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

backend/src/inventory/inventory.service.ts

@@ -14,6 +14,26 @@ type InventoryQuery = {
 export class InventoryService {
   constructor(private prisma: PrismaService) {}
 
+  private throwInventoryItemNotFound(id: number): never {
+    throw new NotFoundException(`Inventory item with id ${id} not found`);
+  }
+
+  private async findInventoryItemByIdOrThrow(id: number) {
+    const existing = await this.prisma.inventoryItem.findUnique({ where: { id } });
+    if (!existing) {
+      this.throwInventoryItemNotFound(id);
+    }
+    return existing;
+  }
+
+  private async ensureProductExists(productId: number) {
+    const product = await this.prisma.product.findUnique({ where: { id: productId } });
+    if (!product) {
+      throw new NotFoundException('Product not found');
+    }
+    return product;
+  }
+
   async findAll(query?: InventoryQuery) {
     const where: Prisma.InventoryItemWhereInput = {};
     const orderBy: Prisma.InventoryItemOrderByWithRelationInput[] = [];
@@ -46,16 +66,7 @@ export class InventoryService {
   }
   
   async consume(id: number, data: ConsumeInventoryDto) {
-  const existing = await this.prisma.inventoryItem.findUnique({
-    where: { id },
-    include: {
-      product: true,
-    },
-  });
-
-  if (!existing) {
-    throw new NotFoundException(`Inventory item with id ${id} not found`);
-  }
+  const existing = await this.findInventoryItemByIdOrThrow(id);
 
   const currentQuantity = Number(existing.quantity);
   const newQuantity = Math.max(0, currentQuantity - data.amountUsed);
@@ -84,13 +95,7 @@ export class InventoryService {
 }
 
   async findConsumptionHistory(id: number) {
-    const existing = await this.prisma.inventoryItem.findUnique({
-    where: { id },
-  });
-
-  if (!existing) {
-    throw new NotFoundException(`Inventory item with id ${id} not found`);
-  }
+    await this.findInventoryItemByIdOrThrow(id);
 
   return this.prisma.inventoryConsumption.findMany({
     where: {
@@ -129,13 +134,7 @@ export class InventoryService {
   }
 
   async create(data: CreateInventoryDto) {
-    const product = await this.prisma.product.findUnique({
-      where: { id: data.productId },
-  });
-
-  if (!product) {
-    throw new NotFoundException('Product not found');
-  }
+    await this.ensureProductExists(data.productId);
 
   return this.prisma.inventoryItem.create({
     data: {
@@ -161,22 +160,10 @@ export class InventoryService {
 }
 
   async update(id: number, data: UpdateInventoryDto) {
-    const existing = await this.prisma.inventoryItem.findUnique({
-      where: { id },
-    });
-
-    if (!existing) {
-      throw new NotFoundException(`Inventory item with id ${id} not found`);
-    }
+    await this.findInventoryItemByIdOrThrow(id);
 
     if (typeof data.productId === 'number') {
-      const product = await this.prisma.product.findUnique({
-        where: { id: data.productId },
-      });
-
-      if (!product) {
-        throw new NotFoundException('Product not found');
-      }
+      await this.ensureProductExists(data.productId);
     }
 
     const updateData: Prisma.InventoryItemUpdateInput = {};
@@ -241,10 +228,7 @@ export class InventoryService {
   }
 
   async remove(id: number) {
-    const existing = await this.prisma.inventoryItem.findUnique({ where: { id } });
-    if (!existing) {
-      throw new NotFoundException(`Inventory item with id ${id} not found`);
-    }
+    await this.findInventoryItemByIdOrThrow(id);
     return this.prisma.inventoryItem.delete({ where: { id } });
   }
 }