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

next/backend/database/repositories/__init__.py

@@ -0,0 +1,3 @@
+from backend.database.repositories.status import DatabaseStatus, DatabaseStatusRepository
+
+__all__ = ["DatabaseStatus", "DatabaseStatusRepository"]

next/backend/database/repositories/status.py

@@ -0,0 +1,28 @@
+from __future__ import annotations
+
+import sqlite3
+from dataclasses import dataclass
+
+from backend.database.connection import Database
+
+
+@dataclass(frozen=True, slots=True)
+class DatabaseStatus:
+    available: bool
+    schema_version: int
+
+
+class DatabaseStatusRepository:
+    def __init__(self, database: Database) -> None:
+        self._database = database
+
+    def get(self) -> DatabaseStatus:
+        try:
+            with self._database.read() as connection:
+                connection.execute("SELECT 1").fetchone()
+                row = connection.execute(
+                    "SELECT COALESCE(MAX(version), 0) AS version FROM schema_migrations"
+                ).fetchone()
+            return DatabaseStatus(available=True, schema_version=int(row["version"]))
+        except (OSError, sqlite3.Error):
+            return DatabaseStatus(available=False, schema_version=0)