Add initial project

backend/services/challenge_service.py

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+"""Challenge service for business logic."""
+from typing import List, Optional
+from sqlalchemy.orm import Session
+from sqlalchemy import func
+from backend.models.challenge import Challenge
+from backend.schemas.challenge import ChallengeCreate
+
+
+class ChallengeService:
+    """Service for challenge operations."""
+
+    @staticmethod
+    def create_challenge(
+        db: Session,
+        challenge_data: ChallengeCreate,
+        user_id: int
+    ) -> Challenge:
+        """Create a new challenge for a user."""
+        # Calculate next display_order for THIS user
+        max_order = db.query(func.max(Challenge.display_order)).filter(
+            Challenge.user_id == user_id
+        ).scalar()
+        new_order = (max_order if max_order is not None else -1) + 1
+        
+        db_challenge = Challenge(
+            **challenge_data.dict(),
+            display_order=new_order,
+            user_id=user_id
+        )
+        db.add(db_challenge)
+        db.commit()
+        db.refresh(db_challenge)
+        return db_challenge
+
+    @staticmethod
+    def get_user_challenges(
+        db: Session,
+        user_id: int
+    ) -> List[Challenge]:
+        """Get all challenges for a user."""
+        challenges = db.query(Challenge).filter(
+            Challenge.user_id == user_id
+        ).order_by(Challenge.display_order.asc()).all()
+        return challenges
+
+    @staticmethod
+    def reorder_challenges(
+        db: Session,
+        ordered_ids: List[int],
+        user_id: int
+    ) -> None:
+        """Reorder challenges for a user."""
+        for index, challenge_id in enumerate(ordered_ids):
+            db.query(Challenge).filter(
+                Challenge.id == challenge_id,
+                Challenge.user_id == user_id
+            ).update({"display_order": index})
+        db.commit()
+
+    @staticmethod
+    def delete_challenge(
+        db: Session,
+        challenge_id: int,
+        user_id: int
+    ) -> Optional[Challenge]:
+        """Delete a challenge for a user."""
+        db_challenge = db.query(Challenge).filter(
+            Challenge.id == challenge_id,
+            Challenge.user_id == user_id
+        ).first()
+        if db_challenge:
+            db.delete(db_challenge)
+            db.commit()
+        return db_challenge
+
+    @staticmethod
+    def get_challenge_by_id(
+        db: Session,
+        challenge_id: int,
+        user_id: int
+    ) -> Optional[Challenge]:
+        """Get a challenge by ID for a user."""
+        return db.query(Challenge).filter(
+            Challenge.id == challenge_id,
+            Challenge.user_id == user_id
+        ).first()