feat: add ActivityRepository and TaskRepository with CRUD operations for activities and tasks

app/repositories/activity_repo.py

@@ -0,0 +1,68 @@
+"""Repository helpers for deal activities."""
+from __future__ import annotations
+
+from collections.abc import Sequence
+from dataclasses import dataclass
+
+from sqlalchemy import Select, select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.models.activity import Activity, ActivityCreate
+from app.models.deal import Deal
+
+
+class ActivityOrganizationMismatchError(Exception):
+    """Raised when a deal/activity pair targets another organization."""
+
+
+@dataclass(slots=True)
+class ActivityQueryParams:
+    """Filtering options for fetching activities."""
+
+    organization_id: int
+    deal_id: int
+    limit: int | None = None
+    offset: int = 0
+
+
+class ActivityRepository:
+    """Provides CRUD helpers for Activity model."""
+
+    def __init__(self, session: AsyncSession) -> None:
+        self._session = session
+
+    @property
+    def session(self) -> AsyncSession:
+        return self._session
+
+    async def list(self, *, params: ActivityQueryParams) -> Sequence[Activity]:
+        stmt = (
+            select(Activity)
+            .join(Deal, Deal.id == Activity.deal_id)
+            .where(Activity.deal_id == params.deal_id, Deal.organization_id == params.organization_id)
+            .order_by(Activity.created_at)
+        )
+        stmt = self._apply_window(stmt, params)
+        result = await self._session.scalars(stmt)
+        return result.all()
+
+    async def create(self, data: ActivityCreate, *, organization_id: int) -> Activity:
+        deal = await self._session.get(Deal, data.deal_id)
+        if deal is None or deal.organization_id != organization_id:
+            raise ActivityOrganizationMismatchError("Deal belongs to another organization")
+
+        activity = Activity(**data.model_dump())
+        self._session.add(activity)
+        await self._session.flush()
+        return activity
+
+    def _apply_window(
+        self,
+        stmt: Select[tuple[Activity]],
+        params: ActivityQueryParams,
+    ) -> Select[tuple[Activity]]:
+        if params.offset:
+            stmt = stmt.offset(params.offset)
+        if params.limit is not None:
+            stmt = stmt.limit(params.limit)
+        return stmt