introduce databricksClient interface and thrift backend implementation

WARNING: incomplete - result set still aligned heavily with thrift and
the necessity of some defined functions is to be validated

Signed-off-by: varun-edachali-dbx <varun.edachali@databricks.com>

Author: varun-edachali-dbx

src/databricks/sql/client.py

@@ -804,7 +804,7 @@ def execute(
         self.active_result_set = ResultSet(
             self.connection,
             execute_response,
-            self.thrift_backend,
+            self.backend,
             self.buffer_size_bytes,
             self.arraysize,
             self.connection.use_cloud_fetch,

src/databricks/sql/db_client_interface.py

@@ -0,0 +1,135 @@
+from abc import ABC, abstractmethod
+from typing import Dict, Tuple, List, Optional, Any, Union
+
+from databricks.sql.thrift_api.TCLIService import ttypes
+from databricks.sql.utils import ExecuteResponse
+from databricks.sql.types import SSLOptions
+
+
+class DatabricksClient(ABC):
+    # == Connection and Session Management ==
+    @abstractmethod
+    def open_session(
+        self,
+        session_configuration: Optional[Dict[str, Any]],
+        catalog: Optional[str],
+        schema: Optional[str],
+    ) -> ttypes.TOpenSessionResp:
+        pass
+
+    @abstractmethod
+    def close_session(self, session_handle: ttypes.TSessionHandle) -> None:
+        pass
+
+    # == Query Execution, Command Management ==
+    @abstractmethod
+    def execute_command(
+        self,
+        operation: str,
+        session_handle: ttypes.TSessionHandle,
+        max_rows: int,
+        max_bytes: int,
+        lz4_compression: bool,
+        cursor: Any,
+        use_cloud_fetch: bool,
+        parameters: List[ttypes.TSparkParameter],
+        async_op: bool,
+        enforce_embedded_schema_correctness: bool,
+    ) -> Any:
+        pass
+
+    @abstractmethod
+    def cancel_command(self, operation_handle: ttypes.TOperationHandle) -> None:
+        pass
+
+    @abstractmethod
+    def close_command(self, operation_handle: ttypes.TOperationHandle) -> ttypes.TStatus:
+        pass
+
+    @abstractmethod
+    def get_query_state(self, operation_handle: ttypes.TOperationHandle) -> ttypes.TOperationState:
+        pass
+
+    @abstractmethod
+    def get_execution_result(
+        self,
+        operation_handle: ttypes.TOperationHandle,
+        cursor: Any,
+    ) -> ExecuteResponse:
+        pass
+
+    # == Metadata Operations ==
+    @abstractmethod
+    def get_catalogs(
+        self,
+        session_handle: ttypes.TSessionHandle,
+        max_rows: int,
+        max_bytes: int,
+        cursor: Any,
+    ) -> Any:
+        pass
+
+    @abstractmethod
+    def get_schemas(
+        self,
+        session_handle: ttypes.TSessionHandle,
+        max_rows: int,
+        max_bytes: int,
+        cursor: Any,
+        catalog_name: Optional[str] = None,
+        schema_name: Optional[str] = None,
+    ) -> Any:
+        pass
+
+    @abstractmethod
+    def get_tables(
+        self,
+        session_handle: ttypes.TSessionHandle,
+        max_rows: int,
+        max_bytes: int,
+        cursor: Any,
+        catalog_name: Optional[str] = None,
+        schema_name: Optional[str] = None,
+        table_name: Optional[str] = None,
+        table_types: Optional[List[str]] = None,
+    ) -> Any:
+        pass
+
+    @abstractmethod
+    def get_columns(
+        self,
+        session_handle: ttypes.TSessionHandle,
+        max_rows: int,
+        max_bytes: int,
+        cursor: Any,
+        catalog_name: Optional[str] = None,
+        schema_name: Optional[str] = None,
+        table_name: Optional[str] = None,
+        column_name: Optional[str] = None,
+    ) -> Any:
+        pass
+
+    # == Utility Methods ==
+    @abstractmethod
+    def handle_to_id(self, handle: ttypes.TSessionHandle) -> bytes:
+        pass
+
+    @abstractmethod
+    def handle_to_hex_id(self, handle: ttypes.TSessionHandle) -> str:
+        pass
+
+    # Properties related to specific backend features
+    @property
+    @abstractmethod
+    def staging_allowed_local_path(self) -> Union[None, str, List[str]]:
+        pass
+
+    @property
+    @abstractmethod
+    def ssl_options(self) -> SSLOptions:
+        pass
+
+    @property
+    @abstractmethod
+    def max_download_threads(self) -> int:
+        pass