Refactor code structure for improved readability and maintainability

apps/edr-freight-api/src/modules/rule-engine/services/rates.service.ts

@@ -753,6 +753,19 @@ export class RatesService {
     await this.buildUpdate(await this.findById(id), dto);
   }
 
+  /**
+   * The exact column changes applying this patch would make, without writing.
+   *
+   * A change request diffs against THIS rather than the raw patch: the form
+   * posts selectors that are never stored (`cargoKind`, `intercityKind`), and
+   * the real edit they encode lands on derived columns — flipping a rate to
+   * bulk moves `rateType` and swaps `containerTypeId`/`cargoTypeId`. Diffing
+   * the raw patch missed all of it, so the approver saw an empty change list.
+   */
+  async previewUpdate(id: string, dto: UpdateRateDto): Promise<Partial<Rate>> {
+    return this.buildUpdate(await this.findById(id), dto);
+  }
+
   private async applyUpdate(existing: Rate, dto: UpdateRateDto): Promise<Rate> {
     const updates = await this.buildUpdate(existing, dto);
     const updated = await this.repository.update(existing.id, updates);