feat: implement repository and unit-of-work patterns for service layer operations

services/unit_of_work.py

@@ -0,0 +1,53 @@
+from __future__ import annotations
+
+from contextlib import AbstractContextManager
+from typing import Callable
+
+from sqlalchemy.orm import Session
+
+from config.database import SessionLocal
+from services.repositories import (
+    FinancialInputRepository,
+    ProjectRepository,
+    ScenarioRepository,
+    SimulationParameterRepository,
+)
+
+
+class UnitOfWork(AbstractContextManager["UnitOfWork"]):
+    """Simple unit-of-work wrapper around SQLAlchemy sessions."""
+
+    def __init__(self, session_factory: Callable[[], Session] = SessionLocal) -> None:
+        self._session_factory = session_factory
+        self.session: Session | None = None
+
+    def __enter__(self) -> "UnitOfWork":
+        self.session = self._session_factory()
+        self.projects = ProjectRepository(self.session)
+        self.scenarios = ScenarioRepository(self.session)
+        self.financial_inputs = FinancialInputRepository(self.session)
+        self.simulation_parameters = SimulationParameterRepository(self.session)
+        return self
+
+    def __exit__(self, exc_type, exc_value, traceback) -> None:
+        assert self.session is not None
+        if exc_type is None:
+            self.session.commit()
+        else:
+            self.session.rollback()
+        self.session.close()
+
+    def flush(self) -> None:
+        if not self.session:
+            raise RuntimeError("UnitOfWork session is not initialised")
+        self.session.flush()
+
+    def commit(self) -> None:
+        if not self.session:
+            raise RuntimeError("UnitOfWork session is not initialised")
+        self.session.commit()
+
+    def rollback(self) -> None:
+        if not self.session:
+            raise RuntimeError("UnitOfWork session is not initialised")
+        self.session.rollback()