Add a small wrapper for APSW use (#3202)

* Add a small wrapper for APSW use

* changelog

redbot/core/utils/dbtools.py

@@ -0,0 +1,61 @@
+from __future__ import annotations
+
+from contextlib import contextmanager
+from pathlib import Path
+from typing import Generator, Union
+
+import apsw
+
+__all__ = ["APSWConnectionWrapper"]
+
+
+# TODO (mikeshardmind): make this inherit typing_extensions.Protocol
+# long term: mypy; short term: removing the pylint disables below
+class ProvidesCursor:
+    def cursor(self) -> apsw.Cursor:
+        ...
+
+
+class ContextManagerMixin(ProvidesCursor):
+    @contextmanager
+    def with_cursor(self) -> Generator[apsw.Cursor, None, None]:
+        """
+        apsw cursors are relatively cheap, and are gc safe
+        In most cases, it's fine not to use this.
+        """
+        c = self.cursor()  # pylint: disable=assignment-from-no-return
+        try:
+            yield c
+        finally:
+            c.close()
+
+    @contextmanager
+    def transaction(self) -> Generator[apsw.Cursor, None, None]:
+        """
+        Wraps a cursor as a context manager for a transaction
+        which is rolled back on unhandled exception,
+        or commited on non-exception exit
+        """
+        c = self.cursor()  # pylint: disable=assignment-from-no-return
+        try:
+            c.execute("BEGIN TRANSACTION")
+            yield c
+        except Exception:
+            c.execute("ROLLBACK TRANSACTION")
+            raise
+        else:
+            c.execute("COMMIT TRANSACTION")
+        finally:
+            c.close()
+
+
+class APSWConnectionWrapper(apsw.Connection, ContextManagerMixin):
+    """
+    Provides a few convenience methods, and allows a path object for construction
+    """
+
+    def __init__(self, filename: Union[Path, str], *args, **kwargs):
+        super().__init__(str(filename), *args, **kwargs)
+
+
+# TODO (mikeshardmind): asyncio friendly ThreadedAPSWConnection class