rebuild(stage-2): establish runtime and persistence foundations

next/backend/database/connection.py

@@ -0,0 +1,43 @@
+from __future__ import annotations
+
+import sqlite3
+from collections.abc import Iterator
+from contextlib import contextmanager
+from dataclasses import dataclass
+from pathlib import Path
+
+
+@dataclass(frozen=True, slots=True)
+class Database:
+    path: Path
+    timeout_seconds: float = 20.0
+
+    def connect(self) -> sqlite3.Connection:
+        self.path.parent.mkdir(parents=True, exist_ok=True)
+        connection = sqlite3.connect(self.path, timeout=self.timeout_seconds)
+        connection.row_factory = sqlite3.Row
+        connection.execute("PRAGMA foreign_keys = ON")
+        connection.execute("PRAGMA journal_mode = WAL")
+        connection.execute(f"PRAGMA busy_timeout = {int(self.timeout_seconds * 1000)}")
+        return connection
+
+    @contextmanager
+    def read(self) -> Iterator[sqlite3.Connection]:
+        connection = self.connect()
+        try:
+            yield connection
+        finally:
+            connection.close()
+
+    @contextmanager
+    def transaction(self) -> Iterator[sqlite3.Connection]:
+        connection = self.connect()
+        try:
+            connection.execute("BEGIN IMMEDIATE")
+            yield connection
+            connection.commit()
+        except Exception:
+            connection.rollback()
+            raise
+        finally:
+            connection.close()