initial

backend/app/api/v1/feed.py

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+from fastapi import APIRouter
+from sqlalchemy import select, func
+from sqlalchemy.orm import selectinload
+
+from app.api.deps import DbSession, CurrentUser
+from app.models import Activity, Participant
+from app.schemas import FeedResponse, ActivityResponse, UserPublic
+
+router = APIRouter(tags=["feed"])
+
+
+@router.get("/marathons/{marathon_id}/feed", response_model=FeedResponse)
+async def get_feed(
+    marathon_id: int,
+    current_user: CurrentUser,
+    db: DbSession,
+    limit: int = 20,
+    offset: int = 0,
+):
+    """Get activity feed for marathon"""
+    # Check user is participant
+    result = await db.execute(
+        select(Participant).where(
+            Participant.user_id == current_user.id,
+            Participant.marathon_id == marathon_id,
+        )
+    )
+    if not result.scalar_one_or_none():
+        return FeedResponse(items=[], total=0, has_more=False)
+
+    # Get total count
+    total = await db.scalar(
+        select(func.count()).select_from(Activity).where(Activity.marathon_id == marathon_id)
+    )
+
+    # Get activities
+    result = await db.execute(
+        select(Activity)
+        .options(selectinload(Activity.user))
+        .where(Activity.marathon_id == marathon_id)
+        .order_by(Activity.created_at.desc())
+        .limit(limit)
+        .offset(offset)
+    )
+    activities = result.scalars().all()
+
+    items = [
+        ActivityResponse(
+            id=a.id,
+            type=a.type,
+            user=UserPublic.model_validate(a.user),
+            data=a.data,
+            created_at=a.created_at,
+        )
+        for a in activities
+    ]
+
+    return FeedResponse(
+        items=items,
+        total=total,
+        has_more=(offset + limit) < total,
+    )