maximum number of rows to fetch in a single batch
+            max_bytes: Maximum number of bytes to fetch in a single batch
+            cursor: The cursor object that will handle the results
+            catalog_name: Optional catalog name pattern to filter by
+            schema_name: Optional schema name pattern to filter by
+            table_name: Optional table name pattern to filter by
+                if table_name is None, we fetch across all tables
+            column_name: Optional column name pattern to filter by
+
+        Returns:
+            ResultSet: An object containing the column metadata
+
+        Raises:
+            ValueError: If the session ID is invalid
+            OperationalError: If there's an error retrieving the columns
+        """
+        pass
+
+    @property
+    @abstractmethod
+    def max_download_threads(self) -> int:
+        """
+        Gets the maximum number of download threads for cloud fetch operations.
+
+        Returns:
+            int: The maximum number of download threads
+        """
+        pass