feat: refactor inventory and recipe services for improved error handling and code reuse; add systematic backend review plan

backend/src/products/products.service.ts

@@ -236,10 +236,7 @@ export class ProductsService {
   }
 
   async permanentDelete(id: number) {
-    const product = await this.prisma.product.findUnique({ where: { id } });
-    if (!product) {
-      throw new NotFoundException(`Product with id ${id} not found`);
-    }
+    await this.findOne(id);
     // Ta bort beroenden först
     await this.prisma.productTag.deleteMany({ where: { productId: id } });
     await this.prisma.userProduct.deleteMany({ where: { productId: id } });
@@ -262,30 +259,21 @@ export class ProductsService {
     });
   }
 
+  private async findProductByIdOrThrow(id: number, label: string) {
+    const product = await this.prisma.product.findUnique({ where: { id } });
+    if (!product) {
+      throw new NotFoundException(`${label} product with id ${id} not found`);
+    }
+    return product;
+  }
+
   async merge(sourceProductId: number, targetProductId: number) {
     if (sourceProductId === targetProductId) {
       throw new Error('sourceProductId och targetProductId kan inte vara samma');
     }
 
-    const source = await this.prisma.product.findUnique({
-      where: { id: sourceProductId },
-    });
-
-    if (!source) {
-      throw new NotFoundException(
-        `Source product with id ${sourceProductId} not found`,
-      );
-    }
-
-    const target = await this.prisma.product.findUnique({
-      where: { id: targetProductId },
-    });
-
-    if (!target) {
-      throw new NotFoundException(
-        `Target product with id ${targetProductId} not found`,
-      );
-    }
+    const source = await this.findProductByIdOrThrow(sourceProductId, 'Source');
+    const target = await this.findProductByIdOrThrow(targetProductId, 'Target');
 
     return this.prisma.$transaction(async (tx) => {
       const movedInventoryCount = await tx.inventoryItem.updateMany({
@@ -318,12 +306,8 @@ export class ProductsService {
 
     const [source, target, sourceInventoryCount, targetInventoryCount] =
       await Promise.all([
-        this.prisma.product.findUnique({
-          where: { id: sourceProductId },
-        }),
-        this.prisma.product.findUnique({
-          where: { id: targetProductId },
-        }),
+        this.findProductByIdOrThrow(sourceProductId, 'Source'),
+        this.findProductByIdOrThrow(targetProductId, 'Target'),
         this.prisma.inventoryItem.count({
           where: { productId: sourceProductId },
         }),
@@ -332,18 +316,6 @@ export class ProductsService {
         }),
       ]);
 
-    if (!source) {
-      throw new NotFoundException(
-        `Source product with id ${sourceProductId} not found`,
-      );
-    }
-
-    if (!target) {
-      throw new NotFoundException(
-        `Target product with id ${targetProductId} not found`,
-      );
-    }
-
     return {
       source: {
         ...source,