// new capacity for the position * } * * - Validates that capacity ≥ 0. * - Ensures the new capacity is not less than the sum of existing section capacities. * - Returns JSON { success: true } on success, * or { success: false, error: "
", message: "" } on failure.
     */
    public function update(Request $request, $id)
    {
        // 1) Find the position
        $position = StockPosition::find($id);
        if (!$position) {
            return response()
                ->json(['success' => false, 'error' => 'not_found', 'message' => 'Position not found.'], 404);
        }

        // 2) Validate incoming payload
        $validator = Validator::make($request->all(), [
            'capacity' => 'required|integer|min:0',
        ]);

        if ($validator->fails()) {
            return response()
                ->json([
                    'success' => false,
                    'error'   => 'validation_failed',
                    'message' => $validator->errors()->first(),
                ], 422);
        }

        $newCapacity = $request->input('capacity');

        // 3) Check that new capacity ≥ sum of all existing (non-deleted) sections' capacities
        //    (we assume “sections” relationship returns the live StockSection models)
        $currentSectionsSum = $position
            ->sections()
            ->sum('capacity');

        if ($newCapacity < $currentSectionsSum) {
            return response()
                ->json([
                    'success' => false,
                    'error'   => 'insufficient_capacity',
                    'message' => "New capacity ({$newCapacity}) is less than total of existing section capacities ({$currentSectionsSum}).",
                ], 422);
        }

        // 4) All good → update and save
        $position->capacity = $newCapacity;
        $position->save();

        return response()->json(['success' => true], 200);
    }


    public function getPosition(Request $request, int $id)
    {
        // 1) Eager‐load the real relationships
        $position = StockPosition::with([
            'sections.entries.physicalItem',
            'shelf.rack.line.room',
        ])->findOrFail($id);

        // 2) Compute the storage address string
        $position->storage_address = $position->storageAddress();

        // 3) Return the model itself (now including a top‐level "storage_address" field)
        return response()->json($position);
    }


    public function store(Request $request)
    {
        $data = $request->validate([
            'shelf_id'        => 'required|exists:stock_shelf,shelf_id',
            'position_symbol' => 'required|string|max:50',
            'position_name'   => 'required|string|max:100',
            'capacity'        => 'required|integer|min:0',
        ]);

        $pos = StockPosition::create($data);

        return response()->json($pos, 201);
    }

    public function updateBasic(Request $request, StockPosition $pos)
    {
        $data = $request->validate([
            'position_symbol' => 'sometimes|required|string|max:50',
            'position_name'   => 'sometimes|required|string|max:100',
            'capacity'        => 'sometimes|required|integer|min:0',
        ]);

        $pos->update($data);

        return response()->json($pos);
    }

    public function destroy(StockPosition $pos)
    {
        $pos->delete();
        return response()->json(null, 204);
    }
}