Duplica ricetta: servizio, endpoint e test backend (#52)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/backend/services/recipe_service.py

@@ -253,6 +253,78 @@ async def create_recipe(
     return result.scalar_one()
 
 
+async def duplicate_recipe(
+    db: AsyncSession,
+    recipe_id: int,
+    new_code: str,
+    new_name: str,
+    user: User,
+) -> Recipe:
+    """Duplicate a recipe (#52): new code/name, v1 with the current version's tasks.
+
+    The source recipe is left untouched.
+    """
+    source = await _get_recipe_or_404(db, recipe_id)
+
+    existing = await db.execute(select(Recipe).where(Recipe.code == new_code))
+    if existing.scalar_one_or_none() is not None:
+        raise HTTPException(
+            status_code=status.HTTP_409_CONFLICT,
+            detail=f"Recipe code '{new_code}' already exists",
+        )
+
+    # Same header fields create_recipe persists, taken from the source recipe
+    recipe = Recipe(
+        code=new_code,
+        name=new_name,
+        description=source.description,
+        image_path=source.image_path,
+        measurement_interval_minutes=source.measurement_interval_minutes,
+        requires_lot=source.requires_lot,
+        requires_serial=source.requires_serial,
+        allow_manual_input=source.allow_manual_input,
+        created_by=user.id,
+    )
+    db.add(recipe)
+    await db.flush()
+
+    version = RecipeVersion(
+        recipe_id=recipe.id,
+        version_number=1,
+        is_current=True,
+        created_by=user.id,
+        change_notes=f"Duplicated from {source.code}",
+    )
+    db.add(version)
+    await db.flush()
+
+    # Reuse the existing deep copy of tasks/subtasks from the current version
+    source_version = await _get_current_version(db, source.id)
+    if source_version is not None:
+        await _copy_tasks_to_version(db, source_version, version)
+
+    await _write_audit(
+        db,
+        recipe_id=recipe.id,
+        old_version_id=None,
+        new_version_id=version.id,
+        changed_by=user.id,
+        change_type="CREATE",
+        change_reason=f"Duplicated from recipe {source.code}",
+    )
+
+    result = await db.execute(
+        select(Recipe)
+        .where(Recipe.id == recipe.id)
+        .options(
+            selectinload(Recipe.versions)
+            .selectinload(RecipeVersion.tasks)
+            .selectinload(RecipeTask.subtasks)
+        )
+    )
+    return result.scalar_one()
+
+
 async def create_new_version(
     db: AsyncSession,
     recipe_id: int,