# ScalesApp React Expert Memory

## Key File Paths

- Report Editor root: `frontend/src/components/ReportEditor/`
- Element models: `models/Element.jsx` — OOP class hierarchy, `fromJSON` has `elementClasses` map
- Element CSS: `elements.css` — one block per element type
- Inspector CSS: `ObjectInspector.css`
- Data resolver utils: `utils/dataResolver.js` — `resolveDBTextValue`, `getAvailableObjects`, `getAvailableFields`
- Expression evaluator: `utils/expressionEvaluator.js` — recursive-descent, no eval

## Element Type Pattern

Adding a new element type requires touching 8 files:
1. `models/Element.jsx` — new class + register in `elementClasses` map in `fromJSON`
2. `NewElement.jsx` — component file, modeled on `DBTextField.jsx`
3. `ExpressionEditorPanel.jsx` (or equivalent inspector panel)
4. `EditorCanvas.jsx` — import + `renderElement` case + click handler in `handleCanvasClick`
5. `Toolbar.jsx` — tool button
6. `ObjectInspector.jsx` — import panel + render for `element.type === 'xxx'`
7. `elements.css` — CSS block for new class
8. `ResizeHandles.jsx` — add type to `getHandles` switch, `getHandlePosition` branch, and resize logic branch

## ObjectInspector Band-Detection Pattern

When a panel needs to detect if an element is inside a band (for field resolution):
```js
const parentBand = allElements.find(el => el.type === 'band' && el.children && el.children.includes(element.id));
// Nested band handling:
if (parentBand.parentBandId) {
  const grandparentBand = allElements.find(el => el.id === parentBand.parentBandId);
  // grandparentData[0][parentBand.dataSource] → nestedData array
}
```

## DBTextField / ExpressionField Props Pattern

Both receive: `element, isSelected, isSingleSelection, onSelect, onUpdate, onDelete, onDragStart, onDrag, charWidth, charHeight, previewMode, toolMode, parentBandId`

Uses hooks: `useElementDrag`, `useElementSelection`, `useReportData`, `useBandContext`

## resolveDBTextValue signature

```js
resolveDBTextValue(reportData, objectKey, fieldPath, parentBandId, { currentBandData })
```
- objectKey = `''` for band-relative field access

## ExpressionField Field Ref Format

`[objectKey.fieldPath]` for top-level fields, `[fieldPath]` for band-relative fields.
Strip brackets, split on first `.` to get objectKey and fieldPath.